1

Stormwater Elements of Conservation Design for Huntsville

Industrial Park and the Use of Decision Analysis to Select

Appropriate Control Programs

Robert PittDepartment of Civil and Environmental Engineering

The University of AlabamaTuscaloosa, AL 35487

Stormwater Control Categories in the International Stormwater “BMP” Database:

Structural Controls:•Detention ponds•Grass filter strips•Infiltration basins•Media filters•Porous pavement•Retention ponds•Percolation trenches/wells•Wetland basins•Wetland channels/swales•Hydrodynamic devices

Non-Structural Controls:•Education practice•Recycling practice•Maintenance practice•Source controls

WinSLAMM Treatment PracticesInfiltration Trenches

Biofiltrat-ion/Rain Gardens

Cisterns/ rain

barrels

Wet detention

pond

Grass Drainage

Swale

Street Cleaning

Catch-basins

Porous Pavement

Drainage Discon-nection

RoofPaved parking/storageUnpaved parking/storagePlaygrounds

Drivew ays

Sidew alks/w alks

Streets/alleys

Undeveloped areasSmall landscaped areasOther pervious areasOther impervious areasFreew ay lanes/shouldersLarge turf areas

Large landscaped areas

Drainage system

Outfall

Plus, we now have upflow filters and hydrodynamic devices, and are working on other media filters and combination controls

WinSLAMM Summary Data Outputs• Runoff Volume (ft3, percent reduction; and Rv, runoff coefficient), particulate solids (lbs and mg/L), for:- source area total without controls- total before drainage system- total after drainage system-total after outfall controls

• Total control practice costs:- capital costs- land cost- annual maintenance cost- present value of all costs-annualized value of all costs

• Receiving water impacts due to stormwater runoff:- calculated Rv with and without controls- approximate biological condition of receiving water (good, fair, or poor)- flow duration curves (probabilities of flow rates for current model run and without controls)

2

Detailed Data Outputs for Each Event

Runoff Volume (ft3), source area contributions, particulate solids (lbs and mg/L), pollutants (lbs and mg/L)- by source area for each rain event- land use total- summary for all rains- total for land use and for each event- outfall summary, before and after drainage system and before and after outfall controls- Rv (runoff volume only)- total losses (runoff volume only)- calculated CN (runoff volume only)

3

Additional Details Available for Each Event (with summaries)

rain duration (hours), rain interevent period (days), runoff duration (hours), rain depth (inches), runoff volume (ft3), Rv, average flow (cfs), peak flow (cfs), suspended solids (lbs and mg/L)

The WinSLAMM batch editor can be used to automatically run a large number of files, usually for integration into a GIS-based map.

