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HomeMy WebLinkAboutBENNETT ROAD BUNGALOWS - PDP - 42-01 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTI I I I I I 1 1 1 1 Final Drainage Report Bennett Road Bungalows October 3, 2001 Northern Engineering Services, Inc REFERENCES 1) Canal Importation Basin Master Drainage Plan, Anderson Consulting Engineers, Inc., Fort Collins, Colorado, May 11, 2001. 2) Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright Water Engineers, Inc., Denver, Colorado, Updated June 2001. 3) Erosion Control ReferenceManual for Construction Sites, City of Fort Collins, Colorado, Hydrodynamics, Inc., January 1991. 4) Final Report Spring Creek Basin Hydrologic Model Update, Anderson Consulting Engineers, Inc., Fort Collins, Colorado, Revised December 8, 1999. 5) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, Updated April 1999. 1 7 Final Drainage Report Northem Engineering Services, Inc Bennett Road Bungalows October 3, 2001 VI. EROSION CONTROL PLAN ' 6.1 Erosion Control Criteria The erosion control plan presented here is intended to control both wind and rainfall erosion. The Erosion Control Reference Manual for Construction Sites (ECRM), City of Fort Collins, has been referenced for this erosion control plan. 6.2 Rainfall Erosion Control Plan ' The proposed rainfall erosion control plan during construction will consist of temporary structural erosion control measures. Straw -bale inlet filters will be placed around all drain basins. A straw -bale sediment trap will be placed at the outlet of the proposed ' detention pond. Silt fencing will be installed along the eastern property boundaries to prevent runoff particulates and windblown sediment from migrating off -site. ' The proposed site layout and construction schedule will leave little or no area disturbed without revegetation. The measures proposed above will control surface erosion during the construction process, and prevent sediment from leaving the site. These structures are ' to remain in place until paving is completed and foundations and landscaping have been established. 1 The proposed erosion control'plan after construction will consist of permanent riprap, which will be provided at the locations specified on the construction plans. All open space areas will be revegetated as specified on the Landscape Plan. An erosion control cost estimate for "during construction" sediment control has been provided for the site (See Appendix I). VII. CONCLUSIONS ' 7.1 Compliance with Standards All drainage design considerations are in accordance with the City of Fort Collins Storm — Drainage Design Criteria Manual and the Urban Drainage and Flood Control District's ' Drainage Criteria Manual. The drainage system proposed within this report and the supporting construction documents provide adequate conveyance, detention, and water - quality enhancement for the developed stormwater runoff from Bennett Road Bungalows. t Final Drainage Report Northern Engineering Services, Inc Bennett Road Bungalows October 3, 2001 4.6 Detention A stormwater detention storage volume is being proposed for this project to help mitigate the effects of the development upon the downstream drainage system. This will be accomplished by a rectangular weir section built into the concrete outlet structure, which is designed to limit the 100-year developed release rate to the 2-year historic runoff from the site. Off -site runoff from the Western Heights subdivision will be bypassed through the pond outlet structure, but no storage volume will be provided for the off -site area. An FAA analysis was performed to determine the required detention storage volume for the proposed development. Based upon a 100-year developed C-value of 0.62 and a maximum release rate of 1.1 cfs, it was calculated that approximately 0.432 acre-feet of storage is required. This detention storage volume will be added on top of a water quality storage volume. The approximate 100-year water surface elevation is 5033.20. Detention Pond 1. will discharge directly into the northern flowline of Bennett Road. 1- foot of freeboard exists at the pond up to an elevation of 5034.20. An emergency overflow weir section has been designed into the outlet structure to safely spill flows within the freeboard elevation to the south and into Bennett Road. 4.7 CanalOvertop_pin� 100-year floodwaters overtop the banks of Larimer Canal No. 2 near Bennett Road as described in Section 3.1. The development of Bennett Road Bungalows will redirect this flow down Bennett Road and into Shields Street. The limits of flooding due to the canal overtopping extend beyond the public right-of-way. Portions of the Bennett Road Bungalows and Bennett Elementary School properties will experience a slight submergence when the canal spillover passes through. No building footprints for Bennett Road Bungalows will be located within this boundary. Also, all proposed finished floor elevations will be at least one foot above the canal flood elevation. Homes along Springfield Drive have historically been damaged as a result of the canal overtopping. In order to alleviate this problem, a portion of the floodwaters will extend onto the Bennett Elementary School property. The limit of the flooding on the school property does not endanger any existing structures or other facilities. 