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Home My WebLink AboutREDWOOD APARTMENTS - PDP - 15-99A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTSection A: Developed Hydrology Section B: Detention Pond Calculations Section C: Design of Storm Sewers Section D: Design of Inlets Section E: Design of Swales Section F: Street Capacities Section G: Emergency Overflow Weirs Section H: Riprap Calculations TABLE OF CONTENTS Al -A6 B1-B13 Cl-C13 D1-D18 E1-E2 F1-F14 Gl -G2 H 1-H4 5 REERENCES 1) Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, September 1, 1999. 2) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins Stormwater Utility, May 1984 3) Erosion Control References Manual for Construction Sites, City of Fort Collins, January 1991 4 An existing off -site detention pond northwest of the site will be conveyed through the north drainage swale into the pond. On -site drainage will drain to the detention pond through three storm sewer systems "A", `B" and "C". Emergency overflows have been provided in the event a storm system should get plugged. Storm Line "A" emergency overflows will spill into the adjacent ditch. Storm line `B" emergency overflows will overtop the curb and drain into the detention pond. Storm Line "C" emergency overflows will overtop the high point in Lupine drive and flow south in Bellflower Drive into the pond or overtop the inlet pipe and flow east down the private drive to Bellflower Drive, then into the pond. The emergency overflow for the detention pond will flow into Lake Canal. The storm sewers have been designed to handle the 100-year flows using critical depth at the outlet of the sewer pipe to begin backwater calculations of the hydraulic grade line. All finished floor and top of foundation elevations have been set above the adjacent hydraulic grade line and 18" above the 500-year Dry Creek floodplain elevation when the buildings are within the floodplain. V. EROSION CONTROL & WATER QUALITY 5.1 Erosion Control The erosion control plan presented here is intended to control both wind and rainfall erosion. Rainfall erosion will be evaluated first, with the wind erosion control plan to follow. The City of Fort Collins Erosion Control Reference Manual for Construction Sites, (ECRM), has been referenced for this erosion control plan The rainfall erosion control plan during construction will consist of temporary structural and vegetation control measures. Gravel inlet filters will be places at all area inlets and curb inlets. Temporary sediment control, straw bale dikes, will be places in swales until permanent vegetation is established. Riprap outlet protection will be provided at the outlet of all storm sewers. Vegetative erosion control will be used with this project. It has been noted on the Grading & Erosion Control sheets that no soil shall remain exposed for more than thirty days before requiring temporary or permanent erosion control measures, unless approved by the Stormwater Utility. The proposed wind erosion control plan during construction will consist of silt fencing. From the Wind Erodibility Map of Fort Collins, Colorado, the site is located in a moderate erodibility zone. From table 4.1 (page 19 or the ECM the maximum barrier spacing is 200 feet. Silt fencing will be places along the east and south property line. 5.2 Water Quality The issue of water quality will be addressed with the construction of additional storage in the detention pond for water quality capture volume (WQCV). 3 24" RCP pipes into an existing regional detention pond located northeast of the site next to Conifer Drive. The southwest section of the site is located within the Dry Creek Floodplain. IV DEVELOPED DRAINAGE 4.1 Developed Conditions Planned development for Redwood Apartments includes: • Multifamily Housing with Parking Lots • Single Family Housing Off -site easements for grading and drainage are required - 4.2 Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design a Criteria Manual, (SDDCM) and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been referenced for this drainage report 4.3 Hydrologic Criteria The Rational Method has been used to estimate values of the peak storm water runoff for this project. A minimum time of concentration of five (5) minutes has been used, in accordance with SDDCM. The initial 100-year storm has been used to design the storm drainage system, which includes swales, inlets, storm sewers and detention. The rainfall intensity data for the Rational Method has been taken from the City of Fort Collins new rainfall criteria published April 12, 1999. Hydrologic calculations and supporting material are contained in the appendix of this report. 