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HomeMy WebLinkAboutDELLENBACH SUBARU - PDP - 50-98 - REPORTS - DRAINAGE REPORT.-POL K J will have less hard surface than now exists. No onsite detention is proposed since the proposed new improvements will generate less runoff than that from the historic site. JRunoff from most of the site drains to the southeast comer of the site where there is an existing 4 inch diameter cast iron pipe which extends from the interior curb of the parking lot under the J sidewalk and through the west curb of the frontage road. It is planned to leave this existing 4 inch pipe in place to drain the parking lot. The 4 inch pipe will not carry the 2 year runoff and therefore a small detention ponding area will occur before the interior curb is overtopped. This is not a J designed pond, but it will provide a minor amount of detention volume and will also provide a basin J for some settling out of silt and debris. The north half of the building and the northwest comer of the parking lot have historically drained to Swallow Road, and that will not be changed by the proposed Jconstruction. The historic drainage patterns of the overall site will not be changed by the proposed new construction. j Subbasins have been delineated on the drainage plan, along with concentration points showing J the flow quantities from the basins. The flow quantities will not be increased from the historic flows. The flow in the south gutter of Swallow Road runs east across the frontage road in a concrete Jpan and then southeast around the curb return to two 30 inch wide inlets on the west curb of College Avenue. The proposed construction on the Dellenbach Subaru site will not change the existing storm water flows at the South College -Swallow intersection. There are no offsite flows onto the site. ,The autoparts store located west of the site drains to J Swallow Road and the Dellenbach Motors lot to the south of the site drains to the southeast to the frontage road. There are no water quality features proposed for this site. Most of the existing site is a paved 1 parking lot, and it will remain so after the new construction. There will be sand and oil interceptors J installed in the shop portion of the building. J Erosion control will need to be provided during parts of the construction period. 'The existing pavement will be removed at the new building site and the foundation will be installed immediately after, so bare soil will not be a problem in his area. A gravel filter will be placed over the existing 4 inch diameter outlet pipe during the parking lot reconstruction. All of the areas where pavement is removed are small and narrow, so additional protection from wind erosion is unnecessary. The erosion control collateral should be the minimum of $1,000 dollars. There are calculations included in this report of the storrawater runoff quantities from this site to Swallow Road and to the south. 1 This report has been prepared in compliance with City of Fort Collins.Stormwater Drainage and J Design criteria. ISincerely, a 4502 1 Phillip I. Robinson P.E. & L.S. % k * PIR/meh `'•L'�. STEWART&ASSOCIATES Consulting Engineers and Surveyors June 16, 1999 Mr. Basil Hamdan Storm Water Utility City of Fort Collins P.O. Box 580 Fort Collins, CO 80522-0580 Dear Basil, The Dellenbach Subaru P.D.P. is located at the Southwest comer of South College Avenue and Swallow Road. The site is the existing Round -The -Comer restaurant and parking lot. This project is located in the Foothills Drainage Basin Master plan, prepared by Resource Consultants in February. 1986, and revised by the Warren Farms Alternative Components To The Foothills Basin Master Plan by RBD in April 1996. The original report in 1986 indicated that after construction of the 48 inch pipe _improvements under the Burlington Northern Railroad and under the Larimer County canal No. 2, to carry water `i from the detention ponds on the Warren Farm to east of College Avenue, would cause a localized j flood plain with a 100 year high water elevation of 5025.0 in the area immediately west of College Avenue. The 1996 report indicates that the localized flood plain just west of College Avenue will not occur. There were two runs of the UDSEWER model of the piping system; one that modeled inlet J flows only, and one that modeled the peak discharge amount from Detentions Pond in the Warren Farm - Meadowlark area. The text states that at the time of downstream peak in the pipe system the pond is releasing 31.37 c.£ s. Although there wasn't a UDSEWER run that ,included this flow with the inlet flows, the addition of the 31.37 c.f.s. to the inlet flows would not exceed the amount modeled for the peak discharge from Pond 19 of 105.3 c.£ s. In either of the UDSEWER runs, there was no surcharging of the pipe system until downstream (east) of College Avenue, so there would be no water surface above the ground in the area west of College Avenue. A copy of portions of the 1996 report are included in this report. Previously, it was proposed to vacate the frontage road along College Avenue and to modify the curb on College Avenue to provide a driveway into the Dellenbach property. That is no longer a proposal, and the work which is now planned consists of an addition to the west side of the existing Round -The -Comer building and some revisions to the curbs and islands located within the existing Round -The -Comer parking lot. There will be no new construction within public rights -of -way, other 1 than the relocation of driveway cuts. The existing Round -The -Comer building will be maintained and a new building will be constructed adjoining the west side of the existing Round -The -Comer building. The floor of the new 1 building will be placed at the same grade as the existing Round -The -Comer building. The new building addition will replace existing concrete and asphalt surfaces, and the reconfigured parking lot James H. Stewart 7 and Associates, Inc. 103 S. Meldrum Street P.O. Box 429 Ft. Collins, CO 80522 970/482-9331 Fax 970/482-9382 Table of Contents 1A 2 Letter and Text 3 Vicinity Map 4 & 5 Basin Calculations 6 Concentration Points 7 Historic and Developed "C" Appendix Copies of a Portion'of 1996 Report of Warren Farms Alternative Components to the Foothills Basin Master Plan Pocket Site Drainage Plan STORM DRAINAGE REPORT FOR DELLENBACH SUBARU P.D.P. LOCATED IN THE FOOTHILLS BASIN PREPARED FOR DELLENBACH MOTORS JUKE 16,1999 PREPARED BY STEWART & ASSOCIATES, INC. 103 SOUTH MELDRUM ST. P.O. BOX 429 FORT COLLINS, CO 80522 TEL. 970-482-9331 FAX.970-482-9382