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Home My WebLink AboutTROUTMAN OFFICE PARK PUD - PRELIMINARY & FINAL - 21-89G - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTNo Text FINAL DRAINAGE AND EROSION CONTROL REPORT FOR TROUTMAN OFFICE PARK P.U.D. FORT COLLINS, COLORADO PREPARED FOR: TROUTMAN OFFICE PARK ASSOC., LLC FORT COLLINS, COLORADO 80525 JULY 19, 1996 PREPARED BY: PARSONS & ASSOCIATES CONSULTING ENGINEERS 432 LINK LANE PLAZA FORT COLLINS, COLORADO 80524 (970) 221-2400 PROJECT NUMBER: 96.10 TOP � PARSONS & ASSOCIATES, INC. CONSULTING ENGINEERS July 19, 1996 Mr. Glen Schlueter Fort Collins Stormwater Utility 235 Matthews P.O. Box 580 Fort Collins, CO 80522 RE: Resubmittal of Final Drainage and Erosion Control for Parkway Townhomes, P.U.D. Dear Glen: This drainage and erosion control report has been prepared to provide final design information for the proposed 18,400 sq. ft. commercial office building at the northwesterly corner of Troutman Parkway and JFK Parkway, Fort Collins, Colorado. The parcel has been identified by plat as "Superblock Holding" and was reviewed and approved thru preliminary P.U.D. with Marketplace P.U.D. in 1989. Sincerely, `,,r1�,:'. PARSONS & ASSOCIQwE; J 6 . Gary A. Odehnal, P.E'�'`' •• t"4AL - 0 Project Engineer ''%% '�' �, 1•117;futt.::i•' GAO/gbl Enclosure • 432 Link Lane Plaza . Ft. Collins, Colorado 80524 • 19701 221-2400 TABLE OF CONTENTS I. INTRODUCTION 1 II. SITE DESCRIPTION 1,2 III. HISTORIC/MASTER DRAINAGE 2,3 IV. DRAINAGE CRITERIA 4 V. DRAINAGE UNDER DEVELOPED CONDITIONS 5,6 VI. EROSION CONTROL 7 EXHIBIT 1 VICINITY MAP APPENDIX A DEVELOPED DRAINAGE CALCULATIONS APPENDIX B DRAINAGE REPORTS OF RECORD APPENDIX C EROSION CONTROL -CALCULATIONS BACK POCKET EXHIBIT 2 FINAL DRAINAGE AND EROSION CONTROL REPORT FOR TROUTMAN OFFICE PARK P.U.D. This drainage and erosion control report has been prepared to provide final design information for the proposed 18,400 sq. ft. commercial office building at the northwesterly corner of Troutman Parkway and JFK Parkway, Fort Collins, Colorado. The parcel has been identified by plat as "Superblock Holding" and was reviewed and approved thru preliminary P.U.D. with the Marketplace P.U.D. in 1989. This report was prepared in conformance with the City of Ft.Collins Stnrm DrainagP and Construction Standards and with conformance to "Mail Creek and McClellands Major Drainageway Plan: by Cornell Consulting Company, December, 1980. Troutman Office Park P.U.D. is more specifically identified as a parcel of land situated in the southwest quarter of Section 36, Township 7 North, Range 69 west of the 6th Principal Meridian, City of Fort Collins, Larimer County, Colorado. The site is bounded on the north and west by the fully developed Marketplace P.U.D. and on the south by Troutman Parkway and east by JFK Parkway. Please refer to Figure 1 for a Vicinity Map of the area. The total -1- PROJECT SITE VICINITY _IIAP 1" = 1400' FIG URA' 1 proposed development contains approximately 0.82 acres. The site is currently vacant and contains native grasses and a large cottonwood tree that will be saved as part of the development. The existing site has relatively shallow slopes (approximately 2%) that drain to an open 8" PVC pipe outfall at the southwesterly corner of the site. Troutman Office Park is located in the McClelland Drainage Basin. As detailed in the previous section, the approved Drainage Master Plan was prepared in 1980. This study identifies the master basin as Area 10 or Reach 6D and describes the basin as fully developed and connected by ponds and existing manmade conveyance elements. The Basin upstream of Larimer No. 2 will drain to the canal per the "Final Drainage Report for the Heart Special Improvement District" January, 1985 by EPI. This report allowed for a 2 year Historic release to Larimer No.2 of 0.867 cfs/acre. The capacity of the Larimer No. 2 was established in the "Fort Collins Retail Center P.U.D. Final Drainage Report" by RBD Inc., September, 1985. This report details a total discharge of 240 cfs which is comprised of 155 cfs in irrigation flows and 85 cfs in stormwater flows. The Canal currently is concrete lined along the western edge of the Pioneer Mobile Home Park and is conveyed under Harmony Road in a 3'x 9' CBC. The proposed site was included as part of "The Market Place P.U.D." Final Drainage Report by Parsons & Associates January, 1990. The Market Place Study divided the developed area into approximately 6 sub -basins that provided individual on -site detention and