CIV E 445 - APPLIED HYDROLOGY
SPRING 2011
HOMEWORK 12, CHAPTER 10

Problem 12-1

A 85-km2 catchment has a 4-h concentration time, with isochrones at 1-h intervals resulting in the following time-area histogram:

Time (h) 0-1 1-2 2-3 3-4
Area (km2) 17 21 31 16

Use the time-area method to calculate the outflow hydrograph from the following storm pattern:

Time (h) 0-1 1-2 2-3 3-4 4-5 5-6
Total rainfall (cm/h) 1 2 5 4 3 1

The runoff curve number is CN = 81. Use a spreadsheet. Verify with ONLINE ROUTING 06. Note that the latter only takes effective rainfall.

Problem 12-2

Use the Clark method to derive a 2-h unit hydrograph for a catchment with the following time-area diagram:

Time (h) 0-1 1-2 2-3 3-4 4-5 5-6
Area (km2) 20 40 60 40 24 16

Use Δt = 1 h and K = 3 h. Use a spreadsheet and verify with ONLINE ROUTING 07.

Problem 12-3

Use Example 10-3 in the text (cascade of linear reservoirs) to test ONLINE ROUTING 08. Then route the effective rainfall hyetograph of Example 10-3 (with time interval Δt = 6 h) using: (a) K = 12 h and N = 4 and (b) K = 18 h and N = 5.

Problem 12-4

A 1-h unit hydrograph derived from measured data has the following ordinates:

Time (h) 0 1 2 3 4 5 6 7 8 9 10 11 12 1314
Inflow (m3/s) 0 7 22 48 60 90 74 47 28 17 10 6 4 32

Assuming a time of concentration tc = 6 h, calculate the linear reservoir storage constant K in the Clark method.