Goswami Example 304.4

[crogmobulon]

I was able to find the pre and post development 2-year peak discharge values, but got lost where he calculates the increased upland runoff depth for the two year storm using:

(delta)Q=Q2-(qu1/qu2)Q1 = 1.13in.

What was the point of calculating the qp values, and why is that ratio of the unit peak discharges applied to Q1 before subtracting it from Q2 (i.e. why isn't (delta)Q just Q2-Q1)?

 

[civilized_naah]

What was the point of calculating the qp values, and why is that ratio of the unit peak discharges applied to Q1 before subtracting it from Q2 (i.e. why isn't (delta)Q just Q2-Q1)?

I think if the time of concentration would have remained the same, then the deltaQ would have been simply Q2-Q1. However, the fact that the unit hydrograph changed shape and size due to an increased curve number is accounted for by that adjustment.