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HomeMy WebLinkAboutCOTTONWOOD RIDGE SUBDIVISION - FINAL - 31-94A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTN RSi�F MULBERRY 4`F ST. TO 1-25 a LAUREL ST. COLORADO STATE NRD UNIVERSITY PROSPECT CAMPUSF TO1-25 of w a w a o c DRAKE RD. r a � W � o ,. J O U HORSETOOTH RD, J J � W _ W 4 Z ' F li W J J W a x U F (N M HARMONY RD. LLO 1-25 LL-j PROJECT VICINITY MAP LOCATION N.T.S. Figure 1.1. Vicinity map. Resource Consultants & Engineers 1.2 A Division of Ayres Associates 1. INTRODUCTION 1.1. Overview This report summarizes the storm drainage investigations performed for the proposed Cottonwood Ridge development in Fort Collins, Colorado. A hydrologic analysis of the proposed development was completed to determine the magnitude and location of storm runoff, to design adequate storm water utilities, and to address the stability of a deep ravine in the southwest portion of the property. This study and drainage plan were prepared in accordance with City of Fort Collins Storm Drainage Design Criteria. Cottonwood Ridge is a proposed residential development located along the west side of Shields Street approximately M miles south of Harmony Road in southwest Fort Collins, Colorado (Figure 1.1). It consists of approximately 32.10 acres occupying the northeast quarter of Section 3, Township 6 North, Range 69 West, of the 6th Principal Meridian and lies within both the Fossil and McClellands/Mail Creek drainage basins. The property is currently zoned RLP, which allows for a standard subdivision or planned unit development. 1.2. Previous Studies Previous drainage studies of the area include: 1. "Cottonwood Ridge, Preliminary Drainage and Erosion Report" by Eric Thayer (June 1994) 2. "Preliminary Geotechnical Engineering Report, Cottonwood Ridge" by Empire Laboratories, Inc. (May 1994) 3. "McClellands and Mail Creek Major Drainageway Plan" by Cornell Consulting Company and John S. Griffith, P.E. (December 1980) 4. "Fossil Creek Drainage Basin Master Drainageway Planning Study" by Simons, Li & Associates, Inc. (August 1982) Resource Consultants & Engineers 1.1 A Division of Ayres Associates LIST OF TABLES Table 2.1. Basin Parameters ..................................... 2.6 Table 2.2. Calculated Peak Flows ................................. 2.7 Table 2.3. Gutter and Street Capacities ............................. 2.9 Table 2.4. Detention Pond A Rating Curve .......................... 2.12 Table 2.5. Detention Pond B Rating Curve .......................... 2.14 Table 2.6. Detention Pond C Rating Curve .......................... 2.16 Table 2.7. Subbasin Parameters Used in SWMM Model of Ravine, Existing Conditions ................................... 2.21 Table 2.8. Conveyance Element Parameters Used in SWMM Model of Ravine, Existing Conditions ........... ...................... 2.21 Table 2.9. - Subbasin Parameters Used in SWMM Model of Ravine, Developed Conditions ................................. 2.23 Table 2.10. Conveyance Element Parameters Used in SWMM Model of Ravine, Developed Conditions ................................. 2.23 Table 2.11. Storage -outflow Relationship for Detention Pond C ............ 2.24 Table 2.12. Comparison of Existing and Developed Conditions Computed 100-Year Peak Flows ......................... 2.24 Table 3.1. Computed Hydraulic Parameters in the Ravine for the Design Discharge of 85 cfs .............................. 3.7 Table 3.2. Results of Erosion Energy Analysis for the 100-Year Event ....... 3.10 Table 4.1. Security Requirements ................................. 4.4 Resource Consultants & Engineers iii A Division of Ayres Associates LIST OF FIGURES Figure 1.1. Vicinity map ........................................ 1.2 Figure 2.1. Existing conditions .................................... 2.2 Figure 2.2. Developed conditions runoff ............................. 