HomeMy Public PortalAboutCity of Richmond Stormwater Development Manual
STORMWATER
DEVELOPMENT
MANUAL
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CITY OF RICHMOND
STORMWATER DEVELOPMENT MANUAL
TABLE OF CONTENTS
PART Tab
1.0. INTRODUCTION 1
1.1 Purpose of the Stormwater Development Standards
1.2 Stormwater Management Board Description
1.3 Stormwater Related Ordinances
1.3.1 Erosion and Sediment Control
1.3.2 Post-Construction Stormwater Runoff Control
2.0 STORMWATER CONSTRUCTION PERMIT PROCESS 2
2.1 Review of Stormwater Development Standards
2.2 Kickoff Meeting
2.3 Project Development
2.4 Permit Application
2.5 Maintenance Agreement
2.6 Review for Compliance
2.7 Submittal Response
2.8 Issuance of a Construction Permit
2.9 Inspection
2.10 Project Completion Review
3.0 PERMIT APPLICATION COMPONENTS 3
3.1 Introduction
3.2 Project Information
3.2.1 Project Narrative
3.2.2 Vicinity Map
3.2.3 General Plan Requirements
3.2.4 Existing Project Site Layout
3.2.5 Final Project Site Layout
3.2.6 Grading Plan
3.2.7 Drainage Plan
3.2.8 Erosion and Sediment Control Plan
3.2.9 Post-Construction Stormwater Management Plan
3.2.10 Technical Report
3.2.11 Requirements for Category 3
3.3 Permits for Construction in the Floodway
4.0 HYDROLOGY 4
4.1 Introduction
4.2 Calculating the Peak Discharge
4.3 Design Storm Frequencies
4.3.1 Minor Conveyance Systems
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4.3.2 Major Conveyance Systems
4.3.3 Detention and Retention Facilities
5.0 STORMWATER CONVEYANCE 5
5.1 Introduction
5.2 Hydraulic Capacity
5.3 Storm Sewers
5.3.1 Sewer Pipe
5.3.2 Structures
5.3.3 Joints, Fittings and Appurtenances
5.3.4 Construction Requirements
5.4 Open Channels
5.4.1 Channel Cross-Section and Grade
5.4.2 Side Slopes
5.4.3 Peak Flows
5.4.4 Channel Stability
5.4.5 Drainage of Waterways
5.4.6 Appurtenant Structures
5.4.7 Disposition of Spoils
5.4.8 Materials
6.0 EROSION AND SEDIMENT CONTROL 6
6.1 Introduction
6.1.1 Background and Purpose
6.1.2 Design Principles
6.2 Details on Specific Practices
6.2.1 Temporary Sediment Basin
6.2.2 Rock Check Dam
6.2.3 Temporary Stone Construction Entrance
6.2.4 Silt Fence
6.2.5 Straw Dam
6.2.6 Fabric Drop Inlet Protection
6.2.7 Sandbag Curb Inlet Protection
6.2.8 Riprap Chute Outfall Protection
7.0 POST-CONSTRUCTION STORMWATER QUALITY CONTROL 7
7.1 Introduction
7.1.1 Background and Purpose
7.1.2 Stormwater Quality Control Requirements
7.1.3 Water Quality Volume (WQv)
7.1.4 Structural Best Management Practices
7.2 Pre-Approved BMPs
7.2.1 Stormwater Ponds
7.2.2 Detention Basin
7.2.3 Stormwater Wetlands
7.2.4 Bioretention
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7.2.5 Sand Filters
7.2.6 Dry Water Quality Swales
7.2.7 Biofilters
7.2.8 Catch Basin Inserts
7.2.9 Other Pre-Approved BMPs
APPENDIX A – Ordinances A
Erosion and Sediment Control
Control for Post-Construction Stormwater Runoff
APPENDIX B – Permit Forms B
Permit Application
Submittal Package Checklist for Category 1 Activities
Submittal Package Checklist for Category 2 Activities
Submittal Package Checklist for Category 3 Activities
Maintenance Agreement
Submittal Response
Permit Approval
Inspection Logs
APPENDIX C – Stormwater Conveyance Details C
Structures
Castings
Bedding and Backfilling
Open Channels
APPENDIX D – Erosion and Sediment Control Details D
Temporary Sediment Basin
Rock Check Dam
Temporary Stone Construction Entrance
Silt Fence
Straw Dam
Fabric Drop Inlet Protection
Sandbag Curb Inlet Protection
Riprap Chute Outfall Protection
APPENDIX E – Post-Construction Stormwater Runoff Control Details E
Stormwater Ponds
Dry Detention Basin
Stormwater Wetlands
Bioretention
Sand Filters
Water Quality Swales
Biofilters
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2.0 STORMWATER CONSTRUCTION PERMIT PROCESS
The following sections describe the stormwater construction permit process for
the City of Richmond.
2.1 Review of Stormwater Development Standards
The applicant should review this manual and familiarize themselves with the
permit process, the forms, specifications, construction details, etc. It is also
advised that the applicant review the Erosion and Sediment Control
Ordinance and the Post-Construction Stormwater Run-off Control Ordinance.
Once the applicant is familiar with all three, the manual and ordinances may
then be used as reference documents.
2.2 Kickoff Meeting
The applicant shall request a meeting with a City representative to review
permit requirements. The applicant is encouraged to submit a sketch or
concept plan of the proposed stormwater improvements with the initial
meeting request. There are no fees associated with this submittal.
2.3 Project Development
The applicant shall incorporate stormwater improvements (stormwater
quantity control and quality control) into the design of their project and submit
their proposed development for review to the City. Appropriate stormwater
control measures are discussed in greater detail in Chapters 6 and 7.
2.4 Permit Application
The applicant shall submit the permit application to the Stormwater
Management Board through the City Engineer at 50 North 5th Street,
Richmond, Indiana 47374, the following items:
• The Stormwater Construction Permit Application form;
• Submittal Package Checklist;
• Plans;
• Specifications; and
• Design documentation.
The Stormwater Construction Permit Application form and the Submittal
Package Checklist can be found in Appendix B, Permit Forms. Please note
that there are three separate categories of applications. They are: Category
1, land disturbing activities covering one or more acres, Category 2, single
family residential development consisting of four or fewer lots or a single-
family residential strip development where the developer offers for sale or
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lease without land improvements, and the project is not part of a larger
common plan of development or sale, and Category 3, land disturbing
activities for individual lots of any size within a permitted project that is over
one acre. There is one common permit application, but there are three
separate checklists. A filing fee will be required in order to initiate the
application review process. The components of the permit application are
discussed further in Chapter 3.
2.5 Maintenance Agreement
Maintenance of all stormwater management facilities will be ensured through
the establishment of a formal maintenance agreement. The applicant shall
submit, along with the permit application, a completed Maintenance
Agreement form. The Maintenance Agreement form can be found in
Appendix B, Permit Forms.
2.6 Review for Compliance
Upon receipt of the Stormwater Construction Permit Application and
attachments, the proposed development will be reviewed by a representative
of Richmond’s Stormwater Management Board or its designee. The
proposed development will be reviewed to ensure that the requirements of
this Stormwater Development Manual have been incorporated into the
project.
2.7 Submittal Response
Once the Stormwater Management Board has reviewed the proposed
development and determined whether or not it is in full compliance with the
requirements of this manual, the board will issue a Submittal Response to
the applicant. The Submittal Response form can be found in Appendix B,
Permit Forms. The response will indicate if the required information has
been provided for the proposed development to be reviewed for content or if
additional information is required before the comprehensive review process
can begin. If the required information has been provided, the proposed
development is ready for the comprehensive review process which results in
a construction permit.
2.8 Issuance of a Construction Permit
The proposed development will be reviewed against the design criteria set
forth in this manual. Upon completion of the comprehensive review process,
the project will be issued a Stormwater Construction Permit. The
Construction Permit Form can be found in Appendix B - Permit Forms.
Should the applicant receive a stormwater construction permit, he/she must
then submit the required Notice of Intent (NOI) to IDEM. (Individual lots within
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a permitted project do not have to submit a NOI.)
2.9 Inspection
Construction Inspections
The City will conduct regular inspections of construction sites during land-
disturbing activities, in accordance with the Erosion and Sediment Control
Ordinance, to ensure compliance with a Stormwater Construction Permit.
All inspections will be documented in writing. These reports will contain the
following information when applicable:
• The date and location of the inspection;
• Whether construction is in compliance with the approved stormwater
management plan;
• Variations from the approve construction specifications; and
• Any violations that exist.
Post-Construction Inspections
Post-construction stormwater runoff inspections may also be conducted by
the City, in accordance with the requirements of the Post-Construction
Stormwater Runoff Control Ordinance, to ensure compliance with a
Stormwater Construction Permit.
All inspections will be documented in writing. These reports will contain the
following information when applicable:
• The date and location of the inspection;
• Whether or not the stormwater BMP is being properly maintained
• Whether or not the stormwater BMP is operating properly
• Any violations that exist.
Project Completion Review
When the construction phase of a project has been completed, the person
holding the permit shall request, in writing, City approval of the permanent
erosion and sediment control measures constructed. The City will then
evaluate the adequacy of the constructed control measures.
In the event that the permanent erosion control measures are approved, any
surety bonds and/or letters of credit shall be released. However, all
maintenance responsibilities shall remain with the person owning the land.
In the event that the erosion control measures are not approved because
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they are not in accordance with the Erosion and Sediment Control Plan, the
City shall notify, in writing, the person holding the permit of unacceptable
features.
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3.0 PERMIT APPLICATION COMPONENTS
3.1 Introduction
This chapter describes the permit application components for the
submittal of a stormwater permit application for proposed
developments within the City of Richmond.
3.2 Project Information
The following information for development and redevelopment on real
estate located within the MS4 Area shall be submitted to the Richmond
Stormwater Management Board at the time of application. This
includes data certified by an Indiana licensed professional engineer or
land surveyor engaged in storm drainage design. The following
information requirements apply to: Category 1 - land disturbing
activities covering one or more acres, Category 2 - single family
residential development consisting of four or fewer lots or a single-
family residential strip development where the developer offers for sale
or lease without land improvements, and the project is not part of a
larger common plan of development or sale and Category 3 - Land
disturbing activities for individual lots of any size within a permitted
project that is over one acre.
3.2.1 Project Narrative (Category 1 and Category 2)
The applicant shall provide a project narrative which includes
at a minimum the following:
• The scope of the project;
• The purpose of the project;
• A legal description of the project location;
• Existing soil conditions;
• The construction sequence;
• A project site map or plat;
• The Hydrologic Unit Code; and
• Identification of other State of Federal Water Quality
Permits required.
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3.2.2 Vicinity Map (Category 1 and Category 2)
The applicant shall provide a map illustrating the location and
vicinity with their submittal for a stormwater construction
permit. The vicinity map shall include roads, railroads, water
features and other relevant landmarks.
3.2.3 General Plan Requirements (Category 1 and Category 2)
The plans shall include, in general, the following:
• North arrows, graphic and written scale, legend for
symbols;
• Location and elevation of property benchmark;
• Professional seal, signature, and date; and
• Table of revisions.
3.2.4 Existing Project Site Layout (Category 1 and Category 2)
The existing project site layout shall include the existing site
conditions. This project site layout will require much more site
specific detail than the vicinity map described above. The
project site map shall contain, at a minimum, the following:
• Site location;
• Site boundaries;
• Immediately adjacent sites;
• Lakes, streams, channels, ditches, wetlands and other
water courses on or adjacent to the site;
• 100-year floodplains, floodway fringes and floodways;
• Location of the predominant soil types. Soil types may
be determined by the SCS County Soil Survey, by an
equivalent publication, or as determined by a certified
professional soil scientist;
• Location and delineation of vegetative cover such as
grass, weeds, brush, and trees, and any vegetation
areas that will not be disturbed during construction;
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• Location of natural drainage patterns on and
immediately adjacent to the site, and the location and
approximate dimensions of any structural drainage
systems;
• Locations and approximate dimensions of existing
utilities, structures, roads, highways and paving;
• Site and adjacent topography, both existing and
planned, at a minimum of 2 foot contour interval to
indicate drainage patterns
3.2.5 Final Project Site Layout (Category 1 and Category 2)
The final project site layout shall include the existing site
conditions. This project site layout will require much more site
specific detail than the vicinity map described above. The
project site map shall contain, at a minimum, the following:
• The location of all proposed site improvements
including roads, utilities, lot delineation, structures and
common areas.
3.2.6 Grading Plan (Category 1 and Category 2)
The grading plan shall include, at a minimum:
• A delineation of proposed land disturbing activities,
including those off-site;
• Soil stockpiles and borrow areas;
• Information regarding off-site borrow, stockpile and
disposal areas that are under the control of the project
site owner; and
• Existing and proposed topographic information.
3.2.7 Drainage Plan (Category 1 and Category 2)
The drainage plan shall include, at a minimum, the following:
• The peak discharge of a 10-year storm event, one for
pre-development and one for post-development;
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• The location, size, dimension, slope, and the direction
of flow of all natural and structural stormwater drainage
systems. These shall be prepared as both plan and
profile views.
• When applicable, areas where point source stormwater
discharges have the potential to enter ground water.
• All stormwater discharge points in which stormwater will
leave the site. In addition, if the discharge point is to a
receiving stream, the stream must be labeled by name.
If the discharge point is to a conveyance system, the
name of the receiving stream in which the conveyance
system discharges must be identified.
• The location, size and dimensions of site features used
for stormwater management. Examples of such
features include detention and retention ponds.
• Off-site bypass flow route for detention and retention
ponds, if applicable;
• Bottom pond slope for detention and retention ponds, if
applicable; and
• Flood protection grades for detention and retention
ponds, if applicable.
3.2.8 Erosion and Sediment Control Plan (Category 1 and
Category 2)
The Erosion and Sediment Control Plan shall clearly portray
the methods and means whereby erosion and sediment
control measures are implemented. The plan shall include, at
a minimum, the following site development information.
• A description of potential pollutant sources associated
with construction activities that may be expected to add
a significant amount of pollution to the developments
stormwater discharges;
• The location, dimensions, detailed specifications and
construction details of all temporary and permanent
stormwater quality measures;
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• Temporary and permanent stabilization measures
including: the sequence of implementation;
specifications and application rates for soil
amendments and seed mixtures; and the type and
application rate for anchored mulch;
• The construction sequence describing the relationship
between implementation of stormwater quality
measures and the stages of construction activities; and
• A self monitoring program including procedures and an
on-going maintenance plan for each stormwater quality
measure.
