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HomeMy WebLinkAboutHUGH M WOODS PUD - FINAL - 26-88E - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE STUDY FOR UGH M. WOODS DEVELOPMENT, FORT COLLINS, COLORADO U-1 7 ■ 0 FINAL DRAINAGE STUDY FOR HUGH M. WOODS DEVELOPMENT, FORT COLLINS, COLORADO December 19, 1994 Prepared for: Payless Cashways Two Pershing Square Kansas City, Missouri 64141 Prepared by: RBD, Inc. Engineering Consultants 209 South Meldrum Fort Collins, Colorado 80521 (303) 482-5922 RBD Job No. 638-001 7 MfSOINC. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 303/482-5922 FAX: 303/482-6368 December 19, 1994 Mr. Glen Schlueter City of Fort Collins Utility Services Stormwater 235 Mathews Street Fort Collins, Colorado 80522 RE: Final Drainage Study for Hugh M. Woods Development Dear Glen: We are pleased to submit to you, for your review and approval, this Final Drainage Study for the Hugh M. Woods Development. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Respectfully, RBD Inc. Engineering Consultants Prepared by: !%�J /�' David K. Thaemert, E.I.T. Water Resources Engineer cc: Ms. Kay Force Mr. Barry Hilton Reviewed by: 6vo-r AvA-i L4 e tz-r) Kevin W. Gingery, P.E. Water Resources Project Manager Denver 303/458-5526 TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION 1 A. Location 1 B. Description of Property 1 II. DRAINAGE BASINS 1 A. Major Basin Description 1 B. Sub -basin Description 1 III. DRAINAGE DESIGN CRITERIA 2 A. Regulations 2 B. Development Criteria Reference and Constraints 2 C. Hydrological Criteria 2 D. Hydraulic Criteria 2 E. Variances from Criteria 2 IV. DRAINAGE FACILITY DESIGN 2 A. General Concept 2 B. Specific Details 3 V. STORM WATER QUALITY 3 A. General Concept 3 B. Specific Details 4 VI. EROSION CONTROL 4 A. General Concept 4 B. Specific Details 4 VII. CONCLUSIONS 5 A. Compliance with Standards 5 B. Drainage Concept 5 C. Storm Water Quality Concept 5 D. Erosion Control Concept 6 REFERENCES 6 APPENDIX VICINITY MAP 2 HYDROLOGY 5 DETENTION 13 DESIGN OF INLETS, STORM DRAIN, AND SWALES 27 NORTH LOUDEN DITCH REALIGNMENT 60 0 0 I MEMO 0 m 0 0 ■ TABLE OF CONTENTS (continued) RIPRAP DESIGN EROSION CONTROL CHARTS, FIGURES AND TABLES 70 77 89 Total pages 98 Lj IR 4 4 4 4 1. FINAL DRAINAGE STUDY FOR THE HUGH .N1. WOODS DEVELOPMENT, FORT COLLINS, COLORADO GENERAL LOCATION AND DESCRIPTION A. Location The Hugh M. Woods development is bounded by Foothills Gateway on the west, . Skyway Drive on the north, South College Avenue (U.S. Highway 287) to the east, and by Trilby Road and the remaining Timan P.U.D. on the south. 11 14 O 14 The site location can also be described as situated in Section 11, Township 6 North, Range 69 West of the 6th P.M., City of Fort Collins, Larimer County, Colorado. The site location can be seen on page 2 of the Appendix. B. Description of Property The Hugh M. Woods development contains approximately 16.4 acres, more or less. Presently, the property is undeveloped. The property is being proposed for commercial development within the City of Fort Collins Zoning District and will be developed consistent with the Timan P.U.D. Master Plan. Native grasses presently cover the property. The topography of the site generally slopes from west to east at approximately 5.1 percent. II. DRAINAGE BASINS A. Major Basin Description The proposed development lies within the Fossil Creek Drainageway. The North Louden Irrigation Ditch runs along the upper, western boundary of the project. Runoff from the project area is routed by open channels and culverts along the western edge of College Avenue or under College Avenue by existing culverts. B. Sub -basin Description The Hugh M. Woods development has been divided into 12 sub -basins. All 12 basins will be developed consisting of proposed commercial buildings and street improvements. These sub -basins are shown on the Final Grading and Drainage Plan in the back pocket of this report. 14 4 4 III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. J B. Development Criteria Reference and Constraints Runoff from this site is limited to the 2-year undeveloped flow condition. Additional runoff is detained on -site and released at the 2-year undeveloped flow rate. J C. Hydrological Criteria The Rational Method for determining surface runoff was used for the project site. The 2-year, 10-year, and 100-year storm event criteria, obtained by the City of . Fort Collins, were used in calculating runoff values. The 2-year storm event was used only to determine allowable runoff based on historic conditions. These calculations and criteria are included in the Appendix of this report. D. Hydraulic Criteria ■ All hydraulic calculations within this report have been prepared in accordance with the City of Fort Collins Drainage Criteria and are also included in the Appendix. E. Variances from Criteria A variance is being sought to use vane inlet grates along Skyway Drive to intercept runoff from this street. Further discussion follows under Specific ■ Details of Drainage Facility Design. J IV. DRAINAGE FACILITY DESIGN A. General Concept ■ The on -site runoff produced by the proposed Hugh M. Woods development will flow easterly to the potential on -site detention pond. The outflow from this potential detention pond is then routed east via the existing culvert underneath ■ College Avenue. The proposed drainage, erosion control, and grading plans are included in the back pocket of this report. . 