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Home My WebLink AboutRAVEN VIEW - PDP - 12-05 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTf : i,3."(;:?cl:?i' VII. References 7.1 Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May 1984. 7.2 Urban Strom Drainage Criteria Manual Volume 3, Wright Water Engineers, Denver, Colorado, September 1999. 7.3 Canal Importation Basin Sheldon Lake Drainage Improvements Final Design Report, Sear -Brown, November 22, 2002. Page 8 �}`CiiO:.r'P; : C,1!',.n,_ �� .a ._. .�..t f nii.. ti: �i :_' �i:• � ;; �.. t ;Yc �' � u I ilt yq).i t'i': :}:.,1 iii2: S: that would be harmful to ecological systems downstream. VI. Conclusions 6.1 Compliance with Standards This Preliminary drainage analysis has been performed according to design criteria found in the Storm Drainage Design Criteria and Construction Standards City of Fort Collins, Colorado, dated May 1984 and the Urban Storm Drainage. Criteria Manual Volume 3 Urban Drainage and Flood Control District, Wright Water Engineers, Denver, Colorado, September 1999. Page 7 7�r<,`'-'r, <r?rrt as "J>; Gi- -•; t C iIs `:' ?(�' -.tr 'ti r t r)'!Y• - e :.' :)i r 1 i(--'', .Ir:. iolvw r tC'.L' \Sff?iifl 5.3 Detention In the northeast corner of the site, a detention pond will be constructed to accommodate storage volumes required to physically reduce runoff rates to historic rates after development occurs. SWMM was used to determine the detention volume and release rate for this site. The 100-year water surface elevation in the detention pond is 5061.88 ft. The 100- year detention volume was determined to be 2.3 ac-ft, which will be storage above the water quality capture volume. The overflow channel will be located in the northeast corner of the pond. This overflow channel will flow through the driveway for this residence. This driveway will be lined with concrete. Near the garage entrance there will be a drive-over- outfall curb to add depth to the channel. This will aid in protecting the existing residence from flood damage. According to the SWMM model, 68.0 cfs could pass through the pond in emergency conditions. However, for freeboard purposes, the channel has been designed to pass 1.33 times the 100-year storm event, which is 90.44 cfs. 5.4 Rainfall Erosion Control Plan The proposed rainfall erosion control plan during construction will consist of temporary structural erosion control measures. Gravel inlet filters will be placed at all curb inlets and sidewalk culverts. Straw -bale dikes will be placed in swales an interval of no greater than 200 feet. Silt fencing will be installed at the locations were sediment is expectant to convey to offsite locations. Vegetative erosion control consisting of straw mulch with temporary seeding must be used on all open space areas that are disturbed with this project. It will be clearly noted on the plans that no soils shall remain exposed for more than thirty days before requiring temporary or permanent erosion control measures, unless approved by the City of Fort Collins. All temporary erosion control structures are to remain in place until permanent vegetation has been established. 5.5 Water Quality In the detention pond, water quality capture volume will be 0.174 ac-ft (7579 cf). This water quality capture volume .will be located in the detention pond- and will have a water surface elevation of 5059.21 ft. Additionally, the water quality capture volume will be release at a rate to allow a 40-hour drain time. The water quality capture volume will be provided for low intensity storm events where the concentration of pollutants is higher than average. The 40-hour drain time allows time for sediment, debris, and other pollutants to settle out of the stormwater Page 6 ?}rC%%f.•ii?7it:2 t`!r: trt 3' i.'C (... .! t ..r r. .£.': The model used was the Canal Importation Basin MP Hydrology (Post-1999 Rain), 100-year existing condition with existing facilities, June, 2004, provided by the City of Fort Collins. The model was modified as follows: • Basin 108 was added to repressent the proposed site. • Basins 8 and 21 were modified. • Conveyance element 8 was modified — the length was reduced from 690 feet to 420 feet. • Conveyance element 108 was added to represent conveyed flows to Pond 308. • Pond 308 was added to provide detention for the proposed site. • Conveyance element 148 was added to convey flows from Pond 308 to the storm system in Mulberry Street (Conveyance Element 105). Table 5.2.1 below contains the revisions to the existing SWMM elements. TABLE 5.2.1 SWMM ID Old Area acres New Area acres Old % Im New % Im Old TW I New 8 19.8 12.9 35 45 2860 1863 21 24.1 22.2 45 45 2625 2418 Detention Pond 308 was added specifically for Basin 108 and was designed to detain and release at a rate that would minimally impact the existing storm drain system in Mulberry Street, and subsequent downstream elements. The following table shows the comparison between the original model 100-year flows at selected elements and the revised model 100-year flows. TABLE 5.2.2 SWAM 105 304 Golf Course 311 709 859 944 945 ID Pond 1 Original 461.2 108.2 480.5 201.4 501.5 108.2 201.4 Model 17.7 ac-ft Revised 461.4 108.2 480.5 201.5 501.7 108.2 201.5 Model 17.7 ac-ft There were no other revisions or modifications made to the SWMM model as part of this submittal. In regards to redirecting stormwater to Mulberry Street, there are insignificant effects in the Canal Importation Basin Sheldon Lake Drainage Improvements. Please refer to Appendix E: Mulberry Street Storm Sewer (StormCAD) to compare the existing conditions and revised conditions. Please note that the increase in the I' hydraulic grade lines (HGLs) in the storm sewer along Mulberry Street is less than 0.08 ft. Further, please note that the HGL at the end of the storm sewer is unchanged between existing and developed conditions. l� Page 5 If :..