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HomeMy WebLinkAboutBELLA VISTA - PDP - 45-01A - REPORTS - DRAINAGE REPORTFinal Drainage Report Bella Vista July 31, 2002 Northern Engineering Services, Inc REFERENCES 1) Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright Water Engineers, Inc., Denver, Colorado, Updated June 2001. 2) Erosion Control Reference Manual for Construction Sites, City of Fort Collins, Colorado, Hydrodynamics, Inc., January 1991. i 3) Stormceptor® Owner's Manual, Stormceptor®, November 1999. 4) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, Updated April 1999. ® ® 5) The StormceptorIndustry Newsletter, Fall 2000 — Issue # 8, Stormceptor. Final Drainage Report Bella Vista July 31, 2002 Northern Engineering Services, Inc 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. 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 along with performance standard and effectiveness calculations have been provided for the site (See Appendix G). 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 and water quality enhancement for the developed stormwater runoff from Bella Vista. Final Drainage Report Bella Vista July 31, 2002 Northern Engineering Services, Inc water quality before being discharged into Warren Lake. All storm sewers are sized to convey the full 100-year developed flows with no controls on the release rate from the site. V. WATER QUALITY 5.1 Water Quality Measures and Criteria The Developer of Bella Vista is very conscientious of the impacts of this project, and as such, is proposing three separate water quality features to treat the runoff from the site. All areas, including the rooftops, will be routed through a water quality mechanism before being released under Horsetooth Road into Warren Lake. Two (2) on -site water quality capture volumes (WQCV) are proposed to remove sediment and other pollutants from developed runoff. These WQCV's will be located at Water Quality Pond 1 and Water Quality Pond 2. 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 for Pond 1 was determined to be approximately 0.032 acre-feet. This required WQCV is achieved at an elevation of 4997.25 feet. The required water quality capture volume for Pond 2 was determined to be approximately 0.042 acre-feet. This required WQCV is achieved at an elevation of 5001.63 feet. Steel orifice plates with vertical perforations will be built into the pond outlet structures to control the water quality capture volume. Additionally, a Stormceptor structure will be used to treat the runoff from the underground parking level. "The Stormceptor® System is a vertically -orientated stormwater separator that removes oil, sediment and other pollutants from urban run-off. Its built-in by-pass feature prevents trapped contents from flushing out during intense rain storms."5 A model STC-900 is proposed to treat the runoff from Basins F, G & H. This is a concrete unit with a sediment capacity of 565 gallons and an oil capacity of 280 gallons. 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. Gravel bag inlet filters will be placed around all drain basins and vane drains. Gravel bag sediment traps will be placed at the outlets of the proposed water quality ponds. Gravel bag dikes will be placed in Swale D at an interval of no less than 100 feet and near the reconstructed headwall. Vehicle tracking control pads will be provided at the two entrances to the site. Silt fencing will be installed along Stanford Road, Horsetooth Road, and the reconstructed headwall to prevent runoff particulates and windblown sediment from migrating off -site. 5 Final Drainage Report Bella Vista July 31, 2002 Northern Engineering Services, Inc south of Horsetooth Road will be expanded to accommodate the outfall of Storm Sewer Line.E. 4.5.6 Basin F (0.075 acre) Basin F has been divided into two (2) incontiguous sub -basins labeled F 1 and F2. These basins consist of the drive entrances into the underground parking garage. Basin F1 is located at the western entrance to the garage, and Basin F2 is located at the eastern entrance to the parking garage. Two slotted vane drains will intercept runoff from the basins and convey it to Storm Sewer Line G. 4.5.7 Basin G (1.218 acres) Basin G has been divided into five (5) sub -basins label Gl-G5. This basin consists of the underground parking garage. Since this basin is covered, it will not be subject to normal rainfall or surface runoff. Snowmelt from vehicles and other nuisance flows have been estimated to be 20% of the typical runoff if this basin were to be fully exposed to the elements. Each sub -basin drains to a sump inlet or vane drain before being conveyed in Storm Sewer Line G. Storm Line G will pass through an inline Stormceptor® unit to be treated for water quality before joining Storm Sewer Line E at manhole E2 in Horsetooth Road. 4.5.8 Basin H (0.049 acre) Basin H is located in the courtyard between buildings C and D. This basin is entirely paved. Runoff from this basin travels through an 8" floor drain, and into Storm Sewer Line G. 4.5.9 Basin HR (1.576 acre) Basin HR is consists of the northern half of Horsetooth Road adjacent to the site. Runoff from this basins starts at a high point in the road near the eastern property corner, and travels west towards a proposed on -grade 12.5' Type R inlet. A portion of the 100-year flows will by-pass this inlet and be intercepted by the existing 5'. Type R inlet just west of the proposed new inlet. Basin HR also contains a small portion of on -site area that free releases into Horsetooth Road. Basin HR is not treated for water quality. Flows intercepted by both inlets are conveyed under the street via storm sewer, and into Warren Lake. 4.5.10 Basin SR (1.257 acre) Basin SR is consists of the eastern