The paved entry time is the time it takes the runoff from the paved area to run along a gutter with a hydraulic radius of 60mm and a Manning factor of 0.02 to the inlet. The overland flow time for the runoff to reach the gutter is assumed to be two minutes, which is added to the gutter travel time.
This calculator allows you to calculate the paved area entry time from the following parameters based on Manning's equation:
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Option
|
Description |
|
Length |
The distance from the catchpit to the furthest hydraulic point of the paved area in metres. |
|
Slope |
The slope from the furthest hydraulic point, expressed as a percentage. |
|
Manning Factor |
Specify the Manning factor for the paved area. Typical values are shown below. |
|
OK button |
Click to accept the current entries. |
|
Cancel button |
Click to cancel the function. |
The calculated value will be placed in the Paved Entry Time edit box when you click OK.
Woolhiser recommended the following Manning's coefficients for overland flow.
|
Surface
|
Range |
|
Concrete or asphalt |
0.010 - 0.013 |
|
Bare sand |
0.010 - 0.016 |
|
Gravelled surface |
0.012 - 0.030 |
|
Bare clay - loam soil (eroded) |
0.012 - 0.033 |
|
Sparse vegetation |
0.053 - 0.130 |
|
Veld |
0.100 - 0.200 |
|
Lawns |
0.170 - 0.480 |