1 V. WATER QUALITY `y 5.1 Water Quality Measures and Criteria An on -site water quality capture volume (WQCV) is proposed to remove sediment and other pollutants from developed runoff. This WQCV will be incorporated into Detention Pond 1. Based on criteria for a 40-hour dry extended detention basin outlined in the Urban Storm Drainage Criteria Manual, Volume 3 — Best Management Practices by the Urban Drainage and Flood Control District (September 1999), the required water quality capture volume was determined to be approximately 0.063 acre-feet. This required ' WQCV is achieved at an elevation of 5031.95. A steel orifice plate with vertical perforations will be built into the pond outlet structure to control the water quality capture volume. 5 Final Drainage Report Northern Engineering Services, Inc Bennett Road Bungalows October 3, 2001 garages. Runoff from this basin will be directed overland towards the northern property line into Swale Section A. Swale A will carry flow to the east into _ Detention Pond 1. Swale A has been sized to convey runoff from all of Basin A as well as the off -site runoff from Western Heights. 1 1 1 1 1 1 1 1 1 1 4.5.2 Basin B (1.095 acres) Basin B has been divided into seven (7) sub -basins labeled B 1-B7. This basin is comprised of the front portions of proposed residential lots. Runoff from this basin will be directed overland to the south towards a series of drain basins located in sump areas at the front of the lots. Each sub -basin (B 1-B7) will drain to its own sump area and drain basin. All of the drain basins are sized to convey the full 100-year developed flows. Storm Sewer Line 1 will carry flows from each inline drain into Detention Pond 1. Emergency overflow from each sump area will safely spill to the south into Bennett Road. 4.5.3 Basin C (1.020 acres) Basin C has been divided into eight (8) sub -basins labeled Cl-C8. This is an off - site basin comprised of the rear portions of existing residential lots adjacent to Springfield Drive. Runoff from this basin will follow its historic path by sheet flowing to the south towards the Bennett Road Bungalows north property line. Swale Section A designed with Basins Al-A7 is sized to accommodate the runoff from Basins CI-C7 as well. Basin C8 will drain overland towards its historic destination. Approximately 4.0 cfs of runoff will be bypassed through the detention pond during the 100-year storm. 4.5.4 Basin D (0.545 acre) Basin D has been divided into two (2) sub -basins labeled D1 and D2. Basin D is the open space area containing Detention Pond 1. This basin will be landscaped as shown on the Landscape Plan. A 2' concrete v-pan will carry low flows through this basin. Basin D1 lies within the top of the pond's banks, and will directed towards the outlet structure. Basin D2 is the outer berm of the detention pond, and will drain off -site undetained. Both Swale A and Storm Sewer Line 1 outfall into this basin at its western edge. A concrete outlet structure will be located at the southeast comer of this basin to restrict the developed release rate. Runoff from Basins A, B, C and D are all routed through this outlet structure. The pond's outlet structure contains an emergency overflow weir section designed to safely convey excess flows into Bennett Road. 4.5.5 Basin E (1.127 acres) Basin E consists of the northern half of Bennett Road and its associated right-of- way. This basin will continue to follow its historic drainage patterns. That is, runoff will concentrate in the vertical curb and gutter of Bennett Road and travel to the east towards Shields Street. After reaching Shields Street, flow will continue to the north before being intercepted by curb inlets located near the intersection of Shields Street and South Drive. 4 Final Drainage Report Bennett Road Bungalows October 3, 2001 Northern Engineering Services. Inc. IV. POST -DEVELOPMENT CONDITIONS 4.1 Post -development Conditions The Bennett Road Bungalows development will include the following: • sixteen (16) single-family lots; • new curb, gutter, and detached walk along the north side of Bennett Road; • drainage improvements and utility services. The entire asphalt surface of Bennett Road along the property boundary will be replaced with this development. 4.2 Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual. (SDDCM) and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been referenced for this study. Also, the Canal Importation Basin Master Drainage Plan by Anderson Consulting Engineers has been used for inputting flow values into HEC-RAS. 4.3 Hydrologic Criteria The Rational Method has been used to estimate peak stormwater runoff within the developed site. The minor 2-year and major 100-year design storms have been used in the design of the proposed drainage system, which includes Nyloplase surface drains, HDPE storm sewer, a grass -lined swale with a concrete pan, and a detention pond with an outlet structure. Rainfall intensity data for the Rational Method has been taken from Figure 3-la updated by the City of Fort Collins in 1999. 