2.4 Figure 2.3. Subbasin delineation for developed conditions SWMM models...........................................2.17 Figure 2.4. Subbasin delineation for existing conditions SWMM model ....... 2.19 Figure 2.5. Schematic of SWMM model for runoff into ravine, existing conditions ........................................ 2.20 Figure 2.6. Schematic of SWMM model for runoff into ravine, developed conditions ................................. 2.20 Figure 3.1. Ravine profile and proposed drop structure location ............ 3.12 Figure 3.2. Unprotected banks and upper slope ....................... 3.14 Figure 3.3. Unprotected hillslopes above protected banks ................ 3.15 Figure 3.4. Cabled logs bank protection ............................ 3.16 Figure 3.5. Log cribbing bank protection ............................ 3.17 Figure 3.6. Sacked concrete bank protection ......................... 3.19 Figure 4.1. Construction time table ................................ 4.2 Resource Consultants & Engineers ii A Division of Ayres Associates ITABLE OF CONTENTS 1. INTRODUCTION .......................................... 1.1 1.1. Overview ......................................... 1.1 1.2. Previous Studies .................................... 1.1 2. DRAINAGE PLAN ......................................... 2.1 2.1. Existing Drainage Conditions ............................ 2.1 2.2. Proposed Drainage Conditions ........................... 2.3 2.3. Storm Drainage Facilities .............................. 2.8 2.4. SWMM Modeling ................................... 2.16 3. STABILITY EVALUATION OF RAVINE .......................... 3.1 3.1. Field Reconnaissance ................................. 3.1 3.2. Quantitative Stability Evaluation ....................... 3.4 3.2.1. Hydraulic Analysis of the' Pleasant Valley and Lake Canal .. 3.4 3.2.2. Hydraulics ................................... 3.5 3.2.3. Erosion Analysis ............................... 3.6 3.3. Design of Channel Improvements ........................ 3.10 3.3.1. Stabilization Requirements ...................... 3.10 3.3.2. Drop Structures ............................... 3.11 3.3.3. Bank Toe Protection and Slope Stabilization ........... 3.13 3.4. Pleasant Valley and Lake Canal Spillway .................... 3.18 4. EROSION CONTROL PLAN .................................. 4.1 4.1. Overview ......................................... 4.1 4.2. Wind Erosion ....................................... 4.1 4.3. Rainfall Erosion ..................................... 4.3 APPENDIX A - Design Calculations ................................... -- APPENDIX B - Ravine Analysis ...................................... -- APPENDIX C - PV&L Canal Hydraulic Analysis ........................... -- Resource Consultants & Engineers r, i A Division of Ayres Associates AIRES ASSOCIATES September 18, 1995 Mr. Basil Harridan City of Fort Collins Stormwater Utility 235 Mathews Street Fort Collins, Colorado 80524 Re: Cottonwood Ridge Subdivision Dear Basil, Enclosed please find our "Final Drainage and Erosion Control Report, Cottonwood Ridge." This report was prepared in accordance with the City of Fort Collins Storm Drainage Criteria as revised in May 1991. We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Sincerely, Owen Ayres & Associates, Inc. Chris Carlson, E.I.T. Civil ineer Q `o1SYe�F� -���{, 6 a � . *bo 15094, - �r David M. Frick, Ph.D., P.E. ego , `' e O Regional Vice President *1/ ©, Ci:D1, CC/DMF/sp �f fnitrlle.�Vvx Enclosure Owen Ayres & Associates, Inc. Engineers/Scientists/Surveyors 3665 JFK Parkway, Building 2, Suite 300, P.O. Box 270460, Fort Collins, CO 80527 (970) 223-5556, Denver Metro (303) 572-1806, FAX (970) 223-5578 Printed on recycled paper COTTON-R.LTR 34-0196.00 FINAL DRAINAGE AND EROSION CONTROL REPORT COTTONWOOD RIDGE Prepared for Eric Thayer 31741 RCR No. 35 Steamboat Springs, Colorado 80487 AVMwS ASSOCIATES formerly Resource Consultants & Engineers P.O. Box 270460 Fort Collins, Colorado 80527 (970) 223-5556, FAX (970) 223-5578 AVMS ASSOCIATES