Introduction

5 Case Studies

Impervious Cover (%) for Various Land

Uses [2]

Low Density Residential

10

Medium Density

Residential30

High Density Residential

40

Multifamily 60

Industrial 75

Roadway 80

Commercial 85

“impervious surfaces are responsible for more stormwater runoff than any other type of land use”[1]…

[1] EPA, 2000: Low Impact Development (LID) - A Literature Review. EPA-841-B-00-005, Office of Water, Washington, D.C. [2] http://www.stormwatercenter.net/monitoring%20and%20assessment/simple%20meth/simple%20imp%20table%205.htm

StormwaterQuality

Three paving materials

0.30-0.70

0.18- 0.29

0.03

Interlocking pavers

Porous asphalt

Porous concrete

Manning’s n Runoff Coefficient

Stormwater Quantity

Four Sites

1%

1%

1%

1%

Objective: evaluate various surface materials in urban parking areas to reduce stormwater runoff and annual pollutant loads

Pennsylvania Stormwater Management Manual

Definition:“Porous pavement is a permeable asphalt or concrete surface that allows stormwater to quickly infiltrate to an underlying stone reservoir”

0

5

10

15

20

25

30

35

40

1691.363498 1457.347183 1276.690915 1139.260699 1099.274109 1024.694395

Tr avel time (s)

Congress Porous

Congress Pavers

Burnet porous

Burnet pavers

7th St porous

7th St pavers

Riverside porous

Riverside

Peak Flow

As Tt=Tc increases peak runoff decreases

Q = CiARational Method

•widely used for small urban drainage area•required limited data

Pea

k F

low

(cf

s)

Travel TimeTc= Tt for only one segment

Ferguson, B. 2005. Porous Pavements. CRC Press http://www.dep.state.fl.us/water/nonpoint/docs/erosion/chapter3.pdf

“Travel time ( Tt ) is the time it takes water to travel from one location to another in a watershed”.

Length of Flow Path

434.73 ft

695.10 ft

632.33 ft

509.67 ft

S Congress

E 7th Street

Burnet Road

E. Riverside Dr

695.10 ft

632.33 ft

509.67 ft

632.33 ft

y = 0.5716x + 0.0186

0.00

0.05

0.10

0.15

0.20

0.25

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Length of Flow

Tra

vel

Tim

e

Depth of precipitation (in)

Tim

e of

Tra

vel (

hr)

Recurrence interval 2yr

Annual load (L)

TN TP TSS Zn Cu

(lbs) (lbs) (lbs) (lbs) (lbs)

S Congress 54.49 10.32 4704.94 1.59 0.25

Burnet Rd 63.83 12.08 5511.53 2.16 0.30

E. Riverside Dr 38.27 7.25 3304.65 1.02 0.16

E 7th St 70.70 13.38 6104.58 2.12 0.34

Annual Pollutant Loads

Pollutant concentration: STORMWATER RUNOFF QUALITY AND QUANTITY FROM SMALL WATERSHEDS IN AUSTIN, TX, City Of Austin, Watershed Protection Department, Environmental Resources Management Division, Water Quality Report Series, COA-ERM/WQM 2006-1, November 1, 2006

L = 0.226 * R * C * ASimple Method

•“No significant relationship was found for total suspended sediment based on impervious cover or development condition”

•TP and TN: impervious cover ranges: 0-1% and 5-100%

Water Quality VolumeArea

632,397.80 ft2

621,467.95 ft2

667,667.02 ft2

658,754.68 ft2

S Congress93,5788.57 ft2

E 7th Street1,706,624.16 ft2

Burnet Road1,051,130.49 ft2

E. Riverside Dr902,001.86 ft2

Water Quality Volume WQv

Proposal Actual

(ft3) (ft3)

S Congress 5,777.33 6,441.34

Burnet Rd 6,582.74 7,235.28

E. Riverside Dr 5,517.09 6,208.78

E 7th St 6,711.28 7,412.33

Average 10% reduction in WQv with decrease impervious surfaces

Depth of gravel bed/reservoir S Congress Burnet Rd E. Riverside Dr E 7th St

(in) (feet) (ft3) (ft3) (ft3) (ft3)

6 0.5 126,479.56 124,293.59 131,750.94 133,533.40

12 1 252,959.12 248,587.17 263,501.87 267066.81

An average increase of 21% of WQv

New York State Stormwater Management Design Manual

Porous Concrete Dense Asphalt Porous Asphalt Interlocking Pavers

$ 4.00 $ 0.75 $ 1.00 $ 3.50

S Congress $2,529,591.20 $ 474,298.35 $ 632,397.80 $2,213,392.30

Burnet Rd $2,485,871.79 $ 466,100.96 $ 621,467.95 $2,175,137.82

E. Riverside Dr $2,635,018.70 $ 494,066.01 $ 658,754.68 $2,305,641.37

E 7th St $2,670,668.08 $ 500,750.27 $ 667,667.02 $2,336,834.57

note: Average price per ft2 from EPA, Dr. Barrett, City of Seattle Department of Planning and Development and City of New York;base/storage bed not included in cost estimate.http://www.ci.austin.tx.us/watershed/rsmp_fee_com-mf.htm

on average a 33% increase

•Regional Stormwater Management Participation Fees

•“the number of impervious acres…based on the maximum

allowable impervious cover”

•BMP’s

•Land

Costs! / Incentives?

•Maintaining flow path lengths• Regulation

•Reduce stormrunoff and increase water quality

•Disconnecting impervious surfaces •Porous surfaces

END

Preliminary Conclusions

L = 0.226 * R * C * A

L= Annual load (lbs)P= Pollutant Concentration A= Area (acres)R= Annual Runoff (inches)

Annual rainfall

P

(in)

1990 28.44

1991 52.21

1992 46.05

1993 26.05

1994 41.16

1995 33.98

1996 29.56

1997 47.04

1998 39.11

1999 23.93

2000 37.96

2001 42.9

2002 35.98

2003 21.43

2004 52.27

2005 22.33

2006 34.6

2007 46.95

36.775

*NOAA:National Weather Service

R = P * Pj * Rv

P= Annual Rainfall (in)Pj= Fraction of year rainfall events that produce runoff 0.9Rv= Runoff Coefficient

Rv=0.05+0.9Ia

Ia= Fraction of impervious cover

Simple Method

Rv=0.05+0.9Ia

Ia= Fraction of impervious cover

WQv=Water Quality Volume (ft3)A= Total Area (ft2)P= 90% Rainfall event (inches) 1.4 in for Austin

Ap= Porous Pavement Surface (ft2)n=Porosity of bed gravel (0.4)dt=Depth of gravel bed/reservoir (ft)WQv=Water Quality Volume (ft3)

New York State Stormwater Management Design Manual