4.4 Hydraulic Criteria The City of Fort Collins SDDCM has been referenced for all hydraulic calculations. In addition, the following computer programs have been utilized: • The computer program "Storm Sewer Modeling" by Eagle Point Software has been used to design and analyze the storm sewer lines • The computer program "Watershed Modeling" by Eagle Point Software has been used to design and analyze the weir sections • The computer program "F1owMaster" by Haestad Methods has been used to design and analyze the swales • The computer program "UDPOND" by the Urban Drainage and Flood Control District has been used to size the detention pond by the FAA Method • The computer program "HEC-RAS" by the U.S. Army Corps of Engineers has been used to analyze the overflow from Larimer Canal No. 2. 4.5 Drainage Patterns 4.5.1 Basin A (2.035 acres) Basin A has been divided into seven (7) sub -basins labeled Al -AT This basin is comprised of the rear portions of proposed residential lots, including all of the 1 Final Drainage Report Bennett Road Bungalows IOctober 3, 2001 Northern Engineering Services, Inc. III. PRE -DEVELOPMENT CONDITIONS 3.1 Major Basin Description The site is located in the City of Fort Collins Spring Creek Master Plan Drainage Basin. All runoff from the site eventually reaches Spring Creek. The property is also downstream of the City of Fort Collins Canal Importation Basin. The Canal Importation Basin Master Drainage Plan by Anderson Consulting Engineers, Inc. identifies a spillover from the Canal Importation Basin into Bennett Road near the site. This spill is labeled as node 649 in Volume II: Technical Appendix D of the Canal Importation Basin Master Drainage Plan. There is currently 100.8 cfs that spills into Bennett Road from Larimer Canal No. 2 during the 100-year storm. This occurs at approximately 37 minutes into the storm. In the future, when all of the major drainage improvements outlined in the Canal Importation Basin Master Drainage Plan are operational, Bennett Road will still receive approximately 81.5 cfs of spillover from the canal. Flows overtopping the banks of Larimer Canal No. 2 have historically flooded the residences on the west side of Bennett Road that back up to the canal. Floodwaters then continued to travel to the east onto the Bennett Road Bungalows property. Water concentrated near the low point at the center of the site before traveling through residences adjacent to Springfield Drive and making it into Shields Street. The canal overtopping flows will be redirected down Bennett Road to prevent the flooding -of residences along Springfield Drive when Bennett Road Bungalows is developed. A memorandum summarizing the canal overtopping was written to the City of Fort Collins on September 25, 2001. A copy of this memo can be found in Appendix F. 3.2 Pre -development Drainage Patterns The Bennett Road Bungalows site historically drains from the west to the east at slopes ranging from approximately 0.5% to 5.0%. A localized sump area exists towards the rear of proposed Lot 11. This low area is at roughly an elevation of 5033-feet. Historically, this sump location ponds up to an elevation of approximately 5034-feet before the drainage continues to the east. Proposed Lots 8-14, as well as a portion of the existing Western Heights residences along Springfield Drive, lie within the area of historic ponding. A small ridge divides the property into a northern and southern area. The northern area travels east along the northern property boundary before traveling overland into Bennett Road. The south area sheet flows into Bennett Road where runoff continues to travel to the east. Runoff from both areas combines in Bennett Road and travels to the intersection of Shields Street. Flows in Shields Street travel to the north to curb inlets located near the intersection of Shields Street and South Drive. The historic 2-year runoff from the 3.874-acre site is approximately 1.2 cfs. However, the 3.515 acre -area that will be directed to the detention pond has a historic 2-year discharge of 1.1 cfs. This will be the maximum 100-year developed release rate from the Bennett Road Bungalows site. Approximately 1.03 acres of off -site area from Western Heights residences currently drain through the site. Runoff from this off -site area will be routed through the proposed drainage system and bypassed through the detention pond. Final Drainage Report Bennett Road Bungalows October 3, 2001 L INTRODUCTION Final Drainage Report for Bennett Road Bungalows Fort Collins, Colorado October 3, 2001 Northern Engineering Services, Inc. 1.1 Objective This report summarizes the results of a comprehensive analysis of both pre- and post - development hydrologic and hydraulic conditions for the Bennett Road Bungalows site in Fort Collins, Colorado. 1.2 Manning and Surveying An initial site survey was conducted by Stewart and Associates in August of 2001. The existing topography was given at a one -foot contour interval. In addition, the locations of existing drainage facilities were provided. An additional survey was conducted by Stewart and Associates in September of 2001. The second survey provided topography for the existing backyards adjacent to the northern property boundary. A third survey was conducted by Stewart and Associates in the last week of September 2001. The third survey provided cross sections of Bennett Road and the adjacent properties necessary for the HEC-RAS modeling. 