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HomeMy WebLinkAboutREGISTRY RIDGE PUD, 3RD FILING - FINAL - 32-95E - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORT?"N VICINITY MAP "AR."ONY ROAD FRONT FZAWSE COMMUNITY q COLLEGE >r ly II RLP LL T 5CENI(:,-'KNOLL5 5UB,' OUT 10 II MTN VAL,-E" ACRES SUE. A ;TRILB'l ROAD //-iTT -iMIT II I it FA-1 UCLA II EiOUNDAR't CITl LIMIT — — — — — — — — Ir FA -I i8 Drainage Design Considerations Registry Ridge P.U.D. Third Filing August 30, 1999 Northern Engineering Services, Inc. REFERENCES 1). Final Drainage Report for Registry Ridge P.U.D. First Filing, Fort Collins, Colorado, Northern Engineering Services, Inc., May 19, 1997. 2.) Fossil Creek Drainage Basin Master Drainagewav Planning Study, City Of Fort Collins, Simons, Li & Associates, Inc., August 1982. 3.) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. 4.) Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright - McLaughlin Engineers, Denver, Colorado, March, 1969. Page 6 Drainage Design Considerations Registry Ridge P.U.D. Third Filing August 30, 1999 Northern Engineering Services, Inc. lined swales and detention ponds shall be seeded immediately upon completion as specified on the Drainage Plan (Sheet 9/38). Temporary sediment control consisting of straw bale dikes will be used in swales until permanent vegetation is established. Gravel filters will be required at all curb inlets and silt fencing installed adjacent to ponds and drainageways. See the Grading Plan for additional information. An erosion control cost estimate has been provided for the Third Filing (See Appendix H). VI. CONCLUSIONS 6.1 Compliance with Standards All drainage design considerations are in accordance with the City of Fort Collins Storm Drainage Design Criteria Manual (SDDCM) and the Urban Drainage and Flood Control District's Drainage Criteria Manual. No variances are requested as part of the proposed Third Filing development. Page 5 Drainage Design Considerations Registry Ridge P.U.D. Third Filing August 30, 1999 Northern Engineering Services, Inc. developer of Registry Ridge however, desires to incorporate both on and offsite detention facilities into the drainage system to provide a water quality mechanism as well as negate the possibility of further bank erosion along Lang Gulch and Smith Creek. Also, according to the Master Plan, development would not be allowed in the floodplain. The Registry Ridge development is divided into five (5) major drainage basins 401-405 (See Developed Overall Drainage Plan 2/4). The Third Filing will include a portion of Basin 403 and, Basins 404 and 405 in their entirety. Developed stormwater will be conveyed overland and through the streets to proposed onsite storm drains and swales and then conveyed to either Pond 603 (part of the First Filing) or directly to Lang Gulch undetained. Developed stormwater runoff from Basin 403 is routed to proposed Pond 603 for detention. Pond 603 has been designed as part of the First Filing. Runoff from Basin 404 is routed to Lang Gulch via Swales 47- 49. Developed stormwater from this basin will be undetained. Runoff from Basin 405 flows overland directly to Lang Gulch. Developed stormwater from this basin will be undetained. Basins 405H (1.546 acres) and 405K (0.365 acres) will flow onto adjacent off -site properties at rates which will be less than historic (see Appendix A). 4.6 SWMM Modeling All revisions to the SWMM model will take place when addressing city comments for the First Filing and will be included in the Final DTairwe Report for Reg_rsta Ridge P.U.D. First Filing, Volume 1, Section A. There will be no need to revise the SWMM model unless the site plan for the Third Filing changes drastically, which is not anticipated. 4.7 HEC-2 Modeling All revisions to the HEC-2 model will take place when addressing city comments for the First Filing and will be included in the Final Drainage Report for Re igistly Ridge P.U.D. First Filing, Volume 2, Section I. No HEC-2 modeling will be preformed as part of this analysis. 4.8 Off -site Improvements No offske drainage or roadway improvements are proposed as part of the Third Filing development. 