Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Hydrograph analysis, unit hydrograph theory and application
Question Statement:
A 4-hour unit hydrograph of a watershed of area $A = 180\text{ km}^2$ has a peak discharge. Calculate the total volume of direct runoff represented by this 4-hour unit hydrograph in million cubic meters ($\text{Mm}^3$). (1 UH represents $1\text{ cm}$ of direct runoff over the catchment).
Answer Key:
1.8
Step-by-Step Solution & Explanation
A unit hydrograph represents $1\text{ cm} = 0.01\text{ m}$ depth of direct surface runoff:
$V = A \times d = (180 \times 10^6\text{ m}^2) \times 0.01\text{ m} = 1.8 \times 10^6\text{ m}^3 = 1.80\text{ Mm}^3$