•?tr';i.iiYi�iin`- V. Developed Drainage 5.1 Proposed Site Improvements In the proposed conditions, there will be eighteen (18) single-family lots, six (6) multi -family units, and two (2) duplex units developed for residential uses. Access to this development will be from South Taft Hill Road. A thirty-six foot (36'), flow - line to flow -line, local street will be provided into the development. Inside the development, the street will narrow to a minimum thirty feet (30'), flow -line to flow -line, throughout the development. For fire access requirements, an emergency fire access road will be placed from the northwest boundary to Mulberry Street. Within this development, this local street will loop and intersect itself. All the single-family lots will be along "outside" side of the internally looped street on the east side of the development site. The multi -family units will be located on the "inside" side of the internally looped street and also on the west side of the development. Along the local street accessing from South Taft Hill Road, there will be a high point located approximately 100 ft east of the east flowline along South Taft Hill Road. The portion of the site west of this high point will drain towards South Taft Hill Road, and the remainder and majority of the site will be conveyed toward the east. Inlets will be placed along the street were street capacities are exceeded. Please note that minor basins "Ala" and "Alb" were delineated to check street capacities approaching the low point in the northeast portion of the street system. Street capacities are not exceeded as runoff approaches the low point. However, the street I' capacities are ,exceeded when the entire Sub -basin Al contributes runoff to design point al. Therefore, inlets will be size to capture 100% of the 100-year storm at this �j sump condition. For additional information, please refer to Appendix B: Streets. In the northeast corner of the site, a detention pond will be constructed to accommodate storage volumes required to reduce runoff rates to historic rates after development occurs. In the bottom of this pond, water quality capture volume will be provided. From the outlet structure, a fifteen inch (15") RCP will convey stormwater into the 68" x 43" HERCP in the storm sewer system in Mulberry Street. This storm sewer system was part of the Canal Importation Basin Sheldon Lake Drainage Improvements. Running along the southern and eastern boundaries of the site, a storm sewer system will be placed to collect stormwater from the back of lots. This storm sewer will convey drainage into the detention pond. 5.2 General Description of Flow Routing SWMM was used to determine the detention volume and release rate for this site. Page 4 r < i== r � ; .,r r, ;;: c. .ti.' t i!r i I t,Y_"iY t , r V(r 1 titC. "Sn IH.!e'ri.i 4.2 Hydrologic Criteria The Rational Method was used for determine runoff rates in accordance with the Fort Collins Storm Drainage Design Criteria. City of The design rainfall intensity were based on a memorandum subjected New Rainfall Criteria dated April 16, 1999 provided by the City of Fort Collins Stormwater Department. Figures 3-la and 3-lb City of Fort Collins Rainfall Intensity -Duration -Frequency Table for using the Rational Method were used. The intensity curve table has a five (5) minute time increment. The intensities were interpolated to determine approximate intensities on one (1) minute time steps. The intensity curve data that was provided is included in Appendix F: Figures and Support Documents. In accordance with the City of Fort Collins Design Criteria the 2-year and 100-year storm events were analyzed for this proposed development. In calculating the time of concentration for the rainfall intensities, the procedures outlined Section 3.1.7 Time of Concentration in the City of Fort Collins Storm Drainage Design Criteria. The runoff coefficients in the Rational Method were based on Table 3-3: Rational Method Runoff Coefficients for Composite Analysis in the Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, dated May 1984. This table is included in Appendix F: Figures and Support Documents. Please note that minor basins are delineated within Sub -basins, usually `to analyze street capacities and inlet placements. In the rational method, minor basins hold the same time of concentration, rainfall intensity, and runoff coefficient as the entire sub -basin. Runoff coefficients, time of concentrations, and rainfall intensities are calculated for each basin and sub -basin. 4.3 Hydraulic Criteria The Manning's Equation was utilized in hydraulic computations. The Manning's "n" coefficients were in accordance with the City of Fort Collins Storm Drainage Criteria. For cross -sectional hydraulic computations, Flowmaster version 7 _ by Haestad Methods, Inc. was used. For hydraulic grade line (HGL) and energy grade line (EGL) analysis, StormCAD version 5.5 by Haestad Methods, Inc. was used. The hydraulic computations in the Canal Importation Basin Sheldon Lake Drainage Improvements Final Design Report prepared by Sear -Brown for the City of Fort Collins Utilities dated November 22, 2002 were taken into account with this report. Page 3 l(1' «I (, ...... j(J:' ), ,fG ( t Y n L:Y;v _ .