The person, or persons, responsible for the installation and
maintenance of erosion and sediment control practices, their
business address, and daytime phone number shall be
included. This person must be identified prior to the
commencement of any land disturbing activities.
3.2.9 Post-Construction Stormwater Management Plan
(Category 1 only)
The Post-Construction Stormwater Management Plan shall
clearly portray the methods and means whereby stormwater
quality measures are implemented. The plan shall include, at
a minimum, the following information.
• A description of potential pollutant sources associated
with the proposed land use that may be expected to
add a significant amount of pollution to the
developments stormwater discharges.
• The location, dimensions, detailed specifications,
construction details, and sequence of installation of all
post-construction stormwater quality measures. These
measures must remove or minimize pollutants from
stormwater run-off and prevent or minimize adverse
impacts to stream and riparian habitats.
• A self monitoring program including procedures and an
on-going maintenance plan for each stormwater quality
measure.
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3.2.10 Technical Report (Category 1 and Category 2)
The applicant shall submit a technical report providing all
calculations.
3.2.10.1 Existing and Proposed Stormwater Runoff
Calculations
The existing and proposed stormwater runoff
calculations must include, at a minimum, the
following:
• Drainage area computations;
• Weighted curve number or run-off coefficient
computations; and
• Time of concentration computations.
3.2.10.2 Closed Conduit and Open Channel Design
Calculations
The closed conduit and open channel design
calculations must include, at a minimum, the
following:
• The size of pipe or channel shown as a
cross-section;
• The pipe or channel inverts slope as a
percentage and as invert elevations;
• Material and roughness coefficient;
• Flow velocities in feet per second;
• Pipe length, type, and class;
• Design capacity in cubic feet per second;
• Design run-off of component sheds; and
• Inlet spacing calculations.
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3.2.10.3 Detention and Retention Pond Calculations
The detention and retention pond calculations must
include, at a minimum, the following:
• Shed maps, both pre-development and post-
development;
• Time of concentration, both pre-development
and post-development;
• Overland flow route to pond;
• Peak design discharge;
• Time to peak discharge;
• Total design storm runoff;
• Inflow hydrograph;
• Spillway peak outflow rate;
• Emergency spillway capacity calculations;
• Description of off-site bypass flow route;
• Bottom pond slope; and
• Flood protection grades.
3.2.11 Requirements for Category 3
The following items must be submitted for a Category 3
activity:
• Post-Construction Stormwater Management Plan from
original Category 1 project;
• General layout of lot including position of building;
• North arrow, graphic and written scale, date; and
• Stable construction site access and appropriate
perimeter erosion and sediment control measures.
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3.3 Permits for Construction in the Floodway
It is a requirement that the Department of Natural Resources (DNR)
approve all construction activities being proposed in a floodway, as
well as all works for flood control. This includes bridges, dams, levees,
floodwalls, wharves, piers, booms, weirs, bulkheads, jetties, groins,
excavations, fills, or deposits of any kind, utility lies, or any other
building, structure, or obstruction. This also includes any ditch work
(new construction, deepening or modification) within one-half mile of a
public freshwater lake of 10 acres or more.
The approval of the DNR, in writing, must be obtained before land
disturbing activities can begin. Applications for approval shall be
submitted to:
Indiana Department of Natural Resources
Division of Water
402 West Washington St., Room W264
Indianapolis, IN 46204
All applications shall be sent to the DNR on their standard application
form. Similar to this manual’s filing requirements, the DNR’s
application form shall be accompanied by plans, profiles,
specifications, and other data necessary for the DNR to determine the
effect of the proposed development on the floodway.
It should be noted that an application made to and approved by the
DNR does not in any way relieve the owner of the necessity of
securing easements or other property rights, and permits and/or
approvals from affected property owners and local, State, and Federal
agencies.
The engineering staff of the DNR Division of Water is available to
discuss and offer suggestions regarding requirements in the design of
structures in floodways. High water marks have been set on many of
the streams in the state, and information is available from the Division
of Water on actual and/or potential flooding. Information regarding
benchmarks set to Mean Sea Level Datum, General Adjustment of
1929, is available from the Division of Water, Surveying, and Mapping
Section.
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4.0 HYDROLOGY
4.1 Introduction
This chapter describes the policies and procedures which must be
applied during a hydrologic analysis performed within the City of
Richmond.
4.2 Calculating the Peak Discharge
Runoff quantities shall be computed for the area of the parcel under
development, including runoff that flows to the proposed
development’s site from the site’s surrounding watershed. The
calculation should be done based on pre-development conditions and
again with the proposed post-development conditions. The peak
discharge which is generated as a result of a given rainfall intensity
may be calculated as follows:
Areas up to and Including 200 Acres
For areas up to and including 200 acres, the Rational Method may be
used, to determine the peak discharge rate
Q = CiA
Where:
C = runoff coefficient, representing the characteristics of the
drainage area and defined as the ratio of runoff to rainfall.
i = average intensity of rainfall in inches per hour for a duration
equal to the time of concentration (tc) for a selected rainfall
frequency.
A = tributary drainage area in acres.
The following tables provide guidance to selection of the runoff
coefficient “C” for different types of surface and soil characteristics.
The composite “C” value used for a given drainage area with
various surface types shall be the weighted average for the total
area calculated from a breakdown of the individual areas having
different surface types.
Rainfall intensity shall be determined from rainfall frequency curves.
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TABLE 4-1
Urban Runoff Coefficients
Type of Surface Runoff Coefficient “C”
Asphalt 0.82
Concrete 0.85
Roof 0.85
Lawns (Sandy)
Flat (0-2% slope)
Rolling (2-7% slope)
Steep (>7% slope)
0.07
0.12
0.17
Lawns (Clay)
Flat (0-2% slope)
Rolling (2-7% slope)
Steep (>7% slope)
0.16
0.21
0.30
TABLE 4-2
Rural Runoff Coefficients
Type of Surface Runoff Coefficient “C”
Woodland (Sandy)
Flat (0-5% slope)
Rolling (5-10% slope)
Steep (>10% slope)
0.10
0.25
0.30
Woodland (Clay)
Flat (0-5% slope)
Rolling (5-10% slope)
Steep (>10% slope)
0.30
0.35
0.50
Pasture (Sandy)
Flat (0-5% slope)
Rolling (5-10% slope)
Steep (>10% slope)
0.10
0.16
0.22
Pasture (Clay)
Flat (0-5% slope)
Rolling (5-10% slope)
Steep (>10% slope)
0.30
0.36
0.42
Cultivated (Sandy)
Flat (0-5% slope)
Rolling (5-10% slope)
Steep (>10% slope)
0.30
0.40
0.52
Cultivated (Clay)
Flat (0-5% slope)
Rolling (5-10% slope)
Steep (>10% slope)
0.50
0.60
0.72
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TABLE 4-3
Runoff Coefficients “C” by Land Use and Typical Inlet Times
LAND USE RUNOFF COEFFICIENTS
INLET
TIME
(minutes)
FLAT
(0-2% slope)
ROLLING
(2-7% slope)
STEEP
(>7% slope)
Commercial (CBD) 0.75 0.83 0.91 5
Commercial (NHD) 0.54 0.60 0.66 5
Industrial 0.63 0.70 0.77 5-10
Garden Apartments 0.54 0.60 0.66 5-10
Churches 0.54 0.60 0.66 5-10
Schools 0.31 0.35 0.39 10-15
Semi-Detached Residence 0.45 0.50 0.55 10-15
Detached Residence 0.40 0.45 0.50 10-15
Quarter-Acre Lots 0.36 0.40 0.44 10-15
Half-Acre Lots 0.31 0.35 0.39 10-15
Parkland 0.18 0.20 0.22 To be
determined
Interpolation, extrapolation, and adjustment for local conditions shall
be based on engineering experience and judgment.
The coefficients of these tabulations are applicable to storms of 5- to
10-year frequencies. Coefficients for less frequent, higher intensity
storms shall be modified as follows
Return Period (years) Multiply “C” by
25 1.1
50 1.2
100 1.25
Areas Over 200 Acres
The peak discharge rate for areas in excess of 200 acres shall be
determined by methods approved by the Stormwater Management
Board. The procedures or methods used must receive the prior
approval of the Board. The TR-20 and TR-55 models are approved by
the Board for appropriate use in analysis of the runoff and routing of
stormwater.
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4.3 Design Storm Frequencies
Design storm frequencies shall be chosen based on the following
criteria.
4.3.1 Minor Conveyance Systems
Minor conveyance system components such as inlets, catch
basin inserts, street gutters, swales, sewers, and small
channels which collect stormwater must accommodate peak
runoff from a 10-year return period storm. Rainfall duration
shall be less than or equal to the time of concentration for one
hour, if the time of the concentration is less than or equal to
one hour. A first quartile storm distribution shall be used for
computer modeling.
4.3.2 Major Conveyance Systems
Major conveyance systems are defined as any drainage
system carrying runoff from an area of one or more square
miles and shall be designed in accordance with Indiana
Department of Natural Resources standards.
4.3.3 Detention and Retention Facilities
If an adequate storm sewer outlet exists, all developments will
have in-place stormwater structures capable of collecting the
stormwater runoff from a post-development 10-year storm.
This collection system shall be connected to the existing storm
sewer system.
Where adequate storm sewers do not exist, all new
developments must detain stormwater on their respective
properties. The storage volume required is that to control the
post-development 100-year storm. The outlet structure from
the detention area will discharge no more flow than the pre-
development 10-year storm. The outlet structure will consist
of a pre-developed 2-year storm outlet to retain the lower flows
of the 2 to 10 year storm in the staged detention area.
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5.0 STORMWATER CONVEYANCE
5.1 Introduction
This chapter describes policies, design criteria and information for the
construction of stormwater conveyances. Stormwater conveyance details are
located in Appendix C, Stormwater Conveyance Details.
5.2 Hydraulic Capacity
The hydraulic capacity of all conveyances shall be determined using
Manning’s Equation:
v = (1.486/n) R 2/3 S 1/2.
Where:
v = mean velocity in feet per second
R = the hydraulic radius in feet
S = the slope of the energy grade line in feet per foot
n = the roughness coefficient
The hydraulic radius, R, is defined as the cross-sectional area divided by the
wetted flow surface or wetted perimeter.
The following table provides guidance to the selection of roughness
coefficient (n) values for various materials. Roughness coefficient (n) values
for materials can also be found in standard hydraulics texts and references.
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TABLE 5-1
Typical Values of Manning’s (n) Roughness Coefficient
MATERIAL MANNING’S (n)
DESIRABLE
MAXIMUM
VELOCITIES
Closed Conduits
Concrete
Vitrified Clay
Brick
Cast Iron
0.013
0.013
0.015
0.013
15 fps
15 fps
15 fps
15 fps
Circular Corrugated Metal, Annular
Corrugations (2 2/3” x 1/2”)
Unpaved
25% Paved
50% Paved
100% Paved
0.024
0.021
0.018
0.013
7 fps
7 fps
7 fps
7 fps
C.C.M.P., Helical Corrugations, 2/3” x
1/2” Unpaved Corrugation
12”
18”
24”
36”
48”
60” or larger
0.022
0.023
0.024
0.025
0.026
0.027
7 fps
7 fps
7 fps
7 fps
7 fps
7 fps
Corrugated polyethylene smooth
interior pipe 0.012 15 fps
Concrete Culverts 0.013 7 fps
Open Channels
Concrete, trowel finish
Concrete, broom float
Gunite
Riprap, placed
Riprap, dumped
Gabion
New earth (uniform sodded clay)
Existing earth (fairly uniform,
some weeds)
Dense growth of weeds
Dense weeds and brush
Swale with grass
0.013
0.015
0.018
0.030
0.035
0.028
0.025
0.030
0.040
0.040
0.035
10 fps
10 fps
10 fps
7 fps
7 fps
10 fps
7 fps
7 fps
7 fps
7 fps
7 fps
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5.3 Storm Sewers
Plans for all proposed storm sewer construction must be submitted to the
Richmond Stormwater Management Board prior to the start of land disturbing
activities.
The specifications for the construction of storm sewers shall not be less
stringent than those set forth in the latest edition of the Indiana Department of
Transportation Standard Specifications.
5.3.1 Sewer Pipe
Sewer pipe shall be designed and constructed using the following
criteria.
5.3.1.1 General Specifications
Minimum Size
The minimum size of all storm sewers shall be 12 inches.
The rate of release for detention storage shall be controlled
by an orifice plate or other devices, subject to approval of the
Board, where the 12-inch pipe will not limit the rate of release
as required.
Grade
Sewer grade shall be such that, in general, a minimum of two
feet of cover is maintained over the top of the pipe. Pipe
cover less than the two foot minimum may be used with the
approval of the Board. This approval must occur prior to land
disturbing activities. Uniform slopes shall be maintained
between inlets, manholes, and inlets to manholes. Final
grade shall be set with the full consideration of the capacity
required, sedimentation problems, and other design
parameters. Minimum and maximum allowable slopes shall
be those capable of producing velocities of two and one-half
(2½) and fifteen (15) feet per second, respectively, when the
sewer is full flowing.
Flexible Pipe
All flexible storm sewer pipe must meet a deflection of 7.5%.
5.3.1.2 Pipe Materials
Concrete Pipe, Plain and Reinforced
Concrete pipes, both plain and reinforced, shall conform in all
respects with ASTM C14, AASHO M86, and Federal SS-P-
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371 for Non-Reinforced Concrete Pipe, ASTM C76 AASHO
M170 and Federal S-P-375 for Reinforced Concrete Pipe and
ASTM 361 for Reinforced Low Head Concrete Pipe.
Corrugated Smooth Walled Interior PVC
Corrugated smooth walled interior PVC shall conform in all
respects to the latest edition of ASTM F 794. Ribs shall be
annular.
Truss Pipe
Truss pipes shall conform in all respects to the latest edition
of ASTM D2680 (Non-pressure pipe).
Corrugated Smooth Walled Interior High Density
Polyethylene Pipe (HDPE)
Corrugated HDPE pipe shall conform to AASHTO M294 Type
S for sizes 12” and larger, and AASHTO M252 Type S for
sizes smaller than 12”. Joints shall be bell and spigot and
shall be watertight. Rubber gasket for joints shall conform to
ASTM F477.
