1600 121ST ST SE 2016-01-01 MF Import

Casper Creek Townhouses 6/07/93 WETLAND ANALYSIS 88-4555 CRO It must be shown that the hydrology of the existing on-site wetlands is not significantly altered by the proposed development. The wetland hydrology will be analyzed for the 2- year/24-hour design storm since smaller storms are more critical with respect to wetland hydrology. The peak rate of runoff and volume of runoff er,tering the wetlands for existing site conditions will be calculated and an attempt will be made to mimic existing conditions as closely as possible upon development. Basin "B" Wetland Since a maJority of the existing basin tributary to this wetland will be developed and conveyed to the detention pond, runoff from the rooptops of the buildings surrounding the wetlar.d will be discharged to the wetland to help maintain existing flow characteristics. This undetained flow will be accounted for as bypass in the design of the detention facility. The attached calculations and hydrograph comparison show the peak rate of runoff is increased slightly upon deveiopment while the volume is decreased slightly. However, the shape of the existing and developed hydrographs area similar and developed hydrology should be sufficient to maintain a water level in the wetland which will support both existing and future mitigation plantings. Basln "C" Wetland The hydrograph comparison for the wetland located in Basin "C" shows that although the wetland will experience an increase in the peak rate of runoff for a short duration during developed conditions (due to developed rooftop runoN be'ng discharged to the wetland), the tota� volume of runoff entering the wetland will not be afiected upon development. This should be sufficient to maintain the integrity of this wetland.