The URL can be used to link to this page

Home My WebLink AboutFIRST MAINSTREET BANK - FDP - 37-03A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage Report First Main Street Bank June 30, 2004 REFERENCES DMW Civil Engineers, Inc. I 1) City of Fort Collins, Colorado, Storm Drainage Design Criteria and Construction Standards, Fort Collins, Colorado, May, 1997, revised 1999 2) Urban Drainage and Flood Control District, Urban Storm Drainage Criteria Manual, Wright Water Engineers, Denver, Colorado, June, 2001. 3) Greenhorne & O'Mara, Inc., McClellands Basin Master Drainage Plan, Aurora, Colorado, June 20, 1986 4) United States Department of Agriculture, Soil Survey of Larimer County Area, Colorado, December 1980. I Page 7 t= 4-s), I I I 1 I I I Final Drainage Report First Main Street Bank June 30, 2004 DMW Civil Engineers, Inc. consisting of silt fencing will surround areas of the proposed construction. See the Grading and Erosion Control Plan for locations of proposed erosion control measures. In addition to silt fence, Pond 1 will be utilized as a sediment basin for additional sediment control. 5.5 Water Quality Structural Best Management Practices (BMPs) are proposed for the FirstMain Street Bank site to improve water quality of runoff as recommended by the Urban Storm Drainage Criteria Manual. The detention pond incorporates an extended detention basin for water quality purposes. An extended detention basin (EDB) is a sedimentation basin which uses a much smaller outlet that extends the emptying time of the more frequently occurring runoff events to facilitate pollutant removal. Soluble pollutant removal can be somewhat enhanced by providing a small wetland marsh or ponding area in the basin's bottom to promote biological uptake. The basins are considered to be "dry" because they are designed not to have a significant permanent pool of water remaining between storm runoff events. However, EDB may develop wetland vegetation and sometimes shallow pools in the bottom portions of the facilities. Pond 1 has been designed to provide 0.16 acre feet of water quality capture volume in addition to 0.04 acre feet of sediment storage with a water surface elevation of 4996.93. Release of the captured water is controlled by a steel plate with one column of three 1.25" circular perforations. For detention calculation purposes, this volume has been added to the 100-year storage requirements. VI. CONCLUSIONS - 6.1 Compliance with Standards All drainage analyses have been performed according to the City of Fort Collins' Storm Drainage Design Criteria and Construction Standards manual and the Urban Storm Drainage Criteria Manual, Volume 3, by the Urban Drainage and Flood Control District. A predetermined release rate of 0.5 cfs per acre was used based on the McClellands Basin Master Drainage Plan. I i 7 L Page 6 r. Final Drainage Report First Main Street Bank June 30, 2004 DMW Civil Engineers, Inc. undetained onsite flows from basin 10 are 0.1 and 0.2 cfs respectively. Runoff from Basin 11(0.11 acres) drains to the east along a shallow swale adjacent to Harmony Road. The peak 10 and 100-year flows from this basin are 0.3 and 0.7 cfs respectively. These flows are offsite and are undetained. The offsite pond is assumed to discharge 42.0 cfs from the Pier Condominiums detention pond west of Boardwalk Drive, will enter the proposed 36 inch concrete pipe and will be routed to the northeast corner of the site where the flow will enter a junction box. At the junction box the flow will be combined with the 18 inch RCP pond outlet pipe as well as flow from basins 3, 0-3 that enter the inlet on top of this box. The outlet of this junction box is an existing 36 inch storm pipe. This existing 36 inch storm pipe flows to the east along back lot lines to the existing Whalers Cove detention pond which ultimately outfalls into McClellands Creek. ' 5.3 Detention Detention Pond 1 is located in the northeast corner of the site adjacent to Whalers Way. Pond 1 will utilize a single stage release consisting of a water quality control ' structure and a 6" orifice. Pond 1 detains the peak 100-year developed discharge from the site and releases it at no more than 0.5 cfs per acre. In addition to 0.16 acre-feet of water quality containment volume, Pond 1 provides 0.79 acre-feet of I detention volume. The maximum 100-year release from Pond 1 is 1.64 cfs with an associated water surface elevation of 5000.00. This release rate was obtained by taking the total area (4.82 acres) of the basins that drain into the Pond (Basins 1-5, ' 05) and multiplying them by the allowable release rate of 0.5 cfs per acre (2.41 cfs). Then the onsite 100-yr flows (0.90 cfs) that go undetained from basins 3,9,10 (0.26 acres) were subtracted from the allowable release rate for these basins (0.26 acres ' * 0.5cfs/acre=0.13 cfs). This undetained 0.77cfs was subtracted from the allowable release rate of 2.41 to come up with the final allowable release rate of 1.64 cfs. ' The total required storage for this detention pond was calculated using the FAA Rational Method. These calculations are provided in Appendix C. The total ' storage required for this pond is 0.79 acre-feet. The required Water Quality Capture Volume (0.16 acre-feet) was added to this volume to come up with the provided storage of 0.95 acre-feet. There is more discussion on this in the Water Quality section of this report. 