Stormwater Management

Stormwater Management Level II: Introduction to Design Education and Certification for Persons Involved in Land Disturbing Activities Issued May 2009

Stormwater Management • Stormwater Runoff • Urbanization • Stormwater Controls • Design and Review Focus

What is Stormwater Runoff? • Stormwater is… • Rain that hits the earth’s surface • Stormwater Runoff is… • Rain that runs off hardened surfaces

Stormwater Runoff “Non-Point Source” Pollution • Stormwater runoff picks up pollutants as it runs off impervious surfaces • Oils/Grease • Metal Particles • Pesticides • Pet Wastes/Pathogens • Nutrients • Excessive Sediment Stormwater runoff is the real problem

Erosion and Sedimentation • Sediment is the #1 nonpoint source of water pollution • Erosion causes additional problems • Loss of property • Degradation of streams

Start at the Source • Uncontrolled construction sites dump huge amounts of sediment downstream

Common Misconception • Stormwater from roads and construction sites is directed to storm drains • Stormwater that enters a storm drain gets treated • Where does it really go?

The Truth Is… Stormwater usually receives no treatment at all It goes to the nearest stream!

Impacts of Sedimentation Bare soil easily washes into storm drains and into streams, clouding the water and suffocating aquatic life.

Impacts of Sedimentation Sediments can block culverts and displace flood waters

What’s All the Fuss ? 3% of Earth’s water is freshwater < 1% Earth’s freshwater is potable – limited resources 40% of streams are not clean enough for fishing and swimming

Problem: Stream Pollution

Goal: Clean Healthy Streams

Penalties Builder ordered to pay $2.3 million over storm runoff“A Cobb County jury this week slapped a builder with what may be the largest judgment in a storm water pollution case in Georgia history.” The Atlanta Journal-Constitution 05/12/05

Growth and Development Urbanization happens…

Urbanization Understanding stormwater impacts due to Urbanization Source: District-Wide Watershed Management Plan-Preliminary Draft, Metropolitan North Georgia Water Planning District, March 10, 2003.

Back to Basics Rainfall Infiltration Evapotranspiration Runoff

Stormwater and Urbanization As land is developed: Ground is compacted - less water can naturally infiltrate Less trees and less evapotranspiration MORE stormwater runs off

Stormwater and Urbanization • Arrow lengths indicate increase/decrease

From “River of Fire” to Clean Water Act Cuyahoga River 1949-1969

Stormwater Management Stormwater Quality – “how good” Stormwater Quantity – “how much” Quantity is directly related to … Quality

What’s It All About? Remember… Streams, streams, streams

Stormwater Quantity Impacts StableChannel Downcutting Widening Sedimentation Stable, Entrenched Pre- to Post-Development

Stormwater Quantity Impacts Impervious surfaces cause higher runoff volume High velocity stormwater runoff causes stream erosion Stream erosion causes habitat and property loss

Stormwater Quantity Impacts Downcutting exposes sewer lines that can break, leading to water quality impacts

Stormwater Quality Impacts Increased wash-off of pollutants Increased water temperature Results in: Decrease in aquatic life Loss of vegetation Loss of healthy streams for recreation Declining quality of drinking water supplies

Stormwater Quality Impacts Microbial Pollution Transportation Hydrocarbons Trash & Debris

Construction Site Controls • Use of construction site controls protect water quality Left - stream drains farm/pastureRight - drains development area

Design & Review Focus • Locate streams, drainage patterns • Delineate sub-basins for each phase • Calculate flows • Calculate sediment storage requirements • Permanent vs temporary pond • Locate monitoring stations • Maintenance plan

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

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

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

Sediment Storage • Determine location of temporary and permanent sediment ponds/structures

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

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)

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

Reviewer Focus #2 • Use approved plan review checklist to verify compliance • Look for critical areas where extra measures may be needed

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

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

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

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

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

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

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.

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

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

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)

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

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

Questions?

Stormwater Management