Corrugated Metal Pipe
Corrugated metal pipe shall conform to the requirements of
AASHTO Designation M-36 and Indiana Dept. of
Transportation Specifications for Aluminized Steel Type.
In addition, the pipe shall be of full circle and shall be
fabricated with helical corrugations and a welded seam
extending from end to end of each length of pipe. Pipe made
first by the lock-seam method with the seam welded later will
not be acceptable. The welded seam shall be continuous,
utilizing ultra-high frequency resistance equipment. Seams
shall be welded in such a manner that they will develop the
full strength of the pipe and not affect the shape or nominal
diameter of the pipe. Each pipe end shall be fabricated with
two annular corrugations for the purpose of joining pipes
together with band couplers.
Polyvinyl Chloride (PVC) Pipe
PVC pipe shall be Type PSM conforming to the latest edition
of ASTM D3034 for pipe sizes up to 15-inch and ASTM F679
for pipe sizes 18-inches and larger. HOWEVER, no
reworked material shall be used and the material shall have a
cell classification of 12454-B as defined in the latest edition of
ASTM D1782 and shall have an SDR (Standard Dimension
Ratio) of not greater than 35.
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For depths of bury through fifteen (15) feet a minimum wall
thickness of SDR 35 as defined in Section 7.4.1 of ASTM D-
3034 is required. For depths of bury greater than fifteen (15)
feet, a minimum wall thickness of SDR 26 is required.
5.3.1.3 Pipe Installation
Location
Locate pipes according to dimensions on the drawings.
Where the sewer location is not located clearly by dimensions
on the drawings, locate the sewer where concrete
encasement is used, provide not less than 4-inch thickness
including that of pipe joints.
Laying Pipe
All pipe shall be inspected for soundness and damage that
may have occurred during transportation immediately before
being lowered into the trench. Any pipe found to be unsound
or damaged will be rejected and removed immediately from
the work site.
All sound and intact pipe shall be laid accurately to the
required line and grade in such a manner as to form a close,
concentric joint with the adjoining pipe and to bring the invert
of each section to the required grade. Bell holes shall be dug
in advance of the pipe being laid as required. The supporting
of any pipe on blocks will not be permitted.
Pipe laying shall proceed upgrade, beginning at the lower
end of the sewer, unless otherwise approved by the Board.
Each length of section shall be properly pulled or shoved
“home” with a winch or come-a-long against the section
previously laid to make a proper joint. The pipe shall then be
securely held in position during the backfill operations. Joints
shall not be pulled or cramped more than the design of the
joint will permit and so as not to injure the conduit.
All open ends of pipes and branches shall be sealed with
plugs or bulkheads firmly held in place in a manner
acceptable to the Board. No special payments will be made
for the placement or removal of said plugs or bulkheads. At
the end of each days work, the open ends of all pipes shall
be satisfactorily protected against the entrance of animals,
earth or other materials.
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Dewatering
Dewatering sufficient to maintain the water level below the
surface of the trench bottom shall be accomplished prior to
pipe laying and jointing, if not done prior to excavation and
placement of the bedding as called for. The dewatering
operation, however accomplished, shall be carried out so that
it does not destroy or weaken the strength of the soil under or
alongside the trench. When the dewatering operation is
complete, the trench shall be replaced in such a manner so
as not to disturb the pipe and its foundation.
Abandoning Pipe or Structures
Where called for on the plans to be abandoned, said sewers
or structures shall be permanently plugged or bulkheaded.
Where standard “plugs” are available, they shall be
employed. For other pipes or structures, the use of brick and
mortar or concrete may be used in a manner suitable to the
Board.
Bedding, Rigid Pipe
The following terms apply to all classifications of rigid pipe
bedding.
Definition of Terms for Bedding:
Bc = Outside diameter of pipe, in inches
D = Inside diameter of pipe, in inches
d = Depth of bedding material below the pipe bell, in inches
The values of “d”, depth of bedding material below the bell of
the pipe shall be as follows:
“D” (inside diameter of pipe) “d” (depth of bedding material)
Minimum Requirements
27” and smaller 3”
30” to 60” 4”
66” and larger 6”
Class “A” bedding is that method of bedding in which the
conduit is set on “d” inches of concrete in an earthen
foundation and encased in concrete up to ¼” of “Bc” to fit the
lower part of the conduit’s exterior breadth. The remainder of
the conduit is to be surrounded to a height of at least (12)
inches above its top by densely compacted granular backfill
material carefully placed by hand to completely fill all spaces
under and adjacent to the conduit.
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The fill is to be tamped thoroughly on each side of the
conduit, as far as practicable, shall be in layers not to exceed
six (6) inches in thickness.
The concrete used for Class “A” bedding shall be plain
concrete with a 28-day compressive strength of 3,000 psi,
unless otherwise specified. Refer to “Bedding and Backfill
Details” located in Appendix C, Stormwater Conveyance
Details for further details on Class “A” bedding.
Class “B” bedding is that method of bedding in which the
conduit is set on “d” inches of a fine granular material (sand
cushion) in an earth foundation, carefully shaped to fit the
lower part of the conduit exterior for a width of at least 60% of
the conduit’s breadth. The remainder of the conduit is to be
surrounded to a height of at least twelve (12) inches above its
top by densely compacted granular backfill material carefully
placed by hand to completely fill all spaces under and
adjacent to the conduit. The fill shall be tamped thoroughly
on each side and under the conduit, as far as practicable, in
layers not to exceed six (6) inches in thickness. Bell
excavation is to be provided. Refer to “Bedding and Backfill
Details” located in Appendix C, Stormwater Conveyance
Details for further details on Class “B” bedding.
Class “B” bedding material shall meet the gradation as set
forth in the Indiana Dept. of Transportation Standard
Specifications, current edition, Section 211, Special Fill and
Backfill (“B” Borrow), except that no more than 12% or less
than 5% shall pass the No. 200 sieve (silt or clay).
Each pipe shall be laid in Class "B" bedding unless
specifically noted otherwise, as shown on the plans and the
construction standard drawings.
Class “C” bedding is that method of bedding in which the
conduit is set on an earth foundation, carefully shaped to fit
the lower part of the conduit exterior for a width of at least
50% of the conduit’s breadth. The remainder of the conduit is
to be surrounded to a height of twelve (12) inches above its
top by lightly compacted granular backfill material carefully
around the exterior of the conduit. Bell excavation is to be
provided. Refer to “Bedding and Backfill Details” located in
Appendix C, Stormwater Conveyance Details for further
details on Class “C” bedding.
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Bedding, Flexible Pipe
Each pipe shall be laid in a Class I or Class II bedding, as
shown in Appendix C, Stormwater Conveyance Details.
Pipe bedding installation shall conform to ASTM D 2321.
Existing Sewer Removal and Replacement
When applicable, existing sewer lines shall be completely
removed and replaced with new sewer lines. The contractor
shall be required to maintain service during said removal and
replacement, which may entail bypass pumping. The
contractor shall inform the engineer of the method proposed
for maintaining service.
Sheet Piling
Permanent or temporary sheet piling shall be provided in the
following circumstances: for construction in areas where wide
excavations cannot be permitted; for an excavation that is
open for an extended period; or where soil conditions dictate
to protect adjacent structures, roadways, and utilities.
The section modulus of piling sections shall be as required to
function properly as intended.
Piling sections shall be marked for length and sorted and
stacked at the job site to prevent distortion and to facilitate
proper sequence of setting and driving.
Interlocks shall be protected from becoming obstructed by
sand, gravel, mud or other materials.
Pile tips are approved for use at the contractor’s discretion.
5.3.2 Structures
Structures shall be designed and constructed using the following
criteria.
5.3.2.1 General Specifications
Manholes
Manholes shall be installed to provide access to continuous
underground storm sewers for the purpose of inspection and
maintenance. Manholes shall be provided at the following
locations:
• Where two or more storm sewers converge;
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• At the point of beginning or at the end of a curve, and at
the point of reverse curvature (PC, PT, PRC);
• Where pipe size changes;
• Where an abrupt change in alignment occurs;
• Where a change in grade occurs; and
• At suitable intervals in straight sections of sewer.
The maximum distance between storm sewer manholes shall
be as follows:
Size of Pipe
(inches)
Maximum Distance
(feet)
12 to 42 400
48 and larger 600
Inlets
Inlets or drainage structures shall be utilized to collect surface
water through grated openings and convey the surface water
into storm sewers, channels, or culverts. Inlet design and
spacing shall be in accordance with Section 7-400 of the
Indiana Department of Transportation Road Design Manual -
Volume 1 or other approved design procedures as
determined by the Board prior to any land disturbing
activities. The inlet grate opening must be adequate to
accommodate a 10-year flood event with 50% of the sag inlet
areas clogged. An overloaded channel from the sag inlets to
the overflow channel, or basin, shall be provided at sag inlets.
This will prevent the maximum depth of water ponding in the
street sag from exceeding 7 inches.
Culverts
Culverts shall be capable of accommodating peak runoff from
a 50-year flood event when crossing under a road which is
part of the Indiana Department of Transportation rural
functional classification system and are classified as principal
or minor arterial, or minor collector roads.
Special Hydraulic Structures
The use of special hydraulic structures shall be limited to
those locations justified by prudent planning and by careful
and thorough hydraulic engineering analysis. Special
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hydraulic structures control the flow of water in storm runoff
drainage systems. They include: junction chambers, drop
manholes, inverted siphons, stilling basins, and other special
structures.
5.3.2.2 Materials
Reinforced Concrete Manholes
Reinforced concrete manholes shall be erected of precast, or
cast in place, reinforced concrete sections to the shape of the
manhole. Steps shall be cast in place in accordance with the
standards as shown in Appendix C, Stormwater Conveyance
Details. All concrete, reinforcing and wall thickness shall be
in accordance with the latest edition of ASTM Designation
C-478. All structure joints shall be watertight and constructed
in accordance with the latest edition of ASTM Specification
C-443. The bottom of the structures shall be of either
precast, poured in place, or monolithic bottom stack, with
3,000 psi concrete to conform to the plans. They shall be at
least eight (8) inches thick and reinforced as shown in
Appendix C, Stormwater Conveyance Details.
Precast Manhole Components
Precast manhole components shall conform to the latest
edition of ASTM C-478, and to the design dimensions
indicated by the approved plans. All precast manhole
components shall be manufactured by an experienced and
reputable manufacturer whose precast manhole components
have been used commercially for at least three (3) years.
Cones and sections shall be substantially free from fractures,
large or deep cracks and surface roughness. Slabs shall be
sound and free from gravel pockets.
Monolithic Concrete Manholes
Monolithic concrete manholes shall conform to the contract
drawings and the Stormwater Conveyance Details located in
Appendix C. Walls and base dimensions shall be of
approved thickness and the maximum step spacing shall be
sixteen (16) inches.
Manhole Joints
Storm sewer manhole joints shall be neatly joined by flexible
rubber gasket or approved bitumastic material.
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Cast Iron Frames and Covers
Cast iron frames and covers shall conform to the
requirements of the latest edition of ASTM A48 for Gray Cast
Iron. The dimensions, weights and finish preparation shall
conform to the appropriate construction standards.
Ductile Cast Iron Frames, Covers and Grates
Ductile cast iron frames, covers and grates shall conform to
the requirements of the latest edition of ASTM A536 for
Ductile Cast Iron. The dimensions, weights and finish
preparation shall conform to the appropriate construction
standards.
5.3.2.3 Installation
Dewatering
Dewatering sufficient to maintain the water level below the
surface of the trench bottom shall be accomplished prior to
pipe laying and jointing, if not done prior to excavation and
placement of the bedding as called for. The dewatering
operation, however accomplished, shall be carried out so that
it does not destroy or weaken the strength of the soil under or
alongside the trench. When the dewatering operation is
complete, the trench shall be replaced in such a manner so
as not to disturb the pipe and its foundation.
Sheet Piling
Permanent of temporary sheet piling shall be provided in the
following circumstances: for construction in areas where wide
excavations cannot be permitted; for an excavation that is
open for an extended period; or where soil conditions dictate
to protect adjacent structures, roadways, and utilities.
The section modulus of piling sections shall be as required to
function properly as intended.
Piling sections shall be marked for length and sorted and
stacked at the job site to prevent distortion and to facilitate
proper sequence of setting and driving.
Interlocks shall be protected from becoming obstructed by
sand, gravel, mud or other materials.
Pile tips are approved for use at the contractor’s discretion.
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Bedding for Structures
Precast base sections shall be placed on a well-graded
granular bedding course conforming to the requirements for
sewer bedding, but not less than four (4) inches in thickness
and extending to the limits of the excavation. The bedding
course shall be firmly tamped and made smooth and level to
assure uniform contact and support of the precast element.
Cast-in-Place Bases
Unless otherwise specified, cast-in-place bases shall be at
least eight (8) inches in thickness and shall extend at least six
(6) inches radially outside of the outside dimensions of the
manhole section. The cast-in-place base shall be made of
3,000 psi concrete, 28-day compression test, and shall be
reinforced as shown on the construction standards.
Lift Holes
All lift holes in precast elements shall be thoroughly wetted
and be completely filled with non-shrinking concrete grout,
smoothed and painted both inside and out, to ensure water
tightness.
Placing Precast Sections
Precast sections shall be placed and aligned to provide
vertical sides and vertical alignment of the ladder rungs. The
completed manhole shall be rigid, true to dimensions and
watertight.
Placing of Castings
Castings placed on a concrete surface shall be set in full
grout beds. The grout shall be mixed in proportion of one (1)
part Portland Cement to three (3) parts sand, by volume,
based on dry materials. Castings shall be set accurately to
the finished elevation so that no subsequent adjustment will
be necessary, or unless otherwise specified by the licensed
Engineer.
After grout has cured, use an approved bitumastic material
around the outside of casting to ensure water tightness.
When working in paved streets or areas which have been
brought to grade, not more than fifteen (15) inches shall be
provided between the top of the cone or slab and the
underside of the manhole casting for adjustment of the
casting to street grade.
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When working in an unimproved street or alley, not less than
twelve (12) inches of adjusting rings shall be provided
between the top of the cone or slab and the underside of the
manhole casting for adjustment of the casting to finished
grade. The top of the manhole casting shall be flush with the
finished grade, unless otherwise shown in the plans.
When working in cultivated areas, the top of the manhole
casting shall be buried three (3) feet. In non-cultivated areas,
the casting shall be flush with the finished grade, unless
otherwise directed by the licensed Engineer.
