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HomeMy WebLinkAboutDrainage Reports - 08/01/2014City offt.Collins prov Plans Approved v Date--,- a NORTHERN ADDRESS: PHONE:970.221.4158 wEBSITE: NE I 200 S. College Ave. Suite 10 ENGINEERING , Fort Collins, CO 80524 FAX: 970.221.4159 uww.nodhernengiueering.can Overall Drainage Report Date: July 31, 2013 Project: Waterfield Third Filing Overall Development Plan Fort Collins, Colorado Attn: Mr. Wes Lamarque Fort Collins Utilities 700 Wood Street Fort Collins, Colorado 80524 Mr. Lamarque: This letter report accompanies the submittal for the Waterfield Third Filing Overall Development Plan (ODP). Specifically, this letter report serves to document the overall drainage impacts associated with the proposed Waterfield Third Filing Development. The proposed development site is located northwest of the intersection of Timberline Road and Vine Drive in Fort Collins, Colorado. The overall Waterfield site is roughly 142 acres in size. The currently proposed Third Filing site involves roughly 117 acres. The site is not encroached by any FEMA or City floodplain. The proposed development site is in the City of Fort Collins Dry Creek Basin. Detention requirements for this basin are to detain the difference between the 100-year developed inflow rate and the historic 2-year release rate. The historic 2-year release rate for this basin is 0.20 cfs per acre. Previous submittals for the overall Waterfield site are briefly described below: • Waterfield P.U.D., First Filing, by Northern Engineering, October 1998. Existing .. 4,. development in the southeast corner of the overall Waterfield site was done with First Filing. Detention and water quality was provided in the pond at the southwest corner of the overall Waterfield site. 1 • Waterfield P.U.D., Second Filing, by Nolte, Inc. March 2000. Was not constructed; focused on areas west of Merganser Drive, which are now included in the current Third Filing design. The existing First Filing development in the southeast corner of the site drains to the existing detention pond located at the southwest corner of the site. The outfall for this pond is a siphon storm line which conveys flows under the Lake Canal. This pond is to be modified with the currently proposed development to incorporate detention and water quality measures for the existing development,. as well as the proposed Waterfield Third -Filing development. It is understood that the siphon outfall for this pond is the responsibility of the development to maintain. A conceptual level SWMM model is provided in Attachment 1, showing concept level retention and detention volume requirements. This model shows 19.9 acre-feet of retention volume for "Basin 1" in the model (retention over the existing wetland area), and an addition of 5.2 acre- feet of detention volume for "Basin 2" in the model (modified existing detention pond at the southwest corner of the site). In summary, this Overall Drainage Report letter adequately addresses any potential stormwater changes associated with the proposed development. In general, there are no 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 plans specific for the subject property. Please feel free to contact me with any questions you may have. Sincerely EERING Project 2 s r ATTACHMENT 1 Conceptual Stormwater Management Model (SWMM) It: _. lz$ _ z, 1 �m 4 I %A 0 LO z 3 CD m a ^. I N I N I O I I 4 k N I k ro o. h H 1 i 4 N # P.i �0001 BOO ] b+ I O P 000l0OOO m O + v U I H 1 a I R 940 R p C 1 MOONO OOm0000000 r m 1 « a)E a« >< 1 O I x 10 y# O O I • I R ..I .-1 + N I R i IDt O O Z 1 c Y E R # O .N # O o 0 1 00 U/ U I PO m�D P01 N U I O10000M000 P.4 N I x~ ro O�x E v 1 doQ P iom E v 1 oP 000�000 om o a l k D Y G x N N a U/ 1 r ONmM P 7 N Om O00 m000O. 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