A 5-ha residential development with 0.4-ha lots is to be drained such that the first 25mm of runoff is retained onsite and the postdevelopment peak discharge rate from the site is not to exceed 1m^3/s for thje 25-year 1-d rain event. The natural soil on the site is sandy loam. The IDF curve for the region is given by:
\(i = 7836/(34.110.7052t)\)
Where i is the average rainfall intensity in mm/hr, and t is the duration in minutes. The retention and detention areas are to have square bases with side slopes not greater than 3:1 (H:V) and regulations require that retention areas drain in less than 72hr. Determine the percentage of the ste area that should be set aside for retention and describe how this portion of the site should be developed. If the retention area is also to be used for the detention basin, make a preliminary estimate of the length and elevation of the weir crest in the discharge structure. Describe the physical appearance of the discharge structure.