In the event that the last manhole section is a reducing cone
set to final grade by the licensed Engineer and if it becomes
necessary to lower them below the cone, compensation to
the contractor will be allowed for said adjustment and
changing of the manhole stacks.
When concrete adjusting rings are used to set the castings to
grade, they shall be pointed up and a grout bed placed
between each ring and casting; and made watertight with a
heavy coating of an approved bitumastic material on the
outside of the structure. The casting is flush with the
surrounding pavement.
When rubber adjustment rings are used to set castings to
grade, they shall be positioned so that the casting is flush
with surrounding pavement.
Channels and Inverts
Channels and inverts shall be made to conform accurately to
the sewer characteristics and grades, and shall be brought
together smoothly with well-rounded junctions, satisfactory to
the licensed Engineer and in conformance with the
Stormwater Conveyance Details in Appendix C.
Pipe Connections
Pipes shall be firmly full of jointing material at entrance to
manhole to ensure water tightness. The pipes shall not
protrude farther than three (3) inches into the inside face of
the manhole, measured along the horizontal center of the
pipe. Special care shall be taken to see that the opening
through which pipes enter the structure have all pipe ends
sawed and smoothed completely.
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Rubber water stops, “O”-Ring gaskets, or poured-in-place
pipe sleeves shall be used for water tightness between the
pipe and the manhole for all sidewall pipes.
When new holes are required in the manhole, they shall be
core drilled, or star drilled, in a circle of the required diameter
and then knocked out. In no instance shall new holes be
sledge-hammered out.
5.3.2.4 Grade Adjustment of Existing Structures
When adjusting castings to grade or reconstructing
structures, the applicant shall conform to the applicable
provisions of the Indiana Department of Transportation
Standard Specifications, current edition.
5.3.3 Joints, Fittings and Appurtenances
Joints, fittings and appurtenances shall be designed and constructed
using the following criteria.
Joints
Elastomeric seals for gasketed joints for corrugated and spiral wound
PVC shall meet ASTM F477 and ASTM D3212.
Flexible rubber gasket joints for concrete sewer pipe shall conform to
the requirements of ASTM Designation C-443, joints for circular
concrete sewer and culvert pipe, using flexible watertight, rubber
gaskets. Storm sewer pipe larger than 24-inch diameter may be
tongue and groove plain joint unless the sewer is under a pavement or
the plans specifically say otherwise. If plain joint is used, an approved
bitumastic material shall be applied to each joint.
Coupling bands for use with corrugated metal pipe shall be “hugger”
type with “O” rings.
The PVC joint shall conform to ASTM D3212 “push on” type with a
confined rubber gasket conforming to ASTM F477.
Fittings
PVC sewer fittings shall conform to the requirements of ASTM D-3034
specifications. Four, six, and eight-inch fittings shall be molded in one
piece, with elastomeric joints and minimum socket depths as specified
in Section 6.2 and 7.3.2 of the D-3034 specification. Fittings 10
inches and larger shall be molded or fabricated from pipe meeting
ASTM D-3034 with standard pipe bells and gaskets identified by the
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manufacturer.
The PVC fittings for corrugated and spiral wound pipe shall conform to
the latest edition of ASTM F 794.
Plugs
All fittings shall be capped with a plug of the same material as the
pipe, and gasketed with the same gasket material as the pipe joint, or
be of material approved by the Board. The plug shall be able to
withstand all test pressures involved without leakage.
5.3.4 Construction Requirements
The following construction requirements must be addressed prior to
any land disturbing activities.
5.3.4.1 Surface Conditions
The applicant shall examine the areas and conditions under
which work of this section will be performed. Conditions
detrimental to timely and proper completion of the work to be
done shall be corrected. Work may not be done until
unsatisfactory conditions are corrected.
5.3.4.2 Field Measurements
The applicant shall make necessary measurements in the
field to assure precise fit of items in accordance with the
approved design.
5.4 Open Channels
Open channels shall be designed and constructed using the following criteria.
5.4.1 Channel Cross-Section and Grade
The required channel cross-section and grade are determined by the
design capacity. A minimum depth may be required to provide
adequate outlets for subsurface drains, tributary ditches, or streams.
The channel grade shall be such that the velocity in the channel is
high enough to prevent siltation from occurring and ultimately reducing
the channel cross-section. The maximum permissible velocities in
vegetal-lined channels to be constructed must be considered in design
of the channel section.
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5.4.2 Side Slopes
Earthen channel side slopes shall be no steeper than 2 to 1. Flatter
slopes may be required to prevent erosion and for ease of
maintenance. Where channels will be lined, side slopes shall be no
steeper than 1 ½ to 1 with adequate provisions made for weep holes.
Side slopes steeper than 1 ½ to 1 may be used for lined channels,
provided that the side lining and structural retaining wall are designed
and constructed with provisions for live and dead load surcharge.
5.4.3 Peak Flows
Open channels carrying peak flows greater than thirty (30) cubic feet
per second shall be capable of accommodating peak runoff for a 50-
year flood event within the drainage easement.
5.4.4 Channel Stability
The following characteristics are indicative of a stable channel:
• It neither aggrades nor degrades beyond tolerable limits;
• The channel banks to not erode to the extent that the channel
cross-section changes appreciably;
• Excessive sediment bars do not develop;
• Excessive erosion does not occur around culverts, bridges, or
elsewhere; and
• Gullies do not form or enlarge due to the entry of uncontrolled
surface flow to the channel.
Channel stability shall be determined for an aged condition, and the
velocity shall be based on the design flow or the bank full flow,
whichever is greater, using “n” values for various channel linings. In
no case, is it necessary to check channel stability for discharges
greater than that from a 100-year flood event.
Channel stability must be checked for conditions immediately after
construction. For this stability analysis, the velocity shall be calculated
for the expected flow from a 10-year flood event on the watershed, or
the bank full flow, whichever is smaller. The “n” value for newly
constructed channels in fine-grained soils and sands may be
determined in accordance with the National Engineering Handbook 5,
Supplement B, Soil Conservation Service, and shall not exceed
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channel 0.025.
The allowable velocities for newly constructed channels may be
increased by a maximum of 20 percent to reflect the effects of
vegetation to be established under the following conditions:
• The soil and site in which the channel is to be constructed are
suitable for rapid establishment and support of erosion-controlling
vegetation;
• Species of erosion-controlling vegetation adapted to the area and
proven methods of establishment are shown; and
• The channel design includes detailed plans for establishment of
vegetation on the channel side slopes.
5.4.5 Drainage of Waterways
Vegetated waterways that are subject to low flows of long duration or
where wet conditions prevail shall be drained with a tile system or by
other means such as paved gutters. Tile lines may be outlet through a
standard tile outlet.
5.4.6 Appurtenant Structures
The design of channels shall provide all structures required for the
proper functioning of the channel and the laterals thereto, and
travelways for operation and maintenance. Recessed inlets and
structures needed for entry of surface and subsurface flow into
channels without significant erosion or degradation shall be included
in the design of channel improvements. The design is also to provide
the necessary flood gates, water level control devices, and any other
appurtenances affecting the functioning of the channels and
attainment of the purpose for which they are built.
The effect of channel improvements on existing culverts, bridges,
buried cables, pipelines, and inlet structures for surface and
subsurface drainage on the channel being improved and laterals
thereto shall be evaluated to determine the need for modification or
replacement. Culverts and bridges which are modified or added as
part of channel improvement projects shall meet reasonable standards
for the type of structure, and shall have a minimum capacity equal to
the design discharge or governmental agency design requirements;
whichever is greater.
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5.4.7 Disposition of Spoils
Spoil material resulting from clearing, grubbing, and channel
excavation shall be disposed of in such a manner which will:
• Minimize overbank wash;
• Provide for the free flow of water between the channel and
flood plain unless the valley routing and water surface profile
are based on continuous dikes being installed;
• Not hinder the development of travelways for maintenance;
• Leave the right-of-way in the best condition feasible, consistent
with the project purposes for productive use by the owner;
• Improve the aesthetic appearance of the site to the extent
feasible; and
• Be approved by the IDNR or the U.S. Army Corps of Engineers
(whichever is applicable), if deposited in floodway.
5.4.8 Materials
Materials acceptable for use as channel lining are:
• Grass;
• Revetment riprap;
• Concrete;
• Hand-laid riprap;
• Pre-cast cement concrete riprap;
• Grouted riprap;
• Gabions;
• Coir logs;
• Mesh matting; or
• Cellular walls.
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6.0 EROSION AND SEDIMENT CONTROL
6.1 Introduction
This chapter describes policies, design criteria and information for erosion
and sediment control best management practices (BMPs).
6.1.1 Background and Purpose
Land development necessitates the removal of natural ground cover,
creating the potential for erosion to occur. Erosion from a construction
site negatively impacts water quality, and the ability of stormwater
facilities to continue functioning properly.
This chapter is intended to establish minimum standards for the
design and construction of erosion and sedimentation control BMPs.
6.1.2 Design Principles
The Indiana Handbook for Erosion Control in Developing Areas has
identified ten general principles of erosion and sediment control. They
are as follows:
• Fit the development to the existing terrain and soil;
• Develop an erosion and sediment control plan before land-
disturbing activities begin, and then fully implement the plan
during construction;
• Retain existing vegetation on the construction site wherever
possible;
• Minimize the extent and duration that bare soil is exposed to
erosion by wind and water;
• Retain sediment on-site as much as possible;
• If possible, divert off-site runoff away from disturbed areas;
• Minimize the length and steepness of slopes;
• Stabilize disturbed areas as soon as possible;
• Keep velocity of runoff leaving site low;
• Inspect and maintain erosion control measures regularly.
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These general principles shall be used along with specific erosion and
sediment control measures during construction activities.
6.2 Details on Specific Practices
In addition to the following practices, the applicant should also consult The
Indiana Stormwater Quality Manual (formerly The Indiana Handbook for
Erosion Control in Developing Areas) for detailed design, construction and
maintenance criteria for all erosion and sediment control practices
6.2.1 Temporary Sediment Basin
A temporary sediment basin is a temporary impoundment built to
retain sediment and debris. Sediment basins prevent off-site
sedimentation by retaining sediment on the construction site.
A schematic example of a temporary sediment basin can be found in
Appendix D, Erosion and Sediment Control Details.
6.2.1.1 Site and Design Considerations
The following design and site considerations must be
followed when designing a temporary sediment basin:
• The basin shall have a depth of at least 3 feet with
sufficient surface area to trap the sediment;
• The site shall be of large enough size for the
sedimentation basin to have at least one percent of its
drainage area with 30 acres being the maximum
drainage area;
• The basin shall be able to maintain a three foot
minimum depth; and
• The basin shall not create a condition in which the
discharge rate from a sedimentation basin would
cause scouring in the receiving channel.
6.2.1.2 Materials
Temporary sediment basin design and material selection is
site specific. Materials used must ensure that all design
considerations are met.
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6.2.1.3 Installation
The following installation procedures must be followed when
installing a temporary sediment basin:
• Locate the sediment basin as close to the sediment
source as possible, considering soil type, pool area,
dam length, and spillway conditions;
• Clear, grub, and strip the dam location, removing all
woody vegetation, rocks and other objectionable
material;
• Excavate the area (outlet apron first), stockpiling any
surface soil having high amounts of organic matter for
later use; and
• Clear the sediment pool to facilitate sediment cleanout.
6.2.1.4 Maintenance
The developer is responsible for maintenance and
inspections of all temporary sediment basins. The
maintenance plan must include, but is not limited to:
• Inspection of the sediment basin after each storm
event;
• The removal and proper disposal of sediment that has
accumulate to one-half the design volume;
• The removal of trash and other debris from the riser,
emergency spillway, and pool area; and
• The removal of the basin after the drainage area has
been permanently stabilized, inspected, and approved.
This may be done by draining any water, removing the
sediment to a designated disposal area, smoothing the
site to blend with the surrounding area, and permanent
stabilization.
6.2.2 Rock Check Dam
A rock check dam is a small temporary barrier, grade control structure,
or dam constructed across a swale, drainage ditch, or area of
concentrated flow. The purpose of this structure is to minimize the
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erosion rate by reducing the velocity of stormwater and to capture
larger soil particles.
A schematic example of a rock check dam can be found in Appendix
D, Erosion and Sediment Control Details.
6.2.2.1 Site and Design Considerations
The following design and site considerations must be
followed when designing a rock check dam:
• The contributing drainage area for a rock check dam
shall not exceed two acres;
• Two or more check dams in series shall be used for
drainage areas greater than two acres;
• The maximum spacing between dams shall be such
that the toe of the upstream dam is at the same
elevation as the top of the downstream dam;
• The dam height shall be 2 feet maximum, measured at
the center of the check dam, but at least 9 inches
lower in center than the outer edges at natural ground
elevation; and
• The side slopes of the check dam shall be 2:1 or less.
6.2.2.2 Materials
The developer shall use Revetment Riprap, per INDOT
Standards, for the construction of a rock check dam.
6.2.2.3 Installation
The following installation procedures must be followed when
installing a rock check dam:
• Excavate a cutoff trench into the ditch banks, and
extend it a minimum of 18 inches beyond the
abutments;
• Place the rock in the cutoff trench and channel; and
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• Extend the rock at least 18 inches beyond the channel
banks to keep overflow water from undercutting the
dam.
6.2.2.4 Maintenance
The developer is responsible for the inspection and
maintenance of the rock check dam. The maintenance plan
must include, but is not limited to:
• The inspection of the dam and channel after each
storm event;
• Repairs as a result of damage from a storm event,
which are to be performed immediately following the
event;
• The installation of a riprap liner in the event that there
is significant erosion between dams;
• The removal of sediment accumulated behind each
dam as needed to maintain channel capacity, allow
drainage through the dam, and to prevent large flows
from displacing sediment;
• The addition of rock to the dams, as necessary, to
maintain the height and cross section; and
• The removal of rock and stabilized channel, using an
erosion resistant lining when necessary, shall the dam
no longer be needed.
6.2.3 Temporary Stone Construction Entrance
The purpose of a temporary stone construction entrance is to provide
a stable entrance and exit condition from the construction site and to
keep mud and sediment off public roads.
A schematic example of a temporary stone construction entrance can
be found in Appendix D, Erosion and Sediment Control Details.
