Q = ACi
| |||
A
|
=
|
Acreage of the watershed
| |
Q
|
=
|
Peak discharge from watershed in cubic feet
per second (cfs) resulting from the design storm
| |
C
|
=
|
Coefficient of runoff
| |
i
|
=
|
Intensity of rainfall in inches per hour based
upon the time of concentration for the area under consideration.
|
Q
|
=
|
Flow of conduit in cubic feet per second (cfs)
| ||
a
|
=
|
Cross-sectional area of water flow through conduit
in square feet
| ||
R
|
=
|
a
|
(hydraulic radius) in feet
| |
p
| ||||
S
|
=
|
Slope, in feet/feet
| ||
V
|
=
|
Average velocity of water in feet/second
| ||
p
|
=
|
Wetted perimeter in feet
| ||
n
|
=
|
Roughness coefficient
|
Use
|
Coefficient
| |
---|---|---|
Residential (lot size greater than 20,000 square
feet)
|
0.40
| |
Residential (lot size less than 20,000 square
feet)
|
0.50
| |
Multifamily
|
0.70
| |
Commercial
|
0.85
| |
Industrial
|
0.80
| |
Parks and other permanent open spaces
|
0.2
|
Contributing Area
|
Coefficient
| |
---|---|---|
Paved surfaces (streets, drives, roofs, etc.)
|
0.90
| |
Unpaved bare surfaces
|
0.6
| |
Flat grassed (less than 2%)
|
0.2
| |
Average grassed (between 2% and 10%)
|
0.3
| |
Steep grassed (more than 10%)
|
0.4
|
T
|
=
|
Time of surface flow
| |
C
|
=
|
Coefficient of runoff
| |
D
|
=
|
Distance traveled
| |
S
|
=
|
Average slope of the land
|
When charts reflect the coefficient of runoff
as a surface description, the "poor grass" designation shall be used.
|
Type
|
Coefficient
| |
---|---|---|
Concrete pipe/box culverts and other shapes
|
.015
| |
Corrugated metal pipe/pipe arch
|
.024
| |
Corrugated metal pipe (paved invert)
|
.021
| |
Corrugated metal pipe arch (paved invert)
|
.019
| |
Corrugated metal pipe/pipe arch (fully paved)
|
.015
| |
Vitrified clay pipe
|
.012
|
Type of Channel
|
Valve
| |
---|---|---|
Concrete lined
|
C =.015
| |
Earth
|
C =.026
| |
Natural
|
C = .030 to .040
|
Diameter
(in inches)
|
Minimum radius
(in feet)
| |
---|---|---|
15 to 18
|
350
| |
21 to 24
|
400
| |
27 to 30
|
450
| |
33 to 36
|
500
| |
42 to 60
|
600
| |
Over 60
|
1,000
|
Table 1
Green Infrastructure BMPs for Groundwater Recharge, Stormwater
Runoff Quality, and/or Stormwater Runoff Quantity
| ||||
---|---|---|---|---|
Best Management Practice
|
Stormwater Runoff Quality TSS Removal Rate
|
Stormwater Runoff Quantity
|
Groundwater Recharge
|
Minimum Separation from Seasonal High-Water Table
(feet)
|
Cistern
|
0%
|
Yes
|
No
|
—
|
Dry well(a)
|
0%
|
No
|
Yes
|
2
|
Grass swale
|
50% or less
|
No
|
No
|
2(e)
1(f)
|
Green roof
|
0%
|
Yes
|
No
|
—
|
Manufactured treatment device(a) (g)
|
50% or 80%
|
No
|
No
|
Dependent upon the device
|
Pervious paving system(a)
|
80%
|
Yes
|
Yes(b)
No(c)
|
2(b)
1(c)
|
Small-scale bioretention basin(a)
|
80% or 90%
|
Yes
|
Yes(b)
No(c)
|
2(b)
1(c)
|
Small-scale infiltration basin(a)
|
80%
|
Yes
|
Yes
|
2
|
Small-scale sand filter
|
80%
|
Yes
|
Yes
|
2
|
Vegetative filter strip
|
60% to 80%
|
No
|
No
|
—
|
Table 2
Green Infrastructure BMPs for Stormwater Runoff Quantity
(or for Groundwater Recharge and/or Stormwater Runoff Quality
with a Waiver or Variance from N.J.A.C. 7:8-5.3)
| ||||
---|---|---|---|---|
Best Management Practice
|
Stormwater Runoff Quality TSS Removal Rate
|
Stormwater Runoff Quantity
|
Groundwater Recharge
|
Minimum Separation from Seasonal High-Water Table
(feet)
|
Bioretention system
|
80% or 90%
|
Yes
|
Yes(b)
No(c)
|
2(b)
1(c)
|
Infiltration basin
|
80%
|
Yes
|
Yes
|
2
|
Sand filter(b)
|
80%
|
Yes
|
Yes
|
2
|
Standard constructed wetland
|
90%
|
Yes
|
No
|
N/A
|
Wet pond(d)
|
50% to 90%
|
Yes
|
No
|
N/A
|
Table 3
BMPs for Groundwater Recharge, Stormwater Runoff Quality, and/or
Stormwater Runoff Quantity
only with a Waiver or Variance from N.J.A.C. 7:8-5.3
| ||||
---|---|---|---|---|
Best Management Practice
|
Stormwater Runoff Quality TSS Removal Rate
|
Stormwater Runoff Quantity
|
Groundwater Recharge
|
Minimum Separation from Seasonal High-Water Table
(feet)
|
Blue roof
|
0%
|
Yes
|
No
|
N/A
|
Extended detention basin
|
40% to 60%
|
Yes
|
No
|
1
|
Manufactured treatment device(b)
|
50% or 80%
|
No
|
No
|
Dependent upon the device
|
Sand filter(c)
|
80%
|
Yes
|
No
|
1
|
Subsurface gravel wetland
|
90%
|
No
|
No
|
1
|
Wet pond
|
50% to 90%
|
Yes
|
No
|
N/A
|
Notes to Tables 1, 2, and 3:
| |
(a)
|
Subject to the applicable contributory drainage area limitation specified at § 231-34.1D(15)(b);
|
(b)
|
Designed to infiltrate into the subsoil;
|
(c)
|
Designed with underdrains;
|
(d)
|
Designed to maintain at least a ten-foot-wide area of native
vegetation along at least 50% of the shoreline and to include a stormwater
runoff retention component designed to capture stormwater runoff for
beneficial reuse, such as irrigation;
|
(e)
|
Designed with a slope of less than 2%;
|
(f)
|
Designed with a slope of equal to or greater than 2%;
|
(g)
|
Manufactured treatment devices that meet the definition of "green infrastructure" at § 231-34.1B;
|
(h)
|
Manufactured treatment devices that do not meet the definition of "green infrastructure" at § 231-34.1D.
