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HomeMy WebLinkAboutWORTHINGTON STORAGE - ODP - ODP220001 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORT NORTHERNENGINEERING.COM | 970.221.4158 OVERALL DRAINAGE MEMO: RED ROCKS SELF-STORAGE FORT COLLINS | GREELEY 1 | 2 May 16, 2022 Stormwater Department City of Fort Collins 700 Wood Street Fort Collins, Colorado 80521 RE: OVERALL DRAINAGE MEMORANDUM FOR WORTHINGTON SELF STORAGE FORT COLLILNS, COLORADO NE PROJECT NUMBER: 1853-001 Dear City Staff: This letter report accompanies the submittal for the Worthington Self Storage Overall Development Plan (ODP). Specifically, this letter report serves to document the overall drainage impacts associated with the proposed development. The proposed development site is located in the Centre for Advanced Technology P.U.D. development in Fort Collins, Colorado. The site is situated west of Worthington Circle and surrounded by private development. The overall site is roughly 3.2 acres in size. The approved drainage report for this property is the ‘Final Drainage Report and Erosion Control Study for Cinema Savers’, Center for Advanced Technology Sixteenth Filing, Fort Collins, Colorado. The proposed development site is in the City of Fort Collins Spring Creek Master Drainage Basin. Detention requirements for this basin are to detain the difference between the 100-year development inflow rate and the historic 2-year release rate. Based on the previous drainage report the calculated required detention volume is 1.51 acre-feet, this includes runoff from C.A.T Tenth filing. There is an existing outfall pipe at the northeast corner of the project site with a manhole and orifice plate down-stream of the existing detention pond. The required release rate is 1.91-cfs. Stormwater release is conveyed to the north, across Centre Ave, and discharges to Spring Creek. This outfall is planned to remain for the entire site. Per chapter 6, Section 1.3 (FCSCM), onsite detention is required when there is an increase in impervious area greater that 1000-sqft. Attachment A to this memo shows the planned development of the subject property and the comparison to the existing imperious area. There is no expected rise in the impervious area with the proposed project. Existing detention volume is a combination of the existing detention pond and ponding in the existing parking lot. With the development of the parking lot, the existing detention pond will be modified to meet the current Fort Collins detention requirements. The existing release rate will not be adjusted. The entire lot (Basin 1) will be routed to the proposed detention pond in the northeast corner of the site. Due to the modification of the impervious area, LID systems and water quality treatment will be included in the drainage design of the entire site. No floodplains are located on this site. This project will maintain the 100-yr WSEL and the proposed building will be constructed with a finish floor elevation of at least 1.5’ above the spillway elevation. NORTHERNENGINEERING.COM | 970.221.4158 OVERALL DRAINAGE MEMO: RED ROCKS SELF-STORAGE FORT COLLINS | GREELEY 2 | 2 In summary, this Overall Drainage Memo addresses any potential stormwater changes associated with the proposed Overall Development Plan. In general, there is no significant changes proposed at a major drainage level. The ODP complies with the governing City of Fort Collins Master Drainage Plans, and the previously approved drainage report for the subject property. Sincerely, NORTHERN ENGINEERING SERVICES, INC. MASON RUEBEL, PE Project Engineer Attachments · Attachment A – Impervious Area Computations · Attachment B – Drainage & Erosion Control Plan – Centre for Advanced Technology Sixteenth Filing SSSCVAULTELECSSSELECCELECEDDDTCONTROLIRRGXXVAULTF.O.XXX X X X XXXXXXXXSSSCVAULTELECSSSELECCELECEDDDTCONTROLIRRGXXVAULTF.O.DRAWN BY:SCALE:DATE:EXISTING VS PROPOSEDIMPERVIOUS AREASHEET NO:FORT COLLINS: 301 North Howes Street, Suite 100, 80521GREELEY: 820 8th Street, 80631ENGINEERNGIEHTRONRN970.221.4158northernengineering.comP:\1853-001\DWG\DRNG\1853-001_IMPV.DWG 2525 WORTHINGTON MINI-STORAGEFORT COLLINSCOLORADOMCREXISTINGPROPOSED( IN FEET )01 INCH = 60 FEET6060ROOFTOPCONCRETEASPHALTSURFACEAREA (SF)% IMPERV.IMPERV.AREA (SF)19,2207,17986,223100%100%100%112,622TOTAL=19,2207,17986,223GRAVEL040%01" = 60'5/18/2022IMP 1LANDSCAPING27,0230%0ROOFTOPCONCRETEASPHALTSURFACEAREA (SF)% IMPERV.IMPERV.AREA (SF)52,9838,35249,971100%100%100%111,306TOTAL=52,9838,35249,971GRAVEL040%0LANDSCAPING28,3390%0WO R T H I N G T O N C I R C L E WO R T H I N G T O N C I R C L E