JAWRA - Stormwater Runoff

• Project Type: General OWC
• Title: Stormwater Runoff Quality and Quantity from Traditional & Low Impact Development Watersheds
• Date: 12/15/2009
• Water Conservation - Doc Type: Reports

SEDAN AND CLAUSEN
16 times (p < 0.001) based on values predicted by the
calibration equation (Table 3). Increased runoff dur-
ing the postconstruction period was likely due to the
stormwater drainage system and the impervious
asphalt road. These systems are designed to provide
quick, safe, and efficient transport of stormwater in
urban areas (Tourbier, 1994; Wagner and Geiger,
1996; Chocat et al., 2001). Urbanization generally
results in increased impervious surfaces and storm -
water drainage systems that will increase the total
flow of discharges (Leopold, 1968; Laenen, 1980;
Schueler, 1994).
Low Impact Development Watershed. A signif-
icant (p < 0.001) decrease of 42% in the weekly storm
flow depth from the LID watershed was observed
during the postconstruction period (Table 4). Figure 4
shows that storm flow decreased across the full range
of values observed. As indicated by the regression
lines, for a given flow from the control watershed, the
flow from the treatment watershed declined from cali-
bration to treatment periods. The scatter in paired
weekly values shown in Figure 4 is expected. Such
scatter could be reduced by aggregating data into
longer time periods. These results are consistent with
studies of individual LID practices that have shown
reductions in :storm flow using permeable pavement
(USEPA, 1993a; Brattebo and Booth, 2003),
decreased imperviousness (Urbonas, 1994), and vege-
tated swales (USEPA, 1993a; Rushton, 2001). Grass
swales and pervious pavers can provide the control of
runoff and peak discharge (USEPA, 1993a). The
reduction in storm flow observed in this study was
similar to that observed by Rushton (2001) who found
a 50% reduction with permeable pavement and grass
swales in a parking lot. Grass swales alone reduced
storm flow by 30% when compared with impervious
pavement (Rushton, 2001). Brattebo and Booth (2003)
reported essentially no runoff from four types of per-
meable pavement after 570 mm of total rainfall dur-
ing a six -year study in Seattle, Washington.
During the postdevelopment period after 19 June
2003, mean annual runoff from the traditional
watershed was 36.6 cm, while runoff from the LID
watershed was only 8.6 cm. Runoff from the control
watershed averaged 35.0 cm during the same period.
TABLE 3. Mean Predicted and Observed Values and Percent Change From the Traditional and Control
Watersheds During the Calibration and Postconstruction Periods for the Jordan Cove Project, Connecticut
Characteristic
Calibration Period
(n = 10)
Control Traditional
Postconstruction Period
(n = 56)
Traditional
Control Observed Predicted
Calibration
Equation
% Change
ANCOVA
F p
Storm flow (cm/week)
0.20
0.02
0.35
0.33
0.02
T = 0.028C
+1,550 * **
27.78
<0.001
Peak discharge (m /s /week)
0.0525
0.0005
0.0246
0.0152
0.0005
T = 0.018C -0.073
+2,829 * **
63.58
<0.001
NO (mg /1)
0.5
0.3
1.1
0.3
0.3
T = 0.3400
0
0.50
0.626
N113 -N (mg /1)
0.15
0.08
0.16
0.15
0.13
T = 0.313C0 498
+15
4.00
0.012
TKN (mg /1)
1.3
4.0
1.1
1.0
4.1
T = 3.999C
-76 * **
20.68
<0.001
TP (mg /1)
0.159
1.009
0.156
0.185
0.885
T = 3.494C0 739
-79 * **
10.99
<0.001
TSS (mg /1)
31
132
22
24
114
T = 53.239C 247
-79*
10.18
<0.001
BOD (mg /1)
3.2
15.9
3.2
3.4
11.8
T = 18.00 -0.363
-71 **
10.78
0.008
Fecal coliform (No /100 ml)
13
1
234
22
<1
T = 0.654C -0698
undefined
1.60
0.300
Cu (µg11)
7
8
9
7
10
T = 3.163C0 533
-30 S-
2.64
0.074
6
11
1
1
1
T= 0.762C
0
11.39
<0.001
Pb (µg /1)
Zn (µg 11)
46
65
36
42
67
T = 11.414C 492
_37 N.S.
1.86
0.164
NO -N (kg /ha/year)
0.61
0.01
3.29
0.83
0.04
T = 0.00810
+2,181 * **
38.77
<0.001
NH -N (kg /ha/year)
0.17
0.01
0.48
0.35
0.22
T = 0.085C
+65 * **
12.91
<0.001
TKN (kg /ha /year)
1.42
0.07
3.6
2.4
0.06
T = 0.496C
+76,361 * **
20.09
<0.001
TP (kg /ha/year)
0.186
0.021
0.462
0.412
0.017
T = 0.068C
+46,582 * **
16.87
<0.001
TSS (kg/ha/year)
36
2
64
65
2
T = 0.762C
+64,323 * **
11.42
<0.001
Cu (g /ha /year)
10
0.2
15
18
0.2
T = 30.358C -0078
+8,900 * **
10.65
<0.001
Pb (g /ha/year)
9
0.4
1
2
0.6
T = 54.358C -0.064
+163 N.S.
1.07
0.389
Zn (g/ha/year)
82
0.6
55
17
2
T = 34,215,540C -1.528
+8,650 * **
2.42
0.096
Notes: C = control; N.S. = not significant; T = treatment.
In = number of samples; n for FC, and metals were three and seven, respectively
2 n for metals were 20.
*p < 0.05.
* *p < 0.01.
* * *p < 0.001.
JAWRA 1002 JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION