CIV E 445 - APPLIED HYDROLOGY
SPRING 2014
HOMEWORK No. 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 tc = 60 min.

  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:

    I = (850 T 0.25) / (tr + 18)0.75

    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.

  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 So = 0.015. Use water temperature T = 20°C. What would be the mean overland flow depth if the water temperature increased to 30°C?

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