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Home My WebLink AboutSTETSON CREEK PUD, FOURTH FILING - FINAL - 16-89M - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage Report for Stetson Creek 4" Filing Fort Collins, Colorado March 10, 1999 NORTHERN SERVICES INC Final Drainage Report for Stetson Creek 4tn Filing Fort Collins, Colorado March 10, 1999 Prepared For: Hartford Homes Inc 344 East Foothills Pkwy. Suite 12 Fort Collins, Colorado 80525 Prepared By: Northern Engineering Services, Inc. 420 South Howes, Suite 202 Fort Collins, Colorado 80521 (970)221-4158 Fax (970)221-4159 Project Number: 9842.00 1st Submittal N O R T H E R N R I N G E N G I N E E I N C S E R V I C E S February 3, 1999 Mr. Glen Schlueter City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80522 RE: Stetson Creek &I Filing Fort Collins, Colorado Project Number: 9902.00 Dear Glen: Northern Engineering is pleased to submit this Final Drainage Report for Stetson Creek 41h Filing 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 cf Fort Collins, Storm Drainage Desi n 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. cc: Gary Hoover 420 SOUTH HOWES, SUITE 202, FORT (OLLINS, (OLORADO 80521, (970) 221.4158, FAX (970) 221-4159 Final Drainage Report for Stetson Creek Fourth Filing I. GENERAL LOCATION AND SITE DESCRIPTION Stetson Creek 4`' Filing is located north of Stetson Creek Drive, within the Stetson Creek PUD. The site is also bounded on the north by Timber Creek, on the west by future Stetson Creek 5" Filing, on the south by Stetson Creek 1s` Filing, and on the east by Stetson Creek 3" Filing.. The site can also be described as a portion of the southwest quarter of Section 5, Township 6 North, Range 68 West of the 6th PM, City of Fort Collins, Larimer County, Colorado. A vicinity map of the site is included in the appendix of this report. This site is also located within the McClellands/Mail Creek Major Drainage Basin, as defined by the City of Fort Collins Stormwater Utility. This site includes approximately 10.61 acres, including the adjacent roadways. The site is presently undeveloped, and consist mainly of native grasses. Residential units are being constructed in 3rd Filing, and the 5`h Filing is in the final stages of plan review, and is expected to be under construction in the Spring of 1999. The site generally slopes from the west to the east at slopes less than 2%. There is also an existing regional detention pond located southeast of the site which was constructed with the Stetson Creek ls' Filing project. This pond is referred to as existing Pond 373. Plans for this site include 35 single family lots with the associated residential streets to provide access. II. HISTORIC DRAINAGE As mentioned above, the site is presently undeveloped, and consists mainly of native grasses and vegetation. Currently runoff is directed towards the east to channel section 167, which was constructed as a part of the Timber Creek project, and southeasterly to existing detention pond 373, located within the 3rd Filing. This site was also included as a part of the overall drainage plans for Stetson Creek and Timber Creek, as well as the SWMM model that was developed for this area. Detention for this site has been accounted for, and provided within pond 373. Conveyance for the site has been provided for either in channel section 167, built with Timber Creek, or from Stetson Creek Drive, which was constructed as a part of Stetson Creek lst Filing. III. DEVELOPED DRAINAGE 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 Drainage Study. Wdrol gic 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 Stormwater Utility Intensity curves (Figure 3-1). Hydraulic Criteria City of Fort Collins Storm Drainage Criteria has been used for all hydraulic calculations. Drainage Concepts The site has been broken into 7 smaller subbasins to isolate developed runoff quantities at various design points. We have attempted to show all adjacent drainage basins and what project they are associated with. These are designated on the drainage plan as 1 for those improvements identified as a part of Stetson Creek Pt Filing, 3 with 3r' Filing, 5 with 51h Filing, and T for those associated with Timber Creek. in general, this site conforms with the approved concepts presented in the Overall and Final Drainage study by RBD for Stetson Creek 11t Filing. The only true difference that has occurred from the Overall plan was that 5t' filing was designed with a higher density than the master plan, and therefore, additional onsite detention was located within the 5t<' Filing project boundaries. For the purposes of this study, it will be assumed that Stetson Creek 5th Filing is existing. As mentioned, Stetson Creek Drive and associated storm sewer were installed with Stetson Creek Pt Filing. When Stetson 5" added a detention component to their site, they routed the flows in the existing storm sewer through their detention pond, and re-released these detained flows to catch basin 523. The combined flows at design point 523 are 3.3 cfs in the street for the 2 year storm and 18.08 cfs in the street for the 100 year storm. 