CIV E 445 - APPLIED HYDROLOGY
SPRING 2008
HOMEWORK 7, CHAPTER 5

Problem 7-1

Given the following 2-h unit hydrograph for a certain catchment, find the 3-h unit hydrograph.

Time (h)Flow (m3/s)
00
130
280
3100
470
530
610
70

Using this unit hydrograph, calculate the 1-h unit hydrograph. Verify using Online S-hydrograph.

Problem 7-2

The following 2-h unit hydrograph has been developed for a certain catchment:

Time (h)Flow (ft3/s)
00
2100
4200
670
850
1030
120

A 6-h storm covers the entire catchment and is distributed in time as follows:

Time (h)Total Rainfall (in/h)
0-21.0
2-42.0
4-61.5

Calculate the composite hydrograph for the effective storm pattern, assuming a runoff curve number CN = 84. Verify using Online convolution.

Problem 7-3

A certain basin has the following 2-h unit hydrograph:

Time (h)Flow (m3/s)
00
15
220
335
465
590
670
755
840
920
1010
110

Using Online S-hydrograph and Online convolution, calculate the flood hydrograph for the following effective rainfall hyetograph (CN = 100):

Time (h)Effective Rainfall (cm/h)
0-31.3
3-62.2

Problem 7-4

Calculate the 50-y peak flow by the TR-55 graphical method for the following watershed data: (1) urban watershed, area A = 8.5 km2; (2) surface flow is shallow concentrated, paved; hydraulic length L = 3350 m; slope S = 0.01; (3) 48% of watershed is 1/3-ac lots, lawns with 85% grass cover, 34% total impervious, soil group C; (4) 52% of the watershed is 1/3-ac lots, lawns with 95% grass cover, 24% total impervious, 25% of it unconnected, soil group C; (5) Pacific Northwest region, 50-y 24-h rainfall P = 12 cm; 0.2% ponding.

Problem 7-5

Use ONLINE TR-55 to calculate the peak discharge for a 850-ha catchment with a 100-y 24-h rainfall P = 13 cm, runoff curve number CN = 81, time of concentration tc = 2.5 h, 1% pond and swamp areas, and type I rainfall.