Area ABCD discharges ail its flow into gutter BD. The overland flow time from A
ID: 1845027 • Letter: A
Question
Area ABCD discharges ail its flow into gutter BD. The overland flow time from A to B is 10 min, C to D is 20 min and the gutter flow time is 5 min. Inlet D intercepts ail the flow from Gutter BD and discharges into the storm sewer. Area ABCD has some different urban land use (say; commercial, residential, industrial,...)with the following runoff coefficients: Rainfall intensity is a function of rainfall duration with the equation of 1= 1220/(t+12) where t is in minutes Find: Time of concentration at the inlet D The overall runoff coefficient for the area ABCD The total flow rate entering D What are the maximum and minimum pipe diameters you may use for the storm sewer if slope is flexible If area of EFGH has the same characteristics of the area ABCD what will be the approximate peak flow at manhole J. Assume the storm sewer length of 50 m, minimum pipe diameter for the storm sewer and triangular hydrographs for the discharges from ABCD and EFGH areas.Explanation / Answer
The runoff coefficient (C) is a dimensionless coefficient relating the amount of runoff to the amount of precipitation received. It is a larger value for areas with low infiltration and high runoff (pavement, steep gradient), and lower for permeable, well vegetated areas (forest, flat land).
where Cp=runoff cofficient for a pervious area m= factor from dependent on ARI
30/60= rainfall intensity in mm/h for a 60min duration and ARI of 10yrs for the given location
Cp=m(0.013330/ 60-0.233)
The run-off coefficient of roofed areas (Cr) is 1.0
The run-off coefficient of paved areas (Ci) is 0.9.
Cp=m(0.013330/ 60-0.233)
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