5.4 Erosion Control Plan and Criteria The erosion control plan presented here is intended to control rainfall erosion. The 1 Erosion Control Reference Manual for Construction Sites (ECRM), City of Fort Collins, has been referenced for this erosion control plan.. ' The proposed rainfall erosion control plan during construction will consist of temporary structural erosion control measures. Temporary sediment control Page 5 Final Drainage Report DMW Civil Engineers, Inc. ' First Main Street Bank June 30, 2004 ' discharged into Basin 5 and the proposed detention pond via two curb openings along the east edge of the parking areas. The peak 10 and 100-year flows from Basin 1 are 3.7 and 9.4 cfs respectively. The peak 10 and 100-year flows from ' Basin 2 are 7.6 and 19.2 cfs respectively. Runoff from Basin 3 (0.35 acres) drains overland north of Building C from west to ' east along the north edge of the site. Stormwater is conveyed to the detention pond from the Basin via a proposed 18" RCP under the proposed drive entrance. The peak 10 and 100-year flows from basin 3 are 0.8 and 2.1 cfs respectively. 1 Runoff from Basin 4 (0.25 acres) drains to the east along a shallow swale adjacent to Harmony Road and discharged into Basin 5. The peak 10 and 100-year flows from this basin are 0.7 and 1.9 cfs respectively. These offsite flows are routed through the detention pond. ' Basin 5 (1.50 acres) is comprised mostly of the detention pond and landcape berms and swales around the east and south sides of the parking areas. The peak 10 and 100-year flows from Basin 5 are 1.3 and 3.4 cfs respectively. The cumulative peak ' 10 and 100-year runoff from Basins 1 through 5 and 05 which enter the detention pond are 12.2 and 33.1 cfs respectively. ' Runoff from Basin 6 (0.80 acres) drains to the north along the east gutter of Boardwalk Drive. The peak 10 and 100-year flows from this basin are 3.1 and 8.0 ' cfs respectively. These flows are offsite and are undetained. Basins 7 and 07 (0.59 acres) are located at the northeast corner of the site. Runoff ' from these Basins drains undetained to a proposed storm inletrunction box at the northeast corner of the site. This junction box combines the 36 inch RCP, carrying offsite flow, and the 18 inch RCP pond outfall pipe. Calculations for this 36 inch pipe are included in Appendix B. The peak 10 and 100-year flows to this inlet from Basins 7 and 07 are 0.6 and 1.8 cfs respectively. The peak 10 and 100-year undetained onsite flows from basin 7 are 0.1 and 0.3 cfs respectively. Basin 8 (0.04 acres) consists of the proposed drive entrance from Whalers Way. Runoff from Basin 8 drains overland to the north into Basin 9 where it enters the southern gutter of Whalers Way. The peak 10 and 100-year undetained onsite flows from basin 8 are 0.1 and 0.4 cfs respectively. Runoff from Basin 9 (0.30 acres) drains to the east along the south gutter of Whalers Way. The peak 10 and 100-year flows from this basin are 2.2 and 5.7 cfs respectively. These flows are offsite and are undetained. Runoff from Basin 10 (0.04 acres) drains overland to the south where it enters the ' swale along the north side of harmony Road. The peak 10 and 100-year Page 4 u 1 1 Final Drainage Report First Main Street Bank June 30, 2004 DMW Civil Engineers, Inc. IV. DRAINAGE DESIGN CRITERIA 4.1 Design Criteria and Restraints Drainage design criteria specified in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual and the Urban Storm Drainage Criteria Manual, Volume 3 by the Urban Drainage and Flood Control District have been referenced in the preparation of this study. A predetermined release rate of 0.5 cfs per acre was used based on the McClellands Basin Master Drainage Plan. 4.2 Hydrologic Criteria The rational method has been used to estimate peak stormwater runoff from the project site. An initial 10-year and major 100-year design storms have been used to evaluate the proposed drainage system. Calculations made as part of this investigation, along with other supporting material, are contained in Appendix A. Rainfall intensity data for the rational method has been taken from rainfall intensity data tables contained in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual (see Figure 3-1 a). Composite runoff coefficients were generated using Table 3-3 and 3-4 of the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual. 4.3 Hydraulic Criteria The computer program "Flowmaster° has been used to analyze the capacity of proposed pipes and chases for the site. Various spreadsheets using City of Fort Collins criteria have been used in the design of proposed detention ponds. V. DRAINAGE FACILITIES DESIGN 5.1 Proposed Site Development Development of the First MainStreet Bank site will consist of a bank building and two additional commercial. buildings. The proposed site infrastructure includes paved parking areas with curb, gutter and sidewalk, waterline, sanitary sewer, and storm utilities. 