Page 593 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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Problems/Questions 549
Rainfall intensity (mm/h) as a function of rainfall duration
8 min (min) is:
Block | 1,020
15 min i =
t + 12
A (a) Determine the required size of the 1.5 km drain from
the MH at University Road to the river, so that no
backflow of water from the river into the discharge
15 min pipe is possible under any flow condition in the pipe.
Block || (b) What size of pipe will be required, if depth of excava-
20 min tion is to be kept to a minimum? In this particular
case assume there is no limitation on depth of cover
B as long as no pumping shall be used.
14.16 Area ABC drains its stormwater into one inlet at point C
(see Fig. 14.33). The drainage area has a runoff coefficient of
15 min 0.60 and a surface overland flow velocity of 1.25 m/s. The rain-
Block ||| Inlet C fall intensity i (mm/h) as a function of rainfall duration t (min) is:
8 min
1,120
MH i =
C t + 12
3
(a) Find the total flow Q (m /min) entering the inlet at c.
(b) What are the maximum and minimum storm sewer
10 min
Storm pipe diameters (mm) that can be used? Assume that
Block |V
sewer the required grades for the sewer can be economically
accommodated in all cases.
500 m
A B
Figure 14.32 Layout of Storm Drainage for Problem 14.14.
Overland flow
The rainfall intensity i (mm/h) as a function of rainfall duration
t (min) is: 500 m 500 m
1,900
i =
t + 12
Inlet C
Find: C
3
(a) The total flow at point A (in m /min).
3
(b) The total flow at point B (in m /min).
Storm sewer
(c) What are the maximum and minimum storm sewer di-
ameters that can be used? Assume that the required
slopes can be economically accommodated in all
cases. Q
14.15 The runoff from University Campus is drained through a
Figure 14.33 Layout of Storm Drainage for Problem 14.16.
2 km long main to a manhole located near University Road at
Conversion factor: 1 m 3.28 ft
an invert elevation of 610.50 m. From this MH a drainage pipe
is to be designed to collect the rainwater runoff and discharge it 14.17 The drainage system shown in Fig. 14.34 is designed to
into the river 1.5 km away. The following data are given: collect the stormwater from a football field ABCD (c 0.50)
• Drainage area 2.5 km 2 and a basketball field EFGH (c 0.90). The rainfall intensity i
• Runoff coefficient 0.30 (mm/h), as a function of rainfall duration t (min) is:
• Inlet time to the 2 km-long drain 30 min. 3,000
• Average velocity in the 2 km-long drain 0.90 m/s i =
t + 20
• Manning n for all pipes 0.013
3
• Maximum water level in the river 608.20 m. Determine the design flows (m /h) for pipes 1, 2, and 3.