CE 4603: Water Resources Engineering — David Wagner 2007/03/26 13:18

Homework # 7 Due 3/26 (or 3/28)

Solve problems 5.74 and 5.75 of Water Resources Engineering by David Chin, 2^nd edition, pages 597-598.

5.74

A stormwater detention basin has the following storage characteristics:

[Chin#460-462:Example 5.37] Δt=30 min.

Stage	Storage	$O=3.29(Stage-8)^{3/2}$	2S/Δt+O
8.0	0	0	0
8.5	1041	1.16	2.32
9.0	2288	3.29	5.83
9.5	3761	6.04	10.22
10.0	5478	9.31	15.39
10.5	7460	13.00	21.29
11.0	9726	17.10	27.90

The discharge weir from the detention basin has a crest elevation of 8.0 m, and the weir discharge Q (m³/s) is given by

$Q = 3.29 h^{3/2}$

where h is the height of the water surface above the crest of the weir in meters. The catchment runoff hydrgraph is given by:

Time	Runoff	2S/deltat-O	2S/deltat+O	O
(min)	(m³/s)	(m³/s)	(m³/s)	(m³/s)
0	0	0	0.00	0.00
30	3.6	-0.28	3.60	1.94
60	8.4	-2.26	11.72	6.99
90	5.1	-2.13	11.24	6.69
120	4.2	-1.09	7.17	4.13
150	3.6	-0.97	6.71	3.84
180	3.3	-0.77	5.93	3.35
210	2.7	-0.62	5.23	2.92
240	2.3	-0.44	4.38	2.41
270	1.8	-0.29	3.66	1.97
300	1.5	-0.15	3.01	1.58
330	0.84	-0.01	2.19	1.10
360	0.51	0	1.34	0.67
390	0	0	0.51	0.25
420	0	0	0.00	0.00

If the prestorm stage in the detention basin is 8.0 m, estimate the discharge hydrograph from the detention basin.

The flow hydrograph at a channel section is given by: