Design and Improvement Standards for Subdivisions and Site Plans
Q = AIR |
Where: | ||||
Q | = | The required capacity in cubic feet per second for the collection system at the point of design. | ||
A | = | The tributary drainage area in acres, including areas tributary from outside sources as well as from within such subdivision itself. | ||
I | = | The rainfall intensity in inches per hour, determined from Rainfall Intensity Duration Curves for New Jersey as prepared by the New Jersey Department of Transportation. | ||
R | = | The coefficient of runoff applicable to the area based upon soil conditions, average slope of the area and degree of ultimate area development. In no case shall R equal less than 0.30. | ||
d = | 2.159 QN 3/8 s 1/2 |
Where: | ||||
d | = | The diameter of the pipe in feet. | ||
Q | = | The average discharge in cubic feet per second. | ||
N | = | The coefficient of friction determined by kind of pipe. | ||
s | = | The slope of the pipe in feet per foot. | ||
N | = | 0.015 for pipes < 18 inches | ||
0.013 for pipes > 18 inches | ||||
Land Use Type | Runoff Coefficients | ||
|---|---|---|---|
Commercial | |||
Downtown areas | 0.70 to 0.95 | ||
Neighborhood areas | 1.50 to 0.70 | ||
Design commercial centers | 0.35 to 0.50 | ||
Residential | |||
Single-family | 0.30 to 0.50 | ||
Parks, cemeteries | 0.10 to 0.25 | ||
Playgrounds | 0.20 to 0.35 | ||
Unimproved areas | 0.10 to 0.30 | ||
Surface Type | Runoff Coefficients | ||
|---|---|---|---|
Streets | |||
Asphalt | 0.70 to 0.95 | ||
Concrete | 0.80 to 0.95 | ||
Drives and walks | 0.75 to 0.85 | ||
Roofs | 0.75 to 0.95 | ||
Lawns, sandy soil | |||
Flat, 2% grade | 0.05 to 0.10 | ||
Average, 2% to 7% grade | 0.10 to 0.15 | ||
Lawns, heavy soil | |||
Flat, 2% grade | 0.13 to 0.17 | ||
Average, 2% to 7% grade | 0.18 to 0.22 | ||
The range of coefficients for each land use and surface type reflects differences in slope, development, amount of impervious surface and degree of ground saturation due to antecedent precipitation. |
Design and Improvement Standards for Subdivisions and Site Plans
Q = AIR |
Where: | ||||
Q | = | The required capacity in cubic feet per second for the collection system at the point of design. | ||
A | = | The tributary drainage area in acres, including areas tributary from outside sources as well as from within such subdivision itself. | ||
I | = | The rainfall intensity in inches per hour, determined from Rainfall Intensity Duration Curves for New Jersey as prepared by the New Jersey Department of Transportation. | ||
R | = | The coefficient of runoff applicable to the area based upon soil conditions, average slope of the area and degree of ultimate area development. In no case shall R equal less than 0.30. | ||
d = | 2.159 QN 3/8 s 1/2 |
Where: | ||||
d | = | The diameter of the pipe in feet. | ||
Q | = | The average discharge in cubic feet per second. | ||
N | = | The coefficient of friction determined by kind of pipe. | ||
s | = | The slope of the pipe in feet per foot. | ||
N | = | 0.015 for pipes < 18 inches | ||
0.013 for pipes > 18 inches | ||||
Land Use Type | Runoff Coefficients | ||
|---|---|---|---|
Commercial | |||
Downtown areas | 0.70 to 0.95 | ||
Neighborhood areas | 1.50 to 0.70 | ||
Design commercial centers | 0.35 to 0.50 | ||
Residential | |||
Single-family | 0.30 to 0.50 | ||
Parks, cemeteries | 0.10 to 0.25 | ||
Playgrounds | 0.20 to 0.35 | ||
Unimproved areas | 0.10 to 0.30 | ||
Surface Type | Runoff Coefficients | ||
|---|---|---|---|
Streets | |||
Asphalt | 0.70 to 0.95 | ||
Concrete | 0.80 to 0.95 | ||
Drives and walks | 0.75 to 0.85 | ||
Roofs | 0.75 to 0.95 | ||
Lawns, sandy soil | |||
Flat, 2% grade | 0.05 to 0.10 | ||
Average, 2% to 7% grade | 0.10 to 0.15 | ||
Lawns, heavy soil | |||
Flat, 2% grade | 0.13 to 0.17 | ||
Average, 2% to 7% grade | 0.18 to 0.22 | ||
The range of coefficients for each land use and surface type reflects differences in slope, development, amount of impervious surface and degree of ground saturation due to antecedent precipitation. |