Design a detention basin for the following project. Design storms are the 100-year and 10-year storms. The project is located in Atlanta, Georgia. Use the Modified Rational Method to compute runoff....

Design a detention basin for the following project. Design storms are the 100-year and 10-year storms. The project is located in Atlanta, Georgia. Use the Modified Rational Method to compute runoff. The runoff hydrograph is a triangular hydrograph with base equal to 2.67t_c

Design Criteria:


For each design storm, peak outflow for proposed conditions is equal to or less than peak inflow for existing conditions. Maximum water level in the detention basin cannot exceed the emergency spillway crest.

Existing Conditions:

Area tributary to detention basin 5 10.0 acres

c
 0.25

tc
 20 min

Proposed Conditions:

Area tributary to detention basin 5 10.0 acres

c
 0.50

tc
 15 min

Detention Basin:

Grass-lined open cut

Bottom slope
 2.0%

Side slopes
 3 horizontal to 1 vertical

Primary outlet: 4-inch orifice, inv. elev. 400.00 ft

Secondary outlet: Weir (elev. and length to be chosen) Emergency spillway crest elev.:(Choose an elevation at the maximum 100-year water level.)

Your design will consist of computing inflow hydrographs and then, by trial and error, choosing a detention basin size and a secondary outlet so that the routed inflow hydrographs meet the design criteria. The detention basin size can vary by area and by depth.