half of Stanford Road adjacent to the site. This basin also includes a large amount of off -site area north of the site. Runoff from this basins travels south to an existing 5' Type R inlet at the intersection with Horsetooth Road. Basin SR is not treated for water quality. Flows intercepted by the existing 5' curb inlet are conveyed under the street in existing storm sewer, and into Warren Lake. 4.6 Detention Due to the close proximity to Warren Lake, the Bella Vista project will not provide any on -site stormwater detention storage volume. All developed runoff will be treated for 4 Final Drainage Report Bella Vista July 31, 2002 4.5 Drainage Patterns Northern Engineering Services, Inc 4.5.1 Basin A (0.542 acre) Basin A has been divided into four (4) sub -basins labeled Al-A4. This basin is located on the western portion of the site along Stanford Road. Runoff from this basin will be directed overland to the west towards a series of drain basins located in sump areas behind the walk along Stanford Road. All of the drain basins are sized to convey the full 100-year developed flows. Storm Sewer Line A will carry flows from each inline drain into Water Quality Pond 1 located within Basin A4. Emergency overflow from the drain basins will safely spill to the west into Stanford Road. Should Water Quality Pond 1 itself fail, excess spill will overflow to the south into Horsetooth Road. Storm Sewer Line E1 will carry both the water quality release and the undetained runoff release from Water Quality Pond 1 under Horsetooth Road. 4.5.2 Basin B (0.388 acre) Basin B has been divided into six (6) sub -basins labeled Bli, Blii; B2, B3i, B3ii and B4.. This basin consists mainly of the southern half of the building rooftops. Runoff from this basin will be collected in roof drains and one curb inlet. Storm Sewer Line B will carry flows into Water Quality Pond 1. This storm sewer is sized to convey the full 100-year developed flows. Emergency overflow from Water Quality Pond 1 will safely spill to the south into Horsetooth Road. Storm Sewer Line El will convey the discharge from Water Quality Pond 1 under Horsetooth Road. 4.5.3 Basin C (1.216 acres,) Basin C has been divided into two (2) sub -basins labeled C1 and C2. This basin is located at the center of the site and consists mainly of asphalt parking and rooftops. Runoff from this basin will sheet flow to the north, and travel through a series of curb openings into Swale D. Swale D will convey flows to the southeast into Water Quality Pond 2. 4.5.4 Basin D (0.359 acre) Basin D is located along the northern property boundary adjacent to Aspen Leaf Apartments. This basin contains Swale D and is entirely landscaped. Runoff from this basin travels into Water Quality Pond 2. 4.5.5 Basin E (0.171 acre) Basin E is located at the southeast corner of the site and contains Water Quality Pond 2. Runoff from this basin sheet flows towards the outlet structure of Water Quality Pond 2. Runoff from Basins C, D, and E are all routed through this outlet structure. Emergency overflow from Water Quality Pond 2 will spill to the south into Horsetooth Road. Storm Sewer Line E will carry flows from the outlet structure to the west under the northern half of Horsetooth Road. Storm Line E then conveys flow to the south in a new storm sewer pipe parallel to the existing 29" x 45" HERCP pipes under Horsetooth Road. The existing concrete headwall 3 Final Drainage Report Bella Vista July 31, 2002 Northern Engineering Services, Inc. south via the curb and gutter of Stanford Road. An existing 5' curb inlet located on the east side of Stanford Road just before Horsetooth Road intercepts this runoff and conveys it into the large concrete storm vault located near the southwest property corner. A small amount of runoff from the northern edge of the site enters an existing grass -lined swale section where it N carried to the southeast into Horsetooth Road. Runoff from the majority of the site sheet flows directly into Horsetooth Road. All flow in Horsetooth Road travels to the west towards an existing 5' curb inlet located on the north side of Horsetooth Road just before Stanford Road. This inlet will be relocated with the widening of Horsetooth Road. Flows intercepted by this curb inlet combine with flows from the concrete storm vault and travel south under Horsetooth Road via (3) three 29" x 45" horizontal elliptical concrete pipes. These pipes daylight into a concrete headwall located on the south side of Horsetooth Road. A natural drainage channel conveys water a short distance into Warren Lake. IV. POST -DEVELOPMENT CONDITIONS 4.1 Post -development Conditions The Bella Vista development will include the following: • (3) three new mixed -use buildings; • new curb, gutter, and detached walk along the north side of Horsetooth Road; • drainage improvements and utility services. The entire northern portion of Horsetooth Road along the property boundary will be expanding and repaved with this development. In addition, new utility lines will be ran underneath Horsetooth Road. 4.2 Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual. SDDCMI and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been referenced for this study. 