The Universal Rational Hydrograph uses a set of coefficients and the peak discharge to compute the hydrograph ordinates at different times. The coefficients are shown in the following table and the resulting hydrograph is displayed.
|
Dimensionless Time and Hydrograph Ordinates |
|
|
t/tc |
Q/Qp |
|
0 |
0.00 |
|
1 |
0.21 |
|
2 |
0.30 |
|
3 |
1.00 |
|
4 |
0.54 |
|
5 |
0.39 |
|
6 |
0.25 |
|
7 |
0.18 |
|
8 |
0.15 |
|
9 |
0.14 |
|
10 |
0.13 |
|
11 |
0.00 |
Notice that the peak occurs at 3*tc, and the time base is equal to 11*tc.
where:
tc = time of concentration.
Q = Flow at time t, in cfs.
Qp = Peak flow.
Related Topics:
Computing Hydrographs with Rational Method
Rational Equation