G-11-07-28-11D1 - 7/28/2011ORDINANCE NO. ���� 1(
AN ORDINANCE AMENDING THE "CITY OF ROUND ROCK DESIGN AND
CONSTRUCTION STANDARDS - DRAINAGE CRITERIA MANUAL"
ADOPTED BY ORDINANCE NO. G -04-12-16-13A1 BY ADDING SECTION 9
"EROSION AND SEDIMENTATION CONTROL;" ADDING "APPENDIX C;"
AND PROVIDING FOR A SAVINGS CLAUSE AND REPEALING
CONFLICTING ORDINANCES AND RESOLUTIONS.
BE IT ORDAINED BY THE CITY COUNCIL OF THE CITY OF ROUND ROCK,
TEXAS:
Section 9 entitled "Erosion and Sedimentation Control" is hereby added to the "City of
Round Rock Design and Construction Standards - Drainage Criteria Manual," and same is
attached hereto and made a part hereof as if fully set out in this ordinance.
II.
The accompanying "Appendix C" is hereby added to the "City of Round Rock Design
and Construction Standards - Drainage Criteria Manual," and same is attached hereto and
made a part hereof as if fully set out in this ordinance.
III.
A. All ordinances, parts of ordinances, or resolutions in conflict herewith are
expressly repealed.
B. The invalidity of any section or provision of this ordinance shall not invalidate
other sections or provisions thereof.
C. The City Council hereby finds and declares that written notice of the date, hour,
place and subject of the meeting at which this Ordinance was adopted was posted and that
such meeting was open to the public as required by law at all times during which this
Ordinance and the subject matter hereof were discussed, considered and formally acted
O:\wdox\SCClnts\0112\ 1104\MUNICIPAL \00227985.DOC/jkg
upon, all as required by the Open Meetings Act, Chapter 551, Texas Government Code, as
amended.
Alternative 1.
By motion duly made, seconded and passed with an affirmative vote of all the Council
members present, the requirement for reading this ordinance on two separate days was
dispensed with.
READ, PASSED, and ADOPTED on first reading this 2013 day of
Alevr
, 2011.
Alternative 2.
READ and APPROVED on first reading this the day of
, 2011.
READ, APPROVED and ADOPTED on second reading this the day of
2011.
ATTEST:
SARA L. WHITE, City Secretary
" l
ALAN MCGRAW, Mayor
City of Round Rock, Texas
2
SECTION 9 - EROSION AND SEDIMENTATION CONTROL
Table of Contents
SECTION 9 — EROSION AND SEDIMENTATION CONTROL Table of Contents 9-1
9.1 General 9-2
9.2 Erosion and Sedimentation Control Policy 9-2
9.3 Plans and Computations 9-3
9.3.1 Submittal Requirements 9-3
9.3.2 Procedures during Construction 9-4
9.3.3 Revisions to Controls 9-4
9-1
Drainage Criteria Manual
SECTION 9 - EROSION AND SEDIMENTATION CONTROL
SECTION 9 - EROSION AND SEDIMENTATION CONTROL
9.1 GENERAL
The purpose of this section is to provide a resource document and policy to protect land and
water resources from the adverse effects of erosion and sedimentation, and to promote
compliance with the City of Round Rock's Municipal Separate Storm Sewer System (MS4)
Phase II permit. Additionally, the criteria have been fashioned to complement the language of
the Texas Pollution Discharge Elimination System (TPDES) General Permit (TXR150000).
The conversion of land from its natural state or agricultural use to urban use can accelerate the
processes of erosion and sedimentation. These accelerated processes can negatively impact
natural resources such as drinking water supply, aquatic life, floodplain capacity, natural beauty,
and recreational resources. As additional development and urban growth takes place in the City
of Round Rock, the City's natural resources will experience accelerated degradation if erosion
and sedimentation are not properly controlled. The protection of these natural resources is
easier and less expensive than their restoration.
Construction -related sediment is a significant pollutant of streams, lakes, ponds and reservoirs.
Sedimentation can also carry pesticides, phosphates and many other chemical pollutants on the
soil particles. These pollutants are carried to the waterway on the sediment particle and further
reduce the quality of the water.
Erosion can be quite destructive and can threaten property, roads, utilities, infrastructure and
structures. During most development/construction projects, the major period for erosion
potential exists between the time of existing vegetation removal at commencement of site work
and the time of construction completion or final revegetation. There are numerous activities
associated with construction and land development that accelerate the rate of erosion. Virtually
all of these activities involve the removal of vegetation and/or disturbance of the native geologic
structure. Appropriate planning and implementation of these activities and preventative
measures will reduce the adverse impact upon the site and the environment in general.
The erosion and sediment best management practices (BMPs) included in Appendix C provide
several methods to address the dual problems of erosion and sedimentation, but are in no way
an exhaustive list of possible actions; and alternative site specific methods may be required to
adequately control the problems. The City shall approve BMPs not included in the manual prior
to their use.
9.2 EROSION AND SEDIMENTATION CONTROL POLICY
The City of Round Rock Erosion and Sedimentation Control Policy shall govern the planning,
design, installation, maintenance and inspection of temporary and permanent erosion and
sedimentation controls associated with development/construction within the City. This policy is
the official criteria required by the TPDES MS4 Phase II permit and, as such, strives to comply
with all federal and state mandates associated with the permit.
Erosion and sedimentation BMPs are required for all construction (conducted with or without a
permit), and for all other activities for which land clearing, trenching, or grading is a part. It is the
9-2
intent of the City of Round Rock's policy to closely parallel the requirements set forth in the
Texas Pollution Discharge Elimination System (TPDES) Construction General Permit
(TXR150000), the City of Round Rock's MS4 Phase II Permit, and any applicable updates to
NPDES or TPDES.
The policy objectives are to:
• Ensure Municipal Separate Storm Sewer System (MS4) Phase II Permit & TPDES
Construction General Permit compliance.
• Minimize the erosion and transport of soil resulting from development/construction
activities.
• Minimize sedimentation in streams, creeks, lakes, waterways, storm drains, etc.
• Protect and improve the quality of surface water and maintain and improve the quality
and quantity of recharge to groundwater supplies, especially the Edwards Aquifer.
• Minimize flooding hazards and silt removal costs associated with excessive sediment
accumulation in storm drains and waterways.
Preserve and protect existing vegetation to the greatest extent possible, particularly
native plant and wildlife habitats.
• Provide for revegetation of sites to minimize the negative environmental impacts of
construction activity.
9.3 PLANS AND COMPUTATIONS
Implementation of an effective erosion and sedimentation control plan requires a project
management approach where responsibility is assigned during each phase to assure proper
design, installation, maintenance, inspection and, when necessary, repair or replacement of
controls during the construction. The project owner/developer, engineer and contractor are all
integrally involved in this process from start to finish. In addition, an understanding by the
responsible individuals of the complete process required to design and implement erosion and
sedimentation controls will assist them in preparing appropriate plans, will speed the review and
approval process, will result in fewer on-site changes or problems, and will provide the
appropriate degree of protection for the environment.
The following subsections present the minimum requirements for the planning, design,
construction, operation and maintenance of erosion and sedimentation control facilities. Design
professionals may select an appropriate control method or combinations of methods or
structures described in Appendix C, and are responsible for both the adequacy and
implementation of an effective erosion and sedimentation control plan. Following the end of
construction activities, the developer/developer, contractor and engineer are responsible for
ensuring proper erosion and sedimentation control until all areas are stabilized.
9.3.1 Submittal Requirements
All projects disturbing natural conditions are required to plan, design, and implement BMPs to
minimize erosion and sedimentation to the greatest extent practicable. All activities requiring a
permit shall submit an erosion and sedimentation control plan that identifies, addresses, and
minimizes to the reviewer's satisfaction all potential sources of sediment and other construction
related pollution.
Development/construction disturbing greater than one (1) acre shall also develop and
implement a Storm Water Pollution Prevention Plan (SWPPP) as outlined in TPDES
Construction General Permit (TXR150000).
9-3
Erosion and Sedimentation plan sheets shall include:
A. A comprehensive plan addressing limits of disturbance, phasing, temporary and
permanent erosion and sedimentation BMPs that complies with all applicable federal,
state and local regulations.
B. The graphics necessary to illustrate, review and construct the BMPs to minimize erosion
and sedimentation to the greatest extent practicable; (and where appropriate, correlate
with those outlined in the SWPPP).
C. Standards and schedules for maintenance and replacement for all temporary BMPs in
the plans.
D. Standards for top soil, vegetative materials and schedules for irrigation for all vegetation
BMPs in the plans.
E. BMPs design that avoids causing a flooding to adjacent property or rights-of-way.
F. Computations for BMPs that rely on detention, sedimentation, filtration, diversion and
velocity control. A Licensed Professional Engineer shall certify all engineering
computations with competence in this area as required by Texas Engineering Practice
Act, Section 137. (The reviewer may deny an application if the applicant cannot support
Erosion and Sedimentation control designs with appropriate calculations.)
9.3.2 Procedures during Construction
Proper installation, maintenance, and inspection of the approved control methods during the
construction of a project are the final steps in assuring effective control of erosion and
sedimentation. Implementation requires the combined efforts of the project engineer, contractor,
owner, city inspectors and, when needed, reviewers working together to achieve the best
feasible control.
A. The contractor is responsible for installing, inspecting and maintaining all BMPs
according to the approved erosion and sedimentation controls (and SWPPP as
appropriate).
B. The contractor (and inspector) is responsible for reporting any identified problem areas
to the design engineer for recommended additions or revisions to the erosion and
sedimentation control plan.
C. The design engineer is responsible for modifying the plan as needed to minimize erosion
and sedimentation to the greatest extent practicable.
D. The owner, contractor and design engineer are responsible for installing and maintaining
BMPs in a manner that complies with all applicable federal, state and local regulations.
9.3.3 Revisions to Controls
Most erosion and sedimentation controls will normally require some minor adjustments or
additions during construction. These are known as "field revisions" and will not require a plan
revision if approved by the Engineer and- the inspector. Significant modifications to the controls
or the SWPPP, however, will require a plan revision and resubmittal to the City for review and
approval.
9-4
Table of Contents
APPENDIX C
C.1 INTRODUCTION AC -2
C.2 Erosion Control Best Management Practices (BMPs) AC -3
C.2.1 Interceptor Swale AC -7
C.2.2 Diversion Dikes .... AC -8
C.2.3 Pipe Slope Drain AC -9
C.2.4 Channel Stabilization AC -11
C.2.5 Outlet Stabilization AC -14
C.2.6 Level Spreaders AC -17
C.2.7 Subsurface Drains AC -21
C.2.8 Vegetation AC -26
C.2.9 Mulch AC -30
C.2.10 Blankets and Matting AC -30
C.2.11 Organic Compost Mulch AC -35
C.2.12 Hydraulic Mulch AC -38
C.2.13 Sod AC -39
C.2.14 Dust Control AC -42
C.3 Sediment Control Best Management Practices (BMPs) AC -43
C.3.1 General Guidelines AC -43
C.3.2 Temporary Construction Entrance/Exit AC -46
C.3.3 Silt Fence AC -48
C.3.4 Triangular Sediment Filter Dikes AC -51
C.3.5 Tire Washing Facility AC -53
C.3.6 Rock Berms AC -55
C.3.7 High Service Rock Berms AC -57
C.3.8 Brush Berms AC -60
C.3.9 Check Dams AC -64
C.3.10 Vegetative Buffers AC -67
C.3.11 Inlet Protection AC -68
C.3.12 Stone Outlet Sediment Trap AC -72
C.3.13 Sediment Basins AC -75
C.3.14 Erosion Control Logs AC -78
C.3.15 Dewatering Operations AC -81
C.3.16 Spill Prevention and Control AC -85
C.3.17 Creek Crossings AC -89
C.3.18 Concrete Washout Areas AC -95
APPENDIX C - Erosion and Sediment Control Best
Management Practices
C.1 Introduction
The purpose of this appendix is to provide a resource for the design, installation,
inspection, and maintenance of the most commonly used erosion and sediment
control Best Management Practices (BMP's). Each BMP is presented with a list
of guidelines for proper implementation and a compilation of common trouble
points.
Contractors shall install and maintain erosion and sedimentation controls in a
careful and proper manner. Minor adjustments should be anticipated to assure
proper performance. Intensive maintenance and extensive use of vegetation,
mulch, and other ground covers may be required to achieve optimum
performance. When erosion and sediment controls are removed after final
stabilization of the site, it is important to also remove or stabilize any
accumulated sediment.
Periodic inspection and maintenance is vital to the performance of erosion and
sedimentation control measures. All temporary erosion and sedimentation
controls shall be inspected weekly and after every rainfall or adverse weather
event; however, daily inspections may be warranted when environmentally
sensitive features are located on or immediately adjacent to the site and when
adverse weather events are forecasted. If not properly maintained, some
practices may cause more damage than they prevent.
This appendix includes guidance for minimum design criteria for sizing BMP's
once calculations of storm water runoff and conveyance capacity have been
determined as outlined in the Drainage Criteria Manual Section 2 and Section 6
respectively. Always evaluate the consequences of a measure failing when
considering which control measure to use, as failure of a measure may be
hazardous or damaging to both people and property. For examples, a large
sediment basin failure can have disastrous results; and, low points along dikes
can cause major gullies to form on a fill slope. It is essential to provide
inspections to determine if BMPs are properly installed and functioning, and to
ensure that problems are corrected as soon as they develop. An individual shall
be assigned responsibility for inspection and maintenance of erosion and
sedimentation controls.
AC -2
C.2 Erosion Control BMPs
Temporary Erosion Controls should be considered the first line of defense for
prevention of storm water pollution during construction activities. It is much more
effective to maintain the soil cover in place than to trap sediments that are subject to
movement because of exposure. In addition effective erosion prevention can result
in cost savings, since repair of erosion damage can be minimized.
Permanent Erosion Controls are used to reduce the potential of erosion after
construction activities are complete and to ensure proper stabilization of areas
disturbed by construction.
Primary erosion control strategies are to divert runoff away from unstable
areas or to provide a stable surface that will resist the effects of rain and
runoff. The principle measures for diverting runoff during construction include
perimeter swales and dikes, and slope drains. These measures can direct flow
around the active construction area or transport storm water runoff safely across
unstable areas.
Existing trees and vegetation should be protected to help maintain a stable ground
surface and prevent Toss of sediments and potentially valuable topsoil. Where
temporary vegetation is planted to prevent erosion, blankets, matting and mulches
can help stabilize the area until the vegetation is adequately established.
The following sections describe various erosion control measures. The types and
application of the controls are summarized in Table C-1.
Table C-1 Guidelines for Selection of Temporary Erosion Control BMPs
Erosion Control
Area
Application
Notes
Interceptor Swale
< 5 ac
Used as a perimeter control or to shorten
slope distances
Diversion Dike
<10 ac
Used to route runoff away from disturbed
Areas
Pipe Slope Drain
<5 ac
Transport runoff down steep, erodible
Slopes
Channel Stabilization
Along
Channels
Conveyance of concentrated runoff
Outlet Stabilization
At
Outlets
Prevent erosion at outlet of channel or
Conduit
Level Spreader
Based on
flow
Outlet device for dikes and diversions
Slope <10% and stable
Subsurface Drain
Sized as
Req'd.
Prevent soils from becoming saturated
and prevent seeps
Vegetation
Up to Mild
Slopes
Temporary and permanent stabilization
of disturbed areas
Permanent vegetation required
for all disturbed areas
Blankets/Matting
w/ vegetation
Step Slopes
Used in channels and on steep slopes
Suggested max. slope 2H:1V
for slope applications
Brush Mulch/
Erosion Control Logs
NA
Temp. stabilization of disturbed areas
Stabilization in channels, around inlets,
on steep slopes
Suggested max. slope 2H:1V
for slope applications
Hydraulic Mulch;
Sod
Small
Channel
Up to
Mild Slopes
Stabilization of newly seeded areas
Immediate stabilization in channels,
around inlets, or for aesthetics
Suggested max. slope 3H:1V
Dust Control
As Req'd.
Areas subject to on- or off-site impacts
from surface/air movement of dust
Final Stabilization is defined as a uniform establishment (e.g. unevenly
distributed, without large bare areas) of vegetation cover as defined in Standard
Specification 604 — Seeding for Erosion Control on all unpaved areas and areas
not covered by permanent structures, or other permanent stabilization measures,
such as rip -rap, gabions, or geotextile fabric, have been employed and soil
disturbance activities at the site have ceased.
Removal of vegetative cover and alteration of soil structure by clearing, grading,
and compacting the surface increases an area's susceptibility to erosion. Apply
stabilizing measures immediately after the land is disturbed. Plan and implement
temporary or permanent vegetation, mulches, or other protective practices to
correspond with construction activities. Protect channels from erosive forces by
using protective linings and the appropriate channel design. Table C-2 provides
guidance for appropriate stabilization of temporary and permanent open
channels. Outlet stabilization and flow spreading measures must be
implemented to reduce the effects of concentrated flow. Consider possible future
repairs and maintenance of these practices in the design. Seeding establishes a
AC -4
vegetative cover on disturbed areas and is very effective in controlling soil
erosion once adequate vegetative cover has been established. However, often
seeding and fertilizing do not produce as thick a vegetative cover as do seed and
mulch or netting. Newly established vegetation does not have as extensive of a
root system as existing vegetation and therefore is more prone to erosion,
especially on steep slopes. Care should be taken when fertilizing to avoid
untimely or excessive application. Salvaged topsoil can and should be used to
revegetate a site. Sod can also be used to permanently stabilize an area.
The management of land by using ground cover reduces erosion by reducing the
rate of runoff and raindrop impact. In very flat, non -sensitive areas with favorable
soils, stabilization may involve simply seeding and fertilizing. Erosion
blankets/matting may be necessary on steeper slopes, for erodible soils, and
near sensitive areas. Sediment that has escaped the site due to the failure of
sediment and erosion controls shall be cleaned up as soon as possible to
minimize offsite impacts which may include roadways, ponds, lakes, and creeks.
Permission shall be obtained from adjacent landowners prior to offsite sediment
clean up.
Mulching/mats can be used to protect disturbed areas while vegetation is being
established. Mulching involves applying plant residues or other suitable materials
on disturbed soil surfaces. Mulches/mats used include tacked straw, wood chips,
and jute netting and are often covered by blankets or netting. Mulching alone
shall be used only for temporary protection of the soil surface or when permanent
seeding is not feasible. The useful life of mulch varies with the material used,
exposure of the area to traffic, and the amount of precipitation, but is
approximately 2 to 6 months. During times of year when vegetation cannot be
established, soil mulching shall be applied to moderate slopes and soils that are
not highly erodible. Before stabilizing an area, it is important to have installed all
sediment controls and diverted runoff away from the area to be planted. Runoff
may be diverted away from denuded areas or newly planted areas using dikes,
swales, or pipe slope drains to intercept runoff and convey it to a permanent
channel or storm drain. If runoff cannot be diverted, as is often the case with
drainage channels, the use of erosion blankets/matting should be considered to
protect soil and seed until vegetation becomes established. The cost of the
blankets/matting is often less than the cost of regrading, reseeding, clean-up of
escaped sediments, replacing topsoil and maintaining temporary erosion
controls.