N

Stormwater Investigation City of Racine, Wisconsin

November, 2002

Critical Loading Rates

43247

RR07000

RR13000

NL03001

NL03002Nonreg

Nonreg

NL02000

NL03000

NL03003NL03004

NL03006

IW01000

NL03005

NL01000

NL05000NL08019

NL04000

NL06001

NL08018

NL08023

NL06002NL06003

NL06000

NL06004

NL08017

NL08015NL07000NL07001

NL08016

Nonreg

NL08000

NL08001

NL08004

NL08021

NL08022NL08020

NL08002

RR06000

RR03000

NL08006

NL08003

Nonreg

RR01000

RR06000 NL09000

NL08007 NL08005

NL08014

RR02000

NL08008

NL10002NL10001

NL10000

NL10003RR04000

NL08010NL08011

NL08009

RR46003

NL08012

RR46002

RR47002NL08013

RR47001

RR46004

RR53000

RR47000

NonregRR61000

RR08000

RR50000RR46001

RR22000

RR09000 NL11000

RR10000RR48000

RR46000

RR49000

RR51000

RR11000RR12003

RR15012RR12000

RR22001

RR15014

RR45000

RR44000RR57000RR21000

RR59000

SL12000RR12002

RR15013

RR58000RR14000

RR56000

RR16000

SL13000

RR55000

RR15005

RR52000RR43000

Nonreg

RR33000RR12001RR34000RR23000RR15000

RR17000

SL14000

RR54000

RR15006

RR15000

RR15010

RR24000

RR15011

RR25000

RR32000RR15001

RR18000RR15004 SL15000RR15002

RR15008RR35000

RR26000 SL16000

RR36000

RR15003 RR31000RR27000

RR19000

SL17000

RR15007

RR20000

RR36001RR20001RR15016

RR28000

RR15009

RR29000

RR38000RR30000

RR37001

RR15017

RR60000

RR41000

RR40000

SL17001RR42000

RR37002RR39000RR37000

RR37003

RR36002RR37004

SL17002

RR37005RR37006

RR37007RR37008

SL19005

RR40001RR37009

RR37010

SL19003

RR37011 SL25000

SL18000

RR37012

RR37013

SL19002

RR37014

RR37030

SL19004

RR37015 SL19000

RR37016SL19001

SL19006

RR37017

SL23019

RR37018RR37019

PR12000

Nonreg

RR37021

SL20000

SL23004

SL22001SL23016 SL23015 SL21000

RR37022

SL23032RR37023

RR37024

RR37025

SL23035

PR08001

SL23033

SL23017RR37026

PR07000

SL23018

PR08001SL23028

RR37027

RR37028

SL22000

SL23002PR08002 SL23002

SL23000

SL23005

PR08000

SL23034SL23002PR08003

SL23013

SL23036

SL23029 SL23006SL23030

SL23014

SL23008

RR37029

SL23007

SL23012 SL23003

SL23001

SL23020SL23021SL23001

SL23011SL23027

SL23010SL23011

SL23023

SL23024

SL23025

PR02000

SL23022

SL23023

SL23024SL23024SL23026

PR01000

SL24001

PR06004PR06004

PR03000

PR06003

PR06000

SL23024

PR06001

PR06004

PR09000

Nonreg

Nonreg

PR06002PR10000

PR11000PR05000

PR04000

Nonreg

1600 0 1600 3200 4800 Feet

Corporate LimitsWaterSubbasins

Critical Loading RatesHighMHModerateMLLow

$ 8.7444%1810829145306855501704215207843193328Cost Example - P 50 percent

$ 8.7418%7243325812234220681686307614425257Cost Example - P 20 percent

$ 1.2440%2325151865891000119109223413136146Cost Example - G

n/a0%00000374135246545Cost Example -Base Case No Controls

Cost per lb

Sediment Reduced

% Part.

Solids Reduc.

Sub Basin Total

Present Value Cost

Sub Basin Total

Annual Cost

Sub Basin Maint. Cost

Sub Basin Land Cost

Sub Basin

Capital Cost

Partic. Solids Yield (lbs)

Runoff Volume

(cf)

File Name

WinSLAMM can also calculate life-cycle costs and compare different control programs to obtain unit removal costs with the batch processor: Decision Analysis

• With so much data available, and so many options that can be analyzed, how does one select the “best” stormwater control program?

• The least costly that meets the objective?

4

Possible, if only have one numeric standard:

If 80% SS reduction goal, the least costly would be wet detention. In this example, grass swales, street cleaning, and catchbasins cannot reach this level of control. If 40% SS reduction goal, then grass swales wins.

If multiple goals, then possibly not as clear and need a more flexible approach. Consider the following example (a conservation design industrial park in Huntsville, AL):

Conservation Design Elements for Huntsville Industrial Park

• Grass filtering and swale drainages• Wet detention ponds• Bioretention and site infiltration devices• Critical source area controls• Pollution prevention through material

selection

Grass Filtering of Stormwater Sediment

5

Runoff from Pervious/

impervious area

Trapping of sedimentsand associated pollutantsReducing velocity of

runoff

Infiltration

Reduced volume and treated runoff

Sedimentparticles

Particulate Removal in Shallow Flowing Grass Swales and in Grass Filters

WinSLAMM Input Screens for Grass Swales

Typical stable grass swales (wide and shallow) Grass Swales Designed to Infiltrate Large Fractions of Runoff (AL and OR).

Also incorporate grass filtering before infiltration

6

Swales can be both interesting and fit site development objectives.

WI DNR photo

Conventional curbs with inlets directed to site swales

Head (0ft)

2 ft

25 ft

6 ft

3 ft

116 ft75 ft

Test Date: 10/11/2004

Zoysia grass swale

Blue grass

0

200

400

600

800

1000

1200

0 1 2 3 4 5 6distance (ft)

Tota

l Sus

pend

ed S

olid

s(m

g/L)

1%_10gm1%_15gm1%_20gm3%_10gm3%_15gm3%_20gm5%_10gm5%_15gm5%_20gm

Head works

7

PSD 11-11-04

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10 100 1000

Particle size (um)

Volu

me

(%)

0ft 2ft3ft6ft25ft75ft116ft

TSS: 153 mg/L (head)

Decreasing particle sizes with flow distance

Particulate trapping in grass filters (high initial concentrations and shallow flows)

Wet Detention Ponds

3.0 (approximate maximum pond elevation, or as determined based on flood flow analysis). Additional storage and emergency spillway may be needed to accommodate flows in excess of the design flood flow.

