The URL can be used to link to this page

Home My WebLink AboutPROSPECT COMMONS (FORMERLY GREENS) PUD - FINAL - 15-95A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTVICINITY MAP SCALE.- 1 " = 1000 -, FIGURE 1 conclusion and Recommendations: After reviewing the existing drainage information and site conditions, the following conclusions can be made. 1. The runoff from proposed development will collect to backyard or side yard swales and flow to the curb line of the central street and collect to the far south corner sump. An area inlet and pipe will convey initial storm flows to Spring Creek, major storm flows will overtop the curb and spill into an open channel to Spring Creek. 2. All foundations will be approximately 2.5 to 3.0 feet above the 100-year surface of Spring Creek, per the FIRM, 1979. 3. No on -site detention will be provided due to the developed time to peak being approximately two (2) hours before the Spring Creek peak flows in this reach. 0 EROSION CONTROL: This project is located within an area of moderate wind erosion and moderate rainfall erosion according to the City of Fort Collins wind and rainfall erodibility maps. WIND EROSION: Wind erosion protection will be provided by silt fencing on the northern and western perimeter of the project. Asphalt paving of the parking area and seeding and mulching (or landscaping) of all disturbed areas will provide final stabilization upon completion of this project. WATER EROSION: As stated above, final stabilization will occur with completion of paving and landscaping features. All area disturbed by grading and fill will receive native grass seed and mulch and will be graded to establish positive flow as shown on the enclosed exhibit. 8 IBasin C: I 11 Sub -basin C-1 drains the back. of the single-family lots and into the open area adjacent to the Spring Creek bike path. The developed flows from this area'are minor (2.5 cfs for 100-yr.) and will be conveyed in a shallow channel along the east edge of a pedestrian pathway to Spring Creek. 7 I DEVELOPED DRAINAGE The Site was divided into five separate sub -basins to evaluate ' developed flows and conveyance elements. Basin A: The sub -basin consists of two existing houses, no modifications will occur. Major and minor storm flows will collect to the flowline of Prospect Road and will be conveyed eastward per historic conditions. Basin B: This area was divided into three separate basins. Sub -basins B-1 and B-2 are developed areas that drain to Ukiah Lane and south to a curb inlet at the cul-de-sac. An overflow channel is provided to convey major storm events or provide emergency release in the event of a clogged inlet. Sub -basin B-3 consists largely of an off -site area that drains to the project. A shallow channel along the westerly property line will collect these flows and direct them to the major runoff channel and Spring Creek to the south. N Major (100-Yr.) developed conditions peak at 22.8 minutes at ' a maximum flow of 10.2 cfs, please refer to Appendix B. This ' maximum time to peak is far below the time to peak as shown in Figure 3 at approximately 140 minutes. The peak runoff from the ' proposed development would reach maximum flow almost.two hours before the peak flow in Spring Creek. Detention storage for this ' site has no effect on peak attenuation of flows spilling to Spring Creek. Therefore,. on -site detention was not considered for this development. Pitkin Lateral The existing irrigation ditch currently serves approximately four downstream users to the east. The existing ditch is shallow and varies from 1 to 1.5 feet deep and crosses the property from west to east, as shown on the enclosed back pocket exhibit. The ditch travels upgradient for approximately 200 feet and then turns north on the east side of the Discovery Center. The channel flows from a 15" RCP under E. Prospect the ditch goes underground at the approximate location of Stover and Pitkin. Appendix C of this report contains the letter of agreement signed by the downstream users of the irrigation lateral. Re-routing of the lateral will have no adverse effect on the use or quantity of water delivered to the downstream users. 5 Design criteria: The Rational Method as identified in the "City of Fort Collins Design Criteria" has been used to calculate runoff from the site. The Rational Method is a widely accepted predictor of flows from drainage basins less than two hundred (200) acres. All coefficient, nomegraphs and design values used in this report are from the Fort Collins Design. Criteria or "Urban Storm Drainage Criteria Manual", Volumes 1 and 2. Historic/Drainage conditions: ' The historic runoff conditions were calculated for this area and are available in Appendix A of this report. However, due to the location of the proposed development adjacent to the Spring Creek Floodplain and low in the basin, the associated peak runoff will be released well before the peak flow on Spring Creek. 