4.9 Construction Phasing No construction phasing is proposed as part of the Third Filing development. V. EROSION CONTROL 5.1 Erosion Control Plan Permanent riprap will be provided at the outlet of all culverts and storm sewers. Grass - Page 4 1 Y ' Drainage Design Considerations Northern Engineering Services, Inc. Registry Ridge P.U.D. Third Filing August 30, 1999 Manual.(SDDCM) and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been referenced for this study. 4.3 Hydrologic Criteria The Rational Method has been used to estimate peak stormwater runoff within the developed site. The initial 2-year and major 100-year design storms have been used in the design of the proposed drainage system which include swales, storm inlets, storm drains and culverts. Rainfall intensity data for the Rational Method has been taken from IDF curves and equations generated specifically for the Registry Ridge P.U.D. site by the computer program "Watershed Modeling" by Eagle Point. Input of precipitation amounts have been taken from the NOAA Atlas 2, Volume III - Colorado. Compared to Figure 3-1 in the SDDCM, rainfall intensities generated for the Registry Ridge site were approximately 15% higher than intensities given in Figure 3-1 n (rainfall intensity curves from 1997). fSWMM modeling has also been performed as part of an overall hydrologic analysis of the Registry Ridge development. The Final Drainage Report for Registry Ridge First Filing, Volume 1, Section A, contains all input and output files and supporting calculations pertaining this analysis. The SWMM model will be revised, if required, to include the final developed conditions associated with the Third Filing. 4.4 Hydraulic Criteria The City of Fort Collins Storm Drainage Design Criteria has been referenced for all hydraulic calculations. In addition, the following computer programs have been utilized: • The computer program "HY8" by the U.S. Department of Transportation, Federal Highway Administration has been used to size all culvert crossings and riprap outlet protection at the culverts, • The computer program "UDINLET" has been used to analyze inlet capacities, • The computer program "Flowmaster" has been used to analyze the capacity of proposed swales, The hydraulic analysis of Lang Gulch will be evaluated as part of the First Filing through the use of the HEC-2 computer model. Input and output files of all HEC-2 runs are included in the Final Drainage Report for Registry Ridge P.U.D. First Filing, Volume 3, Section I. There are 11 storm inlets that have been sized to accommodate the 100yr event. These include Inlets 34, 35, 36, 38, 40-46. Typically, these inlets are located at the end of a cul-de-sac and there is an emergency overflow swale provided. The proposed grade of the overflow swale exceeds 2.0% (due to the grading for walkout basements) and therefore produces supercritical flows and possible erosion. The inlets have been sized for the 100-yr storm so that the swale will not be used except in an emergency. 4.5 Drainage Patterns Detention is not a requirement within the Fossil Creek Major Drainage Basin. The Page 3 Drainage Design Considerations Registry Ridge P.U.D. Third Filing August 30, 1999 Northern Engineering Services, Inc. III. PREDEVELOPMENT CONDITIONS 3.1 Major Basin Description The site is located in the Fossil Creek Drainage Basin and is included in the report entitled Fossil Creek Drainage Basin Master Drainagewav Planning Study, by Simons, Li & Associates, Inc., August, 1982. The SWMM model developed as part of this Master Study has been updated by Northern Engineering as part of the First Filing Final Drainage Report to reflect proposed developed conditions for the entire Registry Ridge site, which includes the Third Filing 3.2 Predevelopment Drainage Patterns The Third Filing site historically drains from northwest to southeast at slopes ranging from 2.9 to 10.0% (see Existing Conditions Overall Drainage Plan, Sheet 1 /4). The entire Third Filing site is tributary to Lang Gulch which drains to an existing culvert crossing at Shields Street. The existing culvert crossing under Shields Street at Lang Gulch has been field verified as a sixty (60) inch RCP. During a 100-yr storm, ponding occurs along Lang Gulch at the following locations: upstream of South Shields Street, C&S Railroad Crossing #3 and Trilby Road. Runoff from offsite property to the west enters the site along the west property line. Approximately 68.7 acres of offsite runoff (SWMM Basins 6 and 157) will be routed through the Third Filing to Lang Gulch via SWMM Conveyance Element 800 (see Fossil Creek Basin SWMM Schematic, Sheet 3/4). There are existing wetlands located onsite, adjacent to Lang Gulch, and have been delineated on the Historic Overall Drainage Plan. A separate report, prepared by Riverside Technology, was included with the Preliminary submittal for Registry Ridge P.U.D.. Existing wetlands will remain undisturbed. IV. POSTDEVELOPMENT CONDITIONS 4.1 Postdevelopment Conditions The Third Filing development will include the following: • single family residential homes; • open space areas; • new local streets; • utilities. There are no offsite easements required for drainage as part of the Third Filing development. One offsite easement is required for grading which is located at the west end of Bon Homme Richard Drive. This easement is in the process of being acquired at this time and will be finalized prior to approval of the Utility Plans. 4.2 Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Page 2 I Drainage Design Considerations for Registry Ridge P.U.D. Third Filing Fort Collins, Colorado August 30, 1999 I. INTRODUCTION 1.1 Obiective This report summarizes the results of a comprehensive analysis of both pre and postdevelopment, hydrologic and hydraulic conditions, for the Registry Ridge Third Filing development. 1.2 Mapping and Surveying Aerial topography of the site was provided by JR Engineering with a contour interval of one (1) foot. 1.3 Site Reconnaissance A site visit was conducted on June 28, 1996 by the project engineer. Based on the topographic mapping, existing drainage basins and land use were confirmed as well as existing structures. The location and dimensions of existing culverts were verified as well as their condition and flow direction. II. SITE LOCATION AND DESCRIPTION 2.1 Site Location The site is located within the East Half of Section 15, Township 6 North, Range 69 West of the 6th Principal Meridian in Fort Collins, Colorado. The project is bounded by Trilby Road on the north and Shields Street on the east. (See Vicinity Map). 2.2 Site Description Registry Ridge P.U.D. Third Filing ("Third Filing") is approximately 80.607 acres and has historically been furrowed agricultural land. There are no existing structures or known utilities located on the site. There are two existing residences located south and east of the Third Filing site and, undeveloped property to the west. The Third Filing is located south of Registry Ridge First Filing which is currently beginning construction. 2.3 Irrigation Ditches and Drainagewaxs Lang Gulch traverses the south end of the Third Filing flowing from west to east. The City of Fort Collins ("City") has defined the 100-year floodplain for Lang Gulch which is reflected on the Drainage and Grading Plans. Development of the Third Filing will not encroach into the Lang Gulch floodplain. There are no existing irrigation laterals on the site. August 30, 1999 The city of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80522 RE: Registry Ridge P.U.D. Third Filing Fort Collins, Colorado Project Number: 9735.00 Dear Staff. Northern Engineering Services, Inc. is obliged to resubmit this Final Drainage Report for Registry Ridge P.U.D. Third Filing for your review. We have addressed the comments contained on the "Project Comment Sheet" dated August 26, 1997. 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 and Construction Standards (Standards). 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 30325 Mary B. Wohnrade, INC. 420 SOUTH HOWES, SUITE 202, FORT (OLLINS, (OLORADO 80521, (970) 221-4158, FAX (970) 221.4159 I� C Drainage Design Considerations for• Registry Ridge P.U.D. Third Filing Fort Collins, Colorado August 30, 1999 Prepared For: U.S. Home Corporation Colorado Division 6000 S. Greenwood Plaza Blvd., Suite 200 Englewood, Colorado 80111 Prepared By: NORTHERN rKIr IKir E, Inl n1/' �Miuy [yam MIM Northern Engineering Services, ft 420 S. Howes; Sulte 202 Fort Collins, Colorado 80521 Phone:(970)221-4158 Project Number: 9735.00