19.96 cfs is in the existing storm sewer. An additional 1.5 cfs and 3.5 cfs (2 yr and 100 yr flows, respectively), will be intercepted by the existing 5' type R curb inlet located at design point 523. Subbasins SF-1, SF-2, SF-3 and SF-4 will convey flows to the existing curb and gutter located along the northerly side of Stetson Creek Drive, and ultimately to the sump in Stetson Creek Drive located at design point 705 (at an existing 15' Type R curb inlet). An additional 10' curb inlet was installed at design point 525, and intercepts an additional 3.3 cfs and 8.9 cfs (2 yr and 100 yr flows, respectively). Subbasin SF-5, located along the northerly portion of the project, will direct backyard flows towards the North, and combined with backyard flows from basin 221 of Timber Creek will be conveyed to the east via channel section A -A, to channel 167, designed and built with Timber Creek. Subbasin SF-6 (Madison Creek Drive) will be conveyed to a proposed 5' type R curb inlet located at the back of the Cul-de-Sac, and will be piped to channel section 167. The area shown for subbasin SF-6, also contains the area described as basin B-1 in the 5' Filing study. Similarly, Subbasin SF-7 will be conveyed to curb and gutter, and to a low point on Coal Creek Court. A 5' type R curb inlet will intercept these flows, and storm sewer will convey these flows to Channel 167. All developed flows from Stetson Creek 4" Filing ultimately are conveyed to existing detention pond 373. Detention volume has been provided in this pond for 4t' Filing. This site was also included in a SWMM model, developed as a part of the Stetson Creek Overall/First Filing drainage study by RBD. This site was identified as a part of basin 314 (included in the appendix of this report. Essentially the lots and streets have remained unchanged, with the exception of that area designated as 5' Filing. Therefore, no modifications have been included to the existing SWMM model. IV. EROSION CONTROL General Concept Stetson Creek 4'' Filing lies within the Moderate Rainfall Erodibility Zone, and the Moderate Wind Erodibility Zone, per the City of Fort Collins zone maps. The desired effectiveness goal for this site was estimated to be approximately 80% The intent of the erosion control plan for the site include the following guidelines. As these measures can vary depending on the time of year construction or to work cactivities talosely selace, a well as the construction window involved, we would look to the contra City to insure the intent of the plan is generally complied with. It is the intent of the owner to move quickly ahead with development once overlot grading takes place. It is anticipated that overlot grading would start sometime around July 1999, or sooner if possible. Therefore, once overlot grading and utilities have been completed, the owner would like to restabilize all disturbed areas, not in a roadway or within 75' of the road, either with vegetative means, or by hard surfaces. In no cases shall restabilization occur more than 30 days after disturbance. In addition, silt fence will be provided around most of the exterior of the disturbed areas adjacent to channel 167, gravel inlet filters will be installed at all curb inlets, curb openings, and pipe entrances. Straw bale check dams will be placed in all open channels, at a minimum of 250' intervals. All construction activities must also comply with the State of Colorado permitting process for Stormwater 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 grading and drainage plans adequately provide for the conveyance and detention of developed runoff from the proposed development. 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. 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 REFERENCES Storm Drainage Design Criteria and Construction Standards City of Fort Collins, Colorado, May, 1984. 2. Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. 3. Final Drainage and Erosion Control Study for Timber Creek 1 st Filing, by RBD dated December 31, 1993 4. Final Drainage and Erosion Control Study for Stetson Creek 1st Filing, by RBD, dated April 29, 1994 5. Final Drainage and Erosion Control Study for Stetson Creek 3d Filing, by Northern Engineering Services, dated April 29, 1996 6. Final Drainage and Erosion Control Study for Stetson Creek 5th Filing, by Rocky Mountain Consultants, dated December 1998 APPENDIX fVICINITY MAP