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HomeMy WebLinkAboutPOUDRE RIVER BUSINESS PARK 2ND FILING PDP - FINAL PLAT REVIEW - 24-99 - REPORTS - DRAINAGE REPORT� lutEt <56A� � : 1 G!0 4.'�,/.).- s �r�, a 9cF5 1�DUPizp IZIVPK DUh10hh FAKK , FIt=sI rII K69 poured, the base material will be installed and then the asphalt can be laid. The only utility to be installed is power to the area light. The irrigation system will then be installed. The stormwater runoff calculations and the erosion calculations and the water quality calculations are included as a part of this report. The grading plan and the drainage plan are also included. Also the storm sewer plan and profile of the existing pipe to the Poudre River is enclosed. The original drainage report for the First Filing is included in the appendix. This drainage report and the design of the drainage system, were made in substantial compliance with the City of Fort Collins Storm Drainage Design Criteria and Construction Standards. If you have any questions during your review of this report, please call. Sincerely, Richard A. Rutherford, P.E. L.S. s*S 5 a RAR/meh ' A 6- I Due to the site being adjacent to the Poudre River, there is no detention on the existing clinic ' site and there is no detention planned on the new parking lot site. The Poudre River Business Park Master Plan is divided into two basins. Basin I is the Westerly half of the Master Plan and it drains to the existing drainage system. Basin II is the Easterly part of the Master Plan and it is undeveloped. This site is in Master Plan Basin I. The 100 year runoff from Master Plan Basin I is 31.4 c.f.s. and the 2 year runoff is 9.6 c.f. s.. The capacity of the 24" N-12 A.D.S. pipe is 23 c.f.s.. Since the existing 24 inch ADS pipe has capacity for 23.0 c.f.s., and Poudre River Business Park First and Second Filings have a 100 year runoff rate of 13.9 c.f.s., there is capacity for 9.1 c.f.s. additional runoff. There is approximately 16.9 c.f.s. runoff that will be developed in the 100 year event from the future lots in the Master Plan Basin I. On site storm water detention could be required on future developments in order to use the existing 24 inch A.D. S. storm drain. This site is divided into four sub -basins for the developed condition. Sub -Basin I is the parking area which is being developed at this time. The area of Sub -Basin I is 0.479 acres and the runoff rate for the two year storm is 0.92 c.f.s. and for the 100 year storm is 4.77 c.f.s. Sub -Basin I drains to the existing area inlet and then to the Cache la Poudre River in the existing 24 inch A.D.S. pipe. Sub -Basin II contains 0.098 acres and is being left undisturbed at this time. It historically and also will continue to flow on the surface to the Poudre River. The runoff rate for the two year storm is 0.04 c.f.s. and for the 100 year storm is 0.18 c.f.s. Sub -Basin III contains 0.313 acres and also is being left undisturbed at this time. It historically and also will continue to flow on the surface to the South. There will be no increase or change in the runoff from Sub -Basin III. The runoff rate for the two year storm is 0.10 c.f s. and for the 100 year storm is 0.46 c.f.s.. Sub -Basin IV contains 0.055 acres and is that part of the North half of Poudre River Drive that is having curb, gutter and walk constructed at this time. The runoff will flow to the existing curb inlet on the North side of the street. The two year runoff rate is 0.12 c.f.s. and the 100 year runoff rate is 0.51 c.f.s. A water quality pond will be provided in the Northwest corner of the parking lot. A pit will be constructed for the extended detention volume. The pit will spill the storm water volume,. in excess of the extended detention volume, onto the driveway and the stormwater will flow to the existing area inlet. A water quality riser pipe with water quality outlet holes will carry the extended detention volume to the existing area inlet. The water quality plan is shown on sheets 4 and 5 and the detail of the water quality feature is shown on Sheet 7. EROSION CONTROL: The site is in the moderate rainfall zone and in the moderate wind zone. A silt fence will be constructed along the North property line of the proposed. parking lot prior to beginning grading on the site. A strawbale area inlet filter will also be placed prior to beginning grading on the site. Only the area in the parking lot will be disturbed. As soon as the rough grading -of the lot is completed, -the curb and gutter will be constructed. As soon as the curb and gutter is TABLE OF CONTENTS 1 Vicinity Map 2-4 Text of Report 5-9 Runoff Calculations 10-13 Erosion Control Calculations 14-18 Water Quality Calculations Appendix Final Drainage Report Poudre River Business Park, First Filing Pocket Grading Plan Drainage & Erosion Control Plan Poudre River Business Park, First Filing Storm Sewer Plan & Profile No Text STEWART&ASSOCIATES Consulting Engineers and Surveyors June 23, 2000 Mr. Basil Harridan City of Fort Collins Utilities P.O. Box 580 Fort Collins, CO 80522-0580 Dear Basil, The following is the final drainage report for Poudre River Business Park, Second Filing situate in the Northwest 1/4 of Section 18, Township 7 North, Range 68 West of the 6th P.M., Fort Collins, Colorado. The Internal Medicine Clinic has their office on the lot adjacent to the site on the West. The clinic needs more parking and so is developing the new lot for parking only. A building may be constructed on the site in the future. The two lots have a common driveway and a common drainage outfall system. The site is in the Cache la Poudre River Basin and contains 0.7391 acres. The site has some temporary parking on the Westerly half of the lot. That part of the lot has a ground cover of recycled asphalt. The Easterly half of the lot has a ground cover of grass and weeds. There are many small volunteer Siberian Elm trees and other native plants on the site. The site has a slight ridge running East-West through it. The slopes to the North and to the South are approximately 1.0%. The site is bounded on the West by the existing Internal Medicine Clinic parking lot, on the North by the Cache la Poudre River trail, on the East and South by undeveloped land. There is an existing 15 R.C.P. storm drain on the South side of Poudre River Drive and an 18" R.C.P. crossing Poudre River Drive, as shown on Sheets 4 and 5 of the drainage plans. There is an existing 24" AD. S. storm drain from the North side inlet to the existing area inlet in the parking lot and continues down to the Cache la Poudre River. The final drainage report for Poudre River Business Park, First Filing is enclosed in the appendix of this report. The 100 year runoff rate on the First Filing is 7.98 c.f.s. The 100 year runoff rate on the Second Filing is 5.92 c.f.s. The total 100 year runoff rate is therefore 13.9 c.f.s. The existing 24 inch, N-12 A.D.S. pipe will carry 23 c.f.s. There may be future lots that will use the balance of the capacity of the existing storm drain. The runoff rate to the existing 4.0 foot curb inlet on the North side of Poudre River Drive is 1.00 c.f.s. from the West and 0.51 c.f.s. from the East for a total of 1.51 c.f.s. The inlet is in a sump condition and the capacity of the inlet is 5.0 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 r FINAL DRAINAGE REPORT. FOR POUDRE RIVER BUSINESS PARK, SECOND FILING CACHE LA POUDRE BASIN _r PREPARED FOR INTERNAL MEDICINE CLINIC DUNE 239 2000 PREPARED BY STEWART & ASSOCIATES, INC. 103 SOUTH MELDRUM STREET P.O. BOX 429 FORT COLLINS, CO 80521 TEL. 970-482-9331 FAX.970-482-9382 �I '