5.2 Developed Drainage Patterns The developed site has been divided into eleven (11) on -site and two (2) off -site drainage basins. Stormwater runoff will be conveyed overland to an onsite detention and water quality pond and released into existing stormwater utilities at the northeast corner of the site. The peak 100-year developed discharge from the site will be released at no more than 0.5 cfs per acre in accordance with the McClellands Basin Master Drainage Plan. Basins 1 (0.96 acres) and 2 (1.93 acres) are comprised of a majority of the parking on the First MainStreet Bank site. Runoff from Basins 1, 2 sheet flows across the parking lot and along concrete gutters from southwest to northeast. Stormwater is Page 3 MainStreet Bank site is within Flood Insurance Zone X, the areas determined to be 'outside the 500-year flood plain according to the FEMA Flood Insurance Rate Map, _. Community -Panel No. 080102-0014 C. This FIRM panel has not been printed because the entire panel is within Zone X. III. DRAINAGE BASINS AND SUB -BASINS ' 3.1 Major Basin Description The First MainStreet Bank site is within the McClellands Drainage Basin as ' identified by the City of Fort Collins Master Drainage Plan but not within any regulatory floodplains designated by either the City or FEMA. The McClellands Basin encompasses approximately 3.4 square miles in southeast Fort Collins. The ' storm runoff from the basin originates northeast of College Avenue and Harmony Road and drains southeast through the Oakridge, Willow Springs, Stetson Creek and Harvest Park developments. A single major drainageway, McClellands Creek, conveys flow from the upper end of the basin to the downstream discharge point along the Fossil Creek Reservoir inlet ditch. The majority of the basin is either developed, or is being developed, with residential and commercial land areas. 1 3.2 Sub -Basin Description Stormwater runoff from the First MainStreet Bank site drains overland generally ' from southeast to northwest at slopes ranging from 1.0% to 5.0%. Stormwater runoff is currently conveyed from the site towards the northeast overland and in shallow swales. An existing 24 inch concrete pipe enters the northwest corner of the site from the existing Pier Condominiums detention pond west of Boardwalk Drive. The existing discharge of the pond, according to the most recent Master Plan, is 23.8 cfs. However, according to the Rafferty's Final Storm Drainage Report, the discharge of the pond is 42 cfs. An existing channel crosses the north portion of the site to convey the pond discharge to the east. Runoff is conveyed from the site to the east via a 36 inch concrete pipe. This storm sewer flows to the east along back lot lines to the existing Whalers Cove detention pond which ultimately outfalls into McClellands Creek. Harmony Road, Boardwalk Drive and Whalers Way are all currently developed. Runoff from the north half of Westbound Harmony Road flows to the north and is 1 then carried to the east offsite in a shallow swale at the base of existing berms. Runoff from the East half of Boardwalk drive flows to the north along the gutter to an existing 2 foot combination inlet approximately 80 feet north of Whalers Way. I. I The inlet drains to the existing Pier Condominiums detention pond. There is an existing high point in Whalers Way just East of Boardwalk Drive. Runoff from the west side of this high point flows to the aforementioned inlet. Runoff from the south half of Whalers way east of the high point flows to the along the gutter to an existing 2 foot combination inlet located at the southwest corner of Whalers Way and Seaway Circle approximately 150 feet east of the First Main Street Bank site. Page 2 u 1 1 1 I 1 I I I L� Final Drainage Report for First MainStreet Bank Fort Collins, Colorado July 7, 2004 I. INTRODUCTION 1.1 Objective This study documents the results of a comprehensive hydrologic and hydraulic analysis of both pre and post -development conditions for the proposed First MainStreet Bank development. The construction plans which accompany this report are entitled Final Construction Plans for First MainStreet Bank prepared by DMW Civil Engineers. 1.2 Project History and Previous Studies A Master Drainage Plan for the McClellands Basin was prepared by Greenhorne & O'Mara, Inc., dated June 20, 1986. Also, the First MainStreet Bank site has been previously reviewed as Rafferty's PUD, a restaurant site. The previous study by Stewart and Associates, dated November 27,1995, was approved on December 18, 1995. A portion of both reports are included in Appendices F and G, respectively. 