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Home My WebLink AboutSPRING CREEK CENTER PUD PRELIMINARY - 17 90C - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPreliminary Drainage Report for Spring Creek Center Fort Collins, Colorado November 25, 1996 N O R T H E R N E N G I N E E R I N G S E R V I C E S. I N C VICINITY MAP ainage Report r ek Center , Colorado 25, 1996 Prepared For: W.W. Reynolds Companies 1600 Specht Point Road Fort Collins, Colorado 80525 Prepared By: Northern Engineering Services, Inc. 420 South Howes, Suite 202 Fort Collins, Colorado 80521 (970)221-4158 Fax (970)221-4159 Project Number: 9636.00 Initial Submittal NORTH ENGINEER SERVICES November 25. 1996 Mr. Glen Schlueter City of Fort Collins Stormwater Utility 235 Mathews Fort Collins, Colorado 80522 RE: Spring Creek Center Fort Collins, Colorado Project Number: 9636.00 Dear Glen: Northern Engineering is pleased to submit this Preliminary Drainage Report for Spring Creek Center for your review. It represents a study of existing and proposed stormwater characteristics of the project site. This report was prepared in compliance with technical criteria set forth in the, City of Fort Collins, ~norm Drainage Design Criteria and Construction Standards manual. If you should have any questions or comments as you review this report, please feel free to contact me at your convenience. Sincerely, NORTHERN ENGINEERING SERVICES, INC. 2 Roger A. Curtiss, P.E. 27362 FAUCETT ENGINEERING Andrea H. Faucett, P.E. ERN I N G INC 420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221-4159 Preliminary Drainage Report for The Spring Creek Center I. GENERAL LOCATION AND SITE DESCRIPTION The Spring Creek Center development is located east of Timberline Road and south of East Prospect Road, as shown on the vicinity map included in the appendix. The site also sits immediately south of the Spring Creek channel. More particularly, this site is a portion of the Southwest Quarter of Section 17 and a portion of the Northwest Quarter of section 20, Township 7 North, Range 68 West, of the 6`s P.M. , City of Fort Collins, Larimer County, State of Colorado. The development contains approximately 11 acres, more or less. This area is presently undeveloped, and is currently occupied by native grasses. The site slopes generally from west to east at approximately 1%. The planned development within the site includes 8 buildings and the associated parking. U. HISTORIC DRAINAGE This site is located immediately adjacent to Spring Creek, at the bottom of the Spring Creek Drainage Basin. The 100 year floodplain for the site is shown in the Spring Creek Master Drainageway Plan, by Engineering Professionals, dated March 1988. The 100 year floodplain is shown on plate 1 of 37. This information has been included on the drainage plan for Spring Creek Center. In addition, the Spring Creek Master Drainageway plan shows a shallow flooding area across Timberline Drive of 75 cfs. This is caused by an inadequate bridge structure in the railroad crossing upstream of Timberline Drive. However, during the time that the Timberline Road bridge improvements were made on the west side of the site a rip -rap channel was constructed to convey the excess flows back into Spring Creek. The portion of Spring Creek which borders this site was also included in the Hydrologic Model Update for the Spring Creek Master Drainage Plan, by Lidstone & Anderson, Inc., dated November 28, 1995. Conveyance element 301 is located at the intersection of Timberline Road and East Prospect Road. Conveyance element 201 is located at the downstream end of the site. Currently runoff from the site does not enter Spring Creek but is conveyed by sheet flow into an existing 10 foot curb cut in Specht Point Drive. The runoff is then conveyed by an existing 10 foot concrete pan into the Advanced Energy detention pond. Under current conditions a portion of Timberline Road to the west, Midpoint Drive to the south and East Prospect Road drain onto the site. That will continue to be the case after the site is constructed. M. DEVELOPED DRAINAGE Design Criteria and References Drainage criteria outlined in both the Ciry of Fort Collins Storm Drainage Design Criteria Manual, and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been used for the Preliminary Drainage Study. The Spring Creek Master Drainageway Plan, by Engineering Professionals, Inc. was used for this study, and copies of pertinent excerpts have been included in the Appendix. The Hydrologic Model Update for the Spring Creek Master Drainage Plan, by Lidstone & Anderson was also used for this study, and copies of pertinent excerpts are included in the Appendix. Hydrologic Criteria The