Universal Rational Hydrograph

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