Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Hydrograph analysis, unit hydrograph theory and application
Question Statement:
A 2-hour Unit Hydrograph (for $1\text{ cm}$ effective rainfall) corresponds to a watershed of area $A = 72\text{ km}^2$. The equilibrium discharge ($Q_e = 2.778 \frac{A}{D}$) of the S-curve hydrograph generated from this unit hydrograph in $\text{m}^3\text{/s}$ is ________ (answer in integer).
Answer Key:
100
Step-by-Step Solution & Explanation
The equilibrium discharge of an S-curve represents the maximum steady runoff generated under continuous effective rainfall intensity of $1\text{ cm} / D$:
$Q_e = 2.778 \times \frac{A}{D}$
Where:
• $A = 72\text{ km}^2$
• $D = 2.0\text{ h}$
$Q_e = 2.778 \times \frac{72}{2} = 2.778 \times 36 = 100.008\text{ m}^3\text{/s} \approx 100\text{ m}^3\text{/s}$