9

2.5 (invert elevation of flood flow broad-crested weir). Normal maximum elevation during one and two year rains.

8271.56

1.0 (normal pool elevation, and invert elevation of 30o v-notch weir)

50.7540.530.2520.151

Full-Sized Pond Area (acres)

Pond Elevation

(ft)

Wet Detention Pond to Treat Runoff from Area

8

Suspended Solids Control at Monroe St. Detention Pond, Madison, WI (USGS and WI DNR data)

Consistently high TSS removals for all influent concentrations (but better at higher concentrations, as expected)

Infiltration/Biofiltration

• Infiltration trenches• Infiltrating swales• Infiltration ponds• Porous pavement• Percolation ponds• Biofiltration areas (rain gardens, etc.)

9

Porous paver blocks have been used in many locations to reduce runoff to combined systems, reducing overflow frequency and volumes (Germany, Sweden, and WI).

Small depressions graded near parking lots or buildings for infiltration (older method, using regular turf grass) (MD and WI).

Parking lot medians easily modified for bioretention (OR and MD).

WinSLAMM Input Screen for Biofilters

10

Parking lot bioretention areas for roof runoff and paved area runoff reduction (Portland, OR).

Bioretention area overflow directed to conventional storm drainage system.

Groundwater ContaminationThe potential for groundwater contamination associated

with stormwater infiltration is often asked.

Book published by Ann Arbor Press/CRC, 219 pages. 1996, based on EPA research and NRC committee work.

Road cut showing direct recharge of Edwards Aquifer, Austin, TX

http://civil.eng.ua.edu/~rpitt/Publications/BooksandReports/Groundwater%20EPA%20report.pdf

Infiltration Rates in Disturbed Urban Soils (AL tests)

Sandy Soils Clayey Soils

Field measurements have shown that the infiltration rates of urban soils are strongly influenced by compacted, probably more than by moisture levels.

11

Soil Modifications and Rain Gardens

Proper design will minimize groundwater contamination potential

Critical Source Area Control

Multi-Chambered Treatment Train for large critical source area control Pilot-Scale MCTT Test

Results

12

Wisconsin Full-Scale MCTT Test Results

>75 (<0.2 µg/L)98 (<0.05 µg/L)Pyrene

>65 (<0.2 µg/L)99 (<0.05 µg/L)Phenanthrene

>75 <0.1 µg/L)>95 (<0.1 µg/L)Benzo (b) fluoranthene

90 (15 µg/L)91 (<20 µg/L)Zinc

nd (<3 µg/L)96 (1.8 µg/L)Lead

65 (15 µg/L)90 (3 µg/L)Copper

>80 (<0.1 mg/L)88 (0.02 mg/L)Phosphorus

85 (10 mg/L)98 (<5 mg/L)Suspended Solids

Minocqua (7 events)

Milwaukee (15 events)

(median % reductions and median effluent quality)

Upflow filter insert for catchbasins

Able to remove particulates and targeted pollutants at small critical source areas. Also traps coarse material and floatables in sump and away from flow path.

Upflow FilterTM patent pending

Pelletized Peat, Activated Carbon, and Fine Sand

y = 2.0238x0.8516

R2 = 0.9714

0

5

10

15

20

25

0 5 10 15 20

Headloss (inches)

Flow

(gpm

)

Pollution Prevention through Substitution of Building Materials

• Pavement• Treated wood• Roofing materials

13

Total: 12,200

Dissolved: 11,900

Total: 302Dissolved:

35

Not given Rusty galvanized roof

< 17< 17Total: 166Dissolved:

128

Built-up roof (plywood + roofing paper/tar)

LeadZincCopper

Roof Runoff Concentrations

(µg/L)

The Source Loading and Management Model (WinSLAMM)

• Developed during past 25 years during EPA, state, and Canadian funded research.

• Identifies pollutant sources during different rain and climatic conditions.

• Prioritizes subwatersheds and critical source areas.