6.2.3.1 Site and Design Consideration
The following design and site considerations must be
followed when designing a temporary stone construction
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• The temporary entrance must be at least 12-feet wide
and 50-feet long or the distance to the foundation;
• If wet conditions are expected, geotextile fabric is
required for stabilization; and
• Six inches of clean depth must be maintained.
6.2.3.2 Materials
Materials required for the use of a temporary stone
construction entrance include:
• 2 to 3-inch size washed stone (per INDOT standards);
and
• Geotextile fabric if wet conditions are expected.
6.2.3.3 Installation
The following installation procedures must be followed when
installing a temporary stone construction entrance:
• Avoid locating the entrance on a steep slope or at a
curve in a public roads;
• Remove all vegetation and other objectionable
material from the foundation area, then grade and
crown for positive drainage;
• If slope towards the road exceeds 2%, construct a 6-8
inch high water ridge with 3:1 side slopes across the
foundation area about 15 feet from the entrance to
divert runoff away from the road; and
• Install a temporary culvert under pad to maintain
proper public road drainage, as necessary.
6.2.3.4 Maintenance
The developer is responsible for the inspection and
maintenance of the temporary stone construction entrance.
The maintenance plan must include, but is not limited to:
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• Inspection of the entrance pad and sediment disposal
area on a weekly basis, but also following storm
events or heavy use;
• Reshaping of the pad for drainage and runoff control,
as necessary.
• Topdressing the entrance with clean stone as
necessary;
• The immediate removal of mud and sediment tracked
or washed onto public roads. This shall be performed
by brushing or sweeping; and
• The immediate repair of any broken road pavement.
6.2.4 Silt Fence
A silt fence is a temporary barrier constructed of geotextile fabric,
posts, and depending upon the strength of the fabric used, wire fence
for support. The purpose of a silt fence is to retain sediment on-site
by reducing the velocity of sheet flow.
A schematic example of a silt fence can be found in Appendix D,
Erosion and Sediment Control Details.
6.2.4.1 Site and Design Considerations
The following design and site considerations must be
followed when designing a silt fence:
• The contributing drainage area for a silt fence shall be
limited to ¼ acre per 100 ft of fence and further limited
by slope steepness as shown in the following table;
Land Slope Max Distance
Above Fence
< 2% 100 ft
2 – 5% 75 ft
5 – 10% 50 ft
10 – 20% 25 ft
> 20% 15 ft
• The fabric must be buried at an 8 inch minimum depth;
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• The fence shall be placed on the contour to avoid
channelization; and
• The spacing of the posts shall be 8 foot maximum if
supported by wire and 6 foot maximum if no
supporting wire is used.
6.2.4.2 Materials
Materials required for the installation of a silt fence include:
• 2-inch x 2-inch hardwood posts or steel fence posts;
• Woven or non-woven geotextile fabric;
• When applicable, a 14 gauge, 6-inch mesh wire fence.
6.2.4.3 Installation
The following installation procedures must be followed when
installing a silt fence:
• Install fence parallel to the contour of the land;
• Dig an 8-inch deep flat bottomed or V-trench along the
entire fence line;
• Extend ends upslope into the trench to allow water to
pond behind fence;
• Install fence with posts on the down slope side;
• Join silt fence sections using a wrap joint; and
• Backfill the trench with compacted earth or gravel.
6.2.4.4 Maintenance
The developer is responsible for the inspection and
maintenance of all silt fences. The maintenance plan must
include, but is not limited to:
• The frequency of inspections;
• The requirement for repairs and replacements as
necessary;
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• The removal of sediment deposits when they reach
one half the fence height or in the event that they
cause the fabric to bulge; and
• The removal and proper disposal of all fences. Once
removed, the depressions shall be filled, compacted,
and seeded.
6.2.5 Straw Dam
A straw dam is a temporary sediment barrier constructed of straw
bales across small drainages. The purpose of a straw dam is to retain
sediment on-site by reducing the velocity of sheet flow.
A schematic example of a straw dam can be found in Appendix D,
Erosion and Sediment Control Details.
6.2.5.1 Site and Design Considerations
The following design and site considerations must be
followed when designing a straw dam:
• The contributing drainage area for a straw dam shall
be limited to ¼ acre per 100 ft of dam and further
limited by slope steepness as shown in the following
table.
Land Slope Maximum Spacing
Less than 2% 100 ft
2 – 5% 75 ft
5 – 10% 50 ft
10 – 20% 25 ft
Greater than 20% 15 ft
• The dam shall be located on the contour to prevent
channelization; and
• The straw dam shall be anchored to prevent
movement.
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6.2.5.2 Materials
Materials required for the installation of a straw dam include:
• New, firm, and well compacted straw bales bound with
wire or nylon. Minimum size for bales shall be 14” x
18” x 36”; and
• 2-inch x 2-inch hardwood stakes.
6.2.5.3 Installation
The following installation procedures must be followed when
installing a straw dam:
• Excavate trench at least 4 inches deep, a bale’s width,
and long enough that the end bales are somewhat
upslope of the sediment pool;
• Place each bale in the trench so the bindings are
oriented around the sides rather than top and bottom;
• Anchor the dam by driving stakes through each bale
until nearly flush with the top;
• Insert straw into any gaps between bales to prevent
sediment-laden water from running through; and
• Backfill and compact the excavated soil against the
bales to the ground level on the down-slope side and
to 4 inches above ground level on the up-slope side.
6.2.5.4 Maintenance
The developer is responsible for the inspection and
maintenance of all straw dams. The maintenance plan must
include, but is not limited to:
• The frequency of inspections of the dams;
• The requirement for repairs and replacements when
necessary;
• The removal of sediment deposits not to undermine
the entrenched bales.
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• The removal and proper disposal of all dams. Once
removed, the depressions shall be filled, compacted,
and seeded.
6.2.6 Fabric Drop Inlet Protection
Fabric drop inlet protection is a temporary woven geotextile barrier
placed around a drop inlet to prevent sediment from entering the
storm drains during construction operations.
A schematic example of fabric drop inlet protection can be found in
Appendix D, Erosion and Sediment Control Details.
6.2.6.1 Site and Design Considerations
The following design and site considerations must be
followed when designing fabric drop inlet protection:
• The height of the fabric shall be a maximum of 1.5 feet
and a minimum of 1 foot;
• The base of the fabric shall be buried at least 6 inches
below the ground surface;
• The support posts shall have a minimum length of 3
feet;
• The maximum spacing of the support posts shall be 3
feet;
• Framing shall be used to connect tops of posts to
stabilize the structure; and
• The maximum contributing drainage area for fabric
drop inlet protection is 1 acre.
6.2.6.2 Materials
Materials required for the installation of fabric drop inlet
protection include:
• Steel fence posts or 2-inch x 4-inch wooden posts;
and
• Durable, high-strength synthetic woven fabric.
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6.2.6.3 Installation
The following installation procedures must be followed when
installing fabric drop inlet protection:
• Set the top of the fabric at least 6 inches below the
downslope ground elevation;
• Cut the fabric from a single roll to eliminate joints if
possible. If joints are needed, a wrap joint shall be
used;
• Bury the bottom of the fabric at least 1 foot deep,
backfill, and compact the backfill; and
• Space the support posts evenly against the inlet
perimeter a maximum of 3 feet apart and drive them
about 1.5 feet into the ground.
6.2.6.4 Maintenance
The developer is responsible for the inspection and
maintenance of all fabric drop inlet protection sites. The
maintenance plan must include, but is not limited to:
• Inspection of the fabric barrier after storm events and
making the needed repairs at that time;
• The removal of sediment from the pool area to provide
storage for the next storm, while avoiding damage or
undercutting of the fabric during sediment removal.
• The removal and proper disposal of all construction
material and sediment. The area shall then be graded
to the elevation of the top of the inlet, and stabilized.
6.2.7 Sandbag Curb Inlet Protection
The purpose of sandbag curb inlet protection is to trap sediment on
paved streets that receive relatively small runoff flows, preventing the
sediment from being transported further down the street or into an
inlet.
A schematic example of a sandbag curb inlet protection can be found
in Appendix D, Erosion and Sediment Control Details.
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6.2.7.1 Site and Design Considerations
The following design and site considerations must be
followed when designing a sandbag curb inlet protection:
• 1 to 3 layers of sandbags shall be used;
• The length of the inlet protection structure shall be a
minimum of 3 feet; and
• The maximum contributing drainage area is 1 acre.
6.2.7.2 Materials
All sandbags used for curb inlet protection shall be filled half
full with sand or fine gravel.
6.2.7.3 Installation
The following installation procedures must be followed when
installing sandbag curb inlet protection:
• Lay the bags tightly end to end in a row curving from
the curb and away from the inlet, upslope from the
curb inlet;
• Overlap the barrier onto the curb, and extend it into
the street to intercept the runoff;
• If using more than one row, overlap the bags with the
row beneath, and leave a one-bag gap in the middle of
the top row to serve as a spillway.
6.2.7.4 Maintenance
The developer is responsible for the inspection and
maintenance of all sandbag curb inlet protection sites. The
maintenance plan must include, but is not limited to:
• The frequency of inspection for damage by vehicular
traffic and following each storm event;
• The repair and replacement procedures when
necessary; and
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• The removal of sediment when it reaches half the
height of the barrier.
6.2.8 Riprap Chute Outfall Protection
Riprap chute outfall protection is a pad or apron of rock placed at the
outlet end of culverts or chutes. They are used to reduce velocity and
prevent erosion at the outlet of a channel or culvert.
A schematic example of riprap chute outfall protection can be found in
Appendix D, Erosion and Sediment Control Details.
6.2.8.1 Site and Design Considerations
The following design and site considerations must be
followed when designing riprap chute outfall protection:
• The maximum contributing drainage area shall be 100
acres;
• The minimum thickness shall be 12 inches with a
geotextile foundation and
• Ensure that the apron size is proportional to the pipe
diameter size.
6.2.8.2 Materials
Riprap chute outfall protection materials shall be hard,
angular, and highly weather resistant riprap stone of size and
gradation that will withstand the velocities of the chute.
6.2.8.3 Installation
The following installation procedures must be followed when
installing riprap chute outfall protection:
• Excavate the apron area subgrade below design
elevation to allow for thickness of the filter and riprap;
• Place fabric on compacted and smooth foundation and
install the riprap;
• Make sure the top of the riprap apron is level with or
slightly below the receiving stream;
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• Blend the riprap smoothly to the surrounding grade;
and
• Stabilize all disturbed areas immediately following
installation.
6.2.8.4 Maintenance
The developer is responsible for the inspection and
maintenance of all riprap chute outfall protection sites. The
maintenance plan must include, but is not limited to:
• The inspection of rock chutes after storm events for stone
displacement and for erosion at the sides and ends of the
apron; and
• Making needed repairs immediately using the
appropriately sized stone, while placing them at or below
the finished grade.
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7.0 POST-CONSTRUCTION STORMWATER QUALITY
7.1 Introduction
This chapter describes policies, design criteria and information for water
quality best management practices (BMPs) as required by the City of
Richmond’s National Pollutant Discharge Elimination System (NPDES)
permit.
7.1.1 Background and Purpose
Best management practices (BMPs), both structural and non-
structural, can reduce the amount of pollutants in stormwater. This
section of the manual establishes minimum standards for the design,
maintenance, application, and construction of water quality BMPs. The
information provided in this chapter establishes performance criteria for
stormwater quality management and procedures to be followed when
preparing a BMP plan that must be in compliance with this manual.
BMPs noted in this chapter refer to post-construction BMPs, to be used
after construction has been completed and the site has been
stabilized. The installation of certain BMPs, such as bioretention areas
and sand filters, prior to stabilization can cause failure of the measure
due to clogging from sediment caused during land disturbing activities.
Nonetheless, with a strict construction sequence, detention ponds and
other BMPs can be installed initially during construction and used as
sediment control measures. In those instances, the construction
sequence must require that the pond is cleaned out with pertinent
elevations and storage and treatment capacities re-established as
noted in the approved post-construction stormwater management plan.
7.1.2 Stormwater Quality Control Requirements
The City of Richmond has adopted a policy that city-wide control of
stormwater runoff quality will be based on the management of total
suspended solids (TSS). The target TSS removal rate is 80%.
In addition to TSS removal, BMPs must also be designed to treat the
water quality volume (WQv) or the first flush of runoff.
7.1.3 Water Quality Volume
The storage needed to capture and treat the runoff from the first one
inch of rainfall is referred to as Water Quality Volume (WQv). In
numerical terms, it is equivalent to an inch of rainfall multiplied by the
volumetric runoff coefficient (Rv) and the site area.
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The following equation is used to calculate WQv (in acre-feet):
WQv = (P) (Rv) (A)
12
Where:
WQv = water quality volume (acre-feet)
P = 1 inch of rainfall
Rv = 0.05 + 0.009(I) where I is the percent impervious cover
A = area in acres
All new development projects requiring stormwater quality
management (Category 1 Projects) shall be required to treat the first
one inch of rainfall. Redevelopment projects will be required to obtain
the same approval if the redevelopment is to disturb more than 1 acre.
7.1.4 Structural Best Management Practices
Table 7.1.4-A, at the end of section 7.1, identifies pre-approved
structural BMPs that can be used in Richmond for water quality control
when designed and constructed in the manner in which they are
intended. Note that many of these measures can also be designed to
meet the water quantity control requirements. Specific water quality
design requirements are presented in the following sections.
Table 7.1.4-B, at the end of section 7.1, discusses BMP selection
criteria based on current and planned use of the site. Note that other
approved BMPs and combination of approved BMPs may be used on a
specific site if the target TSS removal rate of 80% is met.
7.1.4.1 Innovative or Otherwise Unapproved BMPs
All plans for unapproved BMPs (BMPs not included in Table
7.1.4-A) must be certified by a professional engineer, land
surveyor, or landscape architect and submitted to the
Stormwater Management Board for approval prior to
installation. ASTM standard methods must be followed when
verifying performance of new measures. New BMPs must
meet the 80% TSS removal rate and must have a low to
medium maintenance requirement to be considered by the
City.
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7.1.4.2 Operation and Maintenance of Structural BMPs
Each BMP must have an operations and maintenance plan.
The maintenance plan must be submitted with the post-
construction stormwater management plan and approved by
the City. The approved operations and maintenance plan will
be returned to the BMP owner, who will then be required to
implement the operations and maintenance plan.
The City must be notified of any changes in BMP ownership,
major repairs or BMP failure in writing within 30 days.