AC -5
Depth
D (ft)
0.1
0.3
0.5
0.7
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
5.5
6.0
6.5
7.0
Table C-2 Ranges of Shear (pounds per square foot) by Depth and Slope
for Open Channel Flow
Assumptions: Approximately 30 inches of rainfall a year (able to sustain a "fair" vegetative cover)
"fair soil" for vegetation growth. Soil silt, sand, clay mixture.
"hydraulically wide" channel with generally straight alignment
Notes: Shear around bends can be greater than these values depending upon ratio of bend radius to bottom width.
This chart is intended to be used as a quick visual guide and does not take the place of individual site analysis.
The divisions between the different zones are estimates and may vary with differing site conditions.
SHEAR RANGE SOIL STABILIZATION REQUIREMENTS
Legend: ZONE 1 under 0.5 psf None - bare soil (depending upon type of soil), vegetation required for permanent channels
ZONE 2 up to 3 psf Grass/vegetation
ZONE 3 up to 6-8 psf Soft armor (e.g. geosynthetic matting, erosion control blankets)
ZONE 4 over 7 to 8 psf Hard armor (e.g. rip rap, gabion)
D = Water Depth
SLOPE (FT/FT)
0.002 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045 0.050 0.055 0.060 0.065 0.070 0.075 0.080 0.085 0.090 0.095 0.100
ZONE 1 1 1 ZONE 2
0.01
0.04
0.06
0.09
0.12
0.15
0.17
0.20
0.22
0.25
0.27
0.30
0.32
0.35
0.37
0.40
0.42
0.45
0.47
0.50
0.52
0.55
0.57
0.60
0.62
0.69
0.75
0.81
0.87
0.03
0.09
0.16
0.22
0.31
0.37
0.44
0.50
0.56
0.62
0.69
0.75
0.81
0.87
0.94
1.00
1.06
1.12
1.19
1.25
1.31
1.37
1.44
1.50
1.56
1.72
1.87
2.03
2.18
0.06 0.09 0.12 0.16 0.19 0.22 0.25 0.28 0.31 0.34 0.37 0.41 0.44 0.47 0.50 0.53 0.56 0.59 0.62
0.19 0.28 0.37 0.471 0.56
0.31 0.471 0.62 0.78 0.94
0.441 0.66 0.87 1.09 1.31
0.62 0.94 1.25 1.56 1.87
0.75 1.12 1.50 1.87 2.25
0.87 1.31 1.75 2.18 2.62
1.00 1.50 2.00 2.50 3.00
1.12 1.68 2.25 2.81 3.37
1.25 1.87 2.50 3.12 3.74
1.37 2.06 2.75 3.43 4.12
1.50 2.25 3.00 3.74 4.49
1.62 2.43 3.24 4.06 4.87
1.75 2.62 3.49 4.37 5.24
1.87 2.81 3.74 4.68 5.62
2.00 3.00 3.99 4.99 5.99
2.12 3.18 4.24 5.30 6.36
2.25 3.37 4.49 5.62 6.74
2.37 3.56 4.74 5.93 7.11
2.50 3.74 4.99 6.24 7.49
2.62 3.93 5.24 6.55 7.86
2.75 4.12 5.49 6.86 8.24
2.87 4.31 5.74 7.18 8.61
3.00 4.49 5.99 7.49 8.99
3.12 4.68 6.24 7.80 9.36
3.43 5.15 6.86 8.58 10.30
3.74 5.62 7.49 9.36 11.23
4.06 6.08 8.11 10.14 12.17
4.37 6.55 8.74 10.92 13.10
ZONE 3
Adapted from Andy Johnston, P.E.
0.66 0.75 0.84
1.09 1.25 1.40
1.53 1.75 1.97
0.94 1.03 1.12 1.22 1.31 1.40 1.50 1.59 1.68 1.78 1.87
1.56 1.72 1.87 2.03 2.18 2.34 2.50 2.65 2.81 2.961-3M
2.18 2.40 2.62 2.84 3.06 3.28 3.49 3.71 3.93 4.15 4.37
2.18 2.50 2.811 3.12
2.62 3.00 3.37 3.74
3.06 3.49 3.93 4.37
3.49 3.99 4.49 4.99
3.93 4.49 5.05 5.62
4.37 4.99 5.62 6.24
4.80 5.49 6.18 6.86
5.24 5.99 6.74 7.49
5.68 6.49 7.301 8.11
6.12 6.99 7.86 8.74
6.55 7.49 8.42 9.36
6.99 7.99 8.99 9.98
7.43 8.49 9.55 10.61
7.86 8.99 10.11 11.23
8.30 9.48 10.67 11.86
8.74 9.98 11.23 12.48
9.17 10.48 11.79 13.10
9.61 10.98 12.36 13.73
10.05 11.48 12.92 14.35
10.48 11.98 13.48 14.98
10.92 12.48 14.04 15.60
12.01 13.73 15.44 17.16
13.10 14.98 16.85 18.72
14.20 16.22 18.25 20.28
15.29 17.47 19.66 21.84
3.43 3.74 4.06 4.37 4.68 4.99 5.30 5.62 5.93 6.24
4.12 4.49 4.87 5.24 5.62 5.99 6.36 6.74 7.11 7.49
4.80 5.24 5.68 6.12 6.55 6.99 7.431 7.86 8.30 8.74
5.49 5.99 6.49 6.99 7.491 7.99 8.49 8.99 9.48 9.98
6.18 6.74 7.30 7.86 8.42 8.99 9.55 10.11 10.67 11.23
6.86 7.49 8.11 8.74 9.36 9.98 10.61 11.23 11.86 12.48
7.55 8.24 8.92 9.61 10.30 10.98 11.67 12.36 13.04 13.73
8.24 8.99 9.73 10.48 11.23 11.98 12.73 13.48 14.23 14.98
8.92 9.73 10.55 11.36 12.17 12.98 13.79 14.60 15.41 16.22
9.61 10.48 11.36 12.23 13.10 13.98 14.85 15.72 16.60 17.47
10.30 11.23 12.17 13.10 14.04 14.98 15.91 16.85 17.78 18.72
10.98 11.98 12.98 13.98 14.98 15.97 16.97 17.97 18.97 19.97
11.67 12.73 13.79 14.85 15.91 16.97 18.03 19.09 20.16 21.22
12.36 13.48 14.60 15.72 16.85 17.97 19.09 20.22 21.34 22.46
13.04 14.23 15.41 16.60 17.78 18.97 20.16 21.34 22.53 23.71
13.73 14.98 16.22 17.47 18.72 19.97 21.22 22.46 23.71 24.96
14.41 15.72 17.04 18.35 19.66 20.97 22.28 23.59 24.90 26.21
15.10 16.47 17.85 19.22 20.59 21.96 23.34 24.71 26.08 27.46
15.79 17.22 18.66 20.09 21.53 22.96 24.40 25.83 27.27 28.70
16.47 17.97 19.47 20.97 22.46 23.96 25.46 26.96 28.45 29.95
17.16 18.72 20.28 21.84 23.40 24.96 26.52 28.08 29.64 31.20
18.88 20.59 22.31 24.02 25.74 27.46 29.17 30.89 32.60 34.32
20.59 22.46 24.34 26.21 28.08 29.95 31.82 33.70 35.57 37.44
22.31 24.34 26.36 28.39 30.42 32.45 34.48 36.50 38.53 40.56
24.02 26.21 28.39 30.58 32.76 34.94 37.13 39.31 41.50 43.68
1 ZONE 4 1
AC -6
C.2.1 Interceptor Swale
Interceptor swales are used to shorten the length of exposed slope by
intercepting runoff and can also serve as perimeter swales preventing off-site
runoff from entering the disturbed area or prevent sediment -laden runoff from
leaving the construction site or disturbed area. They may have a v -shape or be
trapezoidal with a flat bottom and side slopes of 3:1 or flatter. The outflow from a
swale should be directed to a stabilized outlet or sediment -trapping device. The
swales shall remain in place until the disturbed area is permanently stabilized or
until an alternative plan, approved by the City, is in place. A schematic of an
interceptor swale is shown in Figure C-1.
Materials:
• Stone stabilization shall be used when grades exceed 2% or velocities
exceed 6 feet per second and should consist of a layer of crushed stone
three inches thick, riprap or high velocity erosion control mats.
• Stabilization shall extend across the bottom of the swale and up both
sides of the channel to a minimum height of three inches above the design
water surface elevation based on a 1 -year, 3 -hour storm, or the design
discharge of the water conveyance structure, whichever is greater.
Installation:
• An interceptor swale shall be installed across exposed slopes during
construction and shall intercept no more than 5 acres of runoff.
• All earth removed and not needed in construction shall be disposed of in
an approved spoils site or temporarily stored for future use in a protected
area so that it will not interfere with the functioning of the swale or
contribute to siltation in other areas of the site.
• All trees, brush, stumps, obstructions and other material shall be removed
and disposed of so as not to interfere with the proper functioning of the
swale.
• Swales shall have a maximum designed water depth of 1.5 feet with a 0.5
foot freeboard and with side slopes of 3:1 or flatter. Swales shall have
positive drainage for its entire length to an outlet.
• When the slope exceeds 2 percent, or velocities exceed 6 feet per second
(regardless of slope), stabilization is required. Stabilization shall be
AC -7
crushed stone placed in a layer of at least 3 inches thick or may be high
velocity erosion control matting. Check dams (see section C.3.9) are also
recommended to reduce velocities in the swales possibly reducing the
amount of stabilization necessary.
• Minimum compaction for the swale shall be 90% standard proctor density.
Inspection and Maintenance Guidelines:
• Interceptor swales should be inspected weekly, prior to forecasted rain
events, and after each rain event to locate and repair any damage to the
swale or clear debris or other obstructions so as not to diminish flow
capacity.
• Damage from storms or normal construction activities such as tire ruts or
disturbance of swale stabilization shall be repaired immediately.
C.2.2 Diversion Dikes
A temporary diversion dike is a barrier created by the placement of an
embankment to reroute the flow of runoff to an erosion control device or away
from an open, easily erodable area. A diversion dike intercepts runoff from small
upland areas and diverts it away from exposed slopes to a stabilized outlet, such
as a rock berm, sandbag berm, or stone outlet structure. These controls can be
used on the perimeter of the site to prevent runoff from entering the construction
area. Dikes are generally used for the duration of construction to intercept and
reroute runoff from disturbed areas to prevent excessive erosion until permanent
drainage features are installed and/or slopes and disturbed areas are stabilized.
Caution must be exercised when implementing diversion dikes to ensure against
adverse flooding caused to upstream property. A schematic of a diversion dike is
shown in Figure C-2.
Materials:
• Stone stabilization (required for velocities in excess of 6 fps) should
consist of erosion control matting or crushed 3-5 inch stone placed in a
layer at least 5 inches thick extending a minimum height of 8 inches above
the design water surface on the upstream face of the dike and up the
existing slope upstream of the dike. Geotextile fabric shall be a non -woven
polypropylene fabric designed specifically for use as a soil filtration media
with an approximate weight of 4 oz. /yd2
Installation:
AC -8
• Diversion dikes shall be installed prior to and maintained for the duration
of construction and shall intercept no more than 10 acres of runoff.
• Dikes shall have a minimum top width of 2 feet and a minimum height of
compacted fill of 18 inches measured from the top of the existing ground
at the upslope toe to top of the dike and having side slopes of 3:1 or
flatter. The top of the dike shall provide a 0.5 foot freeboard above the
design water elevation.
• The soil for the dike shall be placed in lifts of 8 inches or less and be
compacted to 95 % standard proctor density.
• The channel, which is formed by the dike, must have positive drainage for
its entire length to an outlet.
• When the slope exceeds 2 percent, or velocities exceed 6 feet per second
(regardless of slope), stabilization is required. Situations in which
velocities do not exceed 6 feet per second, vegetation may be used to
control erosion.
Inspection and Maintenance Guidelines:
• Swales shall be inspected weekly, prior to forecasted rain events, and
after each rain event to determine if silt is building up behind the dike or if
erosion is occurring on the face of the dike. Locate and repair any damage
to the dike or channel and clear debris or other obstructions so as not to
diminish flow capacity.
• Silt shall be removed in a timely manner to prevent further sediment
transportation and to maintain the effectiveness of the control.
• If erosion is occurring on the face of the dike, the slopes of the face should
either be stabilized through mulch or seeding or the slopes of the face
should be reduced.
• Damage from storms or normal construction activities such as tire ruts or
disturbance of stone stabilization shall be repaired as soon as practical.
C.2.3 Pipe Slope Drain
A pipe slope drain is an erosion control device that combines a diversion dike
and a pipe to prevent runoff over an exposed slope and to carry runoff to a
stabilized outlet apron. The maximum area contributing to any one drain should
be 5 acres or less. The pipe shall be sized to convey the 1 -year, 3 -hr storm or
AC -9
the design discharge of the water conveyance structure, whichever is greater. A
diagram of a slope drain is shown in Error! Reference source not found.3.
Materials:
• The drain pipe shall be made of any material, rigid or flexible, which is
capable of conveying runoff. The drainpipe shall be completely watertight
so that no water leaks on to the slope to be protected.
• Riprap to be used in the outlet apron should consist of either crushed
stone or broken Portland cement concrete. All stones used should weigh
between 50 and 150 pounds each and should be as nearly uniform as is
practical.
Installation:
• A diversion dike shall be constructed at the top of the slope that is to be
protected. This dike shall be sized and installed in accordance with
section C.2.2 "Diversion Dikes". The soil around and under the entrance
section of the drainpipe shall be hand -tamped in 8 -inch lifts to prevent
piping failure around the inlet.
• The height of the diversion dike at the centerline of the inlet shall be equal
to the diameter of the pipe plus 12 inches.
• A rigid section of pipe shall be installed through the dike. A standard
flared -end section with an integral toe plate extending a minimum of 6 -
inches from the bottom of the end section shall be attached to the inlet
end of the pipe using watertight fittings.
• A riprap-lined apron shall be excavated to accept the runoff from the pipe
and dissipate the energy of the flow. The width of the bottom of the apron
shall be 3 times the pipe diameter and the length shall be a minimum of 6
times the pipe diameter. The apron shall be a minimum of 12 -inches deep
and Tined with riprap with a thickness of at least 12 inches. The apron
shall be designed so that the released flow has a velocity Tess than 3 feet
per second.
Inspection and Maintenance Guidelines:
AC -10
• Temporary pipe slope drains shall be inspected weekly and after each rain
event to locate and repair any damage to joints or clogging of the pipe.
• In cases where the diversion dike has deteriorated around the entrance of
the pipe, it may be necessary to reinforce the dike with sandbags or to
install a concrete collar to prevent failure.
• Signs of erosion around the pipe drain shall be addressed in a timely
manner by stabilizing the area with erosion control mats, crushed stone,
concrete or other appropriate method.
C.2.4 Channel Stabilization
Temporary roadside ditches, drainage channels and similar conveyances must
be properly designed and stabilized to resist erosion from the design flows. New
or altered channels can be lined with grass, erosion blankets/matting, rip rap
revetment or other materials. The channels should be designed in accordance
with section 6 of this manual. Key parameters in channel design include
permissible velocity, roughness coefficient, side slope, curvature, bottom width,
and freeboard.
Materials:
• Grass, erosion blankets/matting, or rip rap revetment as determined by
maximum velocity and shear stress (see Table C-2). The grass species
selected must be suitable for permanent application based upon the
anticipated operation and maintenance of the channel or waterway.
Design Guidelines:
• The maximum permissible velocity for a grassed channel is six (6) feet per
second and includes all transitions to or from channels and waterways
with similar or different materials. In all cases, the velocity for design
storm must be non-erosive. Shear stress may be significant even at lower
velocities. Table C-2 should be consulted to determine if armoring of the
channel is appropriate. Refer to Section C.2.11 for erosion
blanket/matting guidance. Figure C-4 provides sizing guidelines for rock
rip rap. U.S. Army Corps of Engineers Circular HEC -11 should be
referenced for further details regarding rip rap revetment design.
AC -11
• Side slopes shall be 3H:1V or flatter. Steeper slopes will require
stabilization in the form of erosion blankets/matting, rock rip rap or
structural methods. Refer to Section C.2.11 for blankets/matting.
• The roughness coefficients selected shall be based on the degree of
retardance of vegetation. Section 6 of this manual provides minimum
Manning's Coefficients for channel design. The roughness coefficient shall
be adjusted to reflect the relationship between the depth of flow and the
typical height of the design vegetation, especially for shallow depths of
flow, as well as other factors affecting channel conveyance.
Installation:
• Refer to section C.2.8 and C.2.11 for guidance regarding vegetation
establishment and blankets/matting.
Inspection and Maintenance Guidelines:
• Channels shall be inspected periodically and after any significant rain
events to locate and repair any damage to the channel or clear debris or
other obstructions so as not to diminish flow capacity.
• Damage from storms or vehicles should be repaired as soon as practical.
AC -12
STONE DIAMETER IN INCHES
48
42
36
30
24
18
12
6
0
II 1I1III1I1.III
THE RIPRAP SHOULD BE
- COMPOSED OF A WELL -GRADED
- MIXTURE, BUT MOST OF THE
- STONE SHOULD BE OF THE SIZE
- INDICATED BY THE CURVE.
- RIPRAP SHOULD BE PLACED OVER
A FILTER BLANKET OR BEDDING
- GRADED GRAVEL IN A LAYER 1.5
TIMES (OR MORE) AS THICK AS
_ THE LARGEST STONE DIAMETER.
0
5
10
15
20
BOTTOM VELOCITY IN FEET PER SECOND
5000
4000
3500
3000
2500
2000
1500
1000
900
800
700
600
500
400
300
250
200
150
100
75
50
25
10
5
0
Figure C-4 Rock Riprap Size Selection
AC -13
C.2.5 Outlet Stabilization
The goal of outlet stabilization is to prevent erosion at the outlet of a channel or
conduit by reducing the velocity of flow and dissipating the energy. This practice
applies where the discharge velocity of a pipe, box culvert, diversion, open
channel, or other water conveyance structure exceeds the permissible velocity of
the receiving channel or disposal area.
The outlets of channels, conduits, and other structures are points of high erosion
potential, because they frequently carry flows at velocities that exceed the al-
lowable limit for the area downstream. To prevent scour and undermining, an
outlet stabilization structure is needed to absorb the impact of the flow and
reduce the velocity to non-erosive levels. A riprap-lined apron is the most com-
monly used practice for this purpose because of its relatively low cost and ease
of installation. The riprap apron should be extended downstream until stable
conditions are reached even though this may exceed the length calculated for
design velocity control.
• Riprap-stilling basins or plunge pools reduce flow velocity rapidly. They
should be considered in lieu of aprons where overfalls exit at the ends of
pipes or where high flows would require excessive apron length. Consider
other energy dissipaters such as concrete impact basins or paved outlet
structures where site conditions warrant. U.S. Army Corps of Engineers
Circular HEC -14 should be referenced for further details regarding energy
dissipation.
Materials:
• Materials—Ensure that riprap consists of a well -graded mixture of stone.
Larger stone should predominate, with sufficient smaller sizes to fill the
voids between the stones. The maximum stone diameter should be no
greater than 1.5 times the d50 size. Refer to Figure C-4 for appropriate
stone size.
• Thickness—The minimum thickness of riprap shall be 1.5 times the
maximum stone diameter.
• Stone quality—Select stone for riprap from field stone or quarry stone. The
stone should be hard, angular, and highly weather -resistant. The specific
gravity of the individual stones should be at least 2.5.