1.3 Site Reconnaissance A site visit was conducted in September of 2001 by Northern Engineering Services, Inc.. Existing drainage patterns and land use were confirmed at this time. II. SITE LOCATION AND DESCRIPTION 2.1 Site Location The Bennett Road Bungalows site is located within the southeast quarter of Section 15, Township 9 North, Range 69 West of the a Principal Meridian in the City of Fort Collins, County of Larimer, State of Colorado. The project is bounded by residences of Western Heights Subdivision facing Springfield Drive on the north, Bennett Road and Bennett Elementary School on the south, City Park Avenue to the west, and an existing residence facing Shields Street on the east. (See Vicinity Map) 2.2 Site Description This project is considered an "in -fill' project; meaning it is a small, undeveloped area surrounded by existing development. The Bennett Road Bungalows site is approximately 3.87 acres and has historically been undeveloped. An existing fence exists near the southern property boundary near Bennett Road. Two trees, one upright juniper and one large cottonwood, are located towards the southeast comer of the site. It is desirable to preserve the cottonwood with the development of Bennett Road Bungalows. Overhead telephone lines currently exist along the northern property boundary. These lines will be buried with the development of this project. OCTOBER, 2001 VIC�IITY MAP N NOT TO SCALE Table of Contents VICINITY MAP Page L INTRODUCTION 1.1 Objective.......................................................................................... 1 1.2 Mapping and Surveying................................................................... 1 1.3 Site Reconnaissance......................................................................... 1 H. SITE LOCATION AND DESCRIPTION 2.1 Site Location.................................................................................... 1 2.2 Site Description................................................................................ 1 III. PRE -DEVELOPMENT CONDITIONS 3.1 Major Basin Description.................................................................. 2 3.2 Pre -development Drainage Patterns ................................................ 2 IV. POST -DEVELOPMENT CONDITIONS 4.1 Post -development Conditions.......................................................... 3 4.2 Design Criteria and References....................................................... 3 4.3 Hydrologic Criteria.......................................................................... 3 4.4 Hydraulic Criteria............................................................................ 3 4.5 Drainage Patterns............................................................................ 3 4.6 Detention.......................................................................................... 5 V. WATER QUALITY 5.1 Water Quality Measures and Criteria .............................................. 5 VI. EROSION CONTROL PLAN 6.1 Erosion Control Plan and Criteria .................................................... 6 6.2 Rainfall Erosion Control Plan.......................................................... 6 VII. CONCLUSIONS 7.1 Compliance with Standards............................................................. 6 REFERENCES.......................................................................................... 7 APPENDICES APPENDIX A- Hydrology Calculations APPENDIX B - Detention Calculations APPENDIX C - Water Quality Calculations APPENDIX D- Inlet Calculations APPENDIX E - Storm Sewer & Swale Calculations APPENDIX F - Floodplain Calculations APPENDIX G- Riprap Calculations APPENDIX H - Street Capacity Calculations APPENDIX I - Erosion Control Cost Estimate I October 3, 2001 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Bennett Road Bungalows Fort Collins, Colorado Project Number: 01-065.01 Dear Staff. Northern Engineering Services, Inc. is pleased to submit this Final Drainage Report for the Bennett Road Bungalows site for your review. We understand that review by the City of Fort Collins is to assure general compliance with standardized criteria contained in the Storm DrainageDesign Criteria and Construction Standards. This report was prepared in compliance with technical criteria set forth in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual. If you should have any questions or comments as you review this report, please feel free to contact us at your convenience. Sincerely, NORTHERN ENGINEERING SERVICES, INC. S t. &,�- Nicholas W. Haws, E.I.T. Project Engineer Roger A urtiss, .E. Project ManagerNice President 420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221-4159 Final Drainage Report for Bennett Road Bungalows Fort Collins, Colorado October 3, 2001 Prepared For: Bennett Road Bungalows, L.L.C. 5731 Bueno Drive Unit C Fort Collins, Colorado 80525 Prepared By: NORTHERN ENGINEERING Northern Engineering Services, Inc 420 S. Novies, Suft 2C2 Fort Collins. Colorado W521 Phone: (970) M-4159 Project Number: BRB (01-065.01) First Submittal