In the event that the City finds a BMP in need of maintenance
or repair, the City will notify the BMP owner of the necessary
maintenance, or repairs, and give the landowner a timeframe
for complying with their request. If the maintenance, or
repairs, are not completed within the designated timeframe,
the City shall perform the repairs or maintenance and bill the
landowner for the actual costs for the work.
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Table 7.1.4-A Pre-Approved BMPs
BMP Type Description Quantity Control WQv and 80% TSS removal Ponds
• Wet Pond
• Wet extended
detention pond
• Micropool extended
detention pond
• Multiple pond systems
Stormwater ponds are constructed
stormwater retention basins with a
permanent pool (or micropool) of
water. Runoff from each rain event
is captured and treated in the pool.
Yes Yes
Detention Basins
• Detention Basin
A dry detention basin is an area used
to detain stormwater for a relatively
short period of time. The area
should be dry between storms. The
basin allows particles and pollutants
to settle.
Yes No
Stormwater Wetlands
• Shallow wetland
• Extended detention
wetland
• Pond/wetland
systems
• Pocket wetland
Stormwater wetlands are
constructed, artificial wetland
systems used for stormwater
management. They consist of a
combination of shallow marsh areas,
open water and semi-wet areas
above the permanent pool.
Yes Yes
Bioretention Areas
Bioretention areas are shallow
stormwater basins or landscaped
areas that utilize engineered soils
and vegetation to capture and treat
stormwater run-off.
No Yes
Sand Filters
• Surface sand filter
• Perimeter sand filter
Sand filters are multi-chamber
structures designed to treat
stormwater run-off through filtration,
using a sand bed as its primary filter
media.
No Yes
Water Quality Swales
• Dry Swale
Water quality swales are vegetated
open channels that are designed and
constructed to capture and treat
stormwater run-off within dry cells.
No Yes
Biofilters
• Filter strip
• Grass channel
While biofilters provide some filtering
of stormwater runoff, by themselves
they cannot meet the 80% TSS
removal performance goal. These
measures can only be used as pre-
treatment measures or as part of a
treatment train.
No No
Catch Basin Inserts
• Various designs
Catch basin inserts are small filtering
devices installed in each catch basin
to trap suspended solids and other
pollutants.
No Yes
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Table 7.1.4-B BMP Selection Criteria
Current Use
Planned Use Approved BMPs
Open land
Commercial strip, light
industrial, institutional
(individual lots)
Bioretention, wet pond,
detention basin, artificial
wetland, sand filters,
biofilter, water quality
swale, catch basin insert
Open land
Commercial or industrial
subdivision (regional
stormwater plan)
Wet pond, detention basin,
wetland
Open land Residential
Bioretention, wet pond,
detention basin, artificial
wetland, biofilter, water
quality swale
Commercial building or
strip (medium
imperviousness)
Commercial building or
strip
Bioretention, sand filter,
catch basin insert, wet
pond, detention basin,
wetland
Commercial building or
strip (small lot, high
imperviousness)
Commercial building or
strip
Bioretention, sand filter,
catch basin insert
Transportation
infrastructure
Increased/expanded
transportation
infrastructure
Water quality swales, wet
ponds, detention, basin,
artificial wetlands, catch
basin inserts
7.2 Pre-Approved BMPs
In addition to the following practices, the applicant should also consult The
Indiana Stormwater Quality Manual (formerly The Indiana Handbook for
Erosion Control in Developing Areas) for detailed design, construction and
maintenance criteria for all post-construction stormwater management
practices.
7.2.1 Stormwater Ponds
Wet stormwater ponds can be designed to meet both water quality and
water quantity requirements. If the retention pond is to be designed for
only water quality purposes, then the pond shall be designed to
capture the water quality volumes as noted in Section 7.1.3.
A schematic example of stormwater ponds and variations can be found
in Appendix E, Post-Construction Stormwater Quality Details.
7.2.1.1 Site and Design Considerations
The following design and site considerations must be followed
when designing a stormwater pond:
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• Design the pond with a minimum length to width ratio of
3:1, preferably expanding outward toward the outlet;
• Maximize flow length between the inlet and outlet
structure. Use baffles if short-circuiting cannot be
prevented with inlet-outlet placement. Long flow paths
and irregular shapes are recommended;
• In areas where there is a contributing drainage area,
one must design the BMP as if the entire upstream
watershed is fully developed;
• In areas where flow from the upstream watershed
bypasses the proposed development, the design of the
BMP will only need to consider the drainage from the
site;
• Provide a sediment forebay, or similar pretreatment,
upstream from the BMP inlet;
- The forebay must be sized to contain 0.1 inches of
runoff per impervious acre of contributing drainage.
The forebay storage volume counts toward the total
water quality storage requirements.
- Exit velocities from the forebay must be non-erosive.
- Direct maintenance access for appropriate
equipment must be provided to the forebay.
- The bottom of the forebay may be hardened (e.g.
using concrete, paver blocks, etc.) to make
sediment removal easier.
- A fixed vertical sediment depth marker must be
installed in the forebay to measure sediment
deposition over time.
- Sediment removal in forebay shall occur when 50%
of the total capacity has been lost.
• Side slopes shall be no greater than 3:1 if mowed;
• Rip-rap protection must be provided (or other suitable
erosion control means) for the outlet and all inlet
structures into the pond;
• The minimum drainage area, contributing or effective,
for stormwater ponds is 25 acres. The minimum
drainage area, contributing or effective, for a micro-pool
extended detention facility is 10 acres;
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• Anti-seep collars or filter diaphragms must be provided
for the barrel of principal spillway;
• If reinforced concrete pipe is used for the principal
spillway, “O”-ring gaskets (ASTM C361) shall be used
to create watertight joints;
• Provide a one (1) foot minimum freeboard above the
maximum anticipated flow depth through the
emergency spillway;
• Design and install an emergency drain (i.e. sluice gate
or drawdown pipe) capable of draining within 24 hours;
• Design an emergency spillway to pass 1.25 times the
peak discharge and peak flow velocity from the 100-
year storm event for the entire contributing drainage
area (unless the site has been bypassed), assuming
post-development conditions;
• Provide trash racks, filters, hoods or other debris
control;
• Provide a permanent benchmark within the permanent
pool and sediment forebay for sediment removal;
• The principal spillway/riser system must incorporate
anti-floatation, antivortex, and trash-rack designs;
• To prevent drawdown of the permanent pool, an
impervious soil boundary may be needed;
• Orifice-type outlets are not allowed below the
permanent pool elevation of wet ponds and micropools;
• Construction debris cannot be disposed of within the
facility or used as fill in the embankment; and
• If the pond is used as a sediment control measure
during active construction, the sediment must be
cleaned out of the pond and elevations and grades
reestablished as noted in the approved post-
construction stormwater management plan.
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7.2.1.2 Performance Standards
Wet ponds and variations designed, constructed and
maintained as noted above shall provide the following
pollutant reductions:
Pollutant Percent Reduction
BOD 30%
TSS 85%
Total P 50%
Total N 30%
Metals 30%
7.2.1.3 Variations
Wet extended detention ponds: A wet extended detention
pond is a wet pond where the water quality volume is split
evenly between the permanent pool and the extended
detention storage provided above the permanent pool. During
storm events, water is detained above the permanent pool and
released over 12 - 48 hours. This design has similar pollutant
removal to a traditional wet pond, but consumes less space.
Micropool extended detention pond: The micropool
extended detention pond is a variation of the wet extended
detention pond where only a small micropool is maintained at
the outlet to the pond. The outlet is sized to detain the water
quality volume for 24 hours. The micropool prevents
resuspension of previously settled sediments.
Multiple pond systems: Multiple pond systems consist of
constructed facilities that provide water quality and quantity
volume storage in two or more cells. The additional cells can
create longer pollutant removal pathways and improved
downstream protection.
7.2.1.4 Advantages
The advantages of stormwater ponds are as follows:
• High pollutant removal;
• High community acceptance, if designed and
maintained correctly;
• Opportunity for wildlife habitat; and
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• Multi-objective use for water quality and quantity
control.
7.2.1.5 Disadvantages
The disadvantages of stormwater ponds are as follows:
• Potential for thermal impacts downstream; and
• Dam height restrictions.
7.2.1.6 Maintenance
The developer is responsible for the inspection and
maintenance of each stormwater pond. Each BMP must have
an operations and maintenance plan. The BMP owner must
maintain and update the BMP operations and maintenance
plan, as needed. The operations and maintenance plan must
include, but is not limited to:
• The removal of debris from inlet and outlet structures;
• The removal of invasive vegetation from all side slopes;
• The removal of sediment accumulation from forebay
and permanent pool area when it is 50% full; and
• The removal of woody vegetation from the
embankment.
7.2.2 Detention Basin
A dry detention basin is an area used to detain stormwater for a
relatively short period of time. The area shall be dry between storms.
The basin allows particles and pollutants to settle. However, the TSS
removal provided is less than 80%. Therefore, dry detention basins
must be used in a treatment train in order to provide the 80% TSS
removal performance goal.
A schematic example of dry detention basins can be found in
Appendix E, Post-Construction Stormwater Quality Details.
7.2.2.1 Site and Design Considerations
The following design and site considerations must be followed
when designing a detention basin:
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• The seasonal high water table and bedrock shall be at
least four feet beneath the bottom of the system to
minimize the potential for ground water contamination
and to assure that the bottom is dry;
• The maximum volume of water stored and
subsequently released at the design release rate shall
not result in storage duration in excess of 48 hours
unless additional storms occur within that period;
• Use a sediment forebay at all inflow points to trap
sediments and allow for easy removal;
• The length of the basin shall be at least three times the
width, with the basin narrow at the inlet and wide at the
outlet;
• Side slopes shall be at least 3:1 for safety and ease of
mowing;
• The basin floor shall be flat with a 2% slope toward the
outlet;
• The maximum planned depth of stormwater stored shall
not exceed four feet; and
• If the basin is used as a sediment control measure
during active construction, the sediment must be
cleaned out of the basin and elevations and grades
reestablished as noted in the approved post-
construction stormwater management plan.
7.2.2.2 Performance Standards
Dry detention basins designed, constructed and maintained as
noted above shall provide the following pollutant reductions:
Pollutant Percent Reduction
TSS 60%
Total P 20%
Total N 20%
Metals 40%
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7.2.2.3 Advantages
The primary advantage of detention basins is that thy may be
used as secondary uses (e.g. Parks) because they are dry
between storms.
7.2.2.4 Disadvantages
The disadvantages of detention basins are as follows:
• Poor stormwater treatment effectiveness;
• They have the potential to serve as mosquito breeding
ground if they are not maintained properly; and
• They require a relatively high level of maintenance.
7.2.2.5 Maintenance
The developer is responsible for the inspection and
maintenance of each detention basin. Each BMP must have
an operations and maintenance plan. The BMP owner must
maintain and update the BMP operations and maintenance
plan, as necessary. The operations and maintenance plan
must include, but is not limited to:
• The frequency of the removal of accumulated solids,
debris, and litter from the detention area. As a general
note, sediment shall be removed when it is dry in which
case they will crack and are then able to be separated
from the bottom and surrounding vegetation;
• The removal of debris from the control device,
especially if it has a small orifice;
• The mowing and removal of excess vegetation; and
• The vegetative stabilization of eroding sides or bottom.
7.2.3 Stormwater Wetlands
Stormwater wetlands are artificial wetlands created for the purposes of
stormwater pollutant removal and stormwater quantity control. It is the
intent of the City to encourage regional stormwater wetlands and
discourage artificial wetlands designed for individual sites. However,
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BMP plans proposing stormwater wetlands will be reviewed on a case-
by-case basis to determine their feasibility.
A schematic example of stormwater wetlands and variations can be
found in Appendix E, Post-Construction Stormwater Quality Details.
7.2.3.1 Site and Design Considerations
Prior to the approval of a developments post-construction
stormwater management plan, the following design and site
considerations must be addressed:
• A water balance must be performed to demonstrate that
a stormwater wetland could withstand a thirty-day
drought at summer evaporation rates without
completely drawing down. Also, inflow of water must
be greater than that leaving the basin by infiltration or
exfiltration. The following water balance equation shall
be used in calculations:
S = Qi + R + Inf - Qo - ET
Where:
S = net change in storage
Qi = stormwater runoff inflow
R = contribution from rainfall
Inf = net infiltration (infiltration - exfiltration)
Qo = surface outflow
ET = evapotranspiration
• The wetland must be designed for an extended
detention time of 48 hours for the water quality volume
(WQv). WQv is addressed in Section 7.1.4. The
orifices used for extended detention will be vulnerable
to blockage from plant material or other debris that will
enter the basin with stormwater runoff. Therefore,
some form of protection against blockage (e.g. non-
corrodible wire mesh) must be installed;
• The frequently flooded zone surrounding the wetland
must be located within the permanent easement;
• The surface area of the wetland must account for a
minimum of 1 percent of the area of the watershed
draining into it. A minimum of 1.5 percent shall be
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required for a shallow marsh design. The length to
width ration must be at least 2:1;
• The design must incorporate long flow paths through
the wetland, as appropriate;
• A forebay shall be established at the pond inflow points
to capture larger sediments and be 4 to 6 feet deep.
The depth of the forebay shall contain approximately 10
percent of the total volume of the normal pool. Direct
maintenance access to the forebay must be provided
with an access with a 25 foot minimum width and a
maximum slope of 5:1. Permanent sediment depth
markers must be provided;
• If high water velocity is a potential problem, some type
of energy dissipation device must be installed;
• Site preparation: Soil types conducive to wetland
vegetation shall be used during construction. The
wetland must be designed to allow slow percolation of
the runoff through the substrate. A layer of clay must
be added for porous substrates. Ensure that the
substrate, once flooded, is soft enough to permit
relatively easy insertion of the plants;
• Surrounding slopes must be stabilized with vegetation
to aid in trapping pollutants and preventing them from
entering the wetland;
• Maintain the wetland to prevent loss of area of ponded
water available for emergent vegetation due to
sedimentation and/or accumulation of plant material;
• Obtain local assistance for specifications on plants to
be used, planting schedule, soil requirements, mulch
requirements, etc;
• Construction debris cannot be disposed of in the facility
or used as fill in the embankment;
• If the wetland area or sediment forebay is used as a
sediment control measure during active construction,
the sediment must be cleaned out of the wetland or
forebay and elevations and grades re-established as
noted in the approved post-construction stormwater
management plan;
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• Stormwater wetlands must be designed with the
recommended proportion of depths noted in Table
7.2.3-A.