• Filter Blanket/ Geotextile Fabric—Install appropriate barrier to prevent soil
movement through the openings in the riprap. The barrier should consist
of a graded gravel layer or a synthetic filter cloth beneath the riprap.
AC -14
f
3d0
1
A
Pipe Outlet to Flat Area—
No WeII-defined Channel
doIPi1.�•a
0 0
4!3;Lrt
I�
•%r
Plan
Section AA
Pipe Outlet to WeII-defined
Channel
ger 111/ 111 GOP janaird) Oar/ II I. 110
411 h e00407 %;1!SPS
'WI .....��.–�
1,111trl
� i j e pi%'a�
II
IIIIIi}i
Filter
blanket
11
"�u1-- ilklf�
Filter
blanket
Figure C-5 Schematic Riprap Outlet Design
Notes
1. La is the length of the riprap
apron.
2. d = 1.5 times the maximum
stone diameter but not less
than 6".
3. In a well-defined channel ex-
tend the apron up the channel
banks to an elevation of 6"
above the maximum tailwater
depth or to the top of the bank,
whichever is less.
4. A filter blanket or filter fabric
should be installed between
the riprap and soil foundation.
Design Guidelines:
• Capacity - outlet stabilization should be designed in accordance with local
drainage criteria (see Section 5).
• Apron size - If the water conveyance structure discharges directly into a
well-defined channel, extend the apron across the channel bottom and up
the channel banks to an elevation of 0.5 ft above the maximum tailwater
depth or to the top of the bank, whichever is Tess. Determine the maximum
allowable velocity for the receiving stream, and design the riprap apron to
reduce flow to this velocity before flow leaves the apron. Calculate the
apron length for velocity control or use the length required to meet stable
conditions downstream, whichever is greater. If the allowable downstream
velocity cannot be readily determined, the following relationship may be
used:
Equation C.1 La = 0.5 V* D
Where: La = Length of rip rap apron, ft
V = Culvert discharge velocity, ft/s
D = inside diameter or height of culvert, ft
• Grade - Ensure that the apron has zero grade. There should be no over -
fall at the end of the apron; that is, the elevation of the top of the riprap at
the downstream end should be the same as the elevation of the bottom of
the receiving channel or the adjacent ground if there is no channel.
• Alignment - The apron should be straight throughout its entire length, but if
a curve is necessary to align the apron with the receiving stream, locate
the curve in the upstream section of riprap.
Installation:
• Ensure that the subgrade for the fabric and riprap follows the required
lines and grades shown in the plan. Compact any fill required in the
subgrade to the density of the surrounding undisturbed material. Low
areas in the subgrade on undisturbed soil may also be filled by increasing
the riprap thickness.
• The riprap and fabric must conform to the specified grading limits shown
on the plans.
• Filter cloth must be properly protected from punching or tearing during
installation. Repair any damage by removing the riprap and placing
AC -16
another piece of filter cloth over the damaged area. All connecting joints
should overlap a minimum of 1 ft. If the damage is extensive, replace the
entire filter cloth.
• Riprap may be placed by equipment, but take care to avoid damaging the
fabric.
• The minimum thickness of the riprap should be 1.5 times the maximum
stone diameter.
• Riprap may be field stone or rough quarry stone. It should be hard,
angular, highly weather -resistant and well graded.
• Construct the apron on zero grade with no overfall at the end. Make the
top of the riprap at the downstream end level with the receiving area or
slightly below it.
• Ensure that the apron is properly aligned with the receiving stream and
preferably straight throughout its length. If a curve is needed to fit site
conditions, place it in the upper section of the apron.
• Immediately after construction, stabilize all disturbed areas with
vegetation.
Inspection and Maintenance Guidelines:
Inspect riprap outlet structures after heavy rains to see if any erosion around or below the riprap 1
taken place or if stones have been dislodged. Immediately make all needed repairs to prevent furt
damage.
C.2.6 Level Spreaders
A level spreader is used to convert concentrated runoff into sheet flow and
release it uniformly onto areas stabilized by existing vegetation. Sheet flow
conditions are recommended prior to runoff entering a vegetative filter strip or a
creek buffer. During the construction process, level spreaders can be used
where there is a need to divert storm water away from disturbed areas to avoid
overstressing erosion control measures or where storm runoff can be released in
sheet flow down a stabilized slope without causing erosion.
This section presents a flow spreader consisting of an excavated depression
constructed at zero grade across a slope with a level lip. Multiple options are
provided for the level lip and include a grass hedge row, reinforced vegetation, a
rock berm, and a rigid timber lip. Refer to Figures C-6 and C-7 for a schematic
and cross sections of these various options. Other flow spreader designs can be
AC -17
used as long as they convert concentrated runoff to sheet flow as defined in this
section.
Sheet flow is defined at a flow depth of less than 0.2 feet or 2.4 inches and a
velocity of less than one (1) foot per second during the peak flowrate from the 1 -
year, 3 -hour storm event under fully -developed conditions. The hydrologic and
hydraulic reference tables in Section 2 and 6 of this manual respectively can be
used with the Rational Method to determine the fully -developed peak flow rate.
The following equation based on the Continuity Equation (Q=VA) can be used to
determine the required flow spreader length.
Equation C.2 L = 5Q1Year-Dev
Where: L = minimum required length of flow spreader (ft)
Q1 YR = fully -developed peak flow rate for the 1 -yr, 3 -hr storm
event (cfs)
Particular care should be taken to construct the outlet lip at a level elevation in a
stable, undisturbed soil. Any depression in the lip will concentrate the flow,
potentially resulting in erosion. Under higher design flow conditions, a rigid outlet
Hp design should be used to create the desired sheet flow conditions. Runoff
water containing high sediment loads must be treated in a sediment -trapping
device before being released to a level spreader.
Installation:
• Level spreaders should be constructed on undisturbed soil (not fill
material)
• The entrance to the spreader should be shaped in such a manner as to
insure that runoff enters directly onto the 0% grade channel
• Construct a transition section from the diversion channel to blend
smoothly to the width and depth of the spreader.
• The level lip should be constructed at 0% grade to insure uniform
spreading of storm water runoff.
• Immediately after its construction, establish vegetation along the entire
disturbed area of the spreader. A vegetative cover density of 80% with no
large bare areas is required.
• Level spreaders are to be staked along a contour prior to construction.
AC -18
Inspection and Maintenance Guidelines:
• Level spreaders used temporarily or permanently established during
construction activities shall be inspected weekly, prior to forecasted rainfall
events, and after rainfall events. Level spreaders shall be inspected
annually and repairs made, if required.
• Level spreader lip should remain at 0% slope to allow proper function of
measure.
• The contractor should avoid the placement of any material on and prevent
construction traffic across the structure. If the measure is damaged by
construction traffic, it should be repaired immediately.
AC -19
GRASS HEDGE (ALAMO
SWITCHGRASS OR
APPROVED SUBSTITUTE
MILORGANITE OR EQUIVALENT -
SLOW REALEASE ORGANIC
FERTILIZER AT TOP OF FIRST LIFT ______Z":
2'± DEEP CUT FILLED WITH f 8" MIN.
NATIVE TOPSOIL LIGHTLY
COMPACTED
TEMPORARY SILT
[FENCE
VARIABLE (MIN 7'
MIN. 6'
LEVEL SPREADER WITH GRASS HEDGE ROW
PROTECTIVE COVERING
STAPLED IN PLACE
BURIED 6" MIN.
VARIABLE (MIN. 7'
2:1 OR
FLATTER
LEVEL LIP OF BURIED 6" MIN.
SPREADER
MIN. 6'
LEVEL SPREADER WITH REINFORCED VEGETATED LIP
12" MIN
�---- 2' MIN
3" TO 5" OPEN
GRADED ROCK
WOVEN WIRE
SHEATHING
2:1 OR
FLATTER
6" MIN
LEVEL LIP OF
SPREADER
LEVEL LIP OF SPREADER
COARSE AGGREGATE IN
GALVANIZED WIRE MESH BASKET
SECURE WIRE TO
GROUND WITH WIRE
STAPLES
FILTER CLOTH
MIN. 6'
LEVEL SPREADER WITH ROCK BERM LIP
VARIABLE (MIN. 7'
2:1 OR
FLATTER
6X6 TREATED TIMBER
SECURE WIRE MESH TO TIMBER
#5 REBAR TO SECURE TIMBER
MIN. 6'
LEVEL SPREADER WITH RIGID TIMBER LIP
Figure C-7: Level Spreader Lip Options
2:1 OR
FLATTER
AC -20
C.2.7 Subsurface Drains
A subsurface drain is a perforated conduit such as pipe, tubing or tile installed
beneath the ground to intercept and convey ground water. The main purposes
are to: prevent sloping soils from becoming excessively wet and subject to
sloughing, improve the quality of the growth medium in excessively wet areas by
lowering the water table (see Figure C-8), or drain storm water detention areas or
structures.
WATER TABLE BEFORE DRAINAGE
WATER TABLE AFTER DRAINAGE
INTERCEPTOR DRAIN
SEEPAGE AREA.
Figure C-8 Effect of Subsurface Drain
This measure is appropriate wherever excess water must be removed from the
soil. The soil must be deep and permeable enough to allow an effective system
to be installed. Either a gravity outlet must be available or pumping must be
provided. These standards do not apply to foundation drains.
Subsurface drainage systems are of two types, relief drains and interceptor
drains. Relief drains are used either to lower the water table in order to improve
the growth of vegetation, or to remove surface water. They are installed along a
slope and drain in the direction of the slope. They can be installed in a gridiron
pattern, a herringbone pattern, or a random pattern (see Figure C-9).
Interceptor drains are used to remove water as it seeps down a slope to prevent
the soil from becoming saturated and subject to slippage. They are installed
across a slope and drain to the side of the slope. They usually consist of a single
pipe or series of single pipes instead of a patterned layout.
Materials:
Acceptable materials for subsurface drains include perforated, continuous
closed -joint conduits of pvc, corrugated plastic, concrete, and corrugated metal.
AC -21
The strength and durability of the pipe should meet the requirements of the site in
accordance with the manufacturer's specifications.
.....................
RANDOM PATTERN
HERRINGBONE PATTERN
PARALLEL PATTERN
LATERAL
MAIN
••......• .• ....• ........• .......• ..................................• ...........::::.
Figure C-9 Subsurface Drainage Patterns
General Installation Requirements:
OUTLET
• The trench should be constructed on a continuous grade with no reverse
grades or low spots.
• Soft or yielding soils under the drain should be stabilized with gravel or
other suitable material.
• Deformed, warped, or otherwise unsuitable pipe should not be used. The
minimum diameter for a subsurface drain should be 4 inches.
• Aggregate envelopes (1" to IW crushed stone) and filter material should
be placed as specified with at least 6 inches of material on all sides of the
pipe.
AC -22
• The trench should be backfilled immediately after placement of the pipe.
No sections of pipe should remain uncovered overnight or during a
rainstorm. Backfill material should be placed in the trench in such a
manner that the drain pipe is not displaced or damaged.
Relief Drain Installation:
• Relief drains should be located through the center of wet areas. They
should drain in the same direction as the slope.
• Relief drains installed in a uniform pattern should remove a minimum of 1
inch of groundwater in 24 hours (0.042 cfs/acre). Relief drains installed in
a random pattern should remove a minimum of 1.5 cfs/1000 feet of length.
The design capacity should be increased accordingly to accommodate
any surface water which enters directly into the system (see Figure C-9).
• Relief drains installed in a uniform pattern should have equal spacing
between drains and the drains should be at the same depth. Maximum
depth is limited by the allowable load on the pipe, depth to impermeable
layers in the soil, and outlet requirements. The minimum depth is 24
inches under normal conditions. Twelve inches is acceptable where the
drain will not be subject to equipment loading. Spacing between drains is
dependent on soil permeability and the depth of the drain. In general,
however, a depth of 3 feet and a spacing of 50 feet will be adequate.
• The minimum velocity required to prevent silting is 1.4 ft/sec. The line
should be graded to achieve at least this velocity. Steep grades should be
avoided, however.
• Envelopes of 1" to 1'/z" crushed stone should be used around all drains for
proper bedding and improved flow of groundwater into the drain. The
envelope should consist of 6 inches of aggregate placed completely
around the drain. The stone should be encompassed by a filter cloth
separator to prevent the migration of surrounding soil particles into the
drain (see Figure C-11). Filter cloth must be designed specifically for soil
filtration.
• The outlet of the subsurface drain should empty into a channel or some
other watercourse that will remove the water from the outlet. It should be
above the normal water level in the receiving channel. It should be
protected from erosion, undermining, damage from periods of
submergence, and the entry of small animals into the drain.
Interceptor Drain Installation:
AC -23
• Interceptor drains should remove a minimum of 1.5 cfs/1000 feet of length.
This value should be increased for sloping land. In addition, if a flowing
spring or surface water enters directly into the system, this flow must be
accommodated and the design capacity should be increased accordingly
to take care of this flow.
• The depth of installation of an interceptor drain is influenced mainly by the
depth to which the water table is to be lowered. The maximum depth is
limited by the allowable Toad on the pipe and the depth to an impermeable
layer. The minimum depth should be the same as for relief drains.
• One interceptor drain is usually sufficient; however, if multiple drains are to
be used, determining the required spacing can be difficult. The best
approach is to install the first drain - then if seepage or high water table
problems occur down slope, install an additional drain a suitable distance
down slope.
AC -24
SOD OR COARSE AGGREGATE
COARSE AGGREGATE
1-III-III-III-III-III-IIIII I
NATURAL INLET
(I,Y 4,,; P'1;i!ri IIIIIIIil► 4�`11'1� + 1ttiR;1tC
I. .II -11-11 ' 11x=11=11=11
11=11=11=1 1=11=11-11.
=II=11=11: 11=11=11=
'11=11=11=1 1=11=11`-11:
11x=11 11 11=11=11-
11=11=11=1 1=11.=11.=11:
11=11=11' 11=11x-11=
.11=11m11=.1 1=11=11=11
11'=1L=11=1 11=N-11 11
11:11: I CI1---11 IL1�:11.�11111
11.11=1111=-11=11.11=11=IL=t11
1=11-11=11=11=11
.
GRATED INLET
Figure C-10 Surface Inlets for Subsurface Drains Schematic
FILTER CLOTH
Figure C-11 Subsurface Drain Envelope Schematic
AC -25
Inspection and Maintenance Guidelines:
• Subsurface drains should be checked periodically and after rainfall events
to ensure that they are free flowing and not clogged with sediment.
• The outlet should be kept clean and free of debris.
• Surface inlets should be checked weekly, prior to forecasted rain events,
after rainfall events, and kept open and free of sediment and other debris.
• Trees located too close to a subsurface drain often clog the system with
their roots. If a drain becomes clogged, relocate the drain.
• Where heavy vehicles cross drains, the line should be checked to ensure
that it is not crushed.
C.2.8 Vegetation
Vegetation is used as a temporary or permanent stabilization technique for
disturbed areas. As a temporary control, vegetation can be used to stabilize
stockpiles and barren areas that are inactive for long periods of time.
Vegetative techniques will apply to every construction project with few
exceptions. Vegetation effectively reduces erosion in swales, stockpiles, berms,
mild to medium slopes, and along roadways.
Other techniques may be required to assist in the establishment of vegetation.
These other techniques include erosion control matting, mulches, surface
roughening, swales and dikes to direct runoff around newly seeded areas, and
proper grading to limit runoff velocities during construction. (NCTCOG, 1993b)
Native Versus Introduced Grasses:
Introduced grasses, such as Bermuda grass and K. R. bluestem, are
frequently planted for erosion control purposes. They may provide superior soil
protection, but they may also have disadvantages, particularly in areas where
native grasses are the eventual goal.
Bermuda grass, for example is an excellent soil binder but it provides poor
habitat for ground feeding birds (Anon., 1971). In infertile areas it can only be
maintained with annual additions of nitrogen (Bieber, et. al., 1968). In areas
where it is well established, it forms a uniform dense turf which retards the
invasion of desirable native species and provides very low habitat and species
diversity.
Bermuda grass or another introduced species is appropriate where the
primary objective is erosion control. Alternatively, if there are other objectives
AC -26
which include ecological, aesthetic or practical goals, native grasses are probably
more appropriate. Since the goal of restoration efforts as discussed here is the
establishment of natural vegetation, there seems to be no reason to plant
introduced grasses. The only exception to this is when they are to be used as
temporary ground cover in graded areas where ground work is incomplete and
where they will be graded or plowed under later. If native grasses fail to become
established in an area where it is possible for an introduced species to grow, the
latter should of course be planted. But as a rule, introduced species shall be
avoided.
Materials:
The type of vegetation used on a site is a function of the season and the
availability of water for irrigation. For areas that are not irrigated, the year can be
divided into two temporary planting seasons and one season for planting of
permanent warm weather groundcovers. These periods are shown in Figure C-
12 for central Texas. See Standard Specification 604 for seeding temporary and
permanent areas for erosion control.
Bermuda grass has been traditionally specified for permanent vegetation, with
the addition of Cereal or Winter Rye when seeding during cold months to provide
temporary cover until the onset of the growing season for Bermuda grass.
TxDOT has had success with native grasses and wildflowers and recent testing
indicates that native species are more drought tolerant and equally effective in
terms of erosion control. A native seed mixture containing Texas Wintergrass can
be used throughout the year. Reuse of native topsoil stripped off and stockpiled
during site clearing and grubbing provides an effective means to reestablish
native vegetation as the topsoil will contain seed and root material. Williamson
and Travis County agricultural extension agents are a good source for
suggestions for other types of vegetation. All seed shall be high quality, U.S.
Dept. of Agriculture certified seed.
Installation:
• Interim or final grading must be completed prior to seeding, minimizing all
steep slopes. In addition, all necessary erosion structures such as dikes,
swales, diversions, shall also be installed.
• Seedbed shall be well pulverized, loose, and uniform.
• A soil analysis is recommended to determine the amount of fertilization
required. When seeding with non-native species, fertilizer may be applied at
the rate of 40 pounds of nitrogen and 40 pounds of phosphorus per acre,
which is equivalent to about 1.0 pounds of nitrogen and phosphorus per 1000
square feet. Compost can be used instead of fertilizer and applied at the
same time as the seed.
AC -27
• Seeding rates should be as specified in Standard Specification 604 or as
recommended by a Williamson or Travis County agricultural extension agent.
• The seed shall be applied uniformly with a cyclone seeder, drill, cultipacker
seeder or hydroseeder (slurry includes seed, fertilizer and binder). Seed may
also be combined with hydraulic mulch (see Section C.2.13) and applied
simultaneously.
• Protect the seedbed with a mulch layer to conserve soil moisture. Compost,
hay or straw are recommended. Hay or straw mulch shall be applied at a rate
of approximately 2 tons per acre. Organic Compost mulch application is
covered in section C.2.12. Hay or straw mulch shall be anchored by crimping
or application of an organic tackifier.
• Protect slopes that are steeper than 3H:1 V and not exceeding 2H:1V with
appropriate erosion blankets/matting as described in the section C.2.11 to
prevent Toss of soil and seed.
• Evaluate velocity and shear stress for drainage channels, diversion dikes and
swales and protect with erosion blankets/matting as described in section
C.2.11.
