Section 4: Soil and Water Conservation Engineering
Hydrograph Analysis & Unit Hydrograph Theory
Subtopic: Unit hydrograph runoff volume
Question Statement:
A $4\text{-hour}$ unit hydrograph of a catchment of area $30\text{ km}^2$ has a direct runoff depth of exactly $1\text{ cm}$. The total volume of direct surface runoff represented by the area under this unit hydrograph is ________ $\text{m}^3$.
Answer Key:
300000
Step-by-Step Solution & Explanation
By definition, a unit hydrograph represents $1\text{ cm}$ ($0.01\text{ m}$) of direct runoff volume uniformly over the entire catchment area:
$V = \text{Depth} \times \text{Catchment Area} = 0.01\text{ m} \times (30 \times 10^6\text{ m}^2) = 300000\text{ m}^3$.