The four basic depths and descriptions are:
o Deepwater: 1.5 - 6 feet below normal pool elevation.
Includes the outlet micropool and deep water
channels through the wetland. This zone supports
little emergent wetland vegetation but may support
floating or submerged vegetation.
o Low marsh: 6-18 inches below normal pool
elevation or water surface elevation. This zone is
suitable for the growth of several emergent wetland
species.
o High marsh: 6 inches or less below normal pool
elevation. This zone will support a greater density
and diversity of wetland vegetation than the low
marsh. The high marsh area shall have a greater
surface area to volume ration than the low marsh
area.
o Semi-wet zone: Areas above normal pool elevation
inundated by larger storm events. This area
supports vegetation that can survive periodic
flooding.
Table 7.2.3-A Minimum Required Design Configuration for Stormwater
Wetlands
Design Criteria Shallow Wetland Pond/Wetland Pocket Wetland
Length to width ratio
(min) 2:1 2:1 2:1
Allocation of WQv
(pool/marsh) in % 25/75
70/30
(includes pond
volume)
25/70
Allocation of surface
area (deepwater/low
marsh/high
marsh/semi-wet) in %
20/35/40/5
45/25/25/5
(includes pond
surface area)
10/45/40/5
Forebay Required Required Optional
Micropool Required Required Required
Outlet configuration
Reverse-slope
pipe or hooded
broad crest weir
Reverse-slope
pipe or hooded
broad crest weir
Hooded broad
crest weir
Modified from Massachusetts DEP, 1997; Schueler, 1992
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7.2.3.2 Performance Standards
Artificial wetlands designed, constructed and maintained as
noted above shall provide the following pollutant reductions:
Pollutant Percent Reduction
BOD 55%
TSS 95%
Total P 55%
Total N 45%
Metals 80%
7.2.3.3 Maintenance
The developer is responsible for the inspection and
maintenance of each artificial wetland. Each BMP must have
an operations and maintenance plan. The BMP owner must
maintain and update the BMP operations and maintenance
plan, as necessary. The operations and maintenance plan
must include, but is not limited to:
• The maintenance of the wetland to prevent loss of area
of ponded water available for emergent vegetation due
to sedimentation and accumulation of plant material;
• The cleaning of sediment forebays when they are 50%
full. Pocket wetlands without forebays must be cleaned
after a six-inch accumulation of sediment;
• The maintenance of the ponded water area by raising
the elevation of the water level in the permanent pond,
by raising the height of the orifice in the outlet structure,
or by removing accumulated solids by excavation;
• Water levels may need to be supplemented or drained
periodically until vegetation is fully established; and
• It may be desirable to remove contaminated sediment
bottoms or to harvest above ground biomass and
remove it from the site to permanently remove
pollutants from the wetland.
7.2.4 Bioretention
Bioretention areas, or rain gardens, are structural stormwater controls
that capture and temporarily store the WQv using soils and vegetation
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in landscaped areas to remove pollutants from stormwater runoff.
Bioretention areas are engineered facilities in which runoff is conveyed
as sheet flow to the "treatment area," consisting of a grass buffer strip,
ponding area, organic or mulch layer, planting soil, and vegetation. An
optional sand bed can be included in the design to provide aeration
and drainage of the planting soil. The filtered runoff is typically
collected and returned to the conveyance system, though it can be
exfiltrated into the surrounding soil in areas with porous soils though
exfiltration may not be permitted in Wellfield Zoning Districts.
Bioretention areas are designed for intermittent flow and to drain and
aerate between rainfall events. Sites with continuous flow from
groundwater, sump pumps or other areas must be avoided.
A schematic example of a bioretention area can be found in Appendix
E, Post-Construction Stormwater Quality Details.
Bioretention areas consist of:
• Grass filter strip between the contributing drainage area and the
ponding area;
• Ponding areas containing vegetation with a planting soil bed;
• Organic/mulch layer; and
• Gravel and perforated pipe underdrain system to collect runoff
that has filtered through the soil layers (bioretention areas can
optionally be designed to infiltrate into the soil).
Optional design components include:
• Sand filter layer to spread flow, filter runoff and aid in aeration
and drainage of the planting soil;
• Stone diaphragm at the beginning of the grass filter strip to
reduce velocities and spread flow into the grass filter; and
• Inflow diversion or an overflow structure.
7.2.4.1 Site and Design Considerations
The following design and site considerations must be followed
when designing bioretention areas:
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• The drainage area (contributing or effective) must be 5
acres or less, though 0.5 to 2 acres is preferred;
• The minimum size for facility is 200 ft2, with a length to
width ratio of 2:1. Slope of the site may not exceed 6%;
• Soil filter beds must be sized using a Darcy's Law
equation with a filter bed drain time of 48 hours and a
coefficient of permeability (k) of 0.5 ft/day. The soil bed
must be at least 4 feet deep. Planting soils must be
sandy loam, loamy sand or loam texture with a clay
content rating from 10 to 25 percent. The soil must
have an infiltration rate of at least 0.5 inches per hour
and a pH between 5.5 and 6.5. In addition, the planting
soil shall have a 1.5 to 3 percent organic content and a
maximum 500-ppm concentration of soluble salts;
• The maximum ponding depth in bioretention areas is 6
inches;
• Filter strip design for pre-treatment must follow the
requirements outlined in Section 7.2.7;
• The mulch layer must consist of 2-4 inches of
commercially available fine shredded hardwood mulch
or shredded hardwood chips;
• The sand bed must be 12-18 inches thick. Sand must
be clean and have less than 15% silt or clay content;
• Pea gravel for the diaphragm and curtain, where used,
must be ASTM D 448 size No. 6 (1/8” to 1/4”);
• The underdrain collection system must be equipped
with a 6-inch perforated PVC pipe in an 8-inch gravel
layer. The pipe must have 3/8-inch perforations,
spaced on 6-inch centers with a minimum of 4 holes per
row. The pipe is spaced at a maximum of 10 feet on
center, and a minimum grade of 0.5% must be
maintained. A permeable filter fabric is placed between
the gravel layer and the planting soil bed;
• The required elevation difference needed from the
inflow to the outflow is 5 feet;
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• The depth from the bottom of the bioretention facility to
the seasonally high water table must be a minimum of 2
feet;
• Runoff captured by facility must be sheet flow to
prevent erosion of the organic or mulch layer.
Velocities entering the mulch layer must be between 1-
2 fps;
• Continuous flow from groundwater, sump pumps or
other areas to the bioretention area is prohibited;
• An overflow structure and a non-erosive overflow
channel must be provided to safely pass the flow from
the bioretention area that exceeds the storage capacity
to a stabilized downstream area. The high flow
structure within the bioretention area can consist of a
yard drain catch basin, with the throat of the catch basin
inlet typically 6 inches above the elevation of the
shallow ponding area; and
• If the bioretention area is used as a sediment control
measure during active construction, the sediment must
be cleaned out of the bioretention area and elevations
and grades reestablished as noted in the approved
stormwater management plan for post-construction
runoff control.
7.2.4.2 Performance Standards
Bioretention areas designed, constructed and maintained as
noted in this manual shall provide the following pollutant
reductions:
Pollutant Percent Reduction
TSS 80%
Total P 30%
Total N 50%
Metals 60%
7.2.4.3 Advantages
The advantages of bioretention areas are as follows:
• They are applicable to small drainage areas;
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• They are often located in landscape islands;
• They have the capability for high pollutant removal; and
• There is greater community acceptance, if designed
and maintained correctly.
7.2.4.4 Disadvantages
The disadvantages of bioretention area include:
• They require extensive landscaping; and
• They are not recommended for areas with steep slopes.
7.2.4.5 Maintenance
Landscaping is critical to the performance and function of the
bioretention area. A dense and vigorous groundcover must be
established over the contributing pervious drainage area
before runoff can be diverted into the facility.
The BMP owner is responsible for maintenance and
inspections. Each BMP on a site must have an operations
and maintenance plan. The BMP owner must maintain and
update the BMP operations and maintenance plan. At a
minimum, the operations and maintenance plan must include,
but is not limited to:
• Inspection, repair and replacement of all treatment
components;
• The bioretention area shall be vegetated like a
terrestrial forest ecosystem, with a mature tree canopy,
subcanopy of understory trees, scrub layer and
herbaceous ground cover. Three species of each tree
and shrub type shall be planted;
• The tree-to-shrub ration shall be 2:1 to 3:1. On
average, trees shall be spaced 8 feet apart. Plants
shall be placed at regular intervals to replicate a natural
forest. Woody vegetation shall not be planted at inflow
locations.
• After the trees and shrubs are established, the ground
cover and mulch shall be established; and
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• Use native plants, selected based upon hardiness and
hydric tolerance.
7.2.5 Sand Filters
Sand filters are structural stormwater controls that temporarily store
stormwater and pass it through a filter bed of sand. Most sand filter
systems contain two chambers. The first chamber is a sedimentation
chamber that removes floatables and heavy sediments. The second
chamber is the filtration chamber, which removes additional pollutants
by filtering the runoff through a sand bed. The filtered runoff is typically
collected and returned to the conveyance system, though it can be
partially or fully exfiltrated into the surrounding soil in areas with porous
soils.
Sand filters are primarily designed as off-line structures for stormwater
quality and typically need to be used in conjunction with another
structural BMP to provide water quantity control.
A schematic example of sand filters and variations can be found in
Appendix E, Post-Construction Stormwater Quality Details.
7.2.5.1 Site and Design Considerations
The following design and site considerations must be followed
when designing sand filters:
• The maximum-effective drainage area to an individual
stormwater filtering system is less than 10 acres. Sand
filters cannot be designed to treat the entire contributing
drainage area;
• The design volume must be based on one-inch rainfall
and must be designed to fully empty in 36 hours;
• Adequate pretreatment (e.g., filter strips, see Section
7.2.7) is required to prevent sediment from overloading
the filters. The inlet structure to the filtration chamber
must be designed to spread the flow uniformly across
the surface of the filter media. Stone riprap or other
dissipation devices must be installed to prevent gouging
of the sand media and to promote uniform flow;
• The allowable minimum head is one foot. The
maximum allowable head is 6 feet;
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• Construct sand bed to a depth of at least 18 inches;
• Underdrain pipes must consist of main collector pipes
and perforated lateral branch pipes. Reinforce the
underdrain piping to withstand the weight of the
overburden. Internal diameters of lateral branch pipes
must be 4 inches or greater (6 inches preferred) and
perforations shall be 1/8 inch. Space perforations a
maximum of 6 inches between rows. All piping must be
schedule 40 polyvinyl chloride or greater strength or
similarly rated HDPE pipe. The minimum grade of
piping shall be 1/8 inch per foot (1% slope). Provide
access for cleaning all underdrain piping;
• Surface filters may have a grass cover to aid in
pollution adsorption;
• Establish vegetation over the contributing drainage
areas before runoff can be accepted into the facility;
and
• Two allowable surface sand bed filter configurations
are:
Sand Bed with Gravel Layer
- Top layer of sand must be a minimum of 18 inches
of 0.02 - 0.04 inch diameter sand (smaller sand size
is acceptable).
- A layer of one-half to 2-inch diameter gravel under
the sand must be provided for a minimum of 2
inches of cover over the top of the under-drain
lateral pipes.
- No gravel is required under the lateral pipes.
- A layer of geotextile fabric (permeable filter fabric)
must separate the sand and gravel.
Sand Bed with Trench Design
- Top layer of sand is to be 12-18 inches of 0.02 -
0.04 inch diameter sand (smaller size is
acceptable).
- Laterals to be placed in trenches with a covering of
one-half to 2- inch gravel and geotextile fabric.
- The lateral pipes are to be underlain by a layer of
drainage matting.
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- A presettling basin and/or biofiltration swale is
recommended to pretreat runoff discharging to the
sand filter.
- A maximum spacing of 10 feet between lateral
underdrain pipes is recommended.
7.2.5.2 Performance Standards
Sand filters designed, constructed and maintained as noted in
this manual shall provide the following pollutant reductions:
Pollutant Percent Reduction
BOD 60%
TSS 85%
Total P 65%
Total N 50%
Bacteria 40-80%
Metals 60%
7.2.5.3 Variations
There are three primary sand filter system designs, the
surface sand filter, the perimeter sand filter, and the
underground sand filter.
Surface Sand Filter- The surface sand filter is a ground-level
open-air structure that consists of a pretreatment sediment
forebay and a filter bed chamber. This system can treat
drainage areas up to 10 acres in size and is typically located
off-line. Surface sand filters can be designed as an
excavation with an earthen embankment or as a concrete
structure.
Perimeter Sand Filter- The perimeter sand filter is an
enclosed filter system typically constructed just below grade in
a vault along the edge of an impervious area such as a
parking lot. The system consists of a sedimentation chamber
and a sand bed filter. Runoff flows into the structure through a
series of inlet grates located along the top of the control.
Underground Sand Filter- The underground sand filter is
intended primarily for extremely space-limited and high-density
areas.
7.2.5.4 Advantages
The advantages of sand filters include:
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• They are applicable to small drainage areas;
• They are good for highly impervious areas; and
• They have good retrofit capability.
7.2.5.5 Disadvantages
The disadvantages of sand filters include:
• They are high maintenance;
• They are not recommended for areas with high
sediment content in stormwater;
• They can be relatively costly; and
• There are possible odor problems associated with the
use of them.
7.2.5.6 Maintenance
The developer is responsible for the inspection and the
maintenance of each sand filter. Each BMP must have an
operations and maintenance plan. The BMP owner must
maintain and update the BMP operations and maintenance
plan, as necessary. The operations and maintenance plan
must include, but is not limited to:
• The removal of sediment layer buildup during dry
periods with steel rakes or other devices.
• The replacement of some or all of the sand when
permeability of the filter media is reduced to
unacceptable levels, which shall be specified in the
design of the facility. A minimum infiltration rate of 0.5
inches per hour shall be used for all infiltration designs.
7.2.6 Dry Water Quality Swales
Dry water quality swales are channels designed and constructed to
capture and treat stormwater runoff within dry cells formed by check
dams or other means. Dry water quality swales are also described as
biofiltration swales. These swales are designed with a limited slope for
slow, shallow flow to allow particulates to settle out and to promote
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infiltration. Water quality swales are limited to areas with low
impervious acreage, such as residential and industrial developments.