• Evaluates alternative development scenarios, pollution prevention, and combinations of source area and outfall control options.

A lot of stormwater flow and quality data has been collected during past several decades

It is straight-forward and important to compare these observations with model assumptions

14

Major Stormwater Controls Currently Available with WinSLAMM (in addition

to development options)• Public works practices (street and catchbasin

cleaning, grass swales)• Biofiltration (french drains, infiltration

trenches, bioretention, rain gardens, percolation ponds, etc.)

• Sedimentation (hydrodynamic devices, wet detention ponds, etc.)

• Beneficial uses (rain barrels, cisterns, and pond storage for irrigation or other use)

Additional Controls and Processes being Added Based on Recent and On-

going Research• Treatment trains• Media filtration (both upflow and conventional

filters)• Multiple ponds• Grass filters• Evapotranspiration and multiple soil layers• Interfacing with SWMM (replacement of

RUNOFF block) for detailed drainage system hydraulics

Huntsville Industrial Park Main Drainage Subareas

• Roofs (directly connected): 18.4 acres• Paved parking (directly connected): 2.3 acres• Streets (1.27 curb-miles): 3.1 acres • Small landscaped areas (B or sandy-loam soils, but assumed silty soils due to compaction): 10.0 acres• Large undeveloped area (B or sandy-loam soils, but assumed silty soils due to compaction): 60.2 acres• Isolated areas (sinkholes): 4.6 acres

Subarea A site characteristics:

15

On-site bioretention swales:

These small drainages collect the on-site water from the paved parking and roofs and direct it to the large natural swales. These were assumed to have the following general characteristics: 200 ft long, with 10 ft bottom widths, 3 to 1 (H to V) side slopes (or less), and 2 inches per hour infiltration rates. One of these will be used at each of the 6 sites on the eastern edge of this subarea.These swales will end at the back property lines with level spreaders (broad crested weirs) to create sheetflow towards the large drainage swale, if possible.

Large regional drainage swale:

There is one long regional drainage swale in this subarea that collects the sheetflows from the bioretention swales from each site and directs the excess water to the ponds on the southern property edge. This swale is about 1700 feet long, on about a 2.6% slope, and will be 50 ft wide. It will also have 3 to 1 (H to V) side slopes, or less, and have 1 inch per hour infiltration rates. The bottom of the swale will be deep vibratory cultivated during proper moisture conditions to increase the infiltration rate, if compacted. This swale will also have limestone check dams every 100 ft to add alkalinity to the water and to encourage infiltration. The vegetation in the drainage should be native grasses having deep roots and be mowed to a height of about 6 inches, or longer. Any cut grass should be left in place to act as a mulch which will help preserve infiltration rates. The swale should have a natural buffer on each side at least 50 ft wide. Any road or walkway crossings over the grassed waterway areas should be on confined to a narrow width.

Wet detention pond:

A wet detention pond will be located across the main road next to the southern property boundary. The runoff from the totally connected and curb and gutter drained industrial area in the southwest corner of the site will enter the pond directly opposite from the discharge point. The regional swale will also direct excess water into the pond far from the discharge point.

Calculated Performance of Stormwater Options using Typical Rain Year (1976): Subarea A Example

2,230 (97)191.85 x 106 (72%)Pond, swale, and site bioretention

4,500 (95)371.97 x 106 (65%)Small pond, swale, and site bioretention

3,030 (96)182.69 x 106 (52%)Pond and swale

35,100 (59)1902.93 x 106 (48%)Swale only

5,740 (93)332.81 x 106 (47%)Small pond and swale

70,600 (18)2704.17 x 106 (24%)Site bioretention only

7,640 (91)235.34 x 106 (5%)Pond only

86,3002505.60 x 106Base conditions (no controls)

Particulate Solids Yield (lbs/year) (% reduction compared to base conditions)

Particulate Solids Concentration (mg/L)

Runoff Volume (ft3/year) (% reduction compared to base conditions)

Stormwater Control Options

16

11 x 106 (56%)25 x 106Total site

5.8 x 106 (50%)11 x 106Off-site pond, swale, and site bioretention

D (including off site area)

0.83 x 106 (68%)2.5 x 106Pond and swaleC

1.7 x 106 (69%)5.4 x 106Small pond and swaleB

2.5 x 106 (61%)6.3 x 106Pond, swale, and site bioretention

A

With ControlsBase Conditions

Proposed Stormwater Components

Drainage Area

Runoff Volume (ft3/year)