Mean Precip (Inches)
Mean Temp (Degrees F)
PERMANENT WARM Temporary Warm Temporary Cool ei. Legume
li
er
er
/
Jan Feb Mar Apr May Jun Ju
Aug Sep Oct Nov Dec
Precipitation —- Temp
Figure C-12 Planting Dates for Central Texas
Irrigation Guidance:
AC -28
100
BO
60
40
20
0
Temporary irrigation shall be provided according to the schedule described
below, or to replace moisture Toss to evapotranspiration (ET), whichever is
greater. Significant rainfall (on-site rainfall of 1/2° or greater) may allow watering
to be postponed until the next scheduled irrigation. All automatic irrigation
systems shall have a dual sensor rain shut off switch that automatically shuts off
the irrigation systems when rain begins to fall and turns on the system if less than
1/2 inch of rain occurs.
Time Period
Irrigation Amount and Frequency
Within 2 hours of installation
Irrigate entire root depth, or to germinate seed
During the next 10 business
Days
Irrigate entire root depth every Monday,
Wednesday, and Friday
During the next 30 business
days or until Substantial
Completion
Irrigate entire root depth a minimum of once
per week, or as necessary to ensure vigorous
growth
During the next 4 months or
until Final Acceptance of the
Project
Irrigate entire root depth once every two
Weeks, or as necessary to ensure vigorous
Growth
Refer to Figure C-13, below, for average rainfall/ET data for the Austin area.
This data shall serve as a guide to the overall watering regime; however, actual
frequency and amount of irrigation water used shall be weather -dependent.
Inches
11
s
$
4
2
s
Jan Feb Mar
-
APr
May Jun Jul Aug Sep Oct Nov Dec
+ Rain
— 0-- ET
Figure C-13 Rainfall/ET Data for Austin
If cool weather induces plant dormancy, water only as necessary to maintain
plant health. Irrigate in a manner that will not erode the topsoil but will sufficiently
soak the entire depth of roots.
Inspection and Maintenance Guidelines:
• Areas with newly applied vegetation shall be inspected weekly and after
each rain event to locate and repair any erosion or other damage.
AC -29
• Erosion from storms or other damage shall be repaired as soon as
practical by regrading the area and applying new seed and mulch.
• If the vegetated cover is Tess than 80%, the area shall be reseeded.
C.2.9 Mulch
Mulch can be used as an aid to control erosion on critical sites during land
clearing and periods of construction when re -vegetation is not practical. The best
results are obtained from double shredded (2 - 4 inch) mulch. The most common
uses are as berms at the bottom of long, steep slopes and as a blanket in
channels where designed flow does not exceed 3.5 feet per second; on
interceptor swales and diversion dikes when design flow exceeds 6 feet per
second; and on long slopes where rill erosion hazard is high and planting is likely
to be slow to establish adequate protective cover.
Materials:
Mulch is easily obtained as a by-product of land clearing operations. It can also
be a cost saving item because it is a recycled material and may be suitable for
incorporating into the final vegetation/ landscape.
Inspection and Maintenance Guidelines:
• Mulch shall be inspected weekly and after each rain event to locate and
repair any erosion.
• Erosion from storms or other damage shall be repaired as soon as
practical by applying new layers of mulch.
C.2.10 Blankets and Matting
Blankets and matting material can be used as an aid to control erosion in high
velocity areas during the establishment period of protective vegetation. The most
common uses are: in channels, interceptor swales and diversion dikes where
designed flow exceeds 6 feet per second or where shear stresses exceed
erosion resistance of the channel surface; on short, steep slopes where erosion
hazard is high, where planting is likely to be slow to establish adequate protective
cover; and on stream banks where moving water is likely to wash out new
vegetative plantings. Shear stresses are used in selection of the appropriate
channel protection. Table C-2 shall be consulted in addition to the referenced
AC -30
velocity limits to determine the appropriate level of armoring for a channel, swale
or dike
Blankets and matting can also be used to create erosion stops on steep, highly
erodible watercourses. Erosion stops shall be placed approximately 3 feet down
channel from point of entry of a concentrated flow such as from culverts, tributary
channels or diversions or at points where a change in gradient or course of
channel occurs. Spacing of erosion stops on long slopes will vary, depending on
the erodibility of the soil and velocity and volume of flow.
Biodegradable rolled erosion control products (RECPs) are typically composed of
jute fibers, curled wood fibers, straw, coconut fiber, or a combination of these
materials. In order for an RECP to be considered 100% biodegradable, the
netting, sewing or adhesive system that holds the biodegradable mulch fibers
together must also be biodegradable.
Non -biodegradable RECPs are typically composed of polypropylene,
polyethylene, nylon or other synthetic fibers. In some cases, a combination of
biodegradable and synthetic fibers is used to construct the RECP. Netting used
to hold these fibers together is typically non -biodegradable as well.
Materials:
New types of blankets and matting materials are continuously being developed.
The Texas Department of Transportation (TxDOT) has defined the critical
performance factors for these types of products, and has established minimum
performance standards which must be met for any product seeking to be
approved for use within any of TxDOT's construction or maintenance activities.
The products that have been approved by TxDOT are also appropriate for
general construction site stabilization within the City of Round Rock or its ETJ.
TxDOT maintains a web site at:
http://www.dot.state.tx.us/business/doinq business/product evaluation/default. ht
m
which is continually updated as new products are evaluated.
Installation:
Proper installation of blankets and matting is necessary for these materials to
function as intended. They shall always be installed in accordance with the
AC -3 1
manufacturer's recommendations. Proper anchoring of the material and
preparation of the soil are two of the most important aspects of installation.
Typical anchoring methods are shown in Figure 14 and Figure 15.
DIRECTION OF FLOW
Figure C-14 Typical Initial Anchor Trench for Blankets and Mats
Figure C-15 Typical Terminal Anchor Trench for Blankets and Mats
Soil Preparation and Matting Placement
AC -32
• After site has been shaped and graded to approved design, prepare a
friable seed bed relatively free from clods and rocks more than 1.5 inches
in diameter and any foreign material that will prevent contact of the
protective mat with the soil surface.
• Fertilize and seed in accordance with seeding or other type of planting
plan.
• The protective matting can be laid over sprigged areas where small grass
plants have been planted. Where ground covers are to be planted, lay the
protective matting first and then plant through matting according to design
of planting.
• Install blankets and matting according to manufacturer recommendations
considering proper overlapping, direct of flow, and trenching.
Erosion Stops
• Erosion stops shall extend beyond the channel liner to full design cross-
section of the channel to check any rills that might form outside the
channel lining.
• The trench may be dug with a spade or a mechanical trencher, making
sure that the down slope face of the trench is flat; it shall be uniform and
perpendicular to line of flow to permit proper placement and stapling of the
matting.
• The erosion stop shall be deep enough to penetrate solid material or
below level of ruling in sandy soils. In general, erosion stops will vary from
6 to 12 inches in depth.
• The erosion stop mat shall be wide enough to allow a minimum of 2 inch
turnover at bottom of trench for stapling, while maintaining the top edge
flush with channel surface.
• Tamp backfill firmly and to a uniform gradient of channel.
Final Check:
Make sure:
• All matting is uniformly in contact with the soil.
• All lap joints are secure.
• All staples are flush with the ground.
• All disturbed areas seeded.
AC -33
Inspection and Maintenance Guidelines:
• Blankets and matting shall be inspected weekly and after each rain event
to locate and repair any damage. Apply new material if necessary to
restore function.
AC -34
C.2.11 Organic Compost Mulch
Organic compost mulch consists of applying a mixture of shredded wood fiber,
compost and a seed mixture with blowing equipment, which temporarily protects
exposed soil from erosion by raindrop impact or wind. Organic compost mulch is
suitable for soil disturbed areas requiring temporary protection until permanent
stabilization is established, and disturbed areas that will be re -disturbed following
an extended period of inactivity. It is not appropriate for use in creeks or
waterways, but can be used on steep slopes, not exceeding 2H:1 V. Compost
products specified for use in this application are described in Table C-3. The
product's parameters will vary based on whether vegetation will be established
on the treated slope.
Only compost products that meet all applicable state and federal regulations
pertaining to its production and distribution may be used in this application.
Approved compost products must meet related state and federal chemical
contaminant (e.g., heavy metals, pesticides, etc.) and pathogen limit standards
pertaining to the feedstocks (source materials) in which it is derived.
Materials:
• Very coarse compost shall be avoided if the slope is to be landscaped or
seeded as it will make planting and crop establishment more difficult.
• In regions subject to higher rates of precipitation and/or rainfall intensity,
higher compost application rates should be used. In these particular
regions, as well as regions subject to wind erosion, coarser compost
products are preferred.
Notes: Specifying the use of compost products that are certified by the US
Composting Council's Seal of Testing (STA) Program
(www.compostingcouncil.org) will allow for the acquisition of products that are
analyzed on a routine basis, using the specified test methods. STA participants
are also required to provide a standard product label to all customers, allowing
easy comparison to other products.
AC -35
Table C-3 Compost Blanket Parameters
Parameters"
Reported as
(units of measure)
Surface Mulch to be
Vegetated
Surface Mulch to be left
Un -vegetated
pH2
pH units
5.0 - 8.5
N/A
Soluble Salt Concentration2
(electrical conductivity)
dS/m (mmhos/cm)
Maximum 5
Maximum 5
Moisture Content
%, wet weight basis
30 — 60
30 — 60
Organic Matter Content
%, dry weight basis
25 — 65
25-100
Particle Size
% passing a selected mesh
size, dry weight basis
• 3" (75 mm), 100% passing
• 1" (25mm), 90% to 100% passing
• 3/4" (19mm), 65% to 100%passing
• 1/4" (6.4 mm), 0% to 75% passing
• Maximum particle length of 6"
(152mm)
• 3" (75 mm), 100% passing
• 1" (25mm), 90% to 100% passing
• 3/4" (19mm), 65% to 100%passing
• 1/4" (6.4 mm), 0% to 75% passing
• Maximum particle length of 6"
(152mm)
Stability3
Carbon Dioxide
Evolution Rate
mg CO2 -C per g OM per
day
< 8
N/A
Physical Contaminants
(man-made inerts)
%, dry weight basis
< 1
< 1
Recommended test methodologies are provided in Test Methods for the Examination of Composting and Compost (TMECC, The
US Composting Council)
2 Each specific plant species requires a specific pH range. Each plant also has a salinity tolerance rating, and maximum
tolerable quantities are known. When specifying the establishment of any plant or turf species, it is important to understand their pH
and soluble salt requirements, and how they relate to the compost in use.
Stability/Maturity rating is an area of compost science that is still evolving, and as such, other various test methods could be
considered. Also, never base compost quality conclusions on the result of a single stability/maturity test.
4 Landscape architects and project (field) engineers may modify the allowable compost specification ranges based on specific field
conditions and plant requirements.
Installation:
• The following steps shall be taken for the proper installation of compost as
a soil blanket for erosion/sediment control on sloped areas.
• Slightly roughen (scarify) slopes and remove Targe clods, rocks, stumps,
roots larger than 2 inches in diameter and debris on slopes where
vegetation is to be established. This soil preparation step may be
eliminated where approved by the Project Engineer or Landscape
Architect/Designer, or where seeding or planting is not planned. Where
practical, track (compact) perpendicular to contours on the slope using a
bulldozer before applying compost as soil blanket.
AC -36
• Apply compost at the rates specified in Table C-4.
Table C-4 Compost Blanket Application Rates
Annual Rainfall/
Flow Rate
Total Precipitation &
Rainfall Erosivity
Index
Application Rate For
Vegetated" Compost
Application Rate For
Unvegetated Compost
Surface Mulch
Surface Mulch
Low
1-25",
%2-3/"
1"-1'/"
20-90
(12.5 mm - 19 mm)
(25 mm — 37.5mm)
Average
26-50",
3/ - 1"
1 1/2" — 2"
91-200
(19 mm - 25 mm)
(37 mm — 50 mm)
High
51" and above,
1-2"
2-4"
201 and above
(25 mm - 50 mm)
(50mm— 100mm)
*these lower application rates should only be used in conjunction with seeding, and for compost blankets applied
during the prescribed planting season for the particular region.
Compost blanket application rates should be modified based on specific site
(e.g., soil characteristics, existing vegetation) and climatic conditions, as well as
particular project related requirements. The severity of slope grade, as well as
slope length, will also influence compost application rates.
In regions subjected to higher rates of precipitation and/or rainfall intensity,
higher compost application rates should be used. In these regions, as well as
those with spring snow melt, and on sites possessing severe grades or long
slope lengths, the compost blanket may be used in conjunction with a compost
filter berm. The filter berm may be 1-2 feet high (30 cm — 60 cm), by 2-4 feet wide
(60 cm — 120 cm), and may be placed at the top or base (or both) of the slope. In
these particular regions, as well as regions subject to wind erosion, coarser
compost products are also preferred.
In regions subject to lower rates of precipitation and/or rainfall intensity, lower
compost application rates may be used.
Note: Specific regions may receive higher rainfall rates, but this rainfall is
received through low intensity rainfall events (e.g., the Northwestern U.S.). These
regions may use lower compost application rates.
Compost shall be uniformly applied using a pneumatic (blower) unit, or other unit
that propels the product directly at the soil surface, thereby preventing water from
moving between the soil -compost interface. Thorough watering may be used to
improve settling of the compost. Apply compost layer approximately 3 feet (90
cm) over the top of the slope, or overlap it into existing vegetation.
AC -37
On highly unstable soils, use compost in conjunction with appropriate structural
measures.
Dry or hydraulic seeding may be completed following compost application, as
required, or during the compost application itself, where a pneumatic unit is used
to apply the compost.
Inspection and Maintenance Guidelines:
• Mulched areas shall be inspected weekly and after each rain event to
locate and repair any damage.
C.2.12 Hydraulic Mulch
Hydraulic mulch consists of applying a mixture of shredded wood fiber or a
hydraulic matrix, and a stabilizing emulsion or tackifier with hydro -mulching
equipment, which temporarily protects exposed soil from erosion by raindrop
impact or wind. Hydraulic mulch is suitable for soil disturbed areas requiring
temporary protection until permanent stabilization is established, and disturbed
areas that will be re -disturbed following an extended period of inactivity. Seed
may be added to the mulch for temporary or permanent vegetation. It is not
appropriate for slopes steeper than 3H:1V or for use in channels.
Wood fiber hydraulic mulches are generally short lived and need 24 hours to dry
before rainfall occurs to be effective. A second application may be necessary in
order to remain effective for an entire rainy season.
Materials:
• Hydraulic Mulches: Wood fiber mulch can be applied alone or as a
component of hydraulic matrices. Wood fiber applied alone is typically
applied at the rate of 2,000 to 4,000 Ib/acre. Wood fiber mulch is
manufactured from wood or wood waste from lumber mills or from urban
sources.
• Hydraulic Matrices: Hydraulic matrices include a mixture of wood fiber and
acrylic polymer or other tackifier as binder. Apply as a liquid slurry using a
hydraulic application machine (i.e., hydro seeder) at the following minimum
rates, or as specified by the manufacturer to achieve complete coverage of
the target area: 2,000 to 4,000 Ib/acre wood fiber mulch, and 5 to 10% (by
weight) of tackifier (acrylic copolymer, guar, psyllium, etc.)
• Bonded Fiber Matrix: Bonded fiber matrix (BFM) is a hydraulically applied
system of fibers and adhesives that upon drying forms an erosion resistant
AC -38
blanket that promotes vegetation, and prevents soil erosion. BFMs are
typically applied at rates from 3,000 Ib/acre to 4,000 Ib/acre based on the
manufacturer's recommendation. A biodegradable BFM is composed of
materials that are 100% biodegradable. The binder in the BFM shall also be
biodegradable and shall not dissolve or disperse upon re -wetting. Typically,
biodegradable BFMs should not be applied immediately before, during or
immediately after rainfall if the soil is saturated. Depending on the product,
BFMs typically require 12 to 24 hours to dry to become effective.
Installation:
• Prior to application, roughen embankment and fill areas by rolling with a
crimping or punching type roller or by track walking. Track walking shall
only be used where other methods are impractical.
• To be effective, hydraulic matrices require 24 hours to dry before rainfall
occurs.
• Avoid mulch over spray onto roads, sidewalks, drainage channels, existing
vegetation, etc.
Inspection and Maintenance Guidelines:
• Mulched areas shall be inspected weekly and after each rain event to
locate and repair any damage.
• Areas damaged by storms or normal construction activities shall be
regraded and hydraulic mulch reapplied as soon as practical.
C.2.13 Sod
Sod is appropriate for disturbed areas which require immediate vegetative
covers, or where sodding is preferred to other means of grass establishment.
Locations particularly suited to stabilization with sod are waterways carrying
intermittent flow, areas around drop inlets or in grassed swales, and residential or
commercial lawns where quick use or aesthetics are factors.
The advantages of properly installed sod include:
• Immediate erosion control.
• An instant green surface with no dust or mud.
AC -39
• Nearly year-round establishment capability.
• Less chance of failure than seed.
• Freedom from weeds.
• Quick use of the sodded surface.
• The option of buying a quality -controlled product with predictable results.
It is initially more costly to install sod than to seed. However, this cost is justified
in places where sod can perform better than seed in controlling erosion. In
swales and waterways where concentrated flow will occur, properly pegged sod
is preferable to seed because there is no lag time between installation and the
time when the channel is protected by vegetation. Drop inlets, which will be
placed in grassed areas, can be kept free of sediment, and the grade
immediately around the inlet can be maintained, by framing the inlet with sod
strips.
Sod can be laid during times of the year when seeded grass may fail, so long as
there is adequate water available for irrigation in the early weeks. Ground
preparation and proper maintenance are as important with sod as with seed. Sod
is composed of living plants and those plants must receive adequate care in
order to provide vegetative stabilization on a disturbed area.
Materials:
• Sod shall be machine cut at a uniform soil thickness of 1 inch at the time
of cutting. This thickness shall exclude shoot growth and thatch.
• Pieces of sod shall be cut to the supplier's standard width and length, with
a maximum allowable deviation in any dimension of 5%. Torn or uneven
pads shall not be acceptable.
• Standard size sections of sod shall be strong enough to support their own
weight and retain their size and shape when suspended from a firm grasp
on one end of the section.
• Sod shall be harvested, delivered, and installed within a period of 36
hours.
Site Preparation:
• Prior to soil preparation, areas to be sodded shall be brought to final grade
in accordance with the approved plan.
• The surface shall be cleared of all trash, debris and of all roots, brush,
wire, grade stakes and other objects that would interfere with planting,
fertilizing or maintenance operations.
AC -40
• Fertilize according to soil tests. Fertilizer needs can be determined by a
soil testing laboratory or regional recommendations can be made by
Williamson or Travis County agricultural extension agents. Fertilizer shall
be worked into the soil to a depth of 3 inches with a disc, springtooth
harrow or other suitable equipment. On sloping land, the final harrowing or
discing operation should be on the contour.
General Installation:
• Sod shall not be cut or laid in excessively wet or dry weather. Sod also
shall not be laid on soil surfaces that are frozen.
• During periods of high temperature, the soil should be lightly irrigated
immediately prior to laying the sod, to cool the soil and reduce root
burning and dieback.
• The first row of sod should be laid in a straight line with subsequent rows
placed parallel to and butting tightly against each other. Lateral joints
should be staggered to promote more uniform growth and strength. Care
should be exercised to ensure that sod is not stretched or overlapped and
that all joints are butted tight in order to prevent voids which would cause
drying of the roots.