Dry swales are channels designed with a filter bed and underdrain
system. They are designed to filter and infiltrate the entire WQv
through the bottom of the swale. Runoff is collected by a perforated
pipe and discharged at the outlet. Water quality swales are dry most of
the time and are therefore well suited for residential areas.
A schematic example of a water quality swale can be found in
Appendix E, Post-Construction Stormwater Quality Details.
7.2.6.1 Site and Design Considerations
The following design and site considerations must be followed
when designing water quality swales:
• Water quality swales treat only the WQv. An additional
measure is needed to provide detention in conjunction
with the water quality swale. The swales can be
designed as on-line or off-line structures. Larger
storms pass non-erosively through the channels;
• Water quality swales are limited to peak discharges
generally less than 5 to 10 cfs and runoff velocities less
than 2.5 ft/sec. The maximum drainage area is 5 acres.
The maximum ponding time must be less than 48
hours, and a minimum ponding time of 30 minutes is
recommended;
• The maximum design flow depth is 1 foot, with a
ponding depth of 18 inches at the end of the channel;
• Swale cross-section must have side slopes of 3:1 (h:v)
or flatter. Bottom widths must be between 2-8 feet
wide;
• Underlying soils shall have a high permeability (fc > 0.5
inches per hour). Seasonally high water table must be
greater than 3 feet below the bottom of the swale;
• Water quality swales must have a minimum length of
100 feet; and
• Provide a sediment forebay at the inlet to the swales.
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7.2.6.2 Performance Standards
Water quality swales designed, constructed and maintained
(on a 4% or flatter slope) as noted in this manual shall provide
the following pollutant reductions:
Pollutant Percent Reduction
BOD 10%
TSS 80%
Total P 83%
Total N 92%
Metals 75%
7.2.6.3 Advantages
The advantages of water quality swales include:
• They are typically well accepted in residential settings;
• They are inexpensive;
• They combine water quality treatment with runoff
conveyance;
• They reduce runoff velocities; and
• They are low maintenance.
7.2.6.4 Disadvantages
The disadvantages of water quality swales include:
• They cannot be used on steep slopes; and
• They only provide a limited amount of stormwater
quantity control.
7.2.6.5 Maintenance
The developer is responsible for the inspection and
maintenance of each water quality swale. Each BMP must
have an operations and maintenance plan. The BMP owner
must maintain and update the BMP operations and
maintenance plan, as necessary. The operations and
maintenance plan must include, but is not limited to:
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• Adequate access for inspection and maintenance.
• The maintenance of dry swales to keep grass cover dense
and vigorous.
• At a minimum, maintenance shall include periodic mowing,
occasional spot reseeding, and weed control. Swale
grasses must never be mowed close to the ground. Grass
heights in the 4 to 6 inch range are recommended.
• The fertilization of grass swale shall be done when needed
to maintain the health of the grass, with care not to over-
apply the fertilizer.
• The removal of sediment accumulated in forebay when it is
50% full.
7.2.7 Biofilters
Biofilters are densely vegetated sections of land, designed to treat run-
off from and remove pollutants through vegetative filtering and
infiltration. Biofilters must receive runoff from adjacent areas as sheet
flow. The vegetation slows the runoff and filters out sediment and
other pollutants. However, the TSS removal provided is less than 80
percent. Therefore, biofilters must be used in a treatment train in
conjunction with other management practices to provide the 80 percent
performance goal.
Biofilters are best suited to treating runoff from roadways, rooftops,
small parking areas and pervious areas. They can be easily
incorporated into residential development as land-use buffers and
setbacks.
A schematic example of biofilters can be found in Appendix E, Post-
Construction Stormwater Quality Details.
7.2.7.1 Site and Design Considerations
The following site and drainage considerations must be
followed when designing biofilters:
• To ensure sheet flow into the filter strips and riparian
buffers, flow spreaders or level spreaders must be
designed and installed where concentrated runoff flows
into filter strips or riparian buffers;
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• Level Spreader: The grade of a level spreader shall be
0%. The channel grade for the last 20 feet of the dike
or diversion entering the level spreader must be less
than or equal to 1% and designed to provide a smooth
transition into spreader. The depth of a level spreader
as measured from the lip must be at least 6 inches.
The level spreader lip must be constructed on
undisturbed soil (not fill material) to uniform height and
zero grade over length of the spreader. The maximum
drainage area to the level spreader shall be 10 acres or
less with the optimal size being less than 5 acres. The
maximum flow into the level spreader must be 30 cfs or
less;
• Appropriate length, width, and depth of level spreaders
shall be selected from the following table;
Design
Flow
(cfs)
Entrance
Width (ft) Depth (ft)
End
Width
(ft)
Length
(ft)
0-10 10 0.5 3 10
10-20 16 0.6 3 20
20-30 24 0.7 3 30
• Capacity of the spreader, filter strip and riparian buffer
length (perpendicular to flow) must be determined by
estimating the volume of flow that is diverted to the
spreader for water quality control;
• The released runoff to the outlet must be on
undisturbed stabilized areas in sheet flow and not
allowed to re-concentrate below the structure;
• Slope of the filter strip from a level spreader must not
exceed 10 percent;
• All disturbed areas must be vegetated immediately after
construction;
• The minimum filter strip width is 20 feet;
• Filter strips must be designed for slopes between 2
percent and 6 percent;
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• Ensure that flows in excess of design flow move across
and around the filter strip without damaging it;
• Filter strips can be used effectively as pretreatment
measures. The minimum sizing criteria are as follows:
Parameters Impervious Area Pervious Area
Maximum inflow
Approach length
(ft)
35 75 75 100
Filter strip slope
(max = 6%) <2% >2% <2% >2% <2% >2% <2% >2%
Filter strip
minimum
length
10 15 20 25 10 12 15 18
• Riparian buffers: The use of buffers is limited to
drainage areas of 10 acres or less with the optimal size
being less than 5 acres;
• Slope of the buffer from a level spreader cannot exceed
10 percent; and
• The top edge of buffer must directly abut the
contributing impervious area and follow the same
elevation contour line.
7.2.7.2 Performance Standards
Biofilters designed, constructed and maintained as noted in
this manual shall provide the following pollutant reductions:
Pollutant Percent Reduction
(riparian buffer/filter strip)
BOD 40/10%
TSS 60/30%
Total P 35/10%
Total N 25/10%
Metals 70/30%
7.2.7.3 Variations
Filter strip: A filter strip is a uniformly graded and densely
vegetated strip of land. The vegetation can be grasses or a
combination of grass and woody plants. Pollutant removal
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efficiencies are based upon a 50-foot wide strip. Uniform
sheet flow must be maintained through the filter strip to
provide pollutant reduction and to avoid erosion.
Riparian buffer: A riparian buffer is a strip of land with
natural, woody vegetation along a stream or other
watercourse. Besides the undergrowth of grasses and
herbaceous vegetation, the riparian buffer includes deep
rooted trees. The 20-foot zone closest to the stream or
watercourse contains the trees, while the outer 30 feet of the
riparian buffer contains a dense stand of grasses. The overall
width of the riparian buffer is 50 feet. Uniform sheet flow must
be maintained through the filter strip to provide pollutant
reduction and to avoid erosion.
7.2.7.4 Advantages
The advantages of biofilters include:
• Filter strips and riparian buffers can easily be
incorporated into new development design;
• They are low maintenance once a dense ground cover
is established in filter strips and level spreaders and
once trees and other woody vegetation is established in
riparian buffers; and
• Riparian buffers provide wildlife habitat.
7.2.7.5 Disadvantages
The disadvantages of biofilters include:
• Filter strips, riparian buffers and level spreaders have
limited drainage areas; and
• Constructing a level lip on a level spreader can be
difficult. Failure to construct a level lip makes the level
spreader ineffective.
7.2.7.6 Maintenance
The developer is responsible for the inspection and
maintenance of all biofilters. Each BMP must have an
operations and maintenance plan. The BMP owner must
maintain and update the BMP operations and maintenance
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plan, as necessary. The operations and maintenance plan
must include, but is not limited to:
• The mowing of the biofilter as necessary, or the
utilization of an appropriate management technique for
existing species.
• The removal of sediment accumulation and debris in
order to sustain sediment removal efficiency.
7.2.8 Catch Basin Inserts
Many variations of catch basin insert designs exist. Catch basin
inserts can be designed and installed in a storm drain system provided
the following minimum criteria for the inserts are met:
• Provide an overflow weir to pass storm events larger than the
design storm.
• Catch basin inserts must meet the 80% TSS removal rate.
• Each design for catch basins can have specific maintenance
needs or issues. Maintenance requirements must be clearly
defined, and a specific maintenance agreement submitted to the
City for review and approval.
Supporting documentation from the manufacturer to verify
maintenance requirements and TSS removal rates must be submitted
to the City for verification and approval. A maintenance plan must be
submitted to the City prior to stormwater management plan approval
and maintained and updated by the BMP owner. The BMP owner is
responsible for routine maintenance, operation and inspection.
7.2.9 Other Pre-Approved BMPs
Other pre-approved BMPs include, but are not limited to, porous
pavement systems, gravity oil grit separators, equipment maintenance
and washing areas, infiltration trenches, hydrodynamic separators,
hazardous material storage, subsurface detention, and parking lot
islands.
The applicant should consult The Indiana Stormwater Quality Manual
(formerly The Indiana Handbook for Erosion Control in Developing
Areas) for detailed design, construction and maintenance criteria for
these post-construction stormwater management practices.
AGREEMENT FOR THE CONSTRUCTION, MAINTENANCE, AND REPAIR OF A
STORMWATER MANAGEMENT FACILITY
WHEREAS, the undersigned is/are the owner(s) (hereinafter “Owners”) of certain real estate
located in Wayne County, Indiana, and legally described herein as Exhibit “A;” and
WHEREAS, the Owners are desirous of constructing a stormwater management facility over a
portion of said real estate described at Exhibit “A;” and
WHEREAS, in order to construct such stormwater detention the Owners must obtain review and
permits from the City of Richmond (hereinafter “City”).
NOW THEREFORE, for good and valuable consideration, receipt of which is herein
acknowledged, the Owner covenants with the City as follows:
1. Owner agrees to obtain prior approval from the City for design and construction of the
stormwater management facility. Plans and specifications, which Owner shall strictly
adhere to, will be on file with the Development Services Department of the City of
Richmond, Indiana. Failure to obtain said approval will render this Agreement void
and any stormwater management facility on this property illegal.
2. Owner agrees to construct and be responsible for the perpetual, maintenance, repair,
and replacement, if necessary, of the stormwater management facility that will serve
the real estate identified in Exhibit “A.” Owner agrees to maintain said facility in a
condition acceptable to the City.
a. Maintenance shall include, but not be limited to cosmetic maintenance (including
structural) to the stormwater management facility during and after construction,
mowing, weed control, trash pick-up, algae, mosquito control, and general
maintenance.
b. All maintenance will be done so as to assure that all stormwater runoff designed
to be detained within the stormwater management facility will be so detained, and
the designed rate of runoff will not be increased after the improvements have
been constructed as contemplated upon the said real estate.
c. Owner expressly grants the right of entry over, across, and through the real
estate described herein at Exhibit “A” to the City for the purpose of inspecting,
evaluating, or repairing the stormwater management facility.
d. City will notify the Owner in writing of maintenance or repairs required. Said
notice may be delivered by U.S. mail to the last provided address of the Owner.
If the Owner fails to address the problems outlined satisfactorily within thirty (30)
days of said notice, City shall have the right to enter over and upon all necessary
portions of the real estate as described in Exhibit “A” for the purpose of repairing
and maintaining said stormwater management facility.
e. In the event that an emergency situation exists, as defined by the Board of Public
Works of the City of Richmond, and the City is unable to locate the Owner or its
agent after reasonable attempts have been made to do so, the City shall have
the right to enter upon the real estate and make such emergency repairs as it
deems necessary.
f. At any time the City is required to enter upon the real estate of the Owner and
make such repairs, the costs of same shall be the obligation of the Owner. If the
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Owner does not pay said costs within thirty (30) days after receiving written
notice of the same from the City, the City shall have the right to place a lien
against and upon the real estate (described in Exhibit “A”) for costs incurred by it
for the repair and maintenance of the stormwater management facility, including
interest at the rate of eight (8%) percent per annum, and reasonable attorney’s
fees.
3. The Owner agrees to indemnify and hold harmless the City from all claims arising out
of the installation, maintenance, or use of the stormwater management facility.
4. The most recent deed of record for the real estate has been recorded in the Office of
the Recorder of Wayne County, Indiana, as document number_____________.
5. This Agreement may only be amended by prior written consent signed by the Owner
and the City.
6. The rights and obligations created by this Agreement shall be binding upon and shall
run with the real estate for the benefit of the heirs, personal representative,
successors and assigns of the Owner.
7. The laws of the State of Indiana shall govern this Agreement.
IN WITNESS WHEREOF, the parties hereto have executed this Agreement the day and year
first above written.
Date:________________________ Owner:_______________________________
Printed Name:________________________________
Owner:______________________________________
Printed Name:________________________________
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STATE OF INDIANA )
SS: )
COUNTY OF WAYNE )
BEFORE ME, a Notary Public, in and for said County and State, this ____ day of ________,
200 personally appeared the within named _________________ and
_____________________ who being first duly sworn upon their oath state that they are
Owners of the subject real estate at Exhibit A and as such duly authorized to execute the
foregoing instrument and acknowledged the same as their voluntary act and deed for the
uses and purposes therein set forth.
IN WITNESS WHEREOF, hereunto subscribed my name, affixed my official seal.
__________________________
Notary Public
__________________________
Printed Name of Notary
My Commission Expires:
Resident of _________County
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For the CITY OF RICHMOND – Stormwater Engineering
BY:_____________________________ Printed Name _____________________
STATE OF INDIANA )
SS: )
COUNTY OF WAYNE )
BEFORE ME, a Notary Public, in and for said County and State, this _______day of
_______________, personally appeared the within named, __________________, by me
personally known, who being by me duly sworn has authority so to do and acknowledges
said instrument to be the voluntary act and deed of said City for the uses and purposes
therein set forth.
IN WITNESS WHEREOF, hereunto subscribed my name, affixed my official seal.
________________________________
Notary Public
________________________________
Printed Name of Notary
My Commission Expires:
Resident of ________County
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