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11
Stormwater ManagementStormwater Management
Issued May 2009
Level II: Introduction to DesignEducation and Certification for Persons Involved in Land Disturbing Activities
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Stormwater ManagementStormwater Management
Stormwater RunoffStormwater Runoff UrbanizationUrbanization Stormwater ControlsStormwater Controls Design and Review FocusDesign and Review Focus
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What is Stormwater Runoff?What is Stormwater Runoff?
Stormwater is…Stormwater is… Rain that hits the eartRain that hits the eart
hh’’s surfaces surface Stormwater Stormwater Runoff Runoff
is…is… Rain that runs off Rain that runs off
hardened surfaceshardened surfaces
Transpiration Eva poration
Percolation Runoff Runoff Runoff
Transpiration Eva poration
Percolation Runoff Runoff Runoff
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Stormwater Runoff Stormwater Runoff ““Non-Point Non-Point SourceSource”” Pollution Pollution
Stormwater runoff picks Stormwater runoff picks up pollutants as it runs up pollutants as it runs off impervious surfaces off impervious surfaces Oils/GreaseOils/Grease Metal ParticlesMetal Particles PesticidesPesticides Pet Wastes/PathogensPet Wastes/Pathogens NutrientsNutrients ExcessiveExcessive Sediment Sediment
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Erosion and SedimentationErosion and Sedimentation
Sediment is the #1 Sediment is the #1 nonpoint source of nonpoint source of water pollutionwater pollution
Erosion causes Erosion causes additional problemsadditional problems Loss of propertyLoss of property Degradation of Degradation of
streams streams
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Start at the SourceStart at the Source
Uncontrolled Uncontrolled construction construction sites dump sites dump hugehuge amounts of amounts of sediment sediment downstreamdownstream
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Common MisconceptionCommon Misconception
Stormwater from roads Stormwater from roads
and construction sites and construction sites
is directed to storm is directed to storm
drainsdrains Stormwater that enters Stormwater that enters
a storm drain gets a storm drain gets
treatedtreated Where does it really Where does it really
go?go?
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The Truth Is…The Truth Is…
Stormwater usually Stormwater usually receives no treatment receives no treatment at allat all
It goes to the nearest It goes to the nearest stream!stream!
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Impacts of SedimentationImpacts of Sedimentation
Bare soil easily Bare soil easily washes into washes into storm drains and storm drains and into streams, into streams, clouding the clouding the water and water and suffocating suffocating aquatic life.aquatic life.
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Impacts of SedimentationImpacts of Sedimentation
Sediments can Sediments can block culverts block culverts and displace and displace flood watersflood waters
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WhatWhat’’s All the Fuss ?s All the Fuss ?
3% of Earth3% of Earth’’s water is freshwaters water is freshwater < 1% Earth< 1% Earth’’s freshwater is potable – limited s freshwater is potable – limited
resourcesresources 40% of streams are not clean enough for fishing 40% of streams are not clean enough for fishing
and swimmingand swimming
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Problem: Stream PollutionProblem: Stream Pollution
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Goal: Clean Healthy StreamsGoal: Clean Healthy Streams
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PenaltiesPenalties
Builder ordered to pay $2.3 million over Builder ordered to pay $2.3 million over storm runoffstorm runoff
““A Cobb County jury this week slapped a builder A Cobb County jury this week slapped a builder with what may be the largest judgment in a with what may be the largest judgment in a storm water pollution case in Georgia history.storm water pollution case in Georgia history.””
The Atlanta Journal-Constitution The Atlanta Journal-Constitution 05/12/05 05/12/05
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Growth and DevelopmentGrowth and Development Urbanization happens…Urbanization happens…
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UrbanizationUrbanization
Understanding Understanding stormwater stormwater impacts due to impacts due to UrbanizationUrbanization
Source: District-Wide Watershed Management Plan-Preliminary Draft, Metropolitan North Georgia Water Planning District, March 10, 2003.