• On slopes sod should be laid with staggered joints and secured by
stapling or other approved methods. On slopes greater than 3:1 or
wherever excessive erosion may be a problem, sod should not be used.
• As sodding of clearly defined areas is completed, sod should be rolled or
tamped to provide firm contact between roots and soil.
• After rolling, sod should be irrigated to a depth sufficient that the underside
of the sod pad and the soil 4 inches below the sod is thoroughly wet.
• Until such time as a good root system becomes developed, in the absence
of adequate rainfall, watering should be performed as often as necessary
to maintain moist soil to a depth of at least 4 inches.
• The first mowing should not be attempted until the sod is firmly rooted,
usually 2-3 weeks. Not more than one third of the grass leaf should be
removed at any one cutting.
Installation in Channels:
• Sod strips in waterways should be laid perpendicular to the direction of
flow. Care should be taken to butt ends of strips tightly.
AC -41
• After rolling or tamping, sod should be pegged or stapled to resist washout
during the establishment period. Mesh or other netting may be pegged
over the sod for extra protection in critical areas.
Inspection and Maintenance Guidelines:
• Sod should be inspected weekly and after each rain event to locate and
repair any damage.
• Damage from storms or normal construction activities such as tire ruts or
disturbance of swale stabilization should be repaired as soon as practical.
C.2.14Dust Control
The purpose of dust control is to: prevent blowing and movement of dust from
exposed soil surfaces; reduce on and off-site damage and health hazards; and,
improve traffic safety. This practice is applicable to areas subject to dust blowing
and movement where on and off-site damage is likely without treatment.
Construction activities inevitably result in the exposure and disturbance of soil.
Fugitive dust is emitted both during the activities (i.e., excavation demolition,
vehicle traffic, human activity) and as a result of wind erosion over the exposed
earth surfaces. Large quantities of dust are typically generated in 'heavy'
construction activities, such as road and street construction and subdivision,
commercial or industrial development, which involve disturbance of significant
areas of the soil surface. Research on construction sites has established an
average dust emission rate of 1.2 tons/acre/month for active construction. Earth
moving activities comprise the major source of construction dust emissions, but
traffic and general disturbance of the soil also generate significant dust
emissions.
Temporary Methods:
• Vegetative Cover - See Section C.2.8.
• Mulches - See Section C.2.10 or C.2.13 — Chemical mulch binders may be
used to bind mulch material. Commercial binders should be used
according to manufacturer's, recommendations.
• Commercially available dust suppressors if applied in accordance with the
manufacturers' directions.
AC -42
• Tillage - to roughen surface and bring clods to the surface. This is an
emergency measure that should be used before soil blowing starts. Begin
plowing on windward side of site. Chisel -type plows spaced about 12
inches apart, spring -toothed harrows and similar plows are examples of
equipment that may produce the desired effect.
• Irrigation - Site is sprinkled with water until the surface is moist. Repeat as
needed. Irrigation can be particularly effective for controlling dust during
trenching operations. A dedicated water truck placed next to the trencher
and using a "pulse" fog pattem applied to the discharge belt can effectively
control dust. This method is more effective than spraying the ground
ahead of the trencher or the trench itself as it is being dug.
• Barriers - Solid board fences, snow fences, burlap fences, crate walls,
bales of hay and similar materials can be used to control air currents and
soil blowing. Barriers placed at right angles to prevailing currents at
intervals of about 15 times their height are effective in controlling soil
blowing.
Permanent Methods:
• Permanent Vegetation -- trees or Targe shrubs may afford valuable
protection if left in place.
• Topsoil - Covering with less erosive soil material.
• Stone - Cover surface with crushed stone or coarse gravel.
Inspection and Maintenance Guidelines:
• When dust is evident during dry weather, reapply or repair implemented
dust control BMPs and/ or revise dust control plan to implement more
effective or appropriate BMPs.
C.3 Sediment Control BMPs
C.3.1 General Guidelines
Construction activities normally result in disturbed/ exposed soil areas due to
grading operations, clearing and other activities. Erosion will occur in the
disturbed areas and Best Management Practices (BMPs) should be used to
contain the sediment transported by storm water runoff. Although the names of
many controls suggest that filtration is an important component of sediment
removal, almost all reduction in sediment Toad is the result of particle settling
under relatively quiescent conditions. Consequently, sediment barriers, such as
AC -43
erosion control Togs, silt fences, and rock berms, should be designed and
installed as temporary (although leaky) dams.
When viewed as temporary dams, it is easier to see the importance of installing
these devices along the contour or with a constant top elevation to prevent
concentrating the runoff at the lowest spot in the barrier. Concentrating the
runoff in this fashion can result in more erosion than if no barrier was installed at
all. Therefore, great care should be taken in the placement and installation of
these types of controls.
For larger areas or where effective installation of sediment barriers is not an
option, sediment traps and sediment basins should be used to control sediment
in runoff: These devices are essentially larger, more permanent dams that
temporarily detain storm water runoff.
All of the sediment control BMPs are potentially very effective for removing
sediment from storm water runoff when properly maintained and installed.
However, this potential is often squandered. Casual observation of many active
construction sites reveals silt fences that are torn or damaged by equipment,
evidence of storm water bypass, or controls installed in inappropriate locations
(i.e., silt fences used in channels). In these cases, significant funds are
expended for little in the way of water quality protection. Consequently, proper
installation and maintenance should form a key component of any temporary
sediment control plan.
A list of the temporary sediment controls and their appropriate siting criteria are
contained in Table C-5. More detailed guidance on siting and maintenance are
contained in the subsequent sections. Note that hay bales are no longer
considered an effective sediment control measure. Compost amended soils can
be used to promote vegetation growth, but they are not considered a sediment
control technology.
Table C-5 Guidelines for Selection of Sediment Control BMPs
Sediment Control
Applications
Drainage Area
Slope
Spacing
Construction Exit
Should be used at all designated access points.
NA
NA
NA
Silt Fence (interior)
Areas of minor sheet flow.
2 acres
< 20%
200 ft
Silt Fence (exterior)
Down slope borders of site; up slope
border is necessary to divert offsite drainage.
For larger areas use diversion swale or berm.
NA
See Table C-6
See Table C-6
Triangular Filter Dike
Areas within site requiring frequent
access.
< 1 acre
< 10%
NA
Rock Berm
Drainage swales and ditches with and
below site.
< 5 acres
< 30%
See Table C-7
High Service Rock
Berm
Around sensitive features, high flow
areas within and below site.
< 5 acres
< 30%
See Table C-7
Brush Berm
Small areas of sheet flow
< 2 acres
< 20%
See Table C-7
AC -44
Vegetative Buffer
Strips
On floodplains, next to wetlands,
along stream banks, and on steep slopes.
NA
NA
NA
Inlet Protection
Prevent sediment from entering storm
drain system.
< 1 acre
NA
NA
Sediment Trap
Used where flows concentrated in a
swale or channel
1-5 acres
NA
NA
Sediment Basin
Appropriate for large disturbed areas
5 — 100 acres
NA
NA
Filter Rolls
On slopes to interrupt slope
< 1 acre
<30%
See Table C-7
Dewatering Operations
Used to remove groundwater or
accumulated storm water from
excavations
NA
NA
NA
Spill Prevention
Used on all sites to reduce spills
NA
NA
NA
Creek Crossings
Crossings of drainage ways and creeks
>5 acres
NA
NA
Concrete Washout
Use on all concrete pouring operations
NA
NA
NA
Table C-6
Silt Fence Spacing on Sloping Sites
Slope Angle
Soil Type
Silty
Clays
Sandy
Very steep (1:1)
50 ft.
75 ft.
100 ft.
Steep (2:1)
75 ft.
100 ft.
125 ft.
Moderate (4:1)
100 ft.
125 ft.
150 ft.
Slight (10:1)
125 ft.
150 ft.
200 ft.
Table C-7
Rock and Brush Berm and Erosion Control Logs Spacing on Channels
Ditch slope
Spacing
30%
10 ft.
20%
15 ft.
15%
20 ft.
10%
35 ft.
5%
55 ft.
3%
100 ft.
2%
150 ft.
1%
300 ft.
0.50%
600 ft.
AC -45
C.3.2 Stabilized Construction Entrance/Exit
The purpose of a stabilized construction entrance/ exit is to provide a stable
entrance/exit condition from the construction site and keep mud and sediment
from being deposited from vehicles and equipment onto public roads or other
paved areas used by private or public parties. A stabilized construction entrance
is a stabilized pad of 3" to 8" stone located at any point traffic will be entering or
leaving the construction site from/ to a right-of-way, street, drive, alley, sidewalk
or parking area. This practice should be used at all points of construction ingress
and egress. See City standard detail for stabilized construction entrance/exit.
Excessive amounts of mud can also present a safety hazard to roadway users.
To minimize the amount of sediment Toss to nearby roads, access to the
construction site should be limited to as few points as possible and vegetation
around the perimeter should be protected where access is not necessary. A rock
stabilized construction entrance should be used at all designated access points.
Materials:
• The aggregate should consist of 3 to 8 inch washed stone over a stable
foundation as specified in the plan.
• The aggregate should be placed with a minimum thickness of 8 inches.
• The geotextile fabric should be designed specifically for use as a soil
filtration media with an approximate weight of 4 oz/yd2.
• If a washing facility is required, a level area with a minimum of 4 inch
diameter washed stone or commercial rack should be included in the
plans. Divert wash water to a sediment trap or basin.
Installation:
• Avoid curves on public roads and steep slopes. Remove vegetation and
other objectionable material from the foundation area. Grade crown
foundation for positive drainage.
• The minimum width of the entrance/exit shall not be less than the full width
of ingress/ egress or 12 feet, whichever is greater.
• The construction site entrance should be at least 50 feet long.
AC -46
• If the slope toward the road exceeds 2%, construct a ridge, 6 to 8 inches
high with 3:1 (H:V) side slopes, across the entrance/ exit width
approximately 15 feet from the beginning of the entrance to divert runoff
away from the public road.
• Place stone to dimensions and grade shown on plans. Leave surface
smooth and sloped for drainage.
• Divert all surface runoff and drainage from the stone pad to a sediment
trap or basin if necessary.
• Install pipe under pad as needed to maintain proper public road drainage.
Common trouble points
• Inadequate runoff control — sediment washes onto public road or other
paved area.
• Stone too small resulting in muddy condition as stone is pressed into soil.
• Pad too short for heavy construction traffic — extend pad beyond the
minimum 50 foot length as necessary.
• Pad not flared sufficiently at road intersection, results in mud being
tracked on to road and possible damage to road edge.
• Pad not turned or raked after a period of time.
• Existing curbs damaged and not properly protected.
• Rocks displaced onto roadway and not cleaned up.
Inspection and Maintenance Guidelines:
• The entrance should be maintained in a condition which will prevent
tracking or flowing of sediment onto public rights-of-way. This may require
periodicly turning the top dressing with additional stone as conditions
demand and repair and/or cleanout of any measures used to trap
sediment.
• All sediment spilled, dropped, washed or tracked onto rights-of-way or
other paved areas outside of the construction site shall be removed
immediately by contractor.
AC -47
• When necessary, wheels should be cleaned to remove sediment prior to
exiting the construction site.
• When washing is required, it should be done on an area stabilized with
crushed stone that drains into an approved sediment trap or sediment
basin.
• All sediment should be prevented from entering any storm drain, ditch or
water course by using approved methods.
C.3.3 Silt Fence
A silt fence is a barrier consisting of geotextile fabric supported by metal posts to
prevent soil and sediment loss from a site. When properly used, silt fences can
be highly effective. They help runoff to pond, allowing heavier solids to settle out.
See the City's standard silt fence detail.
AC -48
PLAN VIEW
I, SPACING REQUIREMENTS
DIRECTION OF
SURFACE FLOW
z30 DEGREES
100'
MAX.
II. SIZING REQUIREMENTS: J15, J25
UP -GRADIENT SILT
FENCE AND J -HOOK
ARE ONE CONTINUOUS LINE
41 - FOR CATCHMENT
AREA <0.25 ACRES
NOTE;
J -HOOKS SHALL BE USED WHEN
THE SILT FENCE IS INSTALLED AT
AN ANGLE OF 30 DEGREES OR
GREATER FROM PARALLEL TO TFIE
CONTOURS.
D+RECTION OF
SURFACE FLOW
CONTOURS
START DOWN -GRADIENT
SILT FENCE LINE AS
CLOSE AS POSSIBLE TO
THE UP -GRADIENT J -HOOK
I 25'R —
16'
i
42,5 - FOR CATCHMENT
AREA >0.25 ACRES
Figure C-16 Schematic J -hook Placement
The purpose of a silt fence is to intercept and prevent further transport of water -borne
sediment from unprotected areas of a limited extent. Silt fence is used during
construction near the perimeter of a disturbed area to intercept sediment while allowing
water to percolate through. This fence should remain in place until the disturbed area is
permanently stabilized. Silt fence should not be used where there is a concentration of
water in a channel or drainage way. If concentrated flow occurs after installation,
corrective action must be taken such as placing a rock berm in the areas of
concentrated flow.
Silt fencing within the site may be temporarily moved during the day to allow
construction activity provided it is replaced and properly anchored to the ground at the
AC -49
end of the day or prior to a rain event. Silt fences on the perimeter of the site or around
drainage ways should not be moved at any time.
Use J -hooks to trap and pond runoff flowing along uphill side of silt fence as shown in
Figure C-16. This will filter or settle outflows and prevent runoff from escaping around
the sides of the fence.
Materials:
• Silt fence material should be nonwoven fabric. The fabric with a minimum unit weight
of 4.0 oz/yd.
• Fence posts should be made of hot rolled steel, at least 4 feet long with Tee or Y -bar
cross section, surface painted or galvanized.
• Woven wire backing to support the fabric should be galvanized 2" x 4" welded wire,
12 gauge minimum.
Installation:
• Steel posts, which support the silt fence, should be installed on a slight angle toward
the anticipated runoff source. Posts must be embedded a minimum of 1 -foot
deep and spaced not more than 8 feet on center. Where water concentrates, the
maximum spacing should be 6 feet.
• Lay out fencing down-slope of disturbed area, following the contour as closely as
possible. Utilize J -hooks as necessary as shown in Figure C-16. The fence
should be sited so that the maximum drainage area is'/ acre/100 feet of fence.
• The toe of the silt fence should be trenched in with a spade or mechanical trencher,
so that the down-slope face of the trench is flat and perpendicular to the line of
flow. Where fence cannot be trenched in (e.g., pavement or rock outcrop), weight
fabric flap with 3 inches of pea gravel on uphill side to prevent flow from seeping
under fence.
• The trench must be a minimum of 6 inches deep and 6 inches wide to allow for the
silt fence fabric to be laid in the ground and backfilled with compacted material.
• Silt fence should be securely fastened to each steel support post or to woven wire,
which is in turn attached to the steel fence post. There should be a 3 -foot
overlap, securely fastened where ends of fabric meet.
• Silt fence should be removed when the site is completely stabilized so as not to
block or impede storm flow or drainage.
AC -50
Common Trouble Points:
• Fence not installed along the contour causing water to concentrate and flow over the
fence.
• Fabric not seated securely to ground (runoff passing under fence)
• Fence not installed perpendicular to flow line (runoff escaping around sides)
• Fence treating too large an area, or excessive channel flow (runoff overtops or
collapses fence)
• Damage to silt fencing not repaired in a timely manner.
Inspection and Maintenance Guidelines:
• Inspect all fencing weekly and after any rainfall in excess of 0.5 inch or more.
• Remove sediment when buildup reaches 6 inches.
• Replace any torn fabric.
• Replace or repair any sections crushed or collapsed in the course of construction
activity. If a section of fence is obstructing vehicular access, consider relocating it
to a spot where it will provide equal protection, but will not obstruct vehicles. A
triangular filter dike may be preferable to a silt fence at common vehicle access
points.
• When construction is complete, the sediment should be disposed of in a manner that
will not cause additional siltation and the prior location of the silt fence should be
revegetated. The fence itself should be disposed of in an approved landfill.
C.3.4 Trianqular Sediment Filter Dikes
The purpose of a triangular sediment filter dike is to intercept and prevent further
transport of water -borne sediment from unprotected areas of limited extent. The
triangular sediment filter dike is used where there is no concentration of water
upstream of the dike and the contributing drainage area is less than one acre. If
the uphill slope above the dike exceeds 10%, the length of the slope above the
dike should be less than 50 feet. If concentrated flow occurs after installation,
corrective action should be taken such as placing rock berm in the areas of
concentrated flow.
AC -51
This measure is effective on paved areas where installation of silt fence is not
possible or where vehicle access must be maintained. The advantage of these
controls is the ease with which they can be moved to allow vehicle traffic, then
reinstalled to maintain sediment control.
Materials:
• Silt fence material should be nonwoven fabric. The fabric width should be
36 inches, with a minimum unit weight of 4.0 oz/yd.
• The dike structure should be 6 gauge 6" x 6" wire mesh folded into
triangular form being eighteen (18) inches on each side.
• The sand bag material should be polypropylene, polyethylene, polyamide
or cotton burlap woven fabric, minimum unit weight 4 ozlyd2, mullen burst
strength exceeding 300 psi and ultraviolet stability exceeding 70 percent.
• The bag length should be 24 to 30 inches, width should be 16 to 18 inches
and thickness should be 6 to 8 inches.
• Sandbags should be filled with coarse grade sand, free from deleterious
material. All sand should pass through a No. 10 sieve. The filled bag
should have an approximate weight of 40 pounds and stapled or tied with
nylon or poly cord.
Installation:
• As shown in the City's standard detail, the frame should be constructed of
6" x 6", 6 gauge welded wire mesh, 18 inches per side, and wrapped with
geotextile fabric the same composition as that used for silt fences.
• Filter fabric should lap over ends six (6) inches to cover dike to dike
junction; each junction should be secured by shoat rings.
• Position dike parallel to the contours, with the end of each section closely
abutting the adjacent sections.
• There are several options for fastening the filter dike to the ground. The
fabric skirt may be toed -in with 6 inches of compacted material, or 12
inches of the fabric skirt should extend uphill and be secured with
sandbags or a minimum of 3 inches of open graded rock, or with staples
AC -52
or nails. If these two options are not feasible the dike structure may be
trenched in 4 inches.
• Triangular sediment filter dikes should be installed across exposed slopes
during construction with ends of the dike tied into existing grades to
prevent failure and should intercept no more than one acre of runoff.
• When moved to allow vehicular access, the dikes should be reinstalled as
soon as possible, but always at the end of the workday or prior to a rain
event.
Common Trouble Points:
• Fabric skirt missing, too short, or not securely anchored (flows passing
under dike).
• Gap between adjacent dikes (runoff passing between dikes).
• Dike not placed parallel to contour (runoff flowing around dike).
Inspection and Maintenance Guidelines:
• Inspection should be made weekly and after each rainfall event of greater
than 0.5 in. and repair or replacement should be made promptly as
required to ensure continued effectiveness.
• Inspect and realign dikes as needed to prevent gaps between sections.
• Accumulated silt should be removed after it reaches a depth of 6 inches,
and disposed of in a manner which will not cause additional siltation.