( (614 South Taft Hill Road). In the existing conditions, the site generally slopes towards the east. For existing utilities, there is an 8" sanitary sewer line and a 6" water line in Mulberry Street. In Taft Hill Avenue, there is an existing 15" sanitary sewer line and a 6" water line. Within the site there are no wet utilities, according to the City of Fort Collins Water and Wastewater Utility Map. According to the Soil Survey of Larimer County Area, Colorado prepared by the United States Department of Agriculture Soil Conservation Service and Forest Service in cooperation with Colorado Agricultural Experiment Station issued December 1980, this site consists mostly of hydrologic soil group `C.' III. Historic Drainage 3.1 Historic Drainage This development is contained within the Canal Importation Drainage Basin, according to the City of Fort Collins Stormwater Basins. The Canal Importation Drainage Basin covers approximately five square miles in west -central Fort Collins. Runoff from this basin empties into the Old Town and Spring Creek Basins. In the historic conditions, the development conveys stormwater towards the east boundary of the site. Sharing this boundary on the east are some lots for Miller Brothers 3`d Subdivision along Crestmore Place. In the existing conditions, there are drainage issues from this site to these described lots in Miller Brothers 3rd Subdivision. IV. References and Design Criteria 4.1 References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria and Construction Standards and the Urban Storm Drainage Criteria Manual Urban Drainage and Flood Control District, Wright Water Engineers, Denver, Colorado, June 2001 have been referenced in the preparation of this study. Additional technical information was the Canal Importation Basin Sheldon Lake Drainage Improvements Final Design Report prepared by Sear -Brown dated November 22, 2002. Page 2 1 .'u;" }(i!, ri Ci if 1";Z£ r t "';w, it Preliminary Drainage and Erosion Control Study for Raven View Subdivision Fort Collins, Colorado February 22, 2004 I. Introduction 1.1 Objective ' This report summarizes the results ofpreliminary storm drainage analysis for Raven View Subdivision. The storm drainage system for Raven View Subdivision has been designed to safely convey up to the 100-year design storm per City of Fort Collins Criteria and discharge at or below allowable release rates. 1.2 Mapping and Surveying Topography of the site with a contour interval of one -foot was prepared by Northern Engineering Services. Northern Engineering Services, Inc. surveyed the site in November 2004. . II. Site Location and Description 2.1 Site Location The proposed Raven View Subdivision site is located in the northwest quarter (V4) of Section 15, Township 7 South, Range 69 West of the 6th Principal Meridian in Fort Collins Colorado. More specifically, the site is located southeast of the intersection between West Mulberry Street and South Taft Hill Road. Currently, this site consists of fenced pastures behind the residential lots that border Mulberry Street and Taft Avenue. On the east and south, this site is bounded by Miller Brothers 3'a Subdivision. This development is contained within the Canal Importation Drainage Basin, according to the City of Fort Collins Stormwater Basins. 2.2. Existing Site Description In the existing conditions, this property is split into several parcels. The existing houses on the parcels are located near Mulberry Street or Taft Hill Road. The proposed conditions will replat this area into one property. The proposed main access for this development will be from South Taft Hill Road. In the proposed access location from the arterial street, there is an existing residence Page 1 Table of Contents VICINITY MAP Page I. Introduction I 1.1 Obj ective 1 1.2 Mapping and Surveying 1 II. Site Location and Description 1 2.1 Site Location 1 2.2 Existing Site Description 1 III. Historic Drainage 2 3.1 Historic Drainage 2 IV. References and Design Criteria 2 4.1 References 2 4.2 Hydrologic Criteria 3 4.3 Hydraulic Criteria 3 ' V. Developed Drainage 4 5.1 Proposed Site Improvements 4 5.2 General Description of Flow Routing 4 ' 5.3 Detention 6 5.4 Rainfall Erosion Control Plan 6 5.5 Water Quality 6 VI. Conclusions 7 6.1 Compliance with Standards 7 VII. References g Appendices APPENDIX A: Onsite Runoff (Rational Method) APPENDIX B: Streets APPENDIX C: Detention APPENDIX D: Storm Water Management Model (SWMM) APPENDIX E: Mulberry Street Storm Sewer (StormCAD) APPENDIX F: Figures and Supporting Documents APPENDIX G: Stuffer Envelope rMarch 9, 2005 City of Fort Collins Stormwater Department 700 Wood Street Fort Collins, Colorado 80521 RE: Raven View Subdivision Fort Collins, Colorado Project Number: 04-123 ' Dear Staff. I Northern Engineering Services, Inc. is pleased to submit this Preliminary Drainage Report for Raven View Subdivision for your review. 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. This report has been prepared in compliance with technical criteria set forth in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards. 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. Seth W. Tourney, E.I. Project Engineer a4ov— 6V4-' 1 Aaron Cvar, P.E. Senior Project Engineer This report is for review purposes only. A signed and stamped original will be provided with final mylar drawings. Preliminary Drainage and Erosion Control Study for Raven View Subdivision Fort Collins, Colorado March 9, 2005 Prepared For: Anchor Development Corporation 1338 Catalpa Drive Fort Collins, CO 80521 Prepared By: NORTHERN ENGINEERING NESERVICES, INC. 420 S. Howes, Suite 202 Fort Collins, Colorado 80521 Phone: (970)221.4158 Fax: (970) 221-4159 Project Number: FRS: 04-123.00