4.4 Hydraulic Criteria The City of Fort Collins Storm Drainage Design Criteria has been used for all hydraulic analyses. In addition the following computer programs have been utilized. • The computer program "UDINLET" has been utilized to analysis inlet capacities • The computer program "Flowmaster" has been used to design swales and check street capacities in conjunction with the SDDCM. • The computer program "UDPOND" has been used to design pond detention • The computer program "Eagle Point" has been used to design the storm sewer system. 4.5 Drainage Concept Detention for the proposed development is required in accordance with the Greenbriar\Evergreen Master Plan. The Greenbriar\Evergreen Master Plan indicates the release rate to be 0.27 cfs/acre for this development. The detention pond will be used to detain on -site flows while bypassing offsite flows through an overflow structure. Offsite drainage from the existing development to the west will be routed north along the property line, through Storm Line "C" into an existing swale along the north boundary of the site, then into the detention pond. Off -site drainage from the south will be routed through Storm Line "A" to the detention pond. Off -site drainage from the north will be routed through the north drainage swale and drain directly into the pond. II Final Drainage Report for Redwood Apartments P.U.D. Fort Collins, Colorado February 6, 2001 INTRODUCTION 1.1 Objective _ To provide documentation pertaining to the drainage scheme for the proposed Redwood Apartments development based on a comprehensive hydrologic and hydraulic analysis of the developed conditions and the Greenbriar/Evergreen Master Plan. 1.2 Mapping and Surveying Drexel Barrell provided topography of the site to Northern Engineering Services with one (1) foot contour intervals. Ayers Associates provided additional surveying to Northern Engineering Services. 1.3 Site Reconnaissance The project engineer conducted several site visits in December 2000. The topographic mapping, existing drainage basins and land use were confirmed as well as existing structures. The location, dimensions and flow direction of existing culverts were verified. SITE LOCATION AND DESCRIPTION 2.1 Site Location The site is located within the Southeast Quarter of Section 1, Township 7 North, Range 69 West of the 66 Principle Meridian in Fort Collins, Colorado. The project is bounded by an existing single-family development on the West and North, Lake Canal on the East and undeveloped land on the South. (See Vicinity Map) 2.2. Site Description Redwood Apartments is approximately 18.97 acres and is currently vacated agricultural land with weeds and grasses. There are no existing structures on the site. A swale runs along the North boundary connecting an offsite detention pond with a downstream detention pond. III HISTORIC DRAINAGE BASIN 3.1 Major Basin Identification The site is located within the Greenbriar/Evergreen basin. 3.2 Historic Drainage Patterns The site historically drains at slopes ranging from 0.37 % to 2.00%. Storm water runoff predominantly occurs as sheet and shallow concentrated flows. Approximately 9.39 acres flows from the Southwest to the Northeast outfall and 7.52 acres flows from the existing development to the West to the Northeast outfall. An existing drainage swale along the north connects an offsite detention pond located in the Evergreen Park Second Filing with the Northeast outfall. The Northeast outfall flows northeast in three z 3nN3&V AVp7.n N180N r N0 W 5 Ij W Q W D Q rW J W o 0 V N LL W 3nN3nv 393Troo RuaoN Y n N O R T H E R N ENGINEERING S E R V I C E S I N C February 6, 2001 City of Fort Collins Stormwater Utility 700 Woods Street Fort Collins, Colorado 80522 RE: Redwood Apartments P.U.D. Fort Collins, Colorado Project Number: 00-048 Dear Staff: Northern Engineering Services, Inc. is please to submit this Final Drainage Study for Redwood Apartments P.U.D. for your review. 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 me at your convenience. Sincerely NORTHERN ENGINEERING SERVICES, INC. 1' & ZZ7-- Jiih Braim, E.I.T. Project Engineer I Roger A. Curtiss, P.E. Project Manager 27362 420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221-4159 Final Drainage Study for Redwood Apartments Fort Collins, Colorado February 6, 2001 Prepared For: Concorde Capital Corporation 1349 East Broad Street Columbus, OR 43205 Prepared By: Northern Engineering Services, Inc 420 S. Howes, Suite 202 Fort Collins, Colorado 80521 Phone: (970) 2214158 Project Number: 00-048