Problem 5-1

Rain falls on a 175-ha catchment with the following characteristics: (1) 30%, C = 0.3; (2) 40%, C = 0.5; (3) 30%, C = 0.9. Calculate the peak runoff due to a storm of 55 mm/h intensity lasting 2 h. Assume time of concentration t_c = 60 min.

Problem 5-2

Rain falls on a 220-ha composite catchment which drains two subareas, as follows: (1) subarea A, steep, draining 30%, with time of concentration 20 min and C = 0.9; 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 50-y frequency. Use the following IDF function:

in which I = rainfall intensity in millimeters per hour, T = return period in years, and t_r = 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 = 100 m, rainfall excess i = 40 mm/h, and plane slope S_o = 0.015. Use water temperature T = 20°C. What would be the mean overland flow depth if the water temperature increased to 30°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 S_o = 0.01, rainfall excess i = 25 mm/h. Plot q/q_e vs. t/t_e for t/t_e between 0 and 2.