ABE TUTORIALS

AREA 2 PROBLEM 1: PEAK RUNOFF CALCULATION

DETERMINE THE 10-YEAR PERIOD PEAK RUNOFF FOR AN 80-HECTARE WATERSHED HAVING A RUNOFF COEFFICIENT OF 0.4. THE RAINFALL INTENSITY FOR THAT RETURN PERIOD IS 101.25 MM/HR.

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a. 9.0 m³/s

b. 16.5 m³/s

c. 1.5 m³/s

d. 16.3 m³/s

Correct Answer: A

Step-by-Step Solution:

To find the peak runoff, we use the Rational Method formula in metric units:

Q = (C × I × A) / 360

1. Identify Given Data:

• • C (Runoff Coefficient) = 0.4
• • I (Rainfall Intensity) = 101.25 mm/hr
• • A (Area) = 80 hectares

2. Perform Calculation:

Q = (0.4 × 101.25 × 80) / 360
Q = 3240 / 360
Q = 9.0 m³/s

Final Result: a. 9.0 m³/s