- Information Given Manning S Equation Q Ar S Orifice Flow Q C A 2gh Weir Flow Q Ca 2gbhow Pipe Flow Ah F K Discharge 1 (23.67 KiB) Viewed 35 times
- Information Given Manning S Equation Q Ar S Orifice Flow Q C A 2gh Weir Flow Q Ca 2gbhow Pipe Flow Ah F K Discharge 2 (33.25 KiB) Viewed 35 times
- Information Given Manning S Equation Q Ar S Orifice Flow Q C A 2gh Weir Flow Q Ca 2gbhow Pipe Flow Ah F K Discharge 3 (59.74 KiB) Viewed 35 times
(d) A detention basin needs to be designed with a total capacity of 60000m² of storage. The triangle inflow hydrograph for the basin is given in Figure 3. Assume that the basin initially is dry and outflow will cease when the basin is again empty (Inflow volume = outflow volume). Determine the peak outflow from the basin assuming a linear rise and fall in the outflow hydrograph. Draw a sketch of the outflow hydrograph. What time does outflow cease? (3 marks) 7 ^ 3 4 Discharge m³/s 6 N 012 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hour) Figure 3 Inflow hydrograph of detention basin
QUESTION THREE (Total of 30 marks) (a) A storage basin is drained by a weir with crest length of 5m and a discharge coefficient Ca of 0.577. Estimate the basin discharge when the water in the basin is 0.8m above the crest of the weir. (3 marks) (b) A 500 mm diameter round concrete culvert (n = 0.013 or f= 0.02) drains a detention basin. The culvert entrance is well rounded and has a discharge coefficient of 0.9 and an entrance loss coefficient of 0.5. The slope of the culvert is 1.5% and the length of the culvert is 20 m. Estimate the basin discharge when the water in the basin is 1.0m above the invert of the culvert. Assume that the culvert exit is not submerged. (8 marks) (c) A wet detention basin is drained by an outflow weir. The elevation versus storage in the detention basin is shown in Table3.1. Where the weir crest is at elevation 0 m, which is also the initial elevation of the detention basin prior to runoff. The weir discharge, Q (m³/s), is given by Q=1.8Lh¹5 Where L-10m is the length of the weir in meters and h is the height of the water above the crest of the weir. Using time step of 30 minutes and assuming that the initial outflow is zero, the initial storage is zero. The inflow hydrograph is given in Table 3.2. Estimate the outflow hydrograph from the detention basin. (16 marks) Table 3.1 Elevation (m) 0.0 0.25 0.5 0.75 1.0 1.25 Table 3.2 Time (min) 0 30 60 90 120 150 180 Storage (m³) 0 6000 12000 18000 24000 30000 Inflow (m³/s) 0 5.0 10.0 6.5 3.5 2.0 0