The URL can be used to link to this page

Home My WebLink AboutFIRST MAINSTREET BANK - PDP - 37-03 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTI Drainage Design Considerations DMW Civil Engineers ' First Main Street Bank November 4, 2003 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 0.13 acre feet of water quality capture volume in addition to 0.02 acre feet of sediment storage with a water surface elevation of ' 4997.6. Release of the captured water is controlled by a steel plate with one column of three 1.125" circular perforations. For detention calculation purposes, this volume has been added to the 100-year storage requirements. r- 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. u Page 5 11 Drainage Design Considerations DMW Civil Engineers First Main Street Bank November 4, 2003 Runoff from Basin 6 (0.44 acres) drains to the east along a shallow swale adjacent to Harmony Road. The peak 10 and 100-year flows from this basin are 0.8 and 2.2 cfs respectively. Runoff from Basin 7 (0.44 acres) drains to the north along the east gutter of Boardwalk Drive. The peak 10 and 100-year flows from this basin are 2.1 and 5.4 cfs respectively. Runoff from Basin 8 (0.35 acres) drains to the north along the east gutter of Boardwalk Drive. The peak 10 and 100-year flows from this basin are 0.7 and 3.0 cfs respectively ' 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 6" orifice and a water I I I quality control structure. 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 0.15 acre-feet of water quality containment volume, Pond 1 provides 0.60 acre-feet of detention volume. The maximum 100-year release from Pond 1 is 1.32 cfs with an associated water surface elevation of 4998.96. 5.4 Erosion Control Plan and Criteria The erosion control plan presented here is intended to control rainfall erosion. The 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 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 First_ Main 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 Page 4 I I Drainage Design Considerations . DMW Civil Engineers First Main Street Bank November 4, 2003 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 the Appendices. 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. Also, the computer program "Watershed Modeling Module" by Eagle Point Software has been used in the design of proposed detention ponds. V. DRAINAGE FACILITIES DESIGN 5.1 Proposed Site Development Development of the First Main Street Bank site will consist of a bank building and a future pad site for commercial use. 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 eight (8) 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. Runoff from Basins 1, 2, 3 and 0-3 (4.52 acres) drains overland from southwest to northeast to the proposed detention pond. The peak 10 and 100-year inflows to the pond are 8.3 and 21.2 cfs respectively. Runoff from Basins 4, 5 and OS-5 (0.87 acres) drains undetained to the existing storm sewer utilities at the northeast corner of the site. The peak 10 and 100-year on -site generated flows for the basins are 1.2 and 3.2 cfs respectively Page 3 Drainage Design Considerations DMW Civil Engineers ' First Main Street Bank November 4, 2003 III. DRAINAGE BASINS AND SUB -BASINS 3.1 Major Basin Description The First Main Street 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. 3.2 Sub -Basin Description Stormwater runoff from the First Main Street 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 thenortheast 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 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 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. 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. 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 �i Page 2 Drainage Design Considerations for First Main Street Bank Fort Collins, Colorado ANovember 4, 2003 I. INTRODUCTION 1.1 Objective This study documents the results of a comprehensive hydrologic and hydraulic analysis of both historic and post -development conditions for the proposed First Main Street Bank development. The construction plans which accompany this report are entitled Final Construction Plans for First Main Street Bank prepared.by DMW Civil Engineers. 1.2 Project History and Previous Studies The First Main Street 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. Also, a Master Drainage Plan for the McClellands Basin was prepared by Greenhorne & O'Mara, Inc., dated June 20, 1986. 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 Main Street Bank site in Fort Collins in October, 2003. Existing drainage patterns and structures were observed for use in defining drainage basin boundaries and flow pattems. 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). i 2.2 Site Description The First Main Street Bank site is approximately 5.2 acres of vacant land. Vegetation on the site consists of native weeds grasses and trees. 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. j w IMP Am— co 'I0 "li i Lam VICINITY MAP SCALE: 1 °=2000' Zwelof-,11,010, Drainage Design Considerations for First Main Street Bank EXHIBITS Exhibit 1 First Main Street Bank Drainage Plan APPENDICES Appendix A Developed Hydrology Computations Appendix B Developed Hydraulic Computations Appendix C Detention Pond Calculations Appendix D Water Quality Calculations Appendix E McClellands Basin Master Drainage Plan J r r 9I I I Drainage Design Considerations for First Main Street Bank TABLE OF CONTENTS VICINITY MAP I INTRODUCTION Page No. 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 ................................ 2 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 .............................................. 4 VI CONCLUSIONS 6.1 Compliance with Standards ................................... 5 REFERENCES ....... 5 CIVIL ENGINEERS I November 4, 2003 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 Re: Drainage Design Considerations for First Main Street Bank Fort Collins, Colorado Dear Staff: I I I 11 I I 1 43 5 WEST 29" STREET LOVELAND, CO 60536 (970) 461 -2661 Fax (970) 461 -2665 WWW. DMWCIVILENGINEERS.COM DMW Civil Engineers is pleased to submit this drainage study for First Main Street Bank for your review. This report complies with technical criteria set forth in the City of Fort Collins' Storm Drainage Desion 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, currentdesign 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 NC- 2L✓rEIJ auey Jade P. Miller, P.E. (CO #33885) Project Engineer 0 Drainage Design Considerations for First Main Street Bank Fort Collins, Colorado November 4, 2003 Prepared for: Mr. Les Mariotti Chief Operating Officer First MainStreet Financial Ltd. P.O. Box 1159 Longmont, CO 80501-1159 Pre ared by: C7MI CIVIL ENGINEERS 1435 W. 29#1 Street Loveland, Colorado 80538 Phone: (970)461-2661 Fax: (970)461-2665 Project Number: 0311.00-FMS