4 IMaster Drainage: The Flood Insurance Rating Mapping (FIRM) are currently under trevision by City personnel and FEMA. The current mapping in force for the Spring Creek Basin is Dated 1979 and the Zone A and Zone B floodplain are shown on the enclosed back pocket exhibit. Hydrography for Spring Creek was obtained from a "Interim Flood 1 Hvdroloctv_Report or Sprinq Creek by RCI 1977". The Hydrography at I �I Stover Street, immediately upstream of the proposed development, gives a 100-year peak flow of 4780 cfs. at around 140 minutes (Figure 3). The City of Fort Collins Spring Creek Masterplan (EPI, 1988) was reviewed to obtain current floodplain information. This report gives a 100-yr. ,peak flow of 2400 cfs and the approximate floodplain limits are shown in the enclosed back pocket exhibit. 3 The site frontage on East Prospect Street currently has two houses, one house is an existing outlot, the other will remain and be modified,to match the character of,the proposed.development. A shallow irrigation channel divides the parcel and the area to the south of the ditch is undeveloped agricultural land for horses and small livestock. The Spring Creek Floodplain borders the southern extreme of the site and published flood elevations are shown. on the drainage exhibit in this reports back pocket. The existing topography slopes east or southeasterly to the Spring Creek drainage with the exception of the small area around the existing homes that drains to the southern flowline on East Prospect Street. The proposed development for this site will consist of 17 single family units on approximately.3.73 acres. All public improvements, as shown on the enclosed back pocket exhibit will be constructed with the project. 2 I 1 I I I I FINAL DRAINAGE E EROSION CONTROL REPORT FOR PROSPECT GREENS P.U.D. Introduction• This final drainage and erosion control report has been prepared in conjunction with the final engineering plans to provide conceptual information for the development of 17 single family residential lots on E. Prospect Road east of Stover St. (See Vicinity Map, Figure 1). This report is prepared in conformance with the City of Fort Collins "Storm Drainage Design Criteria and Construction Standards and the "Spring Creek Masterplan". Site Description: Prospect Greens P.U.D. is a 3.73 acre parcel on the south side of East Prospect one lot east of the Bauder Elementary School (Discovery Center), within the Fort Collins City limits. More specifically the property is located in the East Half of the East Half of the Northwest Quarter of the Northwest Quarter of Section 24, Township 7 North, Range 69 West of the 6th. Principal Meridian, County of Larimer, State of Colorado. 1 11, TABLE OF CONTENTS INTRODUCTION SITE DESCRIPTION MASTER DRAINAGE DESIGN CRITERIA HISTORIC/ DRAINAGE CONDITIONS PITKIN LATERAL SUB -BASINS A, B SUB -BASIN C EROSION CONTROL CONCLUSION AND RECOMMENDATIONS Figure 1 Vicinity Map Figure 3 Spring Creek 100 year Hydrographs Appendix A Historic Drainage Design Data Appendix B Developed Drainage Design Data Appendix C Erosion Control Information Appendix D Letter of Agreement Back Pocket PARSONS & ASSOCIATES, INC. CONSULTING ENGINEERS May 22, 1995 Mr. Glen D. Schlueter Stormwater Development Manager City of Fort Collins P. O. Box 580 Fort Collins,CO. 80522-0580 RE: Final Drainage & Erosion Control Report for Prospect Greens P.U.D. Dear Mr. Schlueter: This final drainage and erosion control report has been prepared in conjunction with the final engineering plans to provide conceptual information for the development of 17 single family residential lots on E. Prospect Road east of Stover St. This report is prepared in conformance with the City of Fort Collins "Storm Drainage Design Criteria and Construction Standards and the "Spring Creek Masterplan". If you have any questions concerning the enclosed report, please do not hesitate to contact us. Sincerely yours, 1111111, PARSONS & ASSOCIATES, INC. "p`l�� OdIREI \�� \` eeNeese, D ��O�a�p�ten Od �.V 28086 Gary A. Odehnal, P.E. Project Manager .'�P1A\. �t!!llldlfll1111V1' GAO/jd I • 432 Link Lane Plaza • Ft. Collins, Colorado $0524 • (3031 221-2400 FINAL DRAINAGE& EROSION CONTROL REPORT FOR PROSPECT GREENS P.U.D. May 11, 1995 PREPARED FOR: Mr. Larry K. Pedersen Pedersen.Brothers Homes &Development LLC 209 North Link Lane Fort Collins, CO. 80524 PREPARED BY: PARSONS & ASSOCIATES, INC. 432 LINK LANE PLAZA FORT COLLINS, CO. 80524 (303) 221-2400 PROJECT NUMBER 94.09 NLR No Text