routing of accumulated spills to a sub -surface conveyance system. The existing system spills -2- all combined flows to the Larimer No.2 per the design release rate of 0.87 cfs/acre. The text and all calculations sections of the approved Market Place study are available in Appendix C of this report. The outparcel or "Superblock Holding", as identified in the Market Place Study, was designed with an outfall to a shallow manhole at the southwesterly corner of the tract (Manhole MH A-6). The outfall system has adequate excess capacity to spill controlled releases from the proposed site, per allowance from calculations that are included in the Market Place Study. -3- Run-off from each of the site sub -basins was determined by the Rational Method, a widely accepted predictor of run-off from basins less than 200 acres. Flow capacities for swales, gutters, and open channels were determined using the Mannings Equation. All run-off coefficients and Mannings "n" were determined by tables and figures in "Fort CnIfins, Starm Drainage Dpsiq Criteria Manual" -and conforms to "Urban DrainanP and Flood Control ao al1. (UDFCM). Detention storage requirements were determined by the "FAA Method" tables as outlined in the UDFCM. Le For the following discussion, please refer to the Drainage and Erosion Control Plan in the back pocket of this report. As outlined above, the proposed lot is part of a larger, overall drainage plan that was detailed by the Market Place P.U.D. drainage report. Portions of the developed site will drain to existing detention ponds (A-5 and B-1) and release per design rates, as detailed in the Market Place P.U.D. drainage report. Basin B-1 This existing sub -basin was originally designed to drain to two area inlets in the parking lot and landscaped area bordering the north side of the proposed development. This pond was designed to detain 4144 cubic feet of storage with a release rate of 0.30cfs. The proposed development added 3,880 sq. feet to this sub -basin (0.09 Ac) for a revised total area of 0.65 Acres. The design outfall rate of 0.30 cfs was used to calculate a revised storage volume of 3361 cubic feet, well below available storage of 4144 cubic feet, refer to Appendix A for detention pond calculations. -5- storage at a release rate of 2.38 cfs. The proposed development will add 3135 square feet to the existing sub - basin (0.07Ac) for a revised total area of 1.34 Acres. The design outfall rate of 2.38 cfs was used to calculate a revised storage volume of 5617 cubic feet. This volume represents a shortfall of approximately 1300 cubic feet which will be transferred to Sub -basin A-6, which has adequate storage available. Basin A-6 Sub -basin A-6 is the remaining parcel that represents the proposed development area. All roof and driveway flows will spill to a low point at the southeasterly corner of the parking lot. This point drains to a small inlet box and orifice plate that represents a controlled release to a 15" RCP pipe and westerly to the existing 5' Type "R' Inlet in the north flow -line of Troutman Parkway. The detention pond has a total storage volume of 6284 cubic feet, only 3530 cubic feet is required. The additional volume will be used to mitigate the storage shortfall from Sub -basin A-5. Excess spills will flow east along the entrance drive to the pond surface. Please refer to Appendix A for detailed summaries of Developed Basin Flows, detention pond calculations and composite "C" calculations. IRE Wind Erosion: This site is located in an area designated as having moderate wind erosion potential. The anticipated construction will require disturbance of all natural features. Erosion control will be carefully planned in areas of construction, structural measures will be used to mitigate wind erosion during construction. Areas disturbed will require the installation of silt fencing and gravel mulch or black base pavement will most likely work for on -site stabilization during construction of building pads. Water Erosion: This site is located in an area of moderate to high potential for erosion due to storm run- off. Therefore, emphasis will be placed on control of water erosion damage. Silt fencing, straw bales and pavement/foundation paving and timing of construction will be carefully co- crdinated to minimize exposed surfaces for more than two months. The finished site will be largely covered by hard surface, providing adequate stabilization. The on -site slopes are very flat, erosion from embankments should not be a major consideration. -7-