2 0 4 NB. Specific Details The Hugh M. Woods development has been broken down into 16 sub -basins. Runoff from sub -basins 1 through 7, 11, and 16 will be conveyed easterly towards College Avenue by a combination of gutter flows and a storm sewer system. Runoff from sub -basins 8 through 10 and 13 will be conveyed southeasterly towards College Avenue by gutter flows. At College Avenue, all developed runoff will be detained in an existing wetland area, then released in an existing culvert underneath College Avenue at the 2-year historic rate. Basin 15, IN consisting of the existing College Avenue frontage along the site, is partially intercepted by existing 5-foot Type R curb inlets. Basin 14 is an offsite area which contributes flows to the south access road for the site; runoff from Basin 14 14 must be limited to 2-year historic flows. A variance is requested for the inlet grates along Skyway Drive. To divert flows from the south half of Skyway Drive into the proposed site detention pond, two inlets will be required, one on either side of the site access. Because of the significant slope of the existing roadway (8 percent), the Type R curb inlets required by City of Fort Collins storm drainage criteria are not capable of intercepting this flow. Therefore, vane inlet grates will be installed in the gutter flowline. The street access to the existing Hickory House site on the northwest corner of College Avenue and Skyway Drive will be realigned. The runoff from this site currently drains to an existing curb inlet on College Avenue just north of the site. The present drainage pattern is split between Skyway Drive (which then flows east to College Avenue and north to the curb inlet) and the frontage road (which flows north to an existing curb chase, then east to College Avenue and the curb inlet). The proposed revisions to the site access and additional paved parking increases the runoff coefficient from 0.79 to 0.85. However, the 100-year runoff increases only from 11.38 cfs to 11.52 cfs. The downstream 30-inch RCP culvert and storm improvements have the available capacity for the Hugh M. Woods development. V. STORM WATER QUALITY A. General Concept The water quality of storm water runoff is required to be addressed on all final design utility plans. The Hugh M. Woods development is anticipating construction beginning in 1995. Therefore, for this project, we have sought to find various Best Management Practices for the treatment of storm water runoff. The Hugh M. Woods site will include grass swales along a portion of the north . 3 i IN and east property lines. These grass -lined features will provide a mechanism for pollutants to settle out of the storm water runoff. Existing wetlands on the downstream portion of the Hugh M. Woods site will provide an additional mechanism for pollutants to settle out of the storm water runoff before flows are directed further downstream. B. Specific Details Runoff from the sales building roof drains and associated fire access will be directed into a grass -lined swale above D.P. 130, before discharging into the parking lot and then into the site detention pond. The warehouse roofs around the perimeter of the yard also discharge into a grass -lined swale (above D.P. 10) before running onto impervious surfaces. This Best Management Practice is known as minimized Directly -Connected Impervious Areas (DCIA). During construction, a sedimentation basin will be installed in the drainage swale between the site detention pond and design points 90 and 100. This will reduce sediment which passes other upstream erosion control measures before it can enter the detention pond and existing wetlands. VI. EROSION CONTROL A. General Concept This development lies within the High Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. The potential exists for moderate erosion problems after completion of the proposed improvements, due to some existing and proposed site slopes of greater than 2 percent. It is also anticipated that the project site improvements will be subject to both wind and rainfall erosion before new vegetation can take hold. The Erosion Control Performance Standard (PS) during construction for this project was computed to be 82.3 percent per the criteria in the City of Fort Collins