1.3 Mapping and Surveying Field survey information and topographic mapping with a contour interval of 1-foot was obtained by DMW Civil Engineers from King Surveyors, Windsor, Colorado. Additional topography outside of the project boundary was taken from City of Fort Collins Aerial Topography with a two (2) foot contour interval. 1.4 Site Reconnaissance The project engineer performed site visits to the First MainStreet Bank site in Fort Collins in October, 2003. Existing drainage patterns and structures were observed for use in defining drainage basin boundaries and flow patterns. II GENERAL LOCATION AND DESCRIPTION 2.1 Site Location The site is located in the southeast quarter of Section 36, Township 7 North, Range 69 West of the 6th Principal Meridian in the City of Fort Collins, Colorado. The site is bounded by Harmony Road on the south, Boardwalk Drive on the west, Whalers Way on the north and The Mallards Subdivision to the east (See Vicinity Map). 2.2 Site Description The FirstMain Street Bank site is approximately 5.2 acres of vacant land. Vegetation on the site consists of native weeds, grasses and trees, and onsite soils are predominantly Hydrologic Group B with some areas of Hydrologic Group C according to the Natural Resources Conservation Service (NRCS). The site is zoned H-C (Harmony Corridor District) and is surrounded with existing commercial development as well as existing single family and multi family housing. The First ,.I-, Fm F� F f 1� 10 fm lm lm lm lm t� t� t� t� t� t� t� t� j j Min ILI.�' _♦ I VICINITY MAP rt� SCALE: 1 "=2000' Qoo� Final Drainage Report ' for First MainStreet Bank ' EXHIBITS Exhibit 1 First Main Street Bank Drainage Plan Appendix A APPENDICES Developed Hydrology Computations Appendix B Appendix C Developed Hydraulic Computations Detention Pond Calculations Appendix D Erosion Control Calculations Appendix E Water Quality Calculations Appendix F McClellands Basin Master Drainage Plan Appendix G Rafferty's P.U.D., Final Storm Drainage Report I I I I I I I I I I I I I I 1 1 I I Final Drainage Report for First MainStreet Bank TABLE OF CONTENTS VICINITY MAP \ Page No. I INTRODUCTION 1.1 Objective.................................................1 1.2 Project History and Previous Studies ...................... . ..... 1 1.3 Mapping and Surveying ...................................... 1 1.4 Site Reconnaissance............................:...........1 II SITE LOCATION AND DESCRIPTION 2.1 Site Location..............................................1 2.2 Site Description ............................................ 1 III DRAINAGE BASINS AND SUB -BASINS 3.1 Major Basin Description ...................................... 2 3.2 Sub -Basin Description ....................................... 2 IV DRAINAGE DESIGN CRITERIA 4.1 Design Criteria and Constraints ................................ 3 4.2 Hydrologic Criteria ........................................... 3 4.3 Hydraulic Criteria ........................................... 3 V DRAINAGE FACILITIES DESIGN 5.1 Proposed Site Development .................................. 3 5.2 Developed Drainage Patterns ................................. 3 5.3 Detention.................................................4 5.4 Erosion Control ............................................ 4 5.5 Water Quality .............................................. 6 VI CONCLUSIONS 6.1 Compliance with Standards ................................... 6 REFERENCES..................................................7 CIVIL ENGINEERS July 7, 2004 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 Re: Final Drainage Report for First MainStreet Bank Fort Collins, Colorado IDear Staff: 1435 WEST 29" STREET LOVELAND, CO B0538 (970) 461 -2661 FAx (970) 461-2665 WWW. DMWCIVILENGINEERS.COM DMW Civil Engineers is pleased to submit this drainage study for First MainStreet Bank for your review. This report complies with technical criteria set forth in the City of Fort Collins' Storm Drainage Design Criteria and Construction Standards manual and the Urban Storm Drainage Criteria Manual, Volume 3, by the Urban Drainage and Flood Control District. We acknowledge that the City of Fort Collins' review of this study is only for general conformance with submittal requirements, current design criteria and standard engineering principles and practices. If you should have any questions or comments as you review this report, please feel free to contact me at your convenience. Sincerely, DMW CIVIL ENGINEERS %�o Jade P. Miller, P.E. (CO #33885) Project Engineer Final Drainage Report for First MainStreet Bank Fort Collins, Colorado July 7, 2004 Prepared for: Mr. Les Mariotti Chief Operating Officer First MainStreet Financial Ltd. P.O. Box 1159 Longmont, CO 80501-1159 Prepared by: PIVIL&RSMIL- 1435 Project Number: 0311.00-FMS