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HomeMy WebLinkAboutREGISTRY RIDGE PUD, PHASE I - PRELIMINARY - 32-95A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTo' Colorado 9 Southern Railway B i FORT OOLL .v e o o O L a: H i v O o f t o o: o ¢ 0401, : H r oT o a. C . c� i'= w=•' 2 4t. 1 Harmony Rood Trilby d County Rood 32 .n. County Road 30 few LOVELAtro r«+o.w• ---- Watershed Boundary —"— —' - Drainage Coupe COLORADO Rood —'—^— Railroad Troek FOSSIL CREEK DRAO�IASE STUDIY BASIN VICINITY MAP ebnq U 6 AMOCWK NW- EOt CCOke,_ColasAdo WE FIGURE 1. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. 2. Fossil Creek Drainage Basin Master Drainageway Planning Study, Simons, Li & Associates, Inc., August, 1982. 3. Drainage Criteria Maunal, Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. All construction activities must also comply with the State of Colorado permitting process for Storrnwater Discharges associated with construction activities. A Colorado Department of Health NPDES discharge permit will be required before any construction grading can begin. V. CONCLUSIONS Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. Drainage Concept The proposed drainage concepts presented in this study and shown on the preliminary grading and drainage plans adequately provide for the conveyance and detention of developed runoff from the proposed Registry Ridge development. The 100 year SWMM developed SWMM model shows that this development will have no increased flows leaving the site. All detention ponds to be incorporated into final design should include multiple release/water quality outlet structures, along with emergency overflow weirs. If groundwater is encountered during construction, and dewatering is used to install utilities, a State of Colorado Construction Dewatering Wastewater Discharge Permit will be required. Stormwater Quality Because water quality is important to this developer, water quality mechanism will be incorporated into all aspects of final design of drainage systems. The proposed water quality ponds proposed in this study will require regular maintenance to remove deposits as they accumulate. The storm water quality outlet works will release the first flush of storm water runoff over a period of time in order for pollutants to settle out of the runoff. Erosion Control Concepts Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, at the time of Final Design, the erosion control performance standard will need to be calculated and appropriate measures taken to control rain and wind erosion from the site. outlet/water quality structure will be included in final design of this pond. This pond will be located in an area designated as future commercial area. Basin 405 - Developed flows for this Basin will be routed to a small detention pond by a series of curb & gutter, open channels, and storm sewers. This pond will be situated to the south of existing Lang Gulch and the City defined Flood limits. Per the developed SWMM model, detention volume required for this pond is 1.7 ac-ft., with an additional requirement for 1.0 ac-ft for water quality capture volume. peak release from this pond to Lang Gulch is 9.6 cfs. A water quality/multiple release outlet structure will be incorporated into this pond. Developed flows from Basin 407 is tentatively planned to be routed through this pond. Basin 406 - Developed flows from this basin will not be detained. Runoff will be conveyed to Lang Gulch by a series of curb & gutter, open channels, and storm sewers. There is approximately 124 acres upstream of this basin which contribute approximately 328 cfs to Lang Gulch. The contributary area to Lang Gulch in this area was reduced to help mitigate the increased effects of development would have on the peak flows to downstream properties. The peaks flows in conveyance element 75 (directly downstream of that portion of Lang Gulch in this development were decreased from 355.8 cfs to 346.9 cfs. The existing SWMM model showed that 38.5 ac-ft of runoff backed up west of South Shields Street. The developed model reduced this backup to 33.1 ac-ft, and reduced the peak flows in the existing 66" RCP culvert under Shields from 233.5 cfs to 227.1 cfs. Grading in this basin, and especially adjacent to Lang Gulch will be limited. Much of the existing vegetation will remain intact. This will be advantages to this development by providing a water quality mechanism for this basin. Basin 407 - Developed runoff from this basin is shown in this study to be routed through Basin 405 and the associated detention pond by a series of Storm Sewers. The existing topography in this basin historically drains to the southeast into an open channel, and then northerly up to the existing pipe crossing at Shields. It is likely that at final design, developed runoff will be routed to conform closer to historic patterns. There is no easements in place at this time that would allow for developed runoff from this site to be routed as historically flow patterns indicate. IV. EROSION CONTROL General Concept Registry Ridge lies within the Moderate Rainfall Erodibility Zone, and the Moderate Wind Erodibility Zone, per the City of Fort Collins zone maps. At the time of final design, Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, the erosion control performance standard will need to be calculated, and appropriate measures designed to control rain and wind erosion during and after construction. final design, offsite easements are not available, developed runoff from this basin could