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HomeMy WebLinkAboutTIMBERLAKES BUSINESS PARK - ODP - 60-98 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTe V. CONCLUSIONS The drainage concepts for this project are consistent with current policies and practices for storm drainage management. The site will continue to maintain the flow patterns as have been experienced historically. Site runoff will be allowed to "free release" to reduce the major storm peak by allowing the site flow to pass to the major drainage early. Off -site runoff will continue to pass safely through the site. IV. DRAINAGE FACILITY DESIGN The drainage concepts for the developed conditions will be discussed in the following paragraphs. The developed conditions are shown on the "Drainage Concept Plan" located in the map pocket at the end of this report. The improvements include claiming more land by filling -in portions of the ponds and providing the access road, utilities and building lots for business/industrial use. The site will change significantly with the grading operations. On the enclosed map we have delineated five sub -basins that represent the general grading concept. Each basin will be graded flat providing only minimum slopes to flow the runoff. Discharge from the basins will be spread - out in an attempt to have sheet flow as the runoff flows through the buffer areas. This will provide for the opportunity to improve water quality before the runoff enters the ponds by filtering the flows through the landscape areas. It is proposed to "free release" the runoff to the ponds to allow the flows to discharge downstream before the "peak" of the storm reaches the area. Detailed calculations can be found in Appendix A for the developed flow rates for the identified sub -basins. The improvements to this site will allow the off -site runoff to continue to pass through the area without significant impact. Based on the inflow hydrograph (copy enclosed in Appendix A) that was generated by the previous drainage report for "Cache La Poudre Industrial Park and Pitkin — Riverside Storm Drain" dated December 1986 (Rev) by Shiloh, Inc., we modeled the existing site condition and the modified site condition to determine impact. Assumptions for these models include the inflow hydrograph with a peak of 400 cfs, the outflow of the west pond into the east pond through the two 36" culverts of 124 cfs and the outflow of the east pond to Spring Creek of 40 cfs. These reports are located in Appendix A. We also have included a model utilizing more correct flow rates through the piping. As can be seen, there is substantial storage capacity in the ponds. The inflow hydrograph has a total inflow of 18.67 acre-feet which could easily be stored in the modified west pond which has a capacity of 52 acre-feet with one -foot of freeboard. I M. DRAINAGE DESIGN CRITERIA The City of Fort Collins "Storm Drainage Design Criteria and Construction Standards" provides the direction for developing a storm water management plan. This report utilizes those directions. It is not anticipated that the drainage patterns will be altered from historical and the release points will be similar. This drainage report for the Timberlakes Business Park complies with the aforementioned guidelines and references. The plan located in the map pocket at the end of this report shows the overall site development control for the storm water management. The hydrological criteria used for this report are based on the Rainfall Intensity Duration Curve. Using the rational formula method for runoff calculations, flow rates for each sub -basin is determined for the 10 and 100-year occurring storm. Hydrologic calculations are included in Appendix A with the related tables and figures. H. HISTORIC DRAINAGE MAJOR BASIN DESCRIPTION Timberlakes Business Park is located within the Poudre River drainage basin. Recent improvements to the Poudre River channel near this area has caused this area to be removed out of the Poudre River floodplain. SUB -BASIN DESCRIPTION Adjacent to the southeast property corner of this site is the Spring Creek drainageway which discharges easterly to the Poudre River. SITE SUB -BASIN DESCRIPTION Historic drainage patterns have all been modified due to the mining operations in this area. The current drainage patterns has the runoff from this site discharging into the adjacent ponds left from the mining reclamation. The parcel on the west side of Timberline Road discharges into the west pond which connects to the east pond with two 36" culverts under the Road. The easterly parcel has approximately 2/3 of its runoff discharging into the east pond and 1/3 into the north pond. The east pond discharges to the Spring Creek drainageway via a 36" pipe. The north pond does not have a known release, but would overtop easterly to the Poudre River. The City of Fort Collins has an easement through the west and east pond to discharge storm runoff from off -site basins to the west. Previous studies have calculated this runoff to have a peak flow for the 100 year event of 400 cfs. The conveyance of these flows to the east pond is via two 36" culverts which have the capacity of 124 cfs. The east pond release is controlled by a single 36" pipe which discharges into Spring Creek. The ponds currently provide detentioning for this off -site runoff. VICINITY MAP I. GENERAL LOCATION AND DESCRIPTION LOCATION Timberlakes Business Park is located in the SE'/a of Section 18 and the SW'/a of Section 17, T. 7 N, R. 68 W. of the OhP.M. The parcel is a part of Tract 1 and Tract 3 and all of Lot 1 of the Cache La Poudre Industrial Park P.U.D. The site is located on both the east and west sides of Timberline Road approximately 760 feet north of the Prospect Road and Timberline Road intersection. The property is generally bounded by City open space on the north and east, Burlington Northern Railroad on the west and development on the south. A vicinity map showing the site location is enclosed on the next page. The site specific location and boundary is shown on the enclosed map located in the map pocked at the end of this report. TOPOGRAPHY The site consists of two Parcels, Parcel A approximately 6.8 acres and Parcel B approximately 30.2 acres. Parcel A, on the west side of Timberline Road, consists of remnants of the mining operation which includes some natural ground, some pond fill land and some pond. This parcel is void of any development or significant vegetation. The ground cover is bare with a variety of weeds. Parcel B on the east side of Timberline Road, consists of more remnants of the mining operation which includes some natural ground, some pond fill land and some pond. This parcel has some improvements, such as a couple of structures that will be razed. The ground cover is bare with a variety of weeds and scrub bushes. The site generally drains west to east on variable slopes. The enclosed ALTA survey map shows the existing topography on the site. "I hereby certify that this report (plan) for the drainage design of Timberlakes Business Park, was prepared by me (or under my direct supervision) in accordance with the provisions of the City of Fort Collins drainage regulations for the owners thereof." Registered Professional Engineer State of Colorado No. 16726 (Sea TABLE OF CONTENTS Certification I. General Location and Description II. Historic Drainage III. Drainage Design Criteria IV. Drainage Facility Design V. Conclusion Appendix A Map Pocket DRAINAGE REPORT TIMBERLAKES BUSINESS PARK FORT COLLINS, COLORADO Prepared for: SHARP POINT LLC W.W.REYNOLDS 4875 PEARL EAST CIRCLE, SUITE 300 BOULDER, COLORADO 80301 (303) 442-8757 Prepared by: PARK ENGINEERING CONSULTANTS 420 21ST AVENUE, SUITE 101 LONGMONT- COLORADO 80501 (303) 651-6626 November 18, 1998 PEC Job #10756001 EP PARK ENGINEERING CONSULTANTS DRAINAGE REPORT TIMBERLAKES BUSINESS PARK FORT COLLINS, COLORADO 420 21 st Ave. Suite 101 • Longmont, CO 80501 • (303) 651-6626 9 FAX (303) 651-0331