Section 4: Soil and Water Conservation Engineering
Hydrograph Analysis & Unit Hydrograph Theory
Subtopic: Flood peak from unit hydrograph
Question Statement:
The peak ordinate of a $6\text{-hour}$ unit hydrograph of a basin is $18.0\text{ m}^3/\text{s}$. A storm of $6\text{-hour}$ duration produces an effective rainfall excess of $3.5\text{ cm}$. If the constant baseflow is $15.0\text{ m}^3/\text{s}$, the resulting total peak flood discharge is ________ $\text{m}^3/\text{s}$ (round off to one decimal place).
Answer Key:
78.0
Step-by-Step Solution & Explanation
From the linear theory of unit hydrographs (principle of proportionality):
$\text{Direct Runoff Peak} = Q_{p,UH} \times R = 18.0 \times 3.5 = 63.0\text{ m}^3/\text{s}$
Adding baseflow:
$Q_{peak,total} = 63.0 + 15.0 = 78.0\text{ m}^3/\text{s}$