CIV E 445 - APPLIED HYDROLOGY
SPRING 2011
HOMEWORK 5, CHAPTER 4

Problem 5-1

Rain falls on a 80-ha catchment with the following characteristics: (1) 25%, C = 0.3; (2) 35%, C = 0.5; (3) 40%, C = 0.7. Calculate the peak runoff due to a storm of 45 mm/h intensity lasting 1 hr. Assume time of concentration tc = 30 min.

Problem 5-2

Rain falls on a 100-ha composite catchment which drains two subareas, as follows: (1) subarea A, steep, draining 30%, with time of concentration 10 min and C = 0.7; and (2) subarea B, milder steep, draining 70%, with time of concentration 60 min and C = 0.3. Calculate the peak runoff corresponding to the 25-y frequency. Use the following IDF function:

I = (950 T 0.2) / (tr + 28)0.7

in which I = rainfall intensity in millimeters per hour, T = return period in years, and tr = rainfall duration in minutes. Assume linear flow concentration at the catchment outlet.

Problem 5-3

Calculate the mean overland flow depth (at equilibrium) under a laminar flow regime for a plane length L = 144 m, rainfall excess i = 75 mm/h, and plane slope So = 0.01. Use water temperature T = 20°C. What would be the mean overland flow depth if the water temperature increased to 25°C?

Problem 5-4

Calculate the rising limb of an overland flow hydrograph using Horton's equation (Eq. 4-36), assuming 75% turbulent flow. Use: Manning n = 0.05, plane length L = 80 m, plane slope So = 0.01, rainfall excess i = 25 mm/h. Calculate and plot q/qe vs. t/te, for t/te varying between 0 and 2, at intervals of 0.1.