CIVE 445 - ENGINEERING HYDROLOGY

SPRING 2006 - MIDTERM 2 - SOLUTION

PROBLEM 1

Plane length L = 45 m

Plane slope So = 0.006

Manning's n = 0.08

rainfall excess i = 65 mm/hr

Kinematic flow number K = (SoL)/(Fo2ho)


Calculate equilibrium outflow; establish rating; calculate ho from rating; calculate mean velocity vo, and Froude number.

Equilibrium outflow qe = iL = (65 mm/hr × 45 m × 0.001 m/mm) / (3600 s/hr) = 0.0008125 m3/s/m

Rating: qe = b hom

b = (1/n) So1/2 = (1/0.08) (0.006)1/2 = 0.968

Choose m = 5/3 [Manning friction in wide channels (overland flow)]; 1/m = 3/5 = 0.6

Calculate he = (qe/b) 1/m = (0.0008125/0.968)0.6 = 0.014 m

ho = he = 0.014 m

Calculate vo = qe / he = (0.0008125/0.014) = 0.058 m/s

Calculate Fo2 = vo2 / (gho) = (0.058)2 / (9.81 × 0.014) = 0.0245

Calculate K = (SoL)/(Fo2ho) = (0.006 × 45) / (0.0245 × 0.014) = 787 > 20.

The flow is kinematic. ANSWER

Problem 2

 
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