Agenda Packets - 1983/05/16 - Laserfiche WebLink

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Planning Coimnission Page 2 April 13, 1983 rl D-3 zone, even though a residential structure exists on one of thesL commercial lots. Thus, the minimum sclback hclwaan the motel structure and the lot line which soparate:: the metal from the single family home would be 10 feet. The site plan is proposing 30 feet. Rice Creek. Watershed District approved a permit (73-G4) on January 16, 1974 based on Lhc following data: 1) Total drainage area 20.7 acres. 2) Total ulL•imaL•c impervious 7.3 acres (36%). 3) Pond storage volume below 884.5 of 0.8 acre-feet. 4) Outlet discharge of 6.0 cubic feat par second or greater. 5) Ten year, 2 hour design storm which is a 2.5 inch rainfall. Chapter 49A requires the following: 1) Maximum rate of discharge for undeveloped property be at a rate equal to the 5 year storm which in estimated to be 10 cubic feel• per second. 2) Runoff between 5 year, 24 hour and 50 year, 24 hour event k' must be detained on site. This is estimated to be 4.44 acre-feet for total development-, and 0.63 acre-feet for proposed development. Initial analysis would conclude that either the runoff assumptions for the Rice Creek Watershed permit were too low or that proposed development will utilize over 75 percent of the proposed 0.8 acre-feet of storage. Staff, therefore, concludes that the proposed catchment (pending) area may be significantly undersized for total (20.5 acre) development to meet current requirements for Chapter 49A. Staff recommends applicant: 1) Reevaluate storm water runoff taking into consideration the proposed and future development. 2) Resubmit data to Rice Creek Watershed District for update and reapproval, if necessary. 3) Establish drainage easement over catchment and future develop- ment on the balance of the lot being subdivided. Additional future drainage casement may be required when land use and a more exact determination of impervious area can be made. 4) That existing skimmer be modified to allow emergency overflow in the event that skimmer inlet becomes plugged or frozen.