140 ft 90 ft Problem 1: to join at a City parking lots A and B slope Gutter comm

Question

140 ft 90 ft Problem 1: to join at a City parking lots A and B slope Gutter common gutter that discharges to a storm sewer inlet located at one end of the lots, LOT A LOT B as shown. Both lots are 100 ft wide, with lot A being 140 ft deep and lot B being 90 ft 100 fi Slope Slope deep. Lot A slopes at 2% and lot B slopes at 2.5%. Both lots are newly paved with smooth asphalt. For a rainfall storm with an Storm sewer intensity of 0.90 in/hr over a 1 hr period, what is the time of concentration for flow to the gutter? inlet How much flow will be generated for the storm? The City Engineer wants to know what will be size of pipe to catch the runoff at the inlet?

Explanation / Answer

Kirpich Time Of Concentration formula

where L is in ft

t is in min

for LOT A L= 140 ft

Tc = 0.0078(1400.77/0.020.385) =1.58 min

for LOT B

L= 90 ft

tc = 0.0078*900.77 /0.0250.385 =1.032 min

total catchment area = (140+90)*100 = 23000 ft2 =0.528 acer

pick flow q= CiA

C= Runoff Coefficient

I= INTENSITY OF RAINFALL in in/hr

A= Area of catchment in Acer

for asphalt paved road C=0.95

q= =0.95*0.9*0.528 = 0.4515 ft3/sec

assume average velocity in pipe drain is 3 ft/sec

pipe will be design for max flow

area of pipe A= flow/velocity= 0.4515/3=0.1505ft2

dia D= (4A/3.14)0.5 =0.4377 ft = 5.253in = 6 in

thanks

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