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Back to BasicsBack to Basics RainfallRainfall InfiltrationInfiltration EvapotranspirationEvapotranspiration RunoffRunoff
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Stormwater and UrbanizationStormwater and Urbanization
As land is developed:As land is developed: Ground is Ground is
compacted - less compacted - less water can naturally water can naturally infiltrateinfiltrate
Less trees and less Less trees and less evapotranspirationevapotranspiration
MORE stormwater MORE stormwater runs offruns off
Transpiration Eva poration
Percolation Runoff Runoff Runoff
Transpiration Eva poration
Percolation Runoff Runoff Runoff
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Stormwater and UrbanizationStormwater and Urbanization
Arrow lengths Arrow lengths indicate indicate increase/decreaseincrease/decrease
2020
From From ““River of FireRiver of Fire”” to to Clean Water ActClean Water Act
Cuyahoga River 1949-1969Cuyahoga River 1949-1969
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Stormwater ManagementStormwater Management
Stormwater Quality – Stormwater Quality – ““how goodhow good”” Stormwater Quantity – Stormwater Quantity – ““how muchhow much””
QuantityQuantity is directly related to … is directly related to …
QualityQuality
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WhatWhat’’s It All About?s It All About?
Remember…Remember…
Streams, streams, streamsStreams, streams, streams
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Stormwater Stormwater Quantity Quantity ImpactsImpacts
Courtesy: Center for Watershed Protection
Stable Channel Downcutting Widening Sedimentation Stable, Entrenched
Pre- to Post-Development
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Stormwater Stormwater Quantity Quantity ImpactsImpacts
Impervious surfaces Impervious surfaces cause higher runoff cause higher runoff volumevolume
High velocity stormwater High velocity stormwater runoff causes stream runoff causes stream erosionerosion
Stream erosion causes Stream erosion causes habitat and property losshabitat and property loss
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Stormwater Stormwater Quantity Quantity ImpactsImpacts
Downcutting exposes sewer lines that Downcutting exposes sewer lines that can break, leading to water quality can break, leading to water quality impacts impacts
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Stormwater Stormwater QualityQuality Impacts Impacts
Increased wash-off of pollutantsIncreased wash-off of pollutants
Increased water temperatureIncreased water temperature
Results in:Results in: Decrease in aquatic lifeDecrease in aquatic life
Loss of vegetationLoss of vegetation
Loss of healthy streams for recreationLoss of healthy streams for recreation
Declining quality of drinking water suppliesDeclining quality of drinking water supplies
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Stormwater Stormwater QualityQuality Impacts Impacts
Microbial Pollution
Trash & Debris
Transportation
Hydrocarbons
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Construction Site ControlsConstruction Site Controls Use of construction site controls protect water
quality
Left - stream drains farm/pastureRight - drains development area
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Design & Review FocusDesign & Review Focus
Locate streams, drainage patternsLocate streams, drainage patterns Delineate sub-basins for each phaseDelineate sub-basins for each phase Calculate flowsCalculate flows Calculate sediment storage requirementsCalculate sediment storage requirements Permanent vs temporary pondPermanent vs temporary pond Locate monitoring stationsLocate monitoring stations Maintenance planMaintenance plan
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ES&PC Sheets
Determine # phases of construction and ES&PC Plans
Prepare separate sheet for each phase
Clearly identify streams, state waters, wetlands, existing pipe outfalls, discharge points on each sheet
Identify limits of disturbance for each phase
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Delineation of Basins
Identify discharge points Determine drainage patterns based upon
grading plan for each phase Identify off-site drainage and drainage from
undisturbed areas Delineate drainage subbasins for each phase Determine area of each subbasin including
bypass drainage
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Calculations
Calculate sediment storage needed for each subbasin based on 67 cy per acre drained
Provide flow rates and/or runoff coefficients; use consistent methodology throughout various phases
Prepare table with subbasin areas Any storm drain system designed will be
prepared per design standards
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Sediment Storage
Determine location of temporary and permanent sediment ponds/structures
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Reviewer Focus
Check sheets against topo/aerial map Find streams, wetlands Does pattern make sense?
