Question 1. The variation of (2S/dt + Q) with Q, of a basin is given by Q = 0.0015(2S/dt + Q)2 + 0.195(2S/dt + Q) - 0.3833. The outlet structure is a weir with crest length L = 1.5 m set at elevation Y = 30.5 m and discharge coefficient kw = 0.4. The storage of the basin increases linearly from 0 at Y = 30.5 m to 16,980 m3 at Y = 35 m and the initial water level is at Y = 30.9 m.
(i) Determine the peak outflow rate when the following inflow hydrograph is routed through this basin.
(ii) What is the design storage and water surface elevation at the peak outflow rate.
Question 2. Obtain the stage-discharge relationship for a dual outlet detention basin. The bottom outlet is a pipe culvert of diameter 0.5 m and discharge given by ?? = ????????√2gh?? where ko = 0.6, Ao is the area, hc is the depth of water above the pipe centre line and the pipe is situated at the bottom of the basin with its invert at Stage = 0 m. The second outlet consists of a spillway with discharge ?? = ??????h??1.5 √2g where L = 2m, kw = 0.45, hs is the depth of water above the spill way crest which is located at Stage = 2m. Provide a hydraulic design of the outlet structure showing your answer in a table for stage ranging from 0 m to 3 m in 0.5 m increments.
Question 3. Stormwater runoff from a 4.05 ha development is to be routed to a retention basin. The basin design is 7.6 m by 15.2 m and has an average depth of 1.2 m. Estimate the long-term average reduction (EPA, 1986) in total suspended solids that can be obtained for the given basin. The development is 22.2 % impervious, the coefficient of variation of the runoff parameters is the same as that for the rainfall parameters, the fraction of pollutants removed at low flow rates is 1, and the performance n value of the basin is 3. The rainfall statistics for the area are:
(a) Estimate the long-term average reduction (EPA, 1986) in particulates under dynamic conditions.
(b) Estimate the long-term average reduction (EPA, 1986) in particulates under quiescent conditions.
(c) Estimate the overall average reduction (EPA, 1986) in particulates.
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