Rational Method was used to estimate peak stormwater runoff from the proposed site. The 14 year storm and the 100 year storm event were used to evaluate the proposed drainage system. Rainfall intensity data for the Rational method was taken from the City of Fort Collins Stormwater Utility Intensity curves (Figure 3-1). Hydraulic Criteria City of Fort Collins Storm Drainage Criteria has been used for all hydraulic calculations. Preliminary Drainage Concepts Although the site is not located within the Spring Creek Drainage Basin it does sit immediately adjacent to Spring Creek. Runoff from the site drains to the east into the Advanced Energy detention pond. This pond eventually drains into the Poudre River which is where Spring Creek empties into also. Because all of the runoff from this area eventually enters the Poudre River it was decided to redirect the runoff from this site directly into Spring Creek. In addition, because of the location of the site relative to the entire Spring Creek Basin detention will not be necessary for the site. The longest time of concentration for the site is from Basin 3 which is 10.3 minutes for the 100 year storm. Based on the study done by Lidstone & Anderson the time to peak for conveyance elements 301 and 201 is 1 hour and 45 minutes, and 1 hour and 25 minutes respectively. This information is shown in the Appendix. Based on the timing of Spring Creek versus the timing of the site it will lesson the flooding impact to the Creek to discharge the flow from the site undetained before the peak of the Spring Creek channel. For this reason detention will not be provided for the site. ,Specific Drainage Concepts The site has been broken into 4 basins, designated 1, 2, 3 and 4. The shallow flooding from Timberline Road is being provided for in an existing rip -rap channel which lies immediately east of Timberline. This channel redirects the 75 cfs back into Spring Creek. Two cross -sections were taken of the channel to verify that it had the capacity to convey the 75 cfs. The results show that it does and are included in the Appendix. 1 - Basin 1 is conveyed by surface drainage through a curb cut and then to a rip -rap rundown to Spring Creek. 2 - Basin 2 is conveyed by surface drainage through a curb cut and then to a rip -rap rundown to Spring Creek. 3 - Basin 3 is conveyed by surface drainage through a curb cut and then to a drainage swale into Spring Creek. 4 - Basin 4 will drain off of the site and into the existing 10 foot concrete pan in Specht Point Drive which drains into the Advanced Energy detention pond. IV. EROSION CONTROL The Spring Creek Center lies within the Moderate Rainfall Erodibility Zone, and the Moderate Wind Erodibility Zone, per the City of Fort Collins zone maps. At the time of final design, per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, the erosion control performance standard will need to be calculated, and appropriate measures designed to control rain and wind erosion during and after construction. All construction activities must also comply with the State of Colorado permitting process for Stormwater Discharges associated with construction activities. A Colorado Department of Health NPDES discharge permit will be required before any construction grading can begin. V. CONCLUSIONS Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. Some of this study has been based on concepts and conclusions developed in the Spring Creek Master Drainageway Plan by Engineering Professionals, and also on the Hydrologic Model Update for the Spring Creek Master Drainage Plan. Drainage Concept The proposed drainage concepts presented in this study and shown on the preliminary grading and drainage plans adequately provide for the conveyance of developed runoff from the proposed development. If groundwater is encountered during construction, and dewatering is used to install utilities, a State of Colorado Construction Dewatering Wastewater Discharge Permit will be required. Erosion Control Concepts Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, at the time of Final Design, the erosion control performance standard will need to be calculated and appropriate measures taken to contrci rain and wind erosion from the site. REFERENCES 1. Storm, Drainage Design Criteria and Constru. Lion Standards, Ci y of Fort Collins, Colorado, May 1984. 2. Drainage Criteria Manual, Urban Drainage and Food Control Dim rict, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. 3. Spring Creek Master Drainageway Plar► by Engineering Professionals, March 1988. 4. H urolopic Model Update for the Spring Creek Master Drainage 1-� by .7.. O T T L 21 P�a�,, �y Liu�tone «. Anderson, .,-�c., ltiove-nl,er �8, 19 APPENDIX