9630 EVERGREEN WAY 2018-01-02 MF Import

III. PREDEVELOPED DRAINAGE The drainage from the existing site predominantly flows to the south in a sheet flow pattern. It runs towards an existing 12" pipe located at the mouth property line near the center of the property. This pipe connects to additional piping within the commercial site to the south and is directly piped to the drainage system within Evergreen Way. The existing parking area and building on lot I has a drainage system with 2 catch basins. These basins are connected to Evergreen Way with direct piping. One of the catch basins will remain while one will be removed and its drainage basin redirected to the new pond. That portion of the existing parking area that will continue to drain directly onto Evergreen Way will not be included as part of the project area when calculating the peak flows for sizing of the detention pond ad bioswale. The basin areas and this non - project areas are shown on the predeveloped drainage basin map in the appendix. The existing drainage analysis was performed using the "Waterworks" hydrology software and its summary tables and charts are attached for reference. The methods outlined in the City of Everett Drainage Manual were used as guidelines. Following this page are the dota sheets used for the computer input data. The computer summary sheets for peak flow and time of concentration calculations are also attached. Below is a brief description of the existing drainage characteristics: Time of concentration: 88.13 minuses 2 year peak flow: 0.25 CFS 10 year peak flow: 0.53 CFS 100 year peak flow: 1.02 CFS total area: 5.57 acres pervious area: 4.52 acres curve number: 82.27 impervious area: 1.05 acres curve number: 98.0