be piped easterly, and released into Basin 402 conveyance system. There is approximately 50 acres upstream of this basin that will contribute 171.7 cfs peak 100 year flow to Pond 601 (per the developed SWMM model). Basin 402 - Developed runoff from this basin will be conveyed to the Southwest comer of Shields and Trilby Road, by a series of curb and gutter, open channels, and storm sewers to a proposed detention pond, then piped under Shields, and conveyed by open channel to an existing 72" RCP crossing Trilby @ Lang Gulch. This basin also includes areas designated as future patio homes. A multiple release pond outlet structure will be incorporated into final design which will provide a water quality control, as well as to further restrict minor storm events. Per the developed SWMM model, required detetnion volume for this pond is 1.5 ac-ft. An additional 0.6 ac-ft of volume will be included for water quality capture volume. The developer of Registry Ridge also owns the area east of Shields Street to the existing C&S railroad. There is a possibility that during final design, this pond could be moved east of Shields. There will be in any case, a water quality and detention pond incorporated into the system prior to developed runoff being released into Lang Gulch. Trilby Road has been master planned to be widened to a full Arterial section. With this development, Trilby Road will be widened to a 36' section with no curb and gutter. When and if Trilby is widened to a full arterial section, flows shown on this plan as being conveyed in an open channel might need to be conveyed along Trilby Road in a storm sewer system. The intent of the proposed drainage system in this basin will not be affected whether ultimate flows are conveyed by an open channel or a pipe system. Basin 403 - Has been designated as future multi family housing. A small pond has been considered in the southeast comer of this basin. Flows will be routed from this pond through the proposed pond in Basin 404, across Shields, and ultimately into Lang Gulch. There is a possibility that this pond would be incorporated into the Detetnion pond in Basin 404. Per the developed SWMM model, detention volume for this pond is 0.5 ac-ft. Water quality capture volume would require an additional 0.15 ac-ft. Basin 404 - Developed runoff from Basin 404 will be conveyed easterly by a series of curb & gutter, open channels, and storm sewers to a detention pond located to the easterly edge of the basin adjacent to South Shields Street. There is an additional 39 acres upstream of this basin that will contribute approximately 46.6 cfs to be routed through this pond. The pond will outlet to a 27" RCP under Shields, then by open channel to Lang Gulch. Volume requirements for this pond, per the developed SWMM model are 8.2 ac-ft, with an additional 1.7 ac-ft for water quality capture volume. Peak 100 year release form this pond will be 39.0 cfs. A multiple release development on the overall model. The existing 100 year model, prior to development of Registry Ridge was slightly modified to reflect 2 existing culverts under Trilby Road. This model was then used as a base for the developed conditions model. The developed model incorporated 5 separate detention pond within the proposed development. Copies of the existing and revised model output files are included in this report. Hydraulic Criteria City of Fort Collins Storm Drainage Criteria has been used for all hydraulic calculations. Preliminary Drainage Concepts This development has been broken into 7 primary drainage basins, Basins 401 through 407. Basins 401, 402, 403, 404, and 405 have detention facilities incorporated into the system. Basin 407 will be routed through Basins 405 Detention pond. Developed flows from Basin 406 will not be detained. Basins 401 - 407 correspond to Basins 401 - 407 in the developed SWMM model. Basin 401 will ultimately release into the Smith Creek drainage, via an existing tributary which crosses Trilby Road, and flows to the north. Basins 402, 403, and 404 will be detained, directed under South Shields, and on to Lang Gulch, east of the existing crossing under Shields. Developed flows from Basins 405, 406, and 407 will be released into Lang Gulch upstream of the existing crossing at South Shields. Specific Drainage Concepts Basin 401 - Developed runoff from this basin will be routed to the northwest comer of the basin to a proposed detention pond, by a combination of streets, swales and storm sewers. Flows will be routed through the existing 48" RCP culvert under Trilby Road, and ultimately to Smith Creek, approximately 2000' feet north of Trilby. Approximately 5.2 ac-ft of runoff presently ponds south of Trilby. The proposed pond will be increased to accommodate 8.2 ac-ft of detention storage plus an additional 0.6 ac-ft for water quality ponding. A multiple release structure will be incorporated onto the outlet from this pond, to further restrict runoff from smaller storm events than the 100 year peak outflow. Per the existing and developed SWMM model, peak 100 year runoff from this Basin will be reduced from 76.7 cfs to 76.6 cfs. Per City of Fort Collins Storrnwater Criteria, the tributary that drains Basin 401 is not a named Drainageway. Therefore, it will be a requirement at final design for this development to obtain a letter of intent for a drainage easement from all downstream property owners along this tributary. To help mitigate the increased volume of developed runoff, a pond infiltration system will be evaluated at final