Page 595 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch14_500-554.qxd 8/7/10 8:56 PM Page 551

Problems/Questions 551
14.22 Each of the city blocks contributes its stormwater flow
Storm Sewer Length, m Slope n 2
into the street as shown in Fig.14.39. Each block is 8,000 m in
1 120 0.0090 0.013 area with a runoff coefficient of 0.65. The rainfall intensity i
2 120 0.0300 0.013 (mm/h) as a function of rainfall duration t (min), is:
3 240 0.0040 0.013
2,510
4 120 0.0030 0.013 i =
t + 14
The rainfall intensity (mm/h)-duration (min) relationship is: Find:
3,000 (a) The concentration times in minutes at points A, B, C,
i = D, E, and F.
t + 20
(b) The flows (L/s) at points A, B, C, D, E, and F.
14.21 Determine the design flows (L/s) for sewers 1, 2, 3, 4, (c) The flows (L/s) in sewers I and II.
and 5, which serve the drainage blocks A, B, C, D, and E shown
in Fig. 14.38. The following data are given:
10 min 7 min
Overland Flow Runoff 2 min 1 min
Block Area, m 2 Time, min Coefficient
8 min 14 min
A 20,000 11 0.30 A B
B 10,000 8 0.60
C 15,000 12 0.80
D 5,000 5 0.50 8 min 15 min
E 12,000 18 0.70
3 min 2 min

12 min C D 20 min
A B Inlet
MH
1
8 min 10 min
D
2 C 2 min 1 min 2 min
3 12 min E F 9 min
E
MH
4
7 min 7 min
1 min 1 min 1 min
5
8 min 8 min
Figure 14.38 Layout of Storm Drainage for Problem 14.21. G H
MH
Assume that the flow times in storm sewers are as follows:
Storm sewer
Storm Sewer Flow Time, min
1 2 Figure 14.39 Layout of Storm Drainage for Problem 14.22.
2 1
3 1 14.23 Figure 14.40 shows the watershed area that is to be
4 2 drained through a storm outfall sewer to the stream. Assume the
5 4 following design criteria:
• The rainfall intensity i (mm/h) as a function of rainfall
The rainfall intensity (mm/h)-duration (min) relationship is: duration t (min) is:
1,640 3,300
i = i =
t + 17 t + 17