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Home My WebLink AboutFORT COLLINS DISCOVERY MUSEUM - PDP - 6-10 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT1 1 1 1 NORTHERN ENGINEERING Fort Collins Discovery Science Museum 10.0 Additional Water Quality Measures Additional water quality treatment for the site will include the utilization of Bio-Swales and Bio- Retention areas. These features will be located within the parking area south of the proposed building. Details including soil amendment, plantings and landscaping will be provided at final design. 11.0 Erosion and Sediment Control An Erosion and Sediment Control Plan (along with associated details) will be provided during final design. The plan will address both temporary measures to be implemented during construction, as well as permanent erosion control protection, as necessary. Best Management Practices (BMPs) from the UDFCD and the City of Fort Collins Erosion Control Reference Manual for Construction Sites will be utilized. Among the measures expected are: silt fencing along the disturbed perimeter, inlet protection at storm inlets as well as around the water quality pond's outlet structure, and vehicle tracking control pads at each construction entrance. Additional information and detail will be provided with final design. 12.0 Conclusions The proposed development will conform to current City Standards at final design. Proposed storm drainage facilities will adequately convey up to the 100-year storm event and provide adequate treatment of storm runoff prior to discharge into the Cache La Poudre River. No adverse stormwater impacts are expected as a result of this project. Final improvements will be designed in accordance with City of Fort Collins criteria. References 1) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, Updated April 1999. 2) Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, Updated June 2001. 3) Old Town Master Plan for Howes, Udall, and Magnolia Basins, Icon Engineering, Inc., November 2006. ' Preliminary Drainage and Erosion Control Report (NORTHERN ENGINEERING Fort Collins Discovery Science Museum The development will be in compliance with all applicable floodplain regulations per Chapter 10 of City Code. 7.0 Proposed Development The proposed development will include construction of a museum structure and associated parking and utilities. A water quality pond will be constructed at the north end of the site. A portion of onsite drainage will be directed into this pond. The remainder of the site will drain into the existing Howes Street Outfall Water Quality Pond, to the west of the site, which is ' discussed in further detail below. 8.0 Proposed Drainage Plan ' The developed site has been broken into 5 developed drainage basins for this PDP submittal. Further subdivision of basins will occur at final design as necessary for sizing of stormwater features. In general, developed stormwater from the site will be conveyed primarily via gutter flow and through on onsite storm line system into either the onsite water quality pond, or the existing Howes Street Outfall Water Quality Pond. ' 9.0 Water Quality Pond I [1 1 A preliminary required water quality volume for the onsite water quality pond has been calculated in Appendix C. All calculations conform to Volume 3 of the Urban Storm Drainage Criteria Manual (Reference 2) for extended (40-hour) detention basins. The estimated 100-year overflow of 12.1 cfs (see developed runoff calculations, appendix B) will be conveyed via the pond outlet structure and pipe to the Howes Street Outfall channel as shown on the Drainage Exhibit. Pond information is summarized in Table 1, below. TABLE 1— Preliminary Pond Volume Estimate Onsite Water Required Volume Quality Pond Water Quality 0.06 ac-ft Volume Water Surface 4960.89 Elevation 100- ear Overflow 12.1 cfs Water quality capture volume (WQCV) is proposed within the onsite water quality pond to remove sediment and other pollutants from the developed runoff. Criteria for a 40-hour dry extended detention basin outlined in the Urban Storm Drainage Criteria Manual, Volume 3 — Best Management Practices (Reference 5) by the Urban Drainage and Flood Control District will be used to verify adequate water quality capture volume at final design. Preliminary Drainage and Erosion Control Report 3 I I I 1 ■ (NORTHERN E NC IN EE RI NG Fort Collins Discovery Science Museum 5.0 Howes Street Outfall Water Quality Area The Howes Street Outfall Water Quality Area and Outfall Channel are located just west of the proposed development. Significant discussion has occurred with City staff regarding this area. The area has been studied in detail by Icon Engineering, Inc. and Icon's report entitled "Old Town Master Plan for Howes, Udall, and Magnolia Basins", dated November 2006 is referenced in the current study. The Icon study summarizes the area draining to the Howes Street Outfall and provides recommendations for future improvements to the Howes Street Outfall Water Quality Area. Currently, the water quality area is significantly undersized, providing 0.20 acre-feet of water quality volume for the Howes Basin. Improvement of the water quality area would involve the construction of two new water quality ponds as well as the expansion of the existing water quality area. These improvements would result in an addition of 4.1 acre-feet of water quality volume to the existing system. The currently proposed water quality pond is located near the area to be used for one of the additional ponds proposed by Icon. It is anticipated that when the ultimate improvements are made to the water quality area, the current proposed water quality pond will be merged with Icon's design pond. 6.0 Cache La Poudre Floodplain The Cache La Poudre 100-year and 500-year floodplain encroaches the project site and is delineated on the Drainage Exhibit (see back map pocket). FEMA FIRM Panel Numbers 977 and 979 for Larimer County, Dated December 19, 2006 are referenced in this study, and delineation of floodplain and floodway boundaries shown on the Drainage Exhibit are consistent with the FIRM. A copy of portions of these FIRM Panels are provided in Appendix D. The base (100-year) flood elevation in the vicinity of the proposed structure is 4966.0 which is referenced to the City of Fort Collins NGVD 29. The finished floor of the proposed structure is at elevation 4973.0, allowing the regulatory flood protection elevation (minimum 2-feet above base flood elevation) to be met. All HVAC will also exceed the regulatory flood protection elevation. The proposed structure is located outside of the 100-year and 500-year floodplain boundaries. Proposed use of the structure is a children's museum. Based on discussion with the City Floodplain Administrator, the proposed structure is considered a critical facility. The Cache La Poudre half -foot floodway also encroaches the site and is delineated on the Drainage Exhibit. No fill is proposed within the half -foot floodway. It is noted that the vertical datum utilized for site survey work is the City of Fort Collins Benchmark #V 401 (Elevation=4974.64, NGVD 29). A floodplain use permit will be required for each structure and each site construction element (water quality pond, bike path, parking lots, utilities, etc.) in the floodplain. Additionally, FEMA elevation certificates must be completed and approved for any structures in the floodplain prior to issuance of Certificate of Occupancy. I Preliminary Drainage and Erosion Control Report 2 NORTHERN ENGINEERING Fort Collins Discovery Science Museum 1.0 Scope This Preliminary Drainage Report has been prepared for the proposed the Fort Collins Discovery Museum development project, and is intended to document the associated stormwater impacts. ' Existing and preliminary design of proposed storm drainage features are discussed in this report. Comprehensive analysis of proposed storm drainage facilities will be conducted at the final design level for the proposed project. I2.0 Design Criteria References and Drainage criteria outlined in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards (SDDCCS) has been referenced in this preliminary study, and will serve as the main guidelines for final design. ' The Rational Method has been used to estimate the peak discharge rates for the minor and major storm events. The minor and major rainfall events are considered to be the 2-year and 100-year storms, respectively. Runoff coefficients and rainfall values utilized in the Rational Method ' computations are consistent with the SDDCCS. 1 The Urban Drainage and Flood Control District's (UDFCD) Urban Storm Drainage Criteria Manual III has been used for water quality design. ,Volume 3.0 Site Location The project site is located in a portion of the northeast quarter of section 11, Township 7 North, Range 69 West of the 6`h Principal Meridian in the City of Fort Collins, Larimer County, Colorado. The site is bounded on the south by Cherry Street, on the east by College Avenue, and on the north by the Cache La Poudre River. 4.0 Historic Drainage and Major Drainage Basin The area to be developed is roughly 5.4 acres in size and currently cosists of undeveloped land. ' The site slopes generally from south to north at slopes ranging from 0.5% to 3.0%. Ground cover consists of native grasses. Three historic onsite basins have been defined in the Historic Drainage Exhibit (please see back map pocket). No offsite basins contribute to the project site. The site lies entirely within the Old Town Major Drainage Basin. Due to the site's proximity to the Cache La Poudre River, detention is not required for this development. ' It is noted that there are no major irrigation facilities located on the project site. I IPreliminary Drainage and Erosion Control Report (NORTHERN ' ENGINEERING Centre Avenue Residences TABLE OF CONTENTS 1.0 Scope...................................................................................................................................1 2.0 Design Criteria and References.......................................................................................... 1 3.0 Site Location....................................................................................................................... 1 4.0 Historic Drainage and Major Drainage Basin..................................................................... 1 5.0 Howes Street Outfall Water Quality Area.......................................................................... 2 6.0 Cache La Poudre Floodplain............................................................................................... 2 7.0 Proposed Development....................................................................................................... 3 8.0 9.0 Proposed Drainage Plan...................................................................................................... 3 Water Quality Pond............................................................................................................. 3 10.0 Additional Water Quality Measures................................................................................... 4 ' 11.0 12.0 Erosion and Sediment Control............................................................................................ 4 Conclusions............................................................................................4 References....................................................................................................................................... 4 APPENDICES: APPENDIX A— APPENDIX B— Historic Drainage Calculations Proposed Drainage Calculations APPENDIX C— Water Quality Calculations APPENDIX D— FEMA FIRM Panel Excerpts APPENDIX E — Excerpts from Previous Reports BACK MAP POCKET: t Historic Drainage Exhibit Developed Drainage Exhibit I I7 i F Preliminary Drainage and Erosion Control Report 1 ®VICINITY MAP SCALE 1" = 1000' AOON"; PHM:970M4I58 . NORTHERN �srabpAw-suftIM w�B�� ;r&= E N G I N E E R I N G fort Wins, OD W524 RL 9MM.41W �rortlrr�cti� March 2, 2010 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 1 RE 1 1 1 I Preliminary Drainage and Erosion Control Report Fort Collins Discovery Museum Dear Staff: Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report for your review. This report accompanies a Project Development Plan (PDP) application submittal. The PDP submittal is typically considered to have 50% of the final engineering details. The main objectives of the Preliminary Drainage Report are to address the project's detention requirements and the need for any off -site drainage easements or improvements. This report has been prepared in accordance to City of Fort Collins Storm Drainage Design Criteria and Construction Standards (SDDCCS), and serves to document the stormwater impacts associated with the proposed development. We understand that review by the City is to assure general compliance with standardized criteria contained in the SDDCCS. If you should have any questions as you review this report, please feel free to contact us. Sincerely, NORTHERN INEERING SERVICES, INC. Aaron Cvar, PE I Preliminary Drainage and Erosion Control Report for Fort Collins Discovery Museum Fort Collins, Colorado March 2, 2010 1 t 11 I Prepared for Oz Architecture 1805 29" St. Suite 2054 Boulder. CO 80301 Prepared by: NORTHERN ENGINEERING 200 South College Avmw. Suite 100 Fort CWlim, Colorado 80524 Phone: 970 221 4158 Fax: 970.221.4159 u .nordh mgineenng.wm Project Number: 532-002 1