|
Best Management Practice
|
Maximum Contributory Drainage Area
(acres)
|
---|---|
Dry well
|
1
|
Manufactured treatment device
|
2.5
|
Pervious pavement systems
|
Area of additional inflow cannot exceed 3 times the area occupied
by the BMP
|
Small-scale bioretention systems
|
2.5
|
Small-scale infiltration basin
|
2.5
|
Small-scale sand filter
|
2.5
|
Table 4
Water Quality Design Storm Distribution
| |||||
---|---|---|---|---|---|
Time
(minutes)
|
Cumulative Rainfall
(inches)
|
Time
(minutes)
|
Cumulative Rainfall
(inches)
|
Time
(minutes)
|
Cumulative Rainfall
(inches)
|
1
|
0.00166
|
41
|
0.1728
|
81
|
1.0906
|
2
|
0.00332
|
42
|
0.1796
|
82
|
1.0972
|
3
|
0.00498
|
43
|
0.1864
|
83
|
1.1038
|
4
|
0.00664
|
44
|
0.1932
|
84
|
1.1104
|
5
|
0.00830
|
45
|
0.2000
|
85
|
1.1170
|
6
|
0.00996
|
46
|
0.2117
|
86
|
1.1236
|
7
|
0.01162
|
47
|
0.2233
|
87
|
1.1302
|
8
|
0.01328
|
48
|
0.2350
|
88
|
1.1368
|
9
|
0.01494
|
49
|
0.2466
|
89
|
1.1434
|
10
|
0.01660
|
50
|
0.2583
|
90
|
1.1500
|
11
|
0.01828
|
51
|
0.2783
|
91
|
1.1550
|
12
|
0.01996
|
52
|
0.2983
|
92
|
1.1600
|
13
|
0.02164
|
53
|
0.3183
|
93
|
1.1650
|
14
|
0.02332
|
54
|
0.3383
|
94
|
1.1700
|
15
|
0.02500
|
55
|
0.3583
|
95
|
1.1750
|
16
|
0.03000
|
56
|
0.4116
|
96
|
1.1800
|
17
|
0.03500
|
57
|
0.4650
|
97
|
1.1850
|
18
|
0.04000
|
58
|
0.5183
|
98
|
1.1900
|
19
|
0.04500
|
59
|
0.5717
|
99
|
1.1950
|
20
|
0.05000
|
60
|
0.6250
|
100
|
1.2000
|
21
|
0.05500
|
61
|
0.6783
|
101
|
1.2050
|
22
|
0.06000
|
62
|
0.7317
|
102
|
1.2100
|
23
|
0.06500
|
63
|
0.7850
|
103
|
1.2150
|
24
|
0.07000
|
64
|
0.8384
|
104
|
1.2200
|
25
|
0.07500
|
65
|
0.8917
|
105
|
1.2250
|
26
|
0.08000
|
66
|
0.9117
|
106
|
1.2267
|
27
|
0.08500
|
67
|
0.9317
|
107
|
1.2284
|
28
|
0.09000
|
68
|
0.9517
|
108
|
1.2300
|
29
|
0.09500
|
69
|
0.9717
|
109
|
1.2317
|
30
|
0.10000
|
70
|
0.9917
|
110
|
1.2334
|
31
|
0.10660
|
71
|
1.0034
|
111
|
1.2351
|
32
|
0.11320
|
72
|
1.0150
|
112
|
1.2367
|
33
|
0.11980
|
73
|
1.0267
|
113
|
1.2384
|
34
|
0.12640
|
74
|
1.0383
|
114
|
1.2400
|
35
|
0.13300
|
75
|
1.0500
|
115
|
1.2417
|
36
|
0.13960
|
76
|
1.0568
|
116
|
1.2434
|
37
|
0.14620
|
77
|
1.0636
|
117
|
1.2450
|
38
|
0.15280
|
78
|
1.0704
|
118
|
1.2467
|
39
|
0.15940
|
79
|
1.0772
|
119
|
1.2483
|
40
|
0.16600
|
80
|
1.0840
|
120
|
1.2500
|
R = A + B - (A x B)/100
|
Where:
| ||
R
|
=
|
total TSS percent load removal from application of both BMPs.
|
A
|
=
|
the TSS percent removal rate applicable to the first BMP.
|
B
|
=
|
the TSS percent removal rate applicable to the second BMP.
|