26180Total site

26160Off-site pond, swale, and site bioretention

D (including off site area)

8120Pond and swaleC

37160Small pond and swaleB

28250Pond, swale, and site bioretention

A

With Controls

Base Conditions

Proposed Stormwater Components

Drainage Area

Particulate Solids Concentration

(mg/L)

19,000 (93%)

290,000Total site

9,250 (92%)

120,000Off-site pond, swale, and site bioretention

D (including off site area)

1,200 (94%)

19,000Pond and swaleC

3,800 (93%)

54,000Small pond and swaleB

4,400 (96%)

98,000Pond, swale, and site bioretention

A

With Controls

Base Conditions

Proposed Stormwater Components

Drainage Area

Particulate Solids Discharge (lb/year)

Sediment Reductions

Volume Reductions

17

1) Specific criteria or limits that must be met.

It is possible to simply filter out (remove) the options that do not meet all of the absolutely required criteria. If the options remaining are too few, or otherwise not very satisfying, continue to explore additional options. The above examples only considered combinations of 3 types of stormwater control devices, for example. There are many others that can also be explored. If the options that meet the absolute criteria look interesting and encouraging, then continue.

Decision Analysis Approaches

2Yes9445,698Option 8Small pond, reg. swale and biofilter

1Yes9040,217Option 7Small pond and reg. swale

4Yes9754,622Option 6Pond, reg. swale and biofilter

3Yes9449,142Option 5Pond and reg. swale

n/aNo7374,439Option 4Half-sized pond

n/aNo169,710Option 3Site Biofilter

n/aNo5530,008Option 2Regional Swale

5Yes8683,364Option 1Pond

Rank based on annual

cost

Meet 80% particulate solids reduction goal?

Reduction in SS Yield (%)

Total Annual Cost ($/yr)

Stormwater Treatment Option

Control Options Meeting 80% SS Reduction Requirement, Ranked by Cost

2) Goals that are not absolute (based on methods developed by Keeney, R.L. and H. Raiffa. 1976. Decision Analysis with Multiple Conflicting Objectives. John Wiley & Sons. New York.)

Utility curves and tradeoffs can be developed for the remaining attributes, after all the absolutely required goals are met. Theabove example includes attributes of several different types:

- costs- land requirements- runoff volume (volumes, habitat responses, andrates)

- particulate solids (reductions, yields and concentrations)

- particulate phosphorus (reductions, yields and concentrations)

- total zinc (reductions, yields and concentrations) Sum = 1.0

0.1245.5 to 25 lbs/yrPart. Phosphorus yield (lbs/yr)

0.0762,183 to 10,192 lbs/yr

Particulate solids yield (lbs/yr)

0.1830 to 0.05 %% of time flow >10 cfs0.0570.5 to 4 %% of time flow >1 cfs0.3010.06 to 0.29Rv 0.0852.3 to 4.5 acresLand needs (acres)

0.202$40,217 to 83,364Total annual cost ($/year)

Trade-offs between

remaining attributes

Attribute ranks for selection

(after absolute goals are met)

Range of attribute value for acceptable

options

Attribute

Attribute Value Ranges, plus Example Ranks and Trade-offs(ranks and trade-offs could vary for different interested parties)

18

• Volumetric runoff coefficient (Rv) as an indicator of habitat quality and aquatic biology stress:

Attribute Expected UtilityValue Habitat Value

Condition

<0.1 Good 1.00.1 to 0.25 Fair 0.750.26 to 0.50 Poor 0.250.51 to 1.0 Really lousy 0

Utility Curves for Different Attributes (technically based, would not vary for different interested parties)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 10 100

Directly Connected Imperv Area (%)

Rv

(san

dy s

oils

)

Relationship Between Directly Connecting Impervious Area (%) and the Calculated Rv for Each

Soil Type

00.10.20.30.40.50.60.70.80.9

1

1 10 100Directly Connected Impervious Area (%)

Rv

Sandy Soil Rv Silty Soil Rv Clayey Soil Rv

GoodFair

Poor

• Total annual cost: straight line, with $83,364 = 0 and $40,217 = 1.0.

• % of time flow >10 cfs Utility value

<0.05 1.00.05 - 1 0.751.1 – 2.5 0.25>2.5 0

Example Utility Values for Other Attributes:

19

• Part. Phosphorus yield (lbs/yr): straight line, with 25 lbs/yr = 0 and 5.5 lbs/yr = 1.0

• Land needs (acres): straight line, with 4.5 acres = 0 and 2.3 acres = 1.0

• Particulate solids yield (lbs/yr): straight line, with 10,192 lbs/yr = 0 and 2,183 lbs/yr = 1.0

• % of time flow >1 cfs Utility value<1 1.01 – 3 0.753.1 – 10 0.25

>10 0

Example Utility Values for Other Attributes (cont):

0.77100.764,12512.30.8745,698Option 8Small pond, reg. swale and biofilter

0.41170.416,93712.3140,217Option 7Small pond and reg. swale

1.05.51.02,18304.50.6754,622Option 6Pond, reg. swale and biofilter

0.77100.764,13304.50.7949,142Option 5Pond and reg. swale

025010,19204.5083,364Option 1Pond

0.120.070.080.20Tradeoff Value

Phos.utility

Part. Phos. Yield

(lbs/yr)

Part. Solids utility

Part. Solids Yield

(lbs/yr)

Land utility

Land Needs for SW

mgt (acres)

Cost utility

Total Annual

Cost ($/yr)

Stormwater Control Option

Attribute Values and Associated Utilities for Example

1.001.00.81.00.07Option 8Small pond, reg. swale and biofilter

0.750.050.7520.750.15Option 7Small pond and reg. swale

1.001.00.51.00.06Option 6Pond, reg. swale and biofilter

1.000.7520.750.15Option 5Pond and reg. swale

0.750.050.2540.250.29Option 1Pond

0.180.050.30Tradeoff Value

High flow utility

% of time flow >10

cfs

Mod flow

utility

% of time

flow >1 cfs

Rv utilityVolumetric Runoff

Coefficient (Rv)

Stormwater Control Option

Attribute Values and Associated Utilities for Example (cont.)

0.0920.770.0530.760.0810.1740.87Option 8Small pond, reg.

swale and biofilter

0.0490.410.0290.410.0810.201Option 7Small pond and

reg. swale

0.121.00.071.0000.1340.67Option 6Pond, reg. swale

and biofilter

0.0920.770.0530.76000.1580.79Option 5Pond and reg.

swale

00000000Option 1Pond

0.120.070.080.20Tradeoff Value

Phosfactor

Phos. utility

Part. factor

Part. utility

Land factor

Land utility

Cost factor

Cost utility

Stormwater Control Option

Calculation of Factors for Each Option(Attribute Utility times Attribute Trade-off)

20

10.92900.181.00.051.00.301.0Option 8Small pond, reg. swale and biofilter

30.75550.1350.750.03750.750.2250.75Option 7Small pond and reg. swale

20.85400.181.00.051.00.301.0Option 6Pond, reg. swale and biofilter

4 0.74550.181.00.03750.750.2250.75Option 5Pond and reg. swale

50.22250.1350.750.01250.250.0750.25Option 1Pond

0.180.050.30Tradeoff Value

Over-all

Rank

Sum of factors

High flow

factor

High flow

utility

Mod flow

factor

Mod flow

utility

Rv factor

Rv utility

Stormwater Control Option

Calculation of Factors for Each Option (cont.), Sum of Factors, and Overall Rank Conclusions

• Calibrated and verified stormwater models can be used to develop a great deal of information concerning many different stormwater management options.

• Regulations and criteria also need to have different formats to acknowledge site specific problems and objectives.

• The use of clear and flexible decision analysis techniques, as outlined in this presentation, is therefore important when selecting the most appropriate stormwater control program for a site.

Pitt, et al. (2000)

• Smallest storms should be captured on-site for reuse, or infiltrated

• Design controls to treat runoff that cannot be infiltrated on site

• Provide controls to reduce energy of large events that would otherwise affect habitat

• Provide conventional flood and drainage controls

Combinations of Controls Needed to Meet Many Stormwater Management Objectives Acknowledgements

The authors would like to acknowledge the support of the Tennessee Valley Authority (TVA), Economic Development Technical Services, and the Center for Economic Development and Resource Stewardship (CEDARS) of Nashville, TN, which has allowed us to develop extensions to WinSLAMM to enable the use of a decision analysis framework in evaluating alternative stormwater management options. The Stormwater Management Authority of Jefferson County, AL, is also acknowledged for their recent support that enabled the cost analyses to be added to WinSLAMM