design. By installing a outlet control structure, the developed peak runoff rates will also be reduced. In addition, there will be added water quality controls built in the pond. If at of offsite drainage which will be routed through developed basins 402-407 (Lang Gulch tributary). The existing culvert under Trilby Road, tributary to Smith Creek is a 48" RCP. The existing culvert under South Shields Street at Lang Gulch is a 66" RCP. There is some existing wetlands areas within the Lang Gulch Drainage area. A separate report by Riverside Technology is being submitted along with the Preliminary submittal for Registry Ridge. Flood limits, as established by the City of Fort Collins, have been shown on these plans. During final design of the areas affecting flows around these flood limits will include a HEC2 analysis of the existing flows, as well as new development. 111. DEVELOPED DRAINAGE Developed Conditions The proposed development will consist of Low and Medium density single family residential lots, with associated residential streets and utilities. There are parcels included in this site for future Patio Homes, Commercial, School, Park, and Recreational Center. Access to this development will be from Trilby Road and South Shields Street. Detention is not a requirement of development within the Fossil Creek Major Drainage Basin. However, the developer of Registry Ridge wants to incorporate detention facilities into the drainage system to provide a water quality mechanism into this system, as well as negate the possibilities of further bank erosion along Lang Gulch or Smith Creek. Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual. and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been used for this Preliminary Drainage Study. The Fossil Creek Drainage Basin Master Drainageway Planning Study, by Simons, Li & Associates has also been used as a reference for this Study. Hydrologic Criteria The Rational Method was used to estimate peak stormwater runoff from the proposed site. The 2 year storm event and the 100 year storm event was used to evaluate the proposed drainage system. Rainfall intensity data for the Rational method was taken from the City of Fort Collins Storrnwater Utility Intensity curves (Figure 3-1). The existing 100 year SWMM model for Fossil Creek, as developed as a part of the Fossil Creek Master Plan, was also used to determine the effects of this Preliminary Drainage Report for Registry Ridge P.U.D. I. GENERAL LOCATION AND SITE DESCRIPTION The Registry Ridge P.U.D. development is located south of Trilby Road and West of South Shields Street, as shown on the vicinity map included in the appendix. More particularly, this site is located within the East half of Section 15, Township 6 North, Range 69 West of the 6th P.M., Larimer County, Colorado. The Registry Ridge P.U.D. development contains approximately 240 acres, more or less. This area is presently undeveloped, and is currently vegetated farmland. One small metal shed is located on the northeast corner of the property. Lang Gulch runs across the lower leg of the site from west to east. Planned development within Registry Ridge P.U.D. include Low and Medium Density Single Family Residential Homes, and areas set aside for future Patio Homes, Commercial area, Recreation Center area, School site, and future park site. 11. HISTORIC DRAINAGE This site is located within the Fossil Creek Master Drainage basin, as defined by the City of Fort Collins Storrnwater Utility, and is included as a part of a study entitled "Fossil Creek Drainage Basin, Master Drainageway PlanningStudy' tudy' by Simons & Li, dated August 1982. Portions of that study have been included in the appendix. The SWMM model, developed as a part of the Master Study was also utilized within this report. A copy of the original 100 year SWMM model, as well as a revised model including the Registry Ridge development is included in this report The majority of the site is tributary to Lang Gulch (Developed basins 402 through 407), which crosses the southerly leg of the property. The northwest comer of the site drains to a tributary of Smith Creek (developed basin 401). This tributary connects with Smith Creek approximately 2000 feet north of Trilby Road. Smith Creek and Lang Gulch come together approximately 2000 feet east of South Shields Street. Ponding presently occurs along Lang Gulch west of South Shields, west of the C&S railroad, and south of Trilby Road. Ponding occurs along the Smith Creek tributary south of Trilby Road. There is approximately 49.5 acres of offsite drainage which will be routed through developed basin 401 (Smith Creek tributary), and approximately 228.6 acres Preliminary Drainage Report for Registry Ridge P.U.D. City of Fort Collins, Colorado June 19, 1995 Prepared For: Colorado Land Source Ltd. 81-01 East Prentice Ave. Suite M180 Englewood, Colorado 80111 Prepared By: Northern Engineering Services, Inc. 420 South Howes, Suite 202 Fort Collins, Colorado 80521 (970)221-4158 Fax (970)221-4159 Project Number: 9522.00 June 19, 1995 Mr. Glen Schleuter City of Fort Collins Stormwater Utility 235 Mathews Fort Collins, Colorado 80522 RE: Registry Ridge P.U.D. Fort Collins, Colorado Project Number: 9522.00 Dear Glen: Northern Engineering is pleased to submit this Final Drainage Report for Registry Ridge P.U.D. for your review. It represents a study of existing and proposed stormwater characteristics of the project site. 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. Roger A. Curtiss, P. E. = o 27362