Instruction
i. For any extra information please state your assumptions and the reason behind of your assumptions. ii. Use the IDF curve provided in the course documents.
1. For the watershed data shown below, plot the most appropriate simple hydrograph for: (14 marks)
a) a 30-minute, 25-year storm; Drainage area = 42 ha; watershed slope = 1.9%, length of flow path = 1200m; cultivated with crops, clay loam soil b) a 12-hour, 100-year storm Land use: 25 ha neighbourhood business; 10 ha detached residential; 12 ha multiple attached residential; 2 ha playground. c) Estimate the volume of the runoff from these storm events using the simple hydrograph method.
2. Calculate the storage at saturation for the watershed conditions shown below. If 16mm of precipitation occurs, will there be any runoff? If a 48mm rainfall event occurs, will there be any runoff? If runoff does occur, then what will be the total volume of runoff? (10 marks) a) Drainage area = 68ha; sandy clay loam; pastureland b) 24 hectares; Suburban residential; 1/3-acre lots and sandy clay load soil.
3. Calculate the time of concentration for the a 30-minute, 25-year storm; a 12-hour, 100-year storm for the basin conditions described below: 25 ha, suburban residential development, 15 ha of very closely trimmed grass course and 12 ha of unimproved area. If the length of flow path is 1250m, the slope of the drainage area is 2.5% and the soil investigations shown that the land has a clay loam soil. Comment on does the change in the frequency of the event has any effect on the time of concentration if does how it will affect the time of concentration and why. (6 marks)