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HomeMy WebLinkAboutPALMER DESIGN CENTER - PDP - 47-98 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTVI< g CINIT�YM�A P 1 "= 2000' 1 2. 3 4. REFERENCES Storm Drainage Design Criteria and Construction Standards. City of Fort Collins, Colorado, May, 1984. Drainage Criteria Manual. Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. Final Drainage and Erosion Control Study for Strachan Continental Subdivision, by Stewart & Associates, dated July 3, 1981 Final Drainage and Erosion Control Study for Little Caesars PUD. by Stewart & Associates, dated July 6, 1992 In addition, silt fence will be provided around most of the exterior of the disturbed areas, in particular around the east side adjacent to the existing parking lot, along the south side adjacent to the Larimer No. 2 Canal, and along Horsetooth Road. That portion of the site adjacent to Mitchell Drive is downhill from the road, and erosion from the site will not be conveyed to the street. Gravel inlet filters will be installed at all curb inlets, curb openings, and pipe entrances. Temporary vehicle wash pads will be located at the anticipated construction traffic entrances to the site particularly at Mitchell Drive. 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 construction and 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 Flows from the existing storm sewer system, design and installed with the Strachan project were designed to convey the 10 year undetained flows from the site, including the Palmer site. Downstream, the storm system consists of 24" and 30" RCP's along JFK Parkway. Flows are conveyed by 3 - 30" x 19" diagonally across Horsetooth Road at the JFK intersection, through the Marriott storm drain system, across Stanford Road, south across Horsetooth Road and into Warren Lake. Per the Strachan report, Mitchell & Company negotiated with the Warren Lake Reservoir Company to provide detention for the 9.6 acre development. This site was also brought to the City staff as a proposed Little Caesars project (by Stewart & Associates, dated July 6, 1998. This project was reviewed twice by staff, but the project was never approved. With the Little Caesars project, they proposed that the developed runoff sheet flow from the site to the existing catch basin, and ultimately to Warren Lake. At that time the City was concerned of the capacity of the downstream conveyance system, and the choice was given to Palmer properties of proving the capacity of the downstream system, or to provide onsite detention, and detain the difference between the 2 year historic, and the 100 year developed storm events. Palmer properties has elected to provide the onsite detention, and that is what is reflected in the plans. Basins H-1 and M-1 represent the flows from Mitchell Drive and Horsetooth Road adjacent to this site. This development will not contribute additional flows to these streets, in fact will reduce the amounts of flows which enter the public curb and gutter. As it is not a requirement of this site to detain, these basins were considered as historic, and the flows in these basins reduced. IV. General Concept This site 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 85% 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 activities take place, as well as the construction window involved, we would look to the contractor to work closely with the 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 January, 1999, or sooner if possible. Therefore, once overlot grading and utilities have been completed, the owner would like to restabilize all disturbed areas, either with vegetative means, or by hard surfaces. In no cases shall restabilization occur more than 30 days after disturbance. 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. Hydrologic Criteria The Rational Method was used to estimate peak stormwater runoff from the proposed site. The 10 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. In addition, the detention volumes required for this development have been verified using the FAA method for detention ponds developed by the UDFCD was used. Drainage Concepts The site has been broken down into 4 smaller subbasins onsite, as well as 2 subbasins adjacent to the site. There are two detention ponds proposed with this development, designated as Ponds A & B Basin P-1 will be conveyed via curb and gutter to a 5' sidewalk culvert (shown as design point 1), and to Detention Pond A. There is approximately 6,358 cubic feet of storage provided in Pond A, with a release rate of 0.50 cfs. A storm sewer system will interconnect Ponds A & B. Basin P-2 will be conveyed to a Type 13 area inlet, and piped to Pond B. Basin P-3 will be conveyed by a curb and gutter along the easterly edge of the site to Pond B, and will be introduced into Pond B via a 3' curb opening. Basin P4 represents that portion of the site which will sheet flow or be conveyed to Pond B by roof gutters. Basin P4 also includes Pond B. Pond B will provide approximately 4,326 cubic feet of storage volume to an elevation of 20.0. Detained flows from Pond B will be conveyed to an existing Type R curb inlet located at the northeast comer of the existing parking lot by a 15" RCP storm sewer. Released from Pond B, and the site will be restricted to 0.52 cfs, or the 2 year historic flows. Final Drainage Report for the Palmer Design Center PUD L GENERAL LOCATION AND SITE DESCRIPTION The Palmer Design Center PUD project is located at the Southeast comer of the intersection of Horsetooth Road and Mitchell Drive. The site is also bounded on the south by the Larimer Canal No. 2. The site can also be described as a portion of Section 36, Township 7 North, Range 69 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 includes approximately 1.68 acres, including the adjacent roadways. The site is presently undeveloped, and consist mainly of native grasses. The site generally slopes from the west to the east at slopes less than 4%. Plans for this site include an interconnected commercial building, with associated parking - IL HISTORIC DRAINAGE As mentioned above, the site is presently undeveloped, and consists mainly of native grasses and vegetation. Mitchell Drive has been fully developed and paved, adjacent to the westerly side of the project, Horsetooth Road is improved along the north side and a commercial building and parking lot has been developed on the east side of the site. An existing storm sewer was installed with the project to the east, which ultimately drains to Warren Lake. This site was a part of the Strachan Continental Subdivision Storm Drainage Report, dated July 3, 1981 By Stewart & Associates (identified as drainage area P. This basin was shown to be released undetained to the existing storm sewer system located at the northeast comer of the parking lot, then to a storm sewer located at the southwest comer of Horsetooth & JFK Parkway, northeasterly across Horsetooth to the Strachen V Filing subdivision, and ultimately to Warren Lake. The storm sewer system was designed to accommodate the 10 year developed storm event. The Strachen drainage study estimated the 10 year peak developed runoff to be approximately 8.1 cfs. As mentioned the site drains from the west to the east at approximately 3.5%. Given a historic runoff coefficient of 0.20, and a time of concentration of 16.8 minutes, the 2 year peak historic runoff was found to be approximately 0.52 cfs. NORTHERN September 15, 1998 Mr. Glen Schlueter City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80522 RE: Palmer Design Center PDP Fort Collins, Colorado Project Number: 9842.00 Dear Glen: Northern Engineering is exhilarated to submit this Final Drainage Report for the Palmer Design Center PDP 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. K/00-1-L Roger A. Curtiss, P.E. Spiro Palmer - Palmer Properties 420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221-4159 7 Final Drainage Report for Palmer Design Center PUD Fort Collins, Colorado September 15, 1998 Prepared For: Palmer Properties PO Box 270094 Fort Collins, Colorado 80527 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