CIVE 445 - ENGINEERING HYDROLOGY SPRING 2004 - MIDTERM 2 - SOLUTION

PROBLEM 1

Assume runoff concentration without diffusion, and use Eq. 4-12 in the rational formula:

Q_p = I_e ∑A = (I - φ) ∑A = (I - 25) ∑A

Several rainfall durations are tried, as shown in the following table:

tr	I	Ie	Subarea A	Subarea B contribution	∑ A	Qp
(min)	(mm/hr)	(mm/hr)	(ha)	(ha)	∑ A	m3/s
20	70.48	45.48	45	35.0	80.0	10.11
30	59.15	34.15	45	52.5	97.5	9.25
40	51.33	26.33	45	70.0	115.0	8.41
50	45.55	20.55	45	87.5	132.5	7.56
60	41.10	16.10	45	105.0	150.0	6.71

Q_p = I_e ∑ A = 45.48 mm/hr × 80 ha × 10,000 m²/ha × 0.001 m/mm × (1 hr/3600 seconds) =

Q_p = 10.11 m³/s

The peak flow is 10.11 m³/s. ANSWER.

Problem 2

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