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HomeMy WebLinkAboutGUARDIAN SELF STORAGE - FDP210018 - SUBMITTAL DOCUMENTS - ROUND 4 - EROSION CONTROL LETTER/REPORT 7200 South Alton Way, Suite C400 Centennial, CO 80112 303-740-9393  Fax 303-921-7320  5475 Tech Center Drive, Suite 235 Colorado Springs, CO 80919 719-593-2593  Fax 303-921-7320  2900 South College Avenue, Suite 3D Fort Collins, CO 80525 970-491-9888  Fax 303-921-7320 TECHNICAL MEMORANDUM To:Claudia Quezada, EI, CFM From:Rebecca Brush, PE Date:December 17, 2021 Subject: Guardian Storage Fort Collins – Erosion Buffer Waiver Introduction – Purpose and Intent The Guardian Storage project is located on the northeast corner of College Avenue and Fossil Creek Parkway. The proposed development will include the self-storage building, associated drives and parking, as well as the completion of Snead Drive east of the proposed building, from the northern property line to Fossil Creek Parkway at the southeast corner of the site. The proposed development will require work within the Fossil Creek floodplain, floodway, and erosion buffer limit and is subject to the requirements of Section 10-202 and 10-203 of the Fort Collins Municipal Code. Please refer to the attached applicable exhibits for the project, which accompany the Erosion Buffer Waiver. Applicable Ordinance The following sections of Chapter 10 apply to this project: • Section 10-202 – specific standards for erosion buffer zones • Section 10-203 – Erosion buffer zone waivers Background The attached floodplain map and outfall pipe exhibit show the proposed Guardian Storage development north of Fossil Creek Parkway as well as the existing storm outfall pipe and proposed secondary outfall pipe to Fossil Creek. Through the drainage analysis for the Guardian Storage site it was determined that the existing 29’ x 45” HERCP storm outfall pipe was insufficient for conveying the onsite and offsite runoff that comes from the north. Therefore a secondary 29” x45” storm outfall pipe is proposed to adequately convey the stormwater to the designated outfall point, Fossil Creek. In order to properly convey the stormwater to Fossil Creek construction within the Erosion Buffer will occur, including the construction of the additional storm pipe, concrete storm junction structure, concrete headwall, rir rap, 15’ wide maintenance access path, and reseeding to match existing conditions.  7200 South Alton Way, Suite C400 Centennial, CO 80112 303-740-9393  Fax 303-921-7320  5475 Tech Center Drive, Suite 235 Colorado Springs, CO 80919 719-593-2593  Fax 303-921-7320  2900 South College Avenue, Suite 3D Fort Collins, CO 80525 970-491-9888  Fax 303-921-7320 Erosion Buffer Waiver The proposed additional outfall pipe lies within the erosion buffer limit, and thus the appropriate construction measures will be taken to ensure the slope stability of the surrounding area will not be compromised. The additional outfall pipe will be located adjacent to the existing outfall pipe at the same invert elevation, and the proposed grading over the additional pipe will match the existing condition. Some additional construction measures that will be taken to ensure slope stability include: minimizing the area of disturbance at the outfall, the outfall point is positioned in-line with the creek, the used of buried riprap at the outfall for protection, and revegetation of the disturbed area with native species. The area will be revegetated using the recommended upland riparian seed mix with minimal irrigation. Once construction of the outfall pipe is complete, an as-built certification of the outfall pipe invert and surrounding grading will be completed to ensure the constructed elevations match the existing condition. Spot elevations along the outfall pipe area within the floodway have been provided on the floodplain map. These points will need to re surveyed post construction to match grade. The post construction survey tolerance level is 0.0 ft when rounded. Additionally, attached are pre-construction photos of the outfall pipe. Post Constructions photos will also be provided with the post construction no rise certification. Conclusion In order to properly convey the stormwater to the indented outfall point, Fossil Creek, construction within the erosion buffer will need to occur. The appropriate construction measures will be taken to ensure limited disturbance and slope stability within the erosion buffer limit. Please feel free to contact me at rbrush@jrengineering.com or 303-267-6189 if you have any questions or comments.  7200 South Alton Way, Suite C400 Centennial, CO 80112 303-740-9393  Fax 303-921-7320  5475 Tech Center Drive, Suite 235 Colorado Springs, CO 80919 719-593-2593  Fax 303-921-7320  2900 South College Avenue, Suite 3D Fort Collins, CO 80525 970-491-9888  Fax 303-921-7320 Pre-Construction Photos Looking from FES downstream Looking upstream at existing FES A Westrian Company X:\3970000.all\3973701\Drawings\Presentations\2021-12-17 Erosion Buffer Exhibit.dwg, 8.5x11 Portrait, 12/17/2021 12:15:46 PM, FC A Westrian Company”29,825 GSF EEE E E