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HomeMy WebLinkAboutBLOOM FILING ONE - PDP210014 - DOCUMENT MARKUPS - ROUND 5 - DRAINAGE REPORTBloom Filing 1 Final Drainage Report Galloway & Company, Inc.Page 5 of 28 peak discharge and volume) associated with future development within the Upper Cooper Slough Basin to the 100-year existing condition release rates into the lower Cooper Slough area.” Basin H-1 (±72 acres, Q2 = 4.0 cfs, Q100 = 26.0 cfs) is associated with the northeastern portion of the site to the north of the Burlington Northern Railroad tracks. Runoff generally runs south toward the railroad tracks and then is conveyed east into the Cooper Slough. Basin H-2 (±22 acres, Q2 = 1.3 cfs, Q100 = 15.5 cfs) is associated with the northeastern portion of the site on the south side of the Burlington Northern Railroad tracks. Runoff generally runs south into undeveloped land. Basin H-3 (±162 acres, Q2 = 8.7 cfs, Q100 = 52.0 cfs) is associated with the western portion of the site. Runoff currently sheet flows south into the Lake Canal. Basin H-4 (±6.5 acres, Q2 = 0.4 cfs, Q100 = 8.7 cfs) is associated with the southwest portion of the site. Runoff currently sheet flows east into the adjacent property and then to the Lake Canal. Floodplain The Cooper Slough runs along the eastern boundary of the Bloom Filing 1 Development. According to the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map Panels 982 (FIRM Number 08069C0982F) effective date December 19, 2006 and Panel 984 (FIRM Number 08069C0984H) effective date May 2, 2012 included in Appendix A, a portion of the site lies within Zone AE of the Cooper Slough, an area subject to inundation by the 1% annual chance (1-PAC) flood (I.E. the 1-PAC floodplain). In Zone AE, the base flood elevations (BFEs) have been determined. However, a LOMR (FEMA Case No.: 17-08-1354P) became effective February 21, 2019, removing BFEs from the area and replacing them with 1-PAC water surface elevations at cross sections. The LOMR was submitted as a part of a restudy of the Boxelder and Cooper Slough prepared for the Boxelder Stormwater Authority by Ayres Associates. A Preliminary FIRM Panel, 08069C0984J dated January 26, 2021 included in Appendix A, presents the effective 1-PAC floodplain delineation, floodway delineation, and 1-PAC water surface elevations from the 2019 LOMR. The effective 1-PAC floodplain encroaches on planned Pond B and part of Pond C, as well as in a significant portion of the Bloom Development’s southern end south of the planned Donella Drive. No development activities are planned to encroach on the effective floodway. All elevations provided are in reference to the NAVD 1988, with Cooper Slough effective 1-PAC floodplain water surface elevations ranging between 4930.5 ft and 4960.2 ft adjacent to the Bloom Filing 1 Development. Bloom Filing 1 Final Drainage Report Galloway & Company, Inc.Page 6 of 28 The development shall follow floodplain regulations stated in Chapter 10 of the City Code. All structures shall have the elevation of the lowest floor be above regulatory flood protection elevations. It is anticipated that no work shall commence within the floodway. This drainage report is prepared as an addendum to the floodplain use permit application that is submitted to the City of Fort Collins, allowing for the site to be built upon approval. A separate LOMR will be prepared that will analyze the impact of the as-built development on the effective 1-PAC floodplain and associated water surface elevations. The LOMR will be completed and approved before issuance of any certificate of occupancy (CO). III. Project Description The entire Bloom development encompasses approximately 260 acres and will include the development of both single and multi-family homes, commercial use, and associated streets, utilities, and open space. The project site is bordered to the west by East Ridge Second Filing, also referred to as the Mosaic Subdivision, which is a single and multi-family development; to the north by the Trail Head Subdivision, another single-family development; to the southeast by the proposed Peakview development; and to the south (south of Bloom) and southwest by various commercial developments. This report summarizes the drainage facilities for Filing 1 including any channel improvements, limited impact development best management practices and proposed water quality/detention. Existing Conditions Filing 1 is 66.8 acres of vacant undeveloped farming land. Existing grades of the Site generally slope from 0.5 to 3 percent. Proposed Conditions Filing 1 of Bloom encompasses ±66.8 acres in the northwest area of the overall development. It will include the development of 130 single family homes, 138 town homes, associated streets, utilities, and open space. The area of Filing 1 drains from north to south to two detention/irrigation ponds at grades of 0.5 to 4.0 percent. These two onsite ponds will outfall into another offsite pond downstream where it will eventually outfall into the Cooper Slough. Filing 1 will also include the storm infrastructure for Greenfields Drive and main trunk lines for the future development along with their associated ponds.