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HomeMy WebLinkAboutBRIDGES II - AMENDED FINAL - 30-98 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTAmended Bridges lI P.U.D. Page 2 The existing pan in the north -south driveway will be extended to the south to a new area inlet in the new paved turnaround area. The runoff will then -be carried in anew 15-inch storm drain to the existing drop manhole just above the New Mercer Canal. The site will be graded to preclude any increased runoff due to development, from entering the New Mercer Canal. One duplex will be constructed on this site. The 15 inch diameter storm drain was modeled with UDSEWER and the results are enclosed as a part of this report. The HGL is shown on the pipe profile on Sheet 4 of 4. EROSION CONTROL The site is in a moderate wind erodibility area and in a high rainfall erodibility area. There is good existing ground cover on the site. It is proposed to not remove the ground cover immediately. The foundation for the proposed duplex will be constructed first. This will 'eliminate wind erosion on the westerly part of the site. After the duplex is under construction, the s, extension of the driveway and the turnaround will be graded, and the proposed storm drain will be i' constructed. Straw bales will be used around the hole for the area inlet. After the area inlet is constructed, a rock filter will be placed around the inlet if there is any time between the inlet construction and the paving of the cul-de-sac. After the duplex and the cul-de-sac are completed, the remaining ground cover will be removed and finish grading and seeding will be done in areas where bluegrass will be planted. The area between the east six -unit apartment building and the New Mercer Canal will keep the existing ground cover, except the area disturbed by the construction of the 15-inch storm drain which will be reseeded with dryland mix. The runoff calculations and pipe and inlet sizing and the erosion calculations are included as part of this report. The grading and drainage plan is also included. This drainage report and the design of the drainage system are in compliance with the City of i Fort Collins Storm Drainage Specifications and Criteria. If you have any questions concerning this report, please call. Sincerely, Richard A. Rutherford P.E. & L.S. President ITC 5028 A �, c I I I July 15, 1998 ' Mr. Basil Hamdan Storm Water Utility City of Fort Collins P.O. Box 580 Fort Coll ins, CO 80522 IDear Basil, STEWART& SSOCIATES Consulting Engineers and Surveyors ' The following is the storm drainage report for the Amended Bridges H P.U.D. The site is in the Southwest comer of that part of the Bridges P.U.D. lying north of the New Mercer Canal. It is all that part of The Bridges H P.U.D. that was not sold to the City of Fort Collins and contains 22,885 square feet. (0.53 acres). The sits is bounded on the north and east by the developed Bridges P.U.D., on the west by a privately owned single-family residence and on the south by the New Mercer Canal and public open space. The site slopes from north to south. There is no off -site runoff flowing onto this site from the south, west or east adjoining land, but there is from the north. The existing six -unit apartment building on the west side of the existing north -south access driveway drains to the existing pan in the driveway which, under the 1980 plan, would drain in a concrete pan to manhole number 3 but under this plan drains to the area inlet to be constructed in the cul-de-sac. The rear half of the existing six -unit apartment building on the east side of the driveway historically drains across the site and into the New Mercer Canal. The proposed plan has this drainage flowing to the proposed area inlet except for ' the 0.14 acres lying East of the proposed turn around. The drainage plan for the Bridges P.U.D. that was approved in December 1980 has all of the P.U.D. lying north of and above the New Mercer Canal draining to an existing 21-inch storm drain that flows under the New Mercer Canal and over the Larimer County No. 2 Canal to an existing detention pond in the now public open space below the Larimer County No. 2 Canal. ' This amended site plan will continue to drain in the above manner to the existing detention pond. Since the new plan has less hard surfacing than the approved plan, the amount of runoff has ' decreased. This proposed site plan is the only area of The Bridges P.U.D. that has not been developed or sold to the City of Fort Collins. The total area of the Bridges P.U.D. lying northerly of the New Mercer Canal is 6.0 acres more or less. The existing 21 inch diameter pipe under the New Mercer Canal and over the Larimer County No. 2 Canal was designed to carry the 100 year developed runoff from the site which is 20.0 c.f.s. James H. Stewart and Associates, Inc. 103 S. Meldrum Street P.O. Box 429 Ft. Collins, CO 80522 970/482-9331 Fax 970/482-9382 TABLE OF CONTEXT 1-2 Text 3-5 Storm Water Runoff Calculations 6-9 UDSEWER 10 Kutter's Formula Nomograph 11 Grate Capacity Figure 12-14 Erosion Control Calculations 15 Erosion Control Cost Estimate 16 Vicinity Map Appendix 1980 Report r FINAL DRAINAGE REPORT FOR AMENDED BRIDGES H P.U.D. CANAL IMPORTATION BASIN PREPARED FOR MR. BRIAN SOUKUP JULY 15,1998 PREPARED BY STEWART & ASSOCIATES, INC. 103 SOUTH MELDRUM STREET FORT COLLINS, COLORADO 80521 970/482-9331