4.3 Hydrologic Criteria The Rational Method has been used to estimate peak stormwater runoff within the developed site. The minor 10-year and major 100-year design storms have been used in the design of the proposed drainage system, which includes slotted vane drains, drain basins, storm sewer, a grass -lined swale, two water quality ponds, and a Stormceptoro structure. Rainfall intensity data for the Rational Method has been taken from Figure 3- 1 a 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 "StormCAD" by Haestad Methods has been used to design and analyze the storm sewer lines and outlet structures • The computer program "F1owMaster" by Haestad Methods has been used to design and analyze swale sections, curb inlets, weirs, and street capacities 2 Final Drainage Report Bella Vista July 31, 2002 Final Drainage Report for Bella Vista Fort Collins, Colorado July 31, 2002 Northern Engineering Services, Inc. I. INTRODUCTION 1.1 Objective This report summarizes the results of a comprehensive analysis of both pre- and post - development hydrologic and hydraulic conditions for the Bella Vista site in Fort Collins, Colorado. 1.2 Mapping and Surveying A site survey was conducted by Albers, Drexel & Pohly, Inc. in October of 2001. The existing topography was given at a one -foot contour interval. In addition, City of Fort Collins aerial photographs were used for off -site topography. 1.3 Site Reconnaissance A site visit was conducted in October 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 Bella Vista site is located within the southwest quarter of Section 25, Township 7 North, Range 69 West of the 6thPrincipal Meridian in the City of Fort Collins, County of Larimer, State of Colorado. The project is bounded by Aspen Leaf Apartments on the north, Horsetooth Road on the south, and Stanford Road on the west. (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 Bella Vista site is approximately 2.96 acres and has historically been an undeveloped field. There are no existing trees or structures located on the property. A 20' City of Fort Collins sanitary sewer easement does cross the property at an angle near the southwest property corner. Also, a large concrete storm sewer vault exists near the intersection of Stanford Road and Horsetooth Road. III. PRE -DEVELOPMENT CONDITIONS 3.1 Major Basin Description The site is located in the City of Fort Collins Foothills Master Plan Drainage Basin. Runoff from the site drains directly into Warren Lake, which is located south of Horsetooth Road approximately 350 feet from the property boundary. 3.2 Pre -development Drainage Patterns The Bella Vista site historically drains from the north to the south at slopes ranging from approximately 3% to 5%. Runoff from the western edge of the site is conveyed to the DULY, 2002 VICINITY MAP 1V NOT TO SCALE Table of Contents VICINITY MAP Page I. INTRODUCTION 1.1 Objective.......................................................................................... 1 1.2 Mapping and Surveying................................................................... 1 1.3 Site Reconnaissance......................................................................... 1 II. SITE LOCATION AND DESCRIPTION 2.1 Site Location........................................................................:........... 1 2.2 Site Description................................................................................ 1 III. PRE -DEVELOPMENT CONDITIONS 3.1 Major Basin Description.................................................................. 1 3.2 Pre -development Drainage Patterns ................................................ 1 IV. POST -DEVELOPMENT CONDITIONS 4.1 Post -development Conditions.......................................................... 2 4.2 Design Criteria and References....................................................... 2 4.3 Hydrologic Criteria.......................................................................... 2 4.4 Hydraulic Criteria............................................................................ 2 4.5 Drainage Patterns............................................................................ 3 4.6 Detention ........... ..................................................................:............ 4 V. WATER QUALITY 5.1 Water Quality Measures and Criteria .............................................. 5 VI. EROSION CONTROL PLAN 6.1 Erosion Control Plan and Criteria .................................................... 5 6.2 Rainfall Erosion Control Plan .......................................................... 5 VII. CONCLUSIONS 7.1 Compliance with Standards............................................................. 6 REFERENCES.......................................................................................... 7 APPENDICES APPENDIX A- Hydrology Calculations APPENDIX B - Water Quality Calculations APPENDIX C - Inlet Calculations APPENDIX D- Storm Sewer Calculations APPENDIX E - Swale Calculations APPENDIX F - Riprap Calculations APPENDIX G- Erosion Control Calculations APPENDIX H- Street Capacity Calculations APPENDIX I = Review Comments & Other Correspondence NORTHERN ENGINEERING NESERVICES, INC. July 31, 2002 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Bella Vista Fort Collins, Colorado Project Number: 01-037.05 Dear Staff: Northern Engineering Services, Inc. is pleased to re -submit this Final Drainage Report for the Bella Vista site for your review. All review comments from the previous submittal dated January 29, 2002 have been addressed. We understand that review by the City of Fort Collins is to assure general compliance with standardized criteria contained in the Storm Drainage Design 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. Nicholas aw W. Hs, E.I.T. Project Engineer ,�����0\1 27362 Roger A.1Curtj Vice President I420 SOUTH HOWES, SUITE 202 / FORT COLLINS, COLORADO 80521 / 970.221.4158 / FAX 970.221.4159 Final Drainage Report for Bella Vista Fort Collins, Colorado July 31, 2002 Prepared For: Stanford Development, L.L.C. 419 Canyon Avenue, Suite 300 Fort Collins, Colorado 80521 Prepared By: NORTHERN NE ENGINEERING SERVICES, INC. 420 S. Howes, Suite 202 Fort Collins, Colorado 80521 Phone: (970) 221-4158 Fax: (970) 221-4159 Project Number: BLV (01-037.05) Third Submittal EM