1 Stormwater Management Issued May 2009 Level II: Introduction to Design Education and Certification...

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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 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



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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





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Stormwater and UrbanizationStormwater and Urbanization

Arrow lengths Arrow lengths indicate indicate increase/decreaseincrease/decrease

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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 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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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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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?

1 Stormwater Management Issued May 2009 Level II: Introduction to Design Education and Certification...

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