Erosion Control Reference Manual for Construction Sites. The Effectiveness (EFF) of the proposed erosion control plan was calculated to be 99.6 percent. Therefore, the erosion control plan below meets the City of Fort Collins' requirements. The calculations are included in the Appendix. B. Specific Details Access roads, parking lots, and staging yards that are to be paved as part of this development must have a 1-inch layer of gravel mulch ('/a-1'/z" gravel) applied at a rate of at least 135 tons/acre immediately after overlot grading is completed. The pavement structure shall be applied as soon as possible after the utilities have 4 I been installed. After installation of the area and curb inlets, the inlets shall be filtered with a combination of concrete blocks, '/z-inch wire screen, and 3/4-inch coarse gravel. After installation of the storm drains, riprap protection shall be IN installed at the outlets. After overlot grading is completed, all swales and potential detention areas shall be reseeded with a native grass or tall fescue. After seeding, a hay or straw mulch shall be applied over the seed at a minimum rate of 2 tons/acre, and the ■ mulch shall be adequately anchored, tacked, or crimped into the soil. All construction activities must comply with the State of Colorado permitting process for Stormwater Discharges Associated with Construction Activity. A Colorado Department of Health NPDES Permit will be required before any construction grading can begin. VII. CONCLUSIONS 4 A. Compliance with Standards All computations that have been completed within this report are in compliance with the City of Fort Collins Erosion Control Reference Manual for Construction Sites and the Storm Drainage Design Criteria Manual. In addition, all computations are in compliance with the Timan P.U.D. Master Plan and Preliminary Drainage Report, both prepared by RBD, Inc. B. Drainage Concept The proposed drainage concepts presented in this report and on the construction plans adequately provide for the transmission of developed on -site runoff to the existing wetlands and drainage facilities at the eastern property line of the subject site. The combination of onsite street capacities in the curb and gutter and the ■ onsite storm sewer system will provide for the 10-year and the 100-year developed flows to reach the existing wetlands and proposed detention pond. . If, at the time of construction for some unforeseen reason, groundwater is encountered, a Colorado Department of Health Construction Dewatering Permit would be required. • C. Storm Water Quality Concept Because storm water quality has become a requirement, the site has addressed this storm water aspect. Grass -lined swales, minimized DCIA, sedimentation basins, and existing wetlands will provide an opportunity for storm water pollutants to 5 filter out of the storm water runoff before the runoff enters the Fossil Creek Basin. D. Erosion Control Concept The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from the site. Through the construction of the proposed erosion control concepts, the City of Fort Collins performance standard will be met. The proposed erosion control concepts presented in this report and shown on the erosion control plan are in compliance with the City of Fort Collins Erosion Control Criteria. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984, Revised January 1991. 2. Tinian P.U.D. Master Drainage and Utility Plan by RBD, Inc. Engineering Consultants. 3. Preliminary Drainage Study for Hugh M. Woods Development, Fort Collins, Colorado, by RBD, Inc., Engineering Consultants, September 12, 1994. Cl LN 7 �' APPENDIX � 0. Is :PRAJT R CORONA Q so IZ Warner Elem. School OAK CN SEA CT CME DR co 41 now AD HMO ZJ|| 1/o/e � 4 ISOINC. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 303/482-5922 FAX: 303/482-6368 01 M9 Mr. Rob Wilkinson City of Fort Collins Department of Natural Resources 14 281 N. College Avenue Fort Collins, CO 80524 11 RE: Proposed Hugh M. Woods Facility on S. College Avenue December 14, 1994 Dear Mr. Wilkinson: This letter serves as a request to pass stormwater flows through a natural area administered by your department. The natural area is located east of South College Avenue behind the commercial zone between Skyway Drive and Trilby Road. The stormwater flows will be generated by the above development on the southwest corner of College Avenue and Skyway ■ Drive. An existing wetlands area on the site will be the basis of a larger site detention pond. Discharge from this pond will be routed through an existing 30-inch pipe under College Avenue that has historically discharged stormwater flows into the natural area. This detention pond will improve stormwater quality by detaining flows and settling out suspended solids, as well as by utilizing the natural filtering effects of the existing wetlands. The