• After the site is completely stabilized, the dikes and any remaining silt
should be removed. Silt should be disposed of in a manner that will not
contribute to additional siltation.
C.3.5 Tire Washing Facility
The tire washing facility is used in conjunction with a stabilized construction
entrance to provide an area where truck wheels and undercarriages can
be cleaned prior to traversing the stabilized construction entrance/ exit and
entering the public road system. A tire wash may consist of an impervious
area or grate over a swale. Wash water from hand held pressure washers
or fixed nozzles is collected and drained to a sediment trapping device
AC -53
such as a stone outlet sediment trap or sediment basin to provide for
removal of sediment prior to discharge.
Tire washing should be used on large jobs where there is significant truck traffic,
on those sites where site conditions cause the stabilized construction
entrance/ exit to be overloaded with sediment and become ineffective and
in those instances where contaminated solids might be present on site.
They provide added protection and reduce the need to remove sediment
from streets and should be considered an ancillary component to the
stabilized construction entrance/ exit.
Figure C-17 Schematic Tire Wash Facility
Installation
• The location should be within the stabilized construction entrance/ exit so
that the vehicle does not pick up additional sediment load by traversing
disturbed areas.
• The size of the tire wash facility should be sufficient so that all wash water
and sediment is collected and drained to a sediment trapping device such
as a sediment basin or stone outlet sediment trap.
• A tire wash facility design may consist of many different types of materials
or configuration as long as it provides the intended function. Suggested
designs are:
o 4 inch thick asphalt pavement on an 8 inch base of crushed rock
graded so that wash water drains to a swale; or
o Grate suitably designed to support construction vehicles installed
over a swale.
• The tire wash facility should be designed so that it can be cleaned
between uses.
Maintenance
AC -54
• Wheel wash facilities should be inspected at the end of each shift or
workday for damage or repair.
• The surface of the wheel wash should be cleaned between vehicles as
necessary.
• Sediment that has accumulated in the wash water sedimentation BMP
(sediment trap, sediment basin, etc.) must be removed when it reaches a
depth of approximately 1/3 the design depth of the device or 12",
whichever is less.
• The removed sediment shall be stockpiled or redistributed in areas that
are protected from erosion.
• Remove any mud tracked onto adjacent roadway by sweeping or scraping
as necessary.
Inspection Checklist
• Vehicles are leaving the site through designated construction entrance(s) /
exit(s).
• Mud, dust or dirt is removed prior to exit onto the adjacent road.
• The construction entrance/ exit is sufficiently maintained to prevent mud,
dirt, fines and dust from being tracked off-site.
• Stones under wash rack have been maintained and free of deleterious
materials.
C.3.6 Rock Berms
The purpose of a rock berm is to serve as a check dam in areas of concentrated
flow, to intercept sediment -laden runoff, detain the sediment and release the
water in sheet flow. The rock berm should be used when the contributing
drainage area is less than 5 acres. Rock berms are used in areas where the
volume of runoff is too great for a silt fence to contain. They are less effective for
sediment removal than silt fences, particularly for fine particles, but are able to
withstand higher flows than a silt fence. As such, rock berms are often used in
areas of channel flows (ditches, gullies, etc.). Rock berms are most effective at
reducing bed load in channels and should not be substituted for other erosion
and sediment control measures farther up the watershed.
Materials:
• The berm structure should be secured with a woven wire sheathing having
maximum opening of 1 inch and a minimum wire diameter of 20 gauge
galvanized and should be secured with shoat rings.
AC -55
• Clean, open graded 3- to 5 -inch diameter rock should be used, except in
areas where high velocities or Targe volumes of flow are expected, where
5- to 8 -inch diameter rocks may be used.
Installation:
• Lay out the woven wire sheathing perpendicular to the flow line. The
sheathing should be 20 gauge woven wire mesh with 1 inch openings.
• Berm should have a top width of 2 feet minimum with side slopes being
2:1 (H:V) or flatter.
• Place the rock along the sheathing as shown in the diagram (Figure C-18),
to a height not less than 18".
• Wrap the wire sheathing around the rock and secure with tie wire so that
the ends of the sheathing overlap at least 2 inches, and the berm retains
its shape when walked upon.
• Berm should be built along the contour at zero percent grade or as near
as possible.
• The ends of the berm should be tied into existing upslope grade and the
berm should be buried in a trench approximately 3 to 4 inches deep to
prevent failure of the control.
• Follow Table C-7 Rock Berm Spacing on Channels.
Common Trouble Points:
• Insufficient berm height or length (runoff quickly escapes over the top or
around the sides of berm)
• Berm not installed perpendicular to flow line (runoff escaping around one
side)
• Damage not repaired in a timely manner causing erosion of or around rock
berm.
Inspection and Maintenance Guidelines:
AC -56
• Inspection should be made weekly and after each rainfall by the
responsible party. For installations in streambeds, additional daily
inspections should be made.
• Remove sediment and other debris when buildup reaches 6 inches and
dispose of the accumulated silt in an approved manner that will not cause
any additional siltation.
• Repair any loose wire sheathing.
• The berm should be reshaped as needed during inspection.
• The berm should be replaced when the structure ceases to function as
intended due to silt accumulation among the rocks, washout, construction
traffic damage, etc.
• The rock berm should be left in place until all upstream areas are
stabilized and accumulated silt removed.
C.3.7 Hiqh Service Rock Berms
A high service rock berm should be designated in areas of important
environmental significance such as in steep canyons or above permanent
springs, pools, recharge features, or other environmentally sensitive areas that
may require a higher level of protection. This type of sediment barrier combines
the characteristics of a silt fence and a rock berm to provide a substantial level of
sediment reduction and a sturdy enough barrier to withstand higher flows. The
drainage area to this device should not exceed 5 acres and the slope should be
less than 30%.
AC -57
24" MINIMUM
24" MINIMUM
H
Woven Wire Sheathing
Woven Wire Sheathing
3" TO 5" OPEN
GRADED ROCK
tZeVki
,..
Cross - Section
1
4 - FLOW
SILT FENCE
Figure C-19 Schematic Diagram of High Service Rock Berm
Materials:
• Silt fence material should be nonwoven fabric. The fabric width should be
36 inches, with a minimum unit weight of 4.0 oz/yd2.
• Fence posts should be made of hot rolled steel, at least 4 feet long with
Tee or Y -bar cross section, surface painted or galvanized, minimum
nominal weight 1.25 Ib/ft2, and Brindell hardness exceeding 140. Rebar
(either #5 or #6) may also be used to anchor the berm.
• Woven wire backing to support the fabric should be galvanized 2" x 4"
welded wire, 12 gauge minimum.
AC -58
• The berm structure should be secured with a woven wire sheathing having
maximum opening of 1 inch and a minimum wire diameter of 20 gauge
galvanized and should be secured with shoat rings.
• Clean, open graded 3- to 5 -inch diameter rock should be used, except in
areas where high velocities or Targe volumes of flow are expected, where
5- to 8 -inch diameter rocks may be used.
Installation:
• Lay out the woven wire sheathing perpendicular to the flow line. The
sheathing should be 20 gauge woven wire mesh with 1 -inch openings.
• Install the silt fence along the center of the proposed berm placement, as
with a normal silt fence described in Section C.3.3.
• Place the rock along the sheathing on both sides of the silt fence as
shown in the diagram (Figure C-19), to a height not less than 24 inches.
Clean, open graded 3-5 inch diameter rock should be used, except in
areas where high velocities or Targe volumes of flow are expected, where
5- to 8 -inch diameter rock may be used.
• Wrap the wire sheathing around the rock and secure with tie wire so that
the ends of the sheathing overlap at least 2 inches, and the berm retains
its shape when walked upon.
• The high service rock berm should be removed when the site is
revegetated or otherwise stabilized or it may remain in place as a
permanent BMP if drainage is adequate.
• Follow spacing guidelines on Table C-7 Rock Berm Spacing on Channels.
Common Trouble Points:
• Insufficient berm height or length (runoff quickly escapes over top or
around sides of berm).
• Berm not installed perpendicular to flow line (runoff escaping around one
side).
• Internal silt fence not anchored securely to ground (high flows displacing
berm).
• When installed in streambeds, they often result in diversion scour, so their
use in this setting is not recommended.
AC -59
Inspection and Maintenance Guidelines:
• Inspection should be made weekly and after each rainfall by the
responsible party. For installations in streambeds, additional daily
inspections should be made.
• Remove sediment and other debris when buildup reaches 6 inches and
dispose of the accumulated silt in an approved manner.
• Repair any loose wire sheathing.
• The berm should be reshaped as needed during inspection.
• The berm should be replaced when the structure ceases to function as
intended due to silt accumulation among the rocks, washout, construction
traffic damage, etc.
• The rock berm should be left in place until all upstream areas are
stabilized and accumulated silt removed.
C.3.8 Brush Berms
Woody brush material from site clearing operations is usually burned or hauled
away to be dumped elsewhere. Much of this material can be used effectively for
preventing sediment from leaving the construction site. The key to constructing
an efficient brush berm is in the method used to obtain and place the brush. It will
not be acceptable to simply take a bulldozer and push whole trees into a pile.
This method does not assure continuous ground contact with the berm and will
allow uncontrolled flows under the berm.
Brush berms may be used where there is little or no concentration of water in a
channel or other drainage way above the berm. The size of the drainage area
should be no greater than one-fourth of an acre per 100 feet of barrier length; the
maximum slope length behind the barrier should not exceed 100 feet; and the
maximum slope gradient behind the barrier should be less than 50 percent (2:1).
Figure C-20 illustrates a brush berm.
Materials:
AC -60
• The brush should consist of woody brush and branches less than 2 inches
in diameter.
• The filter fabric should conform to the specifications for filter fence fabric.
• The rope should be 1/4 inch polypropylene or nylon rope.
• The rope anchors should be 3/8 -inch diameter rebar stakes that are 18 -
inches long.
Guidelines for installation:
• Lay out the brush berm following the contour as closely as possible.
• The brush limbs should be cut and hand placed with the vegetated part of
the limb in close contact with the ground. Each subsequent branch should
overlap the previous branch providing a shingle effect.
• The brush berm should be constructed in lifts with each layer extending
the entire length of the berm before the next layer is started.
• Drive the rope anchors into the ground at approximately a 45 degree
angle to the ground. The anchors should be place alternately on 6 foot
centers on both sides of the berm so that there is no more than 6 feet
between stakes on any one side of the berm.
• Fasten the rope to the anchors and tighten berm securely to the ground.
• The height of the brush berm should be a minimum of 24" after the
securing ropes have been tightened.
• A trench should be excavated 6 -inches wide and 4 -inches deep along the
length of the barrier and immediately uphill from the barrier.
• The filter fabric should be cut into lengths sufficient to lay across the
barrier from its up-slope base to just beyond its peak. The lengths of filter
fabric should be draped across the width of the barrier with the uphill edge
placed in the trench and the edges of adjacent pieces overlapping each
other. Where joints are necessary, the fabric should be spliced together
with a minimum 6 -inch overlap and securely sealed.
• The trench should be backfilled and the soil compacted over the filter
fabric
• Set stakes into the ground along the downhill edge of the brush barrier,
and anchor the fabric by tying rope from the fabric to the stakes. Drive the
AC -61
rope anchors into the ground at approximately a 45 -degree angle to the
ground on 6 -foot centers.
• Fasten the rope to the anchors and tighten berm securely to the ground
with a minimum tension of 50 pounds.
• The height of the brush berm should be a minimum of 24 inches after the
securing ropes have been tightened.
Follow spacing guidelines on Table C- Rock and Brush Berm and Erosion Control Logs Spacing
Channels.
1. EXCAVATE A 4"X 4- TRENCH ALONG
THE UPHILL EDGE OF THE BRUSH
BARRIER.
2. DRAPE FILTER FABRIC OVER THE
BRUSH BARRIER AND INTO THE
TRENCH. FABRIC SHOULD BE
SECURED IN THE TRENCH WITH
STAKES SET APPROXIMATELY 36"
O.C.
3. BACKFILL AND COMPACT THE
EXCAVATED SOIL.
4. SET STAKES ALONG THE DOWN-
HILL EDGE OF THE BRUSH
BARRIER, AND ANCHOR BY TYING
TWINE FROM THE FABRIC TO THE
STAKES.
Figure C-20 Schematic Diagram of a Brush Berm
Note: Filter fabric may be required in higher velocity situations.
Common Trouble Points:
AC -63
• Gaps between berm and ground due to uneven ground surface,
inadequately compacted berm, or inadequately secured berm (runoff
passing directly under berm).
• Berm receiving excessive volumes or velocities of flow (runoff overtopping
or displacing berm).
Inspection and Maintenance Guidelines:
• The area upstream from the brush berm should be maintained in a
condition that will allow accumulated silt to be removed following the runoff
of a rainfall event.
• The berm should be inspected weekly or after each rainfall event.
• When the silt reaches a depth of 6 inches is should be removed and
disposed of appropriately and in a manner that will not contribute to
additional siltation.
• Periodic tightening of the anchoring ropes may be required due to
shrinkage of the brush berm as it deteriorates over time;
• Brush berms should be replaced after 3 months or be repaired or
reconstructed when Toss of foliage occurs or when they no longer function
as intended.
C.3.9 Check Dams
Check dams are small barriers consisting of rock or earthen berms placed across
a drainage swale or ditch. They reduce the velocity of small concentrated flows,
provide a limited barrier for sediment and help disperse concentrated flows,
reducing potential erosion.
They are used primarily in long drainage swales or ditches in which permanent
vegetation may not be established and erosive velocities are present. They are
typically used in conjunction with other techniques such as inlet protection, riprap
or other sediment reduction techniques. Check dams provide limited treatment.
They are more useful in reducing flow to acceptable levels for other techniques
(NCTCOG, 1993b).
Although check dams are effective in reducing flow velocity and thereby lowering
the potential for channel erosion, it is usually better to establish a protective
vegetative lining before flow is confined or to install a structural channel lining.
However, under circumstances where this is not feasible, check dams are useful.
AC -64
Materials:
Although many different types of material can be used to create check dams,
aggregate and riprap produce a more stable structure.
• If the drainage area is less than 2 acres, coarse aggregate alone can be
used for the dam.
• For drainage areas between 2 and 10 acres, a combination of coarse
aggregate and riprap as shown in Figure C-21 should be used.
Guidelines for installation:
• The dam height should be between 18 and 36 inches.
• The center of the check dam should be at least 6 inches lower than the
outer edges. Field experience has shown that many dams are not
constructed to promote this "weir" effect. Storm water flows are then
forced to the stone -soil interface, thereby promoting scour at that point
and subsequent failure of the structure to perform its intended function.
• The dam should be designed so that the 1 -year, 3 -hour storm or design
storm for the water conveyance, whichever is greater, can pass the dam
without causing excessive upstream flooding.
• For added stability, the base of the check dam can be keyed into the soil
approximately 6 inches.
• The maximum spacing between the dams should be such that the toe of
the upstream dam is at the same elevation as the top of the downstream
dam. Follow spacing guidelines on Table C-7 Rock and Brush Berm and
Erosion Control Logs Spacing on Channels
• Stone should be placed according to the configuration in Figure C-21.
Hand or mechanical placement will be necessary to achieve complete
coverage of the ditch or swale and to insure that the center of the dam is
lower than the edges.
• Filter cloth may be used under the stone to provide a stable foundation
and to facilitate the removal of the stone
AC -65
2 ACRES OR LESS OF DRAINAGE AREA:
FILTER CLOTH
(OPTIONAL)
44•►gifi 4t i����0.i�../iii/���� �\�'�1��.��•���1�►.
Atm.; i:'� 4.1,tr!: n' •t� 1 %.-74•:` �,..
COARSE AGGREGATE
FLOW
(DOWNSTREAM VIEW)
2-10 ACRES OF' DRAINAGE AREA:
FILTER CLOTH ��t��� �� �v�wW�Jf <�e��`'
(OPTIONAL) �,a�i;,.a'�L���
COARSE AGGREGATE
FLOW
(DOWNSTREAM VIEW)
CLASS I RIPRAP
Figure C-21 Schematic Diagram of a Rock Check Dam
i
1
AC -66
Common Trouble Points:
• Check dams installed in grass -lined channels may kill the vegetative lining
if submergence after rains is too long and/or silting is excessive.
• If check dams are used in grass -lined channels that will be mowed, care
should be taken to remove all the stone when the dam is removed. Stones
often wash downstream and can damage mowing equipment and present
a safety hazard.
Inspection and Maintenance Guidelines:
• Check dams should be inspected and checked for sediment accumulation
weekly and after each runoff -producing storm event.
• Sediment should be removed when it reaches one half of the original
height of the measure.
• Regular inspections should be made to insure that the center of the dam is
lower than the edges. Erosion caused by high flows around the edges of
the dam should be corrected immediately.
C.3.10 Vegetative Buffers
Buffer zones are undisturbed strips of natural vegetation or an established
suitable planting that will provide a living filter to reduce soil erosion and runoff
velocities from construction activities. Natural buffer zones are used along
streams and other bodies of water that need protection from erosion and
sedimentation. Vegetative buffers can be used to protect natural swales and be
incorporated into natural landscaping of an area. They can provide critical
habitat adjacent to streams and wetlands, as well as assisting in controlling
erosion, especially on unstable steep slopes.
The buffer zone can be an area of vegetation that is left undisturbed during
construction, or it can be newly planted. If buffer zones are preserved, existing
vegetation, good planning, and site management are needed to prevent
disturbances such as grade changes, excavation, damage from equipment, and
other activities. The creation of new buffer strips requires the establishment of a
good dense turf (at least 80% coverage) and can include trees and shrubs. The
slope cannot exceed 12 percent. The minimum width of a vegetative buffer used
for sediment control should be 50 feet.
AC -67
Guidelines for installation:
• Preserving natural vegetation or plantings in clumps, blocks, or strips is
generally the easiest and most successful method.
• All unstable steep slopes should be left in natural vegetation.
• Fence or flag clearing limits and keep all equipment and construction
debris out of the natural areas.
• Keep all excavations outside the drip -line of trees and shrubs.
• Debris or extra soil should not be pushed into the buffer zone area
because it will cause damage from burying and smothering.
• The minimum width of a vegetative buffer used for sediment control
should be 50 feet.
Inspection and Maintenance Guidelines:
Inspection and careful maintenance are important to ensure healthy vegetation.
The need for routine maintenance such as mowing, fertilizing, irrigating, and
weed and pest control will depend on the species of plants and trees, soil types,
location and climatic conditions. County agricultural extension agencies are a
good source for this type of information.
C.3.11 Inlet Protection
Storm sewers that are made operational prior to stabilization of the associated
capture areas can convey large amounts of sediment to natural drainage ways.
In case of extreme sediment loading, the storm sewer itself may clog and lose a
major portion of its capacity. To avoid these problems, it is necessary to prevent
sediment from entering the system at the inlets. The following guidelines for inlet
protection are based primarily on recommendations by the Virginia Dept. of
Conservation and Recreation (1992) and the North Central Texas Council of
Governments (NCTCOG, 1993b).
In developments for which drainage is to be conveyed by underground storm
sewers, all inlets that may receive storm runoff from disturbed areas should be
protected. Temporary inlet protection is a series of different measures that
provide protection against silt transport or accumulation in storm sewer systems.
AC -68
This accumulation can greatly reduce or completely stop the flow in the pipes.
The different measures are used for different site conditions and inlet types.
