Question

Please show step by step.

A 100-mi² drainage basin with a time of concentration of 100 min receives rainfall at a rate of 2.75 in/hr for a period of 200 min.If the runoff coefficient is 0.8, develop and sketch a flow hydrograph using the modified rational method.

Answer 1

Data Given:

A= 100 mi2 = 64000 acre

Rainfall intensity (i) = 2.75 in/hr

C = 0.8

tc= 100 min

t=200 min

Here t > tc thus for the first 100 min graph is rising than another 100 mn it is constant and then it is falling for a time equal to the time of concentration (100min) as shown below.

equation for rate of runoff by modified ration formula is as follow: