04/14/2021 P&Z Packet - Laserfiche WebLink

Home Search

Ms.Katie Larsen 4/7/2021 Page 2 center of the property which outlets at the southwest corner through a culvert under CSAH 14. A small portion of the east side of the property drains to an existing storm sewer on Otter Lake Road. The surface water will flow to a new stormwater basin. Storm sewer is proposed to collect water from the parking lot and private road and then direct it via overland flow to the proposed Basin 1 P. Basin 1 P is designed to discharge southwest to the existing wetland, Wetland A. Basin 1 P is designed to meet City requirements for water quality, volume control and rate control. After the project is completed, the site will include approximately 1.3 acres of new impervious surfaces including the streets, paths, parking lots, and rooftops. The full build out for the Otter Crossing site, as shown in the WCA Notice of Decision Wetland Plan is anticipated to have approximately 7.35 acres of new impervious surfaces. Basin 1 P is designed to accommodate the 7.35 acres of new impervious for the future build out for the site. The current RCWD CAPROC is for the 1.3 acres of the proposed site disturbance with this first phase. Groundwater was encountered at depths ranging from 3 to 9 feet below the ground surface. Approximately 1" to 1.5" of topsoil was encountered. Below the topsoil, soils consist of native glacial till with lean clay, sandy lean clay, clayey sand, silty sand, and poorly graded sand with silt. The applicant used a HydroCAD model based on the Atlas 14, 24-hour storms to design the storm sewer conveyance system and basin. The site is designed to reduce site runoff rates for the 2-, 10-, and 100-year rainfall events. Pre-and Post- Development Discharge Rates (cfs) 2-Year 10-Year 100-Year Condition North South North South North South Development ment 0-32 0.46 2-.72 29.25 0.70 0.6b 6-.62 57.14 4�5 1.87 1212.18 .75 Development 0.27 2-.36 4.75 0.40 6�9 8.30 0.69 16 2.93 Note: This table considers the entire Otter Crossing site and future development. Post-development stormwater discharge rates are less than the pre-development rates. Comments: The City does Ret ol!Gw 12 inGh diameter storm sewer as part of the p bliG system mn 'I F_innh rliomete-pipe. The 12 inch none has been revised to 15 inch 2. Basip I P assumed to be temporary based on the proposed location and concept plans fer this area. What is the appliGant's ultimate stermwater maRagement plaR fnr WS cite)The + d ' shown the rl Ion rrn�rrr vrc�-rrT�pcni-roaircnr-pvrtv�svnvwrr-vrrcrr��cv�vea�nrur� Basin 1 P is shown as permanent and being graded to future build out conditions with this project. Otter Crossing Engineering Review