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Home My WebLink AboutPARKWAY TOWNHOMES PUD - PRELIMINARY/FINAL - 9-96 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTVI. EROSION CONTROL: Wind Erosion: This site is located in an area designated as having moderate wind erosion potential. The anticipated contruction 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 corrdinated 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. V. DRAINAGE UNDERDEVELOPED CONDITIONS: For the following discussion, please refer to the Drainage and Erosion control report in the back pocket of this report. On -site flows will collect to a detention pond at the southeasterly corner of the parking lot and release at a controlled rate (0.48 cfs), as outlined in the historic section of this study. Total on -site storage will be approximately 9000 cubic feet of detention. Calculations for on - site detention storage and routing are available in Appendix B. Basin AB Basin A consists of the proposed site improvements for the townhome units. All flows will collect to the southeast corner where an orifice plate and outfall pipe will control off -site spills as outlined in the papragraph above. A shallow channel (channel 1) will collect concentrated flows from the southern end of the curb line on JFK Boulevard (Basin B). Concentrated flows will be transferred to this outfall channel, spill southeasterly in a dedicated (existing) utility easement to the historic detention area at the southeasterly corner of the Martin West property, per historic consitions. All calculations for the initial and major storm events, detention pond, orifice plate and outfall channel can be found in Appendix B of this report. IV. DRAINAGE CRITERIA: Run-off from each of the site subbasins 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 Collins Storm Drainage Design Criteria Manual and conforms to "Urban Drainage and Flood Control Manual' CMFCMI. Detention storage requirements were determined by the "FAA Method" as outlined in the UDFCM. Basin Masterplan Conditions and detention storage were also addressed in "The Pier Condominiums Drainage report" by Cornell Consulting Co. September, 1979. This report identifies the requirement of 11.23 acre ft. of storage in the ponds upstream of Boardwalk Drive or Pond 109 per approved Drainage Masterplan. The Masterplan identified a 23 acre ft. pond for this location with a 27 cfs spill downstream. Calculations performed for this study identify the requirement for a 14.1 Acre-ft. detention pond at the 27 cfs release rate. Appendix A contains the Detention Pond and Composite "C" calculations for this portion of the Basin. Given the controlled release rate of the Basin and the contributing upstream area (84.93 Acres) a release rate of 0.32 cfs/acre. 0 TROUTMAN PKWY. h p Heart S1 Basi PAVI.LLION LN. T ilwio" N EXHIBIT-2 MastW Basin R L P \�; IVI Ott z!!; b ul Jul cul Ba sin 12 rplah -10 ..,A b p AM', 6e� 4V EAST HARMONY ROAD (HWY 14 WEST � POND X/P )Z)OIV8 R L H OUT :'> C1 ell a n ds Basin EXIST ZONING/BASIN BOUNDARIES1,.1.. Mc R L H OUT :'> C1 ell a n ds Basin EXIST ZONING/BASIN BOUNDARIES1,.1.. Mc ground along the southern perimeter of the site. The ground to the south of the proposed project falls to the southeast to a historic detention area at the north property line of Pitner Estates, please see Exhibit 2. The slopes across the site vary from 1% to 2%. JFK Parkway flowlines fall from 2% to 0.40%. The east side of the tract is bounded by JFK Parkway right-of-way, the south by the Martin West property and north and west by Larimer No. 2 Canal. M. HISTORIUMASTER DRAINAGE: Parkway Townhomes P.U.D. 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 only portion of the basin currently undeveloped is the Martin West property that lies on the North side of Pioneer Mobile Home Park and Pitner Estates. This area has a historic detention pond and channel per the Masterplan; however, the pond and channel have no recorded easements- The Masterplan calls for a 23 acre ft detention pond and an outfall of 27 cfs. Exhibit 2 details the Basins as identified in the Masterplan and identifies the approved zoning areas. The areas east of the Larimer No. 2 are identified as Basins 10 and Basins 12. 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. 2 PROJECT SITE i VICINITY MAP 1 NTS EXHIBIT 1 J FINAL DRAINAGE AND EROSION CONTROL STUDY FOR PARKWAY TOWNHOMES P.U.D. FORT COLLINS, COLORADO I. INTRODUCTION: This drainage report has been prepared along with preliminary utility plans to provide drainage design information for the development of a 1.7 acre Multi -family development at the southwesterly corner of Troutman Parkway and JFK Parkway, please see enclosed Vicinity Map -Exhibit 1. This report has prepared in conformance with the City of Fort Collins Storm Drainage Design and Construction Standards and with conformance to the "Mail Creek and McClellands Major Drainageway Plan" by Cornell Consulting Co., December, 1980. Other drainage reports were used to prepare this study and are referenced in appropriate sections of this report. II. SITE DESCRIPTION: Parkway Townhomes P.U.D. is more specifically identified as a parcel of land located in a Iportion of the southwest quarter of Section 36, Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. The proposed site is currently undeveloped. The topography falls gradually to the southeast, draining to the open TABLE OF CONTENTS I. INTRODUCTION: ...1 II. SITE DESCRIPTION ...1, 2 M. HISTORIC/MASTER DRAINAGE ...2, 3 IV. DRAINAGE CRITERIA ...4 V. DRAINAGE UNDER DEVELOPED CONDITIONS ... 5 VI. EROSION CONTROL 6 Exhibit 1 Vicinity Map Exhibit 2 Historic Drainage/Approved Zoning Appendix A Drainage Calculations/Pond Sizing for Basin Masterplan Appendix B Developed Drainage Calculations Parkway Townhomes P.U.D. Appendix C Erosion Control -Calculations Back Pocket FINAL DRAINAGE & EROSION CONTROL STUDY FOR PARKWAY TOWNHOMES P.U.D. FORT COLLINS, COLORADO March 14,1996 PREPARED FOR: TRAC 424 PINE STREET FORT COLLINS, COLORADO 80524 PREPARED BY: PARSONS & ASSOCIATES, INC. 432 LINK LANE PLAZA FORT COLLINS, COLORADO 80524 PROJECT NBR: 96.04 RAC No Text