Check critical points of discharge; streams, structures, etc
Check slopes Check discharge points and off-site flows Calculations of sediment volume
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Base Plan Sheet (existing conditions, phase I E&S)
Locate all streams; name and label perennial, intermittent, ephemeral
Identify state waters, required protective buffers, floodplain limits, wetlands
Determine existing drainage basins and flow direction, include existing storm sewer pipe system
Delineate drainage basins Label receiving water bodies and discharge points Identify if stream is impaired (on Georgia 305b/303d
lists)
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Reviewer Focus #1
Verify state waters, buffers, floodplain limits, wetlands
Verify drainage basins using topo/aerial map Ensure all state waters are identified, labeled, &
protected w/ buffers Site visit, if necessary
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Reviewer Focus #2
Use approved plan review checklist to verify compliance
Look for critical areas where extra measures may be needed
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Delineation of Basins (phases II & III)
Identify discharge points on-site Determine drainage patterns based on Grading
Plan for each phase Identify and label off-site drainage and drainage
from on-site undisturbed areas Delineate drainage sub-basins for each phase Determine area of each sub-basin including
bypass drainage
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Reviewer Focus #3
Verify discharge points and check off-site flows Review topo map and verify drainage sub-basins Review construction activities in each phase and
in each sub-basin Mark areas of steep slopes and anticipate
location of sediment ponds and other BMPs
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Sediment Pond Determine location of temporary and permanent sediment ponds/structures
Permanent ponds can be used for sediment ponds in initial and intermediate phases
Sediment ponds are not perfect solution to sediment control; important to use other BMPs
Sediment ponds are most effective under smaller storm events
Permanent ponds are better at controlling sediment
Calculate sediment storage needed based on 67 C.Y. per disturbed acre
Calculate elevation of pond and label elevation of 1/3 storage volume. Provide note stating “Sediment shall be removed from the basin when 1/3 of the storage volume has been lost to sediment accumulation.”
Standpipe in sediment pond acts as 100-year overflow, determine top elevation
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Reviewer Focus #4
Verify sediment storage of 67 C.Y. per acre for entire drainage basin is provided
Verify use of excavated inlet protection, retrofitted detention ponds, or temporary sediment basins for sediment storage
Check elevation/storage table and verify 1/3 depth and 100-year discharge elevation
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Other BMPs
Use other measures with sediment ponds to protect during higher storm events Double silt fence with mulch Berm at downstream construction limits
Protect slopes with appropriate measures
Use applicable vegetative measures
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Reviewer Focus #5
Check slopes
Verify vegetative plan includes all temporary and permanent species with planting dates and seeding, fertilizer and mulching rates appropriate to seasons and region
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Calculations and Data to Provide Prepare table with sub-basin areas
Provide elevation/storage table for sediment storage needed for entire site based on 67 C.Y. per acre
Provide the 100-year hydrograph & flow rate using SCS methodology for Sd3 calculations
Calculate elevation of standpipe to route 100-year storm through sediment pond
Any storm drain system designed will be prepared per design standards
Outfall calculations including energy dissipaters, etc.
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Reviewer Focus #6
Verify chart is provided of storm drain pipe and weir discharge velocities
Verify outlet protection calculations to ensure discharges will not produce erosion
Check calculations of sediment volume
Calculations, stone size, dimensions of outlet protection must be shown
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Monitoring Stations
Goal – to determine increase in sediment due to site disturbance
Option #1 – place at all stormwater outfalls and final discharge points
Option #2 – place upstream and downstream of site, sample within receiving waters
Site may discharge to more than one receiving water body so provide equal # downstream monitoring stations
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Reviewer Focus #7
Verify monitoring stations are identified on plans
Verify each outfall/discharge point has monitoring station labeled (option #1)
Verify each receiving water body has monitoring station labeled (option #2)
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Helpful Tips for Designers Obtain checklist from GSWCC or local
government and use while designing
For pipe outfall design, provide junction box and short section on flat slope (1%) to be effective energy dissipater
Table of sub-basin acreage will help to quickly show what flows bypass and what is collected in a sediment pond
Identification of sub-basins and discharge points helpful in locating monitoring stations
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Helpful Tips for Designers
For large developments, may have discharge points in one phase that flows through unconstructed phase Convey by open channel; or Place into black, flexible pipe until next phase is
constructed Permanent ponds are more effective with less
chance of releasing sediment during high storm events
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Questions?