Protecting Water Resources with Higher-Density Development

Lynn Richards. 2006. EPA 231-R-06-001

25.0

12.5

6.33.1 1.6 0.8 0.4

0.0

5.0

10.0

15.0

20.0

25.0

4 8 16 32 64 128 256

Acres/100 units

DUA Ia

4 0.3

8 0.45

16 0.60

32 0.70

64 0.80

128 0.90

256 1.00

DUA

Tysons Corner, VA 1DUA

Houston, TX 4-5 DUA

8-9 DUA

Civano, Tuscon. 18DUA

New Orleans, French Quarter, 38 DUA

Dallas—Mockingbird Station, 64 DUA

199 DUA

4

8

16

32

64128

256

-

20,000

40,000

60,000

80,000

100,000

120,000

0 50 100 150 200 250 300

cf/a

cre

/ye

ar

DUA

Runoff Volume per acre versus DUA

0

2

4

6

8

10

12

14

16

18

20

4 8 16 32 64 128 256

lbs/

year

/acr

e

DUA

Pollutant Load (lbs/year/acre)

TN

TSS/100

TP

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200 250 300

Runoff Volume per 100 unitscf

÷1

00

0/1

00

un

its/

ye

ar

0

20

40

60

80

100

120

4 8 16 32 64 128 256

lbs

TN/1

00

un

its/

year

DUA

TN per 100 Units

20%20%20%20%20%20%20%20%20%20%20%20%

0 20 40 60 80 100 120

lower

Stormwater Dry Ponds

upper

lower

Stormwater Wetlands

upper

lower

Infiltration Practices

upper

lower

Water Quality Swales

upper

TSS

TP

TN

BMP % Pollutant Removal, median, 25th and 75th percentilesNational Pollutant Removal Performance Database, Center for Stormwater Protection, 2007

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

4 8 16 32 64 128 256

DUA

%Reduction Runoff Volume versus 4DUA

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

4 8 16 32 64 128 256

Pe

rce

nt

load

re

du

ctio

n

DUA

% Load Reduction, Density vs. 4DUA

TN

TP

TSS

-80%

-60%

-40%

-20%

0%

20%

40%

60%

80%

100%

120%

4 8 16 32 64 128 256

% r

ed

uct

ion

ve

rsu

s 4

DU

A

DUA

% Load Reduction for TN, Density versus 4DUA

High Ia

EMC Default

High EMC and Ia

Henry David Thoreau

Jennifer Lorenz

Good

Fair

Poor

Watershed Impervious

Cover

Str

eam

Qu

ality

Urban Drainage

Impervious Cover Model

10% 25% 40% 60% 100%

Center for Watershed Protection

Good

Fair

Poor

Watershed Impervious

Cover

Str

eam

Qu

ality

Urban Drainage

Impervious Cover Model

10% 25% 40% 60% 100%

Center for Watershed ProtectionDwelling Units per Acre

Urb

an

ity

0.001 0.1 2 4 6 8 32 64 100+

Good

Fair

Poor

Str

eam

Qu

ality

maximum repair—LID etc

Urb

an

ity

Dwelling Units per Acre

0.001 0.1 2 4 6 8 32 64 100+

Impervious Cover Model