Care should be taken when choosing a specific type of inlet protection. Field
experience has shown that inlet protection that causes excessive ponding in an
area of high construction activity may become so inconvenient that it is removed
or bypassed, thus transmitting sediment -laden flows unchecked. In such
situations, a structure with an adequate overflow mechanism should be utilized.
It should also be noted that inlet protection devices are designed to be installed
on construction sites and not on streets and roads open to the public. When
used on public streets these devices will cause ponding of runoff, which
can cause flooding and can present a traffic hazard. An example of
appropriate siting would be a new subdivision where the storm drain system is
installed before the area is stabilized and the streets open to the general public.
When construction occurs adjacent to active streets, the sediment should be
controlled on site and not on public thoroughfares. Occasionally, roadwork or
utility installation will occur on public roads. In these cases, inlet protection is an
appropriate temporary BMP.
The following inlet protection devices are for drainage areas of one acre or Tess.
Runoff from larger disturbed areas should be routed to a temporary sediment
trap or basin.
Filter barrier protection using erosion control logs or silt fence is appropriate
when the drainage area is less than one acre and the basin slope is less than
five percent. This type of protection is not applicable in paved areas.
Materials:
• Filter fabric should be a nonwoven fabric with a minimum weight of 4.0
oz/yd2.
• Erosion control Togs should be composed of material as defined in the
erosion control log section.
• Posts for erosion control logs or fabric should be 2" x 4" pressure treated
wood stakes or galvanized steel, tubular in cross-section or they may be
standard fence "T" posts.
• Concrete blocks should be standard 8" x 8" x 16" concrete masonry units.
• Wire mesh should be standard hardware cloth or comparable wire mesh
with an opening size not to exceed 1/2 inch.
AC -69
• The sand bag material should be a minimum unit weight 4 oz/yd2, mullen
burst strength exceeding 300 psi and ultraviolet stability exceeding 70
percent.
Guidelines for installation:
Silt Fence Area Inlet Protection
• Silt fence should conform to the specifications listed above and should be
cut from a continuous roll to avoid joints.
• For stakes, use 2 x 4 -inch wood or equivalent metal with a minimum
length of 3 feet.
• Space stakes evenly around the perimeter of the inlet a maximum of 3 feet
apart, and securely drive them into the ground, approximately 18 inches
deep.
• Place the bottom 12 inches of the fabric in a trench and backfill the trench
with 12 inches of compacted soil.
• Fasten fabric securely by staples or wire to the stakes and frame. Joints
must be overlapped to the next stake.
• It may be necessary to build a temporary dike on the down slope side of
the structure to prevent bypass flow.
If the drop inlet is above the finished grade, the grate may be completely covered
with filter fabric. The fabric should be securely attached to the entire perimeter of
the inlet using 1 "x 2" wood strips and appropriate fasteners.
Erosion Control Log Area Inlet Protection
• Erosion control logs should conform to the specifications listed above and
should be one continuous roll to minimize overlapping.
• For stakes, use 2 x 4 -inch wood or equivalent metal with a minimum
length of 3 feet.
• Space stakes evenly around the perimeter of the inlet a maximum of 3 feet
apart and securely drive them into the ground, approximately 18 inches
deep.
AC -70
• Fasten fabric securely by staples or wire to the stakes and frame. Joints
must be overlapped to the next stake.
• It may be necessary to build a temporary dike on the down slope side of
the structure to prevent bypass flow.
Curb Inlet Protection with Silt Fence
• Cut a continuous piece of wire mesh to extend from the top of curb over
the inlet opening and along the gutter as shown in the Standard Detail.
• Attach the filter fabric to the wire mesh and cut away a 4 inch clear section
near the top of curb to act as a weir.
• Place the assembly against the curb inlet opening and assure the inlet
opening is fully covered.
• Place sand bags or alternate weight to weigh down the assembly at the
top of curb and in the gutter on each side to assure no movement.
• This type of protection should be inspected frequently and the filter cloth
replaced when clogged with sediment.
• Assure that storm flow does not bypass inlet by installing temporary earth
or asphalt dikes directing flow into inlet as necessary.
Curb Inlet Protection with Erosion Control Logs
• Place erosion control log in gutter around inlet opening allowing erosion
control log to extend 12 inches on either side of opening as shown in the
City's Standard Detail. Assure direct contact with surface of gutter flowline.
• Place sandbags between inlet opening and erosion control log to allow for
weir flow.
• An erosion control log may be necessary to be placed on the back of curb
if site is not stabilized with vegetation.
• This type of protection should be inspected frequently and the erosion
control log replaced when clogged with sediment.
AC -71
C.3.12Stone Outlet Sediment Trap
A stone outlet sediment trap is an impoundment created by the placement of an
earthen and stone embankment to prevent soil and sediment Toss from a site.
The purpose of a sediment trap is to intercept sediment -laden runoff and trap the
sediment in order to protect drainage ways, properties and rights of way below
the sediment trap from sedimentation. A sediment trap is usually installed at
points of discharge from disturbed areas. The drainage area for a sediment trap
is recommended to be less than 5 acres. Larger areas should be treated using a
sediment basin. A sediment trap differs from a sediment basin mainly in the type
of discharge structure. A schematic of a sediment trap is shown in Figure C-22.
The trap should be located to obtain the maximum storage benefit from the
terrain, for ease of cleanout and disposal of the trapped sediment and to
minimize interference with construction activities. The volume of the trap should
be at least 1800 cubic feet per acre of drainage area.
Materials:
• All aggregate should be at least 3 inches in diameter and should not
exceed a volume of 0.5 cubic foot.
• The geotextile fabric specification should be woven polypropylene,
polyethylene or polyamide geotextile, minimum unit weight of 4.0 oz/yd2,
mullen burst strength at least 250 Ib/int, ultraviolet stability exceeding
70%, and equivalent opening size exceeding 40.
Installation:
• Earth Embankment: Place fill material in layers not more than 8 inches in
loose depth. Before compaction, moisten or aerate each layer as
necessary to provide the optimum moisture content of the material.
Compact each layer to 95 percent standard proctor density. Do not place
material on surfaces that are muddy or frozen. Side slopes for the
embankment are to be 3:1. The minimum width of the embankment
should be 3 feet.
• A gap is to be left in the embankment in the location where the natural
confluence of runoff crosses the embankment line. The gap is to have a
width in feet equal to 6 times the drainage area in acres.
• Geotextile Covered Rock Core: A core of filter stone having a minimum
height of 1.5 feet and a minimum width at the base of 3 feet should be
placed across the opening of the earth embankment and should be
AC -72
covered by geotextile fabric which should extend a minimum distance of 2
feet in either direction from the base of the filter stone core.
• Filter Stone Embankment: Filter stone should be placed over the
geotextile and should have a side slope which matches that of the earth
embankment of 3:1 and should cover the geotextile/rock core a minimum
of 6 inches when installation is complete. The crest of the outlet should be
at least 1 foot below the top of the embankment.
Common Trouble Points:
• Can cause minor flooding upstream of dam, impacting construction
operations.
• The cost of construction, availability of materials, and the amount of land
required limit the application of this measure.
Inspection and Maintenance Guidelines:
• Inspection should be made weekly and after each rainfall. Check the
embankment, spillways, and outlet for erosion damage, and inspect the
embankment for piping and settlement. Repair should be made promptly
as needed.
• Trash and other debris should be removed after each rainfall to prevent
clogging of the outlet structure.
• Sediment should be removed and the trap restored to its original
dimensions when the sediment has accumulated to half of the design
depth of the trap.
• Sediment removed from the trap should be deposited in an approved
spoils area and in such a manner that it will not cause additional siltation.
AC -73
AREA TO BE
EXCAVATED. IF
NECESSARY.
FOR STORAGE
EARTH EMBANKMENT
YYY
FILTER STONE
EMBANKMENT
A -.IN--
cc
5
•
•
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- • • �,II�I�II 111111 I�.I�I:���l���lll'1111111 �w�
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=111_111-1II=111=1
0:0
►opo°o°o
PLAN VEW
N.T.S.
LENGTH (FT.) _
0
0
6 x DRAINAGE AREA (AC.)
CUTAWAY TO SHOW
GEOTEXTILE COVERED
FILTER STONE CORE
GEOTEXTILE COVERED
FILTER STONE CORE
V MIN.
MWI.
1'-6- MIN.
PROFIF VEW
N.T.S.
GEOTEXTILE COVERED
FILTER STONE CORE
TYPE 'A' RIP RAP
3
•
= ————————
EXCAVATION.
_____
EXCAVATION. IF NECESSARY
FOR STORAGE. 1800 CF/AC..
MINIMUM
EXISTING GROUND
3
1r—
SECTION A - A
N.T.S.
Figure C-22 Schematic Diagram of a Sediment Trap
FLOW
AC -74
C.3.13Sediment Basins
The purpose of a sediment basin is to intercept sediment -laden runoff and trap
the sediment in order to protect drainage ways, properties and rights of way
below the sediment basin from sedimentation. A sediment basin is usually
installed at points of discharge from disturbed areas. The drainage area for a
sediment basin is recommended to be less than 100 acres and located off the
existing creek or channel.
Sediment basins are effective for capturing and slowly releasing the runoff from
larger disturbed areas thereby allowing sedimentation to take place. A sediment
basin can be created where a permanent pond BMP is being constructed.
Guidelines for construction of the permanent BMP should be followed, but
revegetation, placement of underdrain piping, and installation of sand or other
filter media should not be carried out until the site construction phase is
complete. A schematic of a sediment basin is shown in Figure C-23.
Materials:
• Riser should be corrugated metal or reinforced concrete pipe or box and
should have watertight fittings or end to end connections of sections.
• An outlet pipe of corrugated metal or reinforced concrete should be
attached to the riser and should have positive flow to a stabilized outlet on
the downstream side of the embankment.
• An anti -vortex device and rubbish screen should be attached to the top of
the riser and should be made of polyvinyl chloride or corrugated metal.
Basin Design and Construction:
• For common drainage locations that serve an area with ten or more acres
disturbed at one time, the sediment basin volume should be 1800 cubic
feet of storage for each disturbed acre.
• The basin length to width ratio should be at least 2:1 to improve trapping
efficiency. The shape may be attained by excavation or the use of baffles.
The lengths should be measured at the elevation of the riser de -watering
hole.
• Place fill material in layers not more than 8 inches in loose depth. Before
compaction, moisten or aerate each layer as necessary to provide the
optimum moisture content of the material. Compact each layer to 95
AC -75
percent standard proctor density. Do not place material on surfaces that
are muddy or frozen. Side slopes for the embankment should be 3:1
(H:V).
HIGH FLOW OUTLET
EMERGENCY
SPILLWAY
ELEVATION
Z DESIGN HIGH WATER 1' MIN.
' MAX
DESIGN CAPACITY
EXCAVATED AREA
FOR STORAGE AS
NECESSARY, SHAPE
MAY VARY.
ANCHOR BLOCK
CROSS SECTION
N.T.S
EMERGENCY SPILLWAY
DEWATERING OUTLET
STABIUZATION - RIP RAP.
MATTINGS OR OTHER
ACCEPTABLE MATERIAL
ENERGY
DISSIPATION
CONCRETE
BLOCKS
PLAN VIEW
N.T.S
Figure C-23 Schematic of a Sediment Basin
AC -76
• An emergency spillway should be installed adjacent to the embankment
on undisturbed soil and should be sized to carry the full amount of flow
generated by a 10 -year, 3 -hour storm with 1 foot of freeboard Tess the
amount which can be carried by the principal outlet control device.
• The emergency spillway should be lined with riprap as should the swale
leading from the spillway to the normal watercourse at the base of the
embankment.
• The principal outlet control device should consist of a rigid vertically
oriented pipe or box. Attached to this structure should be a horizontal pipe,
which should extend through the embankment to the toe of fill to provide a
de -watering outlet for the basin.
• An anti -vortex device should be attached to the inlet portion of the
principal outlet control device to serve as a rubbish screen.
• A concrete base should be used to anchor the principal outlet control
device and should be sized to provide a safety factor of 1.5 (downward
forces = 1.5 buoyant forces).
• The basin should include a permanent stake to indicate the sediment level
in the pool and marked to indicate when the sediment occupies 50% of the
basin volume (not the top of the stake).
• The top of the riser pipe should remain open and be guarded with a trash
rack and anti -vortex device. The top of the riser should be 12 inches below
the elevation of the emergency spillway. The riser should be sized to
convey the runoff from the 1 -year, 3 -hour storm when the water surface is
at the emergency spillway elevation. For basins with no spillway the riser
must be sized to convey the runoff from the 10 -year, 3 -hour storm.
• Anti -seep collars should be included when soil conditions or length of
service make piping through the backfill a possibility.
• The 48-hour drawdown time will be achieved by using a riser pipe
perforated at the point measured from the bottom of the riser pipe equal to
1/2 the volume of the basin. This is the maximum sediment storage
elevation. The size of the perforation may be calculated as follows:
Equation 3. As = [Ag * (2h)°.5/[Cd * 980,000]
AC -77
Where:
Ao = Area of the de -watering perforation, ft2
As = Surface area of the basin, ft2
Cd = Coefficient of contraction, approximately 0.6
h = head of water above the perforation, ft
Perforating the riser with multiple holes with a combined surface area equal to Ao
is acceptable.
Common Trouble Points:
• Storm events that exceed the design storm event can cause damage to
the spillway structure of the basin and may cause adverse impacts
downstream.
• Piping (flow occurring in the fill material) around outlet pipe can cause
failure of the embankment.
Inspection and Maintenance Guidelines:
• Inspection should be made weekly and after each rainfall. Check the
embankment, spillways, and outlet for erosion damage, and inspect the
embankment for piping and settlement. Repair should be made promptly
as needed by the contractor.
• Trash and other debris should be removed after each rainfall to prevent
clogging of the outlet structure.
• Accumulated silt should be removed and the basin should be re -graded to
its original dimensions at such point that the capacity of the impoundment
has been reduced to 75% of its original storage capacity.
• The removed sediment should be stockpiled or redistributed in areas that
are protected from erosion.
C.3.14Erosion Control Logs
An erosion control log consists of wood excelsior, coconut fibers, mulch, or other
similar materials bound into a tight tubular roll. When erosion control logs are
placed at the toe and on the face of slopes, they intercept runoff, reduce its flow
velocity, release the runoff as sheet flow, and provide removal of sediment from
the runoff. By interrupting the length of a slope, erosion control logs can also
reduce erosion.
AC -78
Erosion control Togs may be suitable:
• Along the toe, top, face, and at grade breaks of exposed and erodible
slopes to shorten slope length and spread runoff as sheet flow
• At the end of a downward slope where it transitions to a steeper slope
• Along the perimeter of a project
• As check dams in unlined ditches
• Down-slope of exposed soil areas
• Around temporary stockpiles
Limitations:
• Erosion control Togs at the toe of slopes greater than 5:1 (H:V) should be a
minimum of 20 in. diameter or installations achieving the same protection
(i.e. stacked smaller diameter erosion control logs, etc.).
• Difficult to move once saturated.
• If not properly staked and trenched in, erosion control Togs could be
transported by high flows.
• Erosion control Togs have a very limited sediment capture zone.
• Erosion control logs should not be used on slopes subject to creep,
slumping, or landslide.
Material:
• Core material: Core material should be biodegradable or recyclable.
Material may be compost, mulch, aspen wood fibers, chipped site
vegetation, agricultural rice or wheat straw, coconut fiber, 100% recyclable
fibers, or similar materials.
• Containment Mesh: Containment mesh should be 100% biodegradable,
photodegradable or recyclable such as burlap, twine, UV photodegradable
plastic, polyester, or similar material. When the erosion control log will
remain in place as part of a vegetative system use biodegradable or
photodegradable mesh. For temporary installation recyclable mesh is
recommended.
Implementation:
• Locate erosion control Togs on level contours spaced as follows:
• Slope inclination of 4:1 (H:V) or flatter: Erosion control logs should be
placed at a maximum interval of 20 ft.
AC -79
• Slope inclination between 4:1 and 2:1 (H:V): Erosion control logs should
be placed at a maximum interval of 15 ft. (a closer spacing is more
effective).
• Slope inclination 2:1 (H:V) or greater: Erosion control logs should be
placed at a maximum interval of 10 ft. (a closer spacing is more effective).
• Turn the ends of the erosion control log up slope to prevent runoff from
going around the roll.
• Stake erosion control logs into a 2 to 4 in. deep trench with a width equal
to the diameter of the erosion control log.
• Drive stakes at the end of each erosion control log and spaced 4 ft
maximum on center.
• Use wood stakes with a nominal classification of 2" by 2" and minimum
length of 24 in.
• If more than one erosion control log is placed in a row, the rolls should be
overlapped, not abutted.
• Follow Table C-7 Rock and Brush Berm and Erosion control logs Spacing
on Channels.
Inspection and Maintenance Guidelines:
• Inspect prior to rain event, daily during extended rain events, after rain
events, and weekly.
• Repair or replace split, torn, unraveling, or slumping erosion control logs.
• If the erosion control log is used as a sediment capture device, or as an
erosion control device to maintain sheet flows, sediment that accumulates
behind the role must be periodically removed in order to maintain its
effectiveness. Sediment should be removed when the accumulation
reaches one-half the designated sediment storage depth, usually one-half
the distance between the top of the erosion control log and the adjacent
ground surface. Sediment removed during maintenance may be
incorporated into earthwork on the site or disposed of at an appropriate
location.
AC -80
C.3.15Dewaterinq Operations
Dewatering operations are practices that manage the discharge of pollutants
when non -storm water and accumulated precipitation or groundwater must be
removed from a work location so that construction work may be accomplished.
The controls detailed in this BMP only allow for minimal settling time for sediment
particles and should only be used when site conditions restrict the use of the
other control methods. When possible avoid dewatering discharges by using the
water for dust control, by infiltration, allowing to evaporate, etc.
A variety of methods can be used to treat water during dewatering operations.
Several devices are presented below and provide options to achieve sediment
removal. When pumping water out or through any of these devices, a floatation
device should be attached to the pump inlet.
Sediment controls are low to high cost measures depending on the dewatering
system that is selected. Pressurized filters tend to be more expensive than
gravity settling, but are often more effective. Simple tanks are generally rented
on a long-term basis (one or more months). Mobilization and demobilization
costs vary considerably.
Inspection and Maintenance
• Inspect and verify that activity -based BMPs are in place prior to the
commencement of associated activities. While activities associated with
the BMP are under way, inspect weekly and after every 0.5 in. or greater
rainfall event to verify continued BMP implementation.
• Inspect BMPs subject to non -storm water discharges daily while non -
storm water discharges occur.
• Unit -specific maintenance requirements are included with the description
of each technology.
• Sediment removed during the maintenance of a dewatering device may be
either spread onsite and stabilized, or disposed of at a disposal site.
• Sediment that is commingled with other pollutants must be disposed of in
accordance with all applicable laws and regulations.
AC -81
Weir Tanks
Description:
A weir tank separates water and waste by using weirs. The configuration of the
weirs (over and under weirs) maximizes the residence time in the tank and
determines the waste to be removed from the water, such as oil, grease, and
sediments.
Appropriate Applications:
The tank removes trash, some settleable solids (gravel, sand, and silt), some
visible oil and grease, and some metals (removed with sediment). To achieve
high levels of flow, multiple tanks can be used in parallel. If additional treatment
is desired, the tanks can be placed in series or as pre-treatment for other
methods.
Implementation:
• Tanks are delivered to the site by the vendor, who can provide assistance
with set-up and operation.
• Tank size will depend on flow volume, constituents of concern, and
residency period required. Vendors should be consulted to appropriately
size tank.
Maintenance:
• Periodic cleaning is required based on visual inspection or reduced flow.
• Oil and grease disposal must be by licensed waste disposal company.
Dewatering Tanks
Description:
A dewatering tank removes debris and sediment. Flow enters the tank through
the top, passes through a fabric filter, and is discharged through the bottom of
the tank. The filter separates the solids from the liquids.
Appropriate Applications:
The tank removes trash, gravel, sand, and silt, some visible oil and grease, and
some metals (removed with sediment). To achieve high levels of flow, multiple
tanks can be used in parallel. If additional treatment is desired, the tanks can be
placed in series or as pre-treatment for other methods.
Implementation:
• Tanks are delivered to the site by the vendor, who can provide assistance
with set-up and operation.
• Tank size will depend on flow volume, constituents of concem, and
residency period required. Vendors should be consulted to determine
appropriate size of tank.
AC -82
Maintenance:
• Periodic cleaning is required based on visual inspection or reduced flow.
• Oil and grease disposal must be by licensed waste disposal company.
Gravity Bag Filter
N9SILP8LE IN VARIOUS
SKIVES SIZES FOR
SEDIMENT CONTAINMENT
WATER PUMP
PUMP DISCI -PAGE HOSE
Description:
A gravity bag filter, also referred to as a dewatering bag, is a square or
rectangular bag made of non -woven geotextile fabric that collects sand, silt, and
fines.
Appropriate Applications:
• Effective for the removal of sediments (gravel, sand, and silt). Some
metals are removed with the sediment.
Implementation:
• Water is pumped into one side of the bag and seeps through the bottom
and sides of the bag.
• A secondary barrier, such as a rock filter bed or erosion control logs, is
placed beneath and beyond the edges of the bag to capture sediments
that escape the bag.
Maintenance:
• Inspection of the flow conditions, bag condition, bag capacity, and the
secondary barrier is required.
• Replace the bag when it no longer filters sediment or passes water at a
reasonable rate. The bag is typically disposed of properly similar to other trash or
rubbish.
AC -83
C.3.16Spi11 Prevention and Control
The objective of this section is to describe measures to prevent or reduce the
discharge of pollutants to drainage systems or watercourses from Teaks and spills
by reducing the chance for spills, stopping the source of spills, containing and
cleaning up spills, properly disposing of spill materials, and training employees.
The following steps will help reduce the storm water impacts of leaks and spills:
Education
• Be aware that different materials pollute in different amounts. Make sure
that each employee knows what a "significant spill" is for each material
they use, and what is the appropriate response for "significant" and
"insignificant" spills. Employees should also be aware of when spills must
be reported to the TCEQ. Information available in 30 TAC 327.4 and 40
CFR 302.4.
• Educate employees and subcontractors on potential dangers to humans
and the environment from spills and Teaks.
• Hold regular meetings to discuss and reinforce appropriate disposal
procedures (incorporate into regular safety meetings).
• Establish a continuing education program to indoctrinate new employees.
• Have contractor's superintendent or representative oversee and enforce
proper spill prevention and control measures.
General Measures
• To the extent that the work can be accomplished safely, spills of oil,
petroleum products, substances listed under 40 CFR parts 110,117, and
302, and sanitary and septic wastes should be contained and cleaned up
immediately.
• Store hazardous materials and wastes in covered containers and protect
from vandalism.
• Place a stockpile of spill cleanup materials where it will be readily
accessible and protected from drainage.
• Train employees in spill prevention and cleanup.
• Designate responsible individuals to oversee and enforce control
measures.
AC -84
• Spills should be covered and protected from storm water runoff during
rainfall to the extent that it doesn't compromise clean up activities.
• Do not bury or wash spills with water.
• Store and dispose of used clean up materials, contaminated materials,
and recovered spill material that is no longer suitable for the intended
purpose in conformance with the provisions in applicable BMPs.
• Do not allow water used for cleaning and decontamination to enter storm
drains or watercourses. Collect and dispose of contaminated water in
accordance with applicable regulations.
• Contain water overflow or minor water spillage and do not allow it to
discharge into drainage facilities or watercourses.
• Place Material Safety Data Sheets (MSDS), as well as proper storage,
cleanup, and spill reporting instructions for hazardous materials stored or
used on the project site in an open, conspicuous, and accessible location.
• Keep waste storage areas clean, well organized, and equipped with ample
cleanup supplies as appropriate for the materials being stored. Perimeter
controls, containment structures, covers, and liners should be repaired or
replaced as needed to maintain proper function.
Cleanup
• Clean up leaks and spills immediately.
• Use a rag for small spills on paved surfaces, a damp mop for general
cleanup, and absorbent material for larger spills. If the spilled material is
hazardous, then the used cleanup materials are also hazardous and must
be disposed of as hazardous waste.
• Never hose down or bury dry material spills. Clean up as much of the
material as possible and dispose of properly.
Minor Spills
• Minor spills typically involve small quantities of oil, gasoline, paint, etc.
which can be controlled by the first responder at the discovery of the spill.
• Use absorbent materials on small spills rather than
burying the spill.
• Absorbent materials should be promptly removed
properly.
• Follow the practice below for a minor spill:
o Contain the spread of the spill.
hosing down or
and disposed of
AC -85
o Recover spilled materials.
o Clean the contaminated area and properly dispose of contaminated
materials.
Semi -Significant Spills
Semi -significant spills still can be controlled by the first responder along with the
aid of other personnel, etc. This response may require the cessation of all other
activities.
Spills should be cleaned up immediately:
• Contain spread of the spill.
• Notify the project foreman immediately.
• If the spill occurs on paved or impermeable surfaces, clean up using "dry"
methods (absorbent materials, cat litter and/or rags). Contain the spill by
encircling with absorbent materials and do not let the spill spread widely.
• If the spill occurs in dirt areas, immediately contain the spill by
constructing an earthen dike. Dig up and properly dispose of
contaminated soil.
• If the spill occurs during rain, cover spill with tarps or other material to
prevent contaminating runoff.
Significant/Hazardous Spills
For significant or hazardous spills that are in reportable quantities:
• Notify the TCEQ by telephone as soon as possible and within 24 hours at
512-339-2929 (Austin)) between 8 AM and 5 PM. After hours, contact the
Environmental Release Hotline at 1-800-832-8224. It is the contractor's
responsibility to have all emergency phone numbers at the construction
site.
• For spills of federal reportable quantities, in conformance with the
requirements in 40 CFR parts 110, 119, and 302, the contractor should
notify the National Response Center at (800) 424-8802.
• Notification should first be made by telephone and followed up with a
written report.
• The services of a spills contractor or a Haz-Mat team should be obtained
immediately. Construction personnel should not attempt to clean up until
the appropriate and qualified staffs have arrived at the job site.
AC -86
• Other agencies which may need to be consulted include, but are not
limited to, the City Police Department, County Sheriff Office, Fire
Departments, etc.
More information on spill rules and appropriate responses is available on the
TCEQ website at: http://www.tceq.state.tx.us/response
Vehicle and Equipment Maintenance
• If maintenance must occur onsite, use a designated area and a secondary
containment, located away from drainage courses, to prevent the runon of
storm water and the runoff of spills.
• Regularly inspect onsite vehicles and equipment for Teaks and repair
immediately
• Check incoming vehicles and equipment (including delivery trucks, and
employee and subcontractor vehicles) for leaking oil and fluids. Do not
allow leaking vehicles or equipment onsite.
• Always use secondary containment, such as a drain pan or drop cloth, to
catch spills or leaks when removing or changing fluids.
• Place drip pans or absorbent materials under paving equipment when not
in use.
• Use absorbent materials on small spills rather than hosing down or
burying the spill. Remove the absorbent materials promptly and dispose
of properly.
• Promptly transfer used fluids to the proper waste or recycling drums.
Don't leave full drip pans or other open containers lying around.
• Oil filters disposed of in trashcans or dumpsters can leak oil and pollute
storm water. Place the oil filter in a funnel over a waste oil -recycling drum
to drain excess oil before disposal. Oil filters can also be recycled. Ask
the oil supplier or recycler about recycling oil filters.
• Store cracked batteries in a non -leaking secondary container. Do this with
all cracked batteries even if you think all the acid has drained out. If you
drop a battery, treat it as if it is cracked. Put it into the containment area
until you are sure it is not leaking.
Vehicle and Equipment Fueling
• If fueling must occur on site, use designated areas, located away from
drainage courses, to prevent the runon of storm water and the runoff of
spills.
• Discourage "topping off" of fuel tanks.
AC -87
• Always use secondary containment, such as a drain pan, when fueling to
catch spills/ Teaks.
AC -88
C.3.17Creek Crossings
Creek crossings represent particularly important areas to employ effective
erosion and sedimentation control. A temporary steam crossing is used to
provide a safe, stable way for construction vehicle traffic to cross a watercourse.
Temporary stream crossings provide streambank stabilization, reduce the risk of
damage to the streambed or channel, and minimize sediment loading from
construction activities and traffic. Underground utility construction and road
construction across creeks requires special measures, as detailed below.
General Considerations
• Creek crossings should be made perpendicular to the creek flowline.
• In -stream controls should only be used as a secondary BMP. Storm water
runoff approaching a creek crossing should be diverted to a sediment
trapping BMP before it reaches the creek.
• If baseflow is present, the City Engineer should be consulted, as it may be
necessary to divert or pump water around the construction area.
• Every effort should be made to keep the zone of immediate construction
free of surface and ground water. For construction in the creek channel, a
pipe of adequate size to divert normal stream flow should be provided
around the construction area. Diversion may be by pumping or gravity flow
using temporary dams
• Where water must be pumped from the construction zone, discharges
should be in a manner that will not cause scouring or erosion. All
discharges shall be on the upstream or upslope side of erosion control
structures/ measures. If discharges are necessary in easily erodible areas,
a stabilized, energy -dissipating discharge apron shall be constructed of
riprap with minimum stone diameter of 6 inches and minimum depth of 12
inches. Size of the apron in linear dimensions shall be approximately 10
times the diameter of the discharge pipe.
Utility Crossings & Excavations
• Before any trenching or excavation, install two rock berms at 100 -ft
spacing across the channel (perpendicular to the flowline) downstream of
the proposed trench. These berms should be located between 100 and
300 feet downstream of the proposed trench. Lay pipe or other utility line
and bury as soon as possible after trenching.
• After installation is complete (or at the end of work day, if installation
cannot be completed by end of day), install erosion control Togs or silt
AC -89
fencing along trench line on either side of creek at 25 -ft intervals, as
shown in Figure C-24.
• Material excavated from the trench in the creek channel should not be
deposited on the channel banks. Excavation should be hauled out of the
channel or used in backfill of open trench. No loose excavated material
should be left in the channel at the end of a work day.
• A concrete cap should be placed over buried pipe within the creek, and
the streambed should be restored to proper grade.
• Revegetate the disturbed area using appropriate native or adapted grass
species incorporated with erosion blankets/matting.
OVERLAND
DRAINAGE
MOIL N332:10
I !
i
SILT FENCES
ROCK
BERMS
<-
UTILITY
PIPELINE
Figure C-24 Utility Crossing or Excavation within Creek Schematic
Road Crossings
A variety of techniques may be used depending on local topography and soil conditions.
These include ford crossings, culvert crossings, dragline mats, and bridges.
AC -90
General Considerations
• Construct temporary crossings at proposed roadway crossings and any
additional crossing points. Minimize the number of additional crossings to
reduce impact to creeks.
• Where a stream crossing is required, select a crossing site with these
features:
1. Straight and narrow creek channel with high banks;
2. Stable creek banks that provide solid foundation for a crossing.
3. Minimal elevation changes (0-10% preferred) on road/trail leading to
crossing.
Installation
• Keep heavy equipment out of creek.
• Construct a swale or berm across the approach to the crossing on both
sides of the crossing. Other water diversion devices (broad based dips,
water bars, etc.) should be used on long approaches to minimize the
amount of water flowing to the crossing).
• Stabilize exposed soil around the crossing with mulch, temporary seeding
and/or erosion control blankets/matting.
Maintenance
• Keep crossing surface free of soil and debris that could enter stream.
• Check crossing components weekly and after rainfall to maintain strength
and integrity.
• Remove Targe branches or other flow obstructions that could impair the
function of the crossing or cause a failure of the crossing.
Removal & Restoration
• Clean off crossing surface; keep debris out of the creek channel.
• Carefully remove crossing materials, minimizing disturbance to the creek
channel.
• Permanently stabilize disturbed portions of creek bank and approaches
with perennial grasses, erosion control blankets/matting and/or rip rap
• Leave appropriate water diversion structures in place on both sides of
creek.
AC -91
Surface flow diverted
by swore. _________
Surface flow diverted
—by swole —
Aggregate bed over
engineering fabric
Aggregate opproch
1:5 (V: H) Maximum slope on rood
/Surface flow diverted
by swole (or berm)
Engineerin
Fabric
Surface (low diverted
by swcle
(or berm)
J
New road
Original stream bed
..re.ote bed over en
ineerin fabric
TYPICAL FORD CROSSING
NOT TO SCALE
Figure C-25 Typical Temporary Ford Crossing Schematic
AC -92
1/2 Diameter of pipe
12". or os needed
to support toads.
whichever is greoter.
Coarse oggregote
-,
Capacity of pipe culverts
together = design flow +
safety factor
Earth fill covered
by large ongulor
rock. upstreom
and downstream.
aloes • .-: xl'�sY a►i�•u..i T
seeding and/or
erosion control
blanket
I Ell I
IE , 111=11Ef1i, ,l1l11l
ELEVATION
Flow r_
Approach
stobdized with
coarse aggregate
Large ongulor
rock over
earth fill.
upstream &
downstream.
Diversion
and/or swole
Engineering
fobric
Approach
stabilized with
coarse aggregate
QM. QM. MOP MIM
mmir
Stream chonnel
PLAN VIEW
Diversion
and/or swole
Top of bank
TYPICAL CULVERT CROSSING
NOT TO SCALE
Figure C-26 Typical Temporary Culvert Crossing Schematic
AC -93
Swale
Stabilized
approach
\O
rr
Stabilized
approach
Swale
Abutment
Abutment
NOTE:
Surface flow of road diverted
by swale and/or dike.
TYPICAL BRIDGE CROSSING
NOT TO SCALE
Figure C-27 Typical Temporary Bridge Crossing Schematic
AC -94
C.3.18Concrete Washout Areas
The purpose of concrete washout areas is to prevent or reduce the discharge of
pollutants to storm water from concrete waste by conducting washout offsite or
performing onsite washout in a designated area, and training employees and
subcontractors.
Application
A number of water quality parameters can be affected by the introduction of
concrete, especially fresh concrete. Concrete affects the pH of runoff, causing
significant chemical changes in water bodies and harming aquatic life.
Unacceptable Waste Concrete Disposal Practices
• Dumping in vacant areas on the job -site.
• Illicit dumping off-jobsite.
• Dumping into ditches or drainage facilities.
Approach
• Avoid unacceptable disposal practices listed above.
• Develop pre -determined, safe concrete disposal areas.
• Provide a washout area with a minimum of 6 cubic feet of containment
area volume for every 10 cubic yards of concrete poured.
• Overflow of washdown water shall be discharged in an area protected by
one or more sediment removal BMPs and shall be done in a manner that
does not result in a violation of groundwater or surface water regulations.
• Incorporate requirements for concrete waste management into material
supplier and subcontractor agreements.
• Do not wash out concrete trucks into storm drains, open ditches, streets,
or streams.
• Perform washout of concrete trucks in designated areas only.
• Wash out wastes into the temporary pit where the concrete can set, be
broken up, and then disposed properly.
Installation
Below grade concrete washout facilities are typical. These consist of a lined
excavation sized to hold expected volume of washout material. Above grade
facilities are used if excavation is not practical. Temporary concrete washout
facility (type above grade) should be constructed with sufficient quantity and
volume to contain all liquid and concrete waste generated by washout
operations. Plastic lining material should be a minimum of 10 mil polyethylene
sheeting and should be free of holes, tears, or other defects that compromise the
impermeability of the material. See Figure C-28 for typical concrete washout
areas.
AC -95
Disposal
When temporary concrete washout facilities are no longer required for the work,
the hardened concrete should be removed and disposed of. Materials used to
construct temporary concrete washout facilities should be removed from the site
of the work and disposed of. Holes, depressions or other ground disturbance
caused by the removal of the temporary concrete washout facilities should be
backfilled and repaired.
AC -96
L—
fLAMING'
04 AL L
SIDE S
BE KM
- SANDBAG
1CtMr
PLASTIC LINING
PL AN
No 10 SCALL
IT PE BELOW GRADE`
W
IC
10 Toy0-sT C10EU IA IC LINING
q.
7 X 1 �►q
SLAKE
CTYP)
PLAN
NO1 TO SCALE
1 YPY `ABOVE GRANr
OZl ON A- A
NUT Iia &A1E
10 Mit.
PLA , iC LINING
//--
WQCii fRAM E SECURELY
fAJ1LNEI] ARCAALT
ENTIRE PE ROAM W11N
TWO STAKES
SEeiION
NO1 10 GALE
Pt01E$
1. ACTUAL LAYOUT DE1EF MINED
IN fiELtL.
Figure C-28 Schematic Diagrams of Concrete Washout Areas
AC -97
ROUND ROCK, TEXAS
PURPOSE. PASSION. PROSPERITY
City Council Agenda Summary Sheet
Agenda Item No. 11D1.
Agenda Caption:
Consider an ordinance amending the City of Round Rock Design and Construction
Standards — Drainage Criteria Manual by adding "Section 9 Erosion and Sediment
Control" and by adding "Appendix C — Erosion and Sediment Control Best Management
Practices." (First Reading)
Meeting Date: July 28, 2011
Department: Utilities and Environmental Services
Staff Person making presentation: Michael Thane, P.E.
Utilities Director
Item Summary:
Federal and State regulations are increasingly targeting erosion and sedimentation as a major source of pollution
effecting urban water quality. As a requirement of the City's Texas Pollutant Discharge Elimination System Phase II
MS4 Permit that was approved by the Texas Commission on Environmental Quality (TCEQ), the City is required to
adopt minimum standards for installation, inspection and maintenance of Erosion and Sedimentation Controls
(ESCs) for construction activities.
This ordinance adoption would add Chapter 9 to the Drainage Criteria Manual meeting the requirements of the MS4
Permit. Chapter 9 requires that design engineers and contractors plan and implement ESC Best Management
Practices (BMPs) and requires them to monitor, maintain and modify the controls as necessary. In addition, this
action adds Appendix C to serve as a resource to local Engineer's, Contractors, Plan Reviewers, and Inspectors for
the most commonly used BMPs. Providing a list of preapproved BMP's should provide a baseline standard as well as
improve review efficiencies.
Strategic Plan Relevance:
29.0 Provide for effective management of storm water. To achieve this goal the City will ensure it is in compliance
with storm water regulations.
Cost: N/A
Source of Funds: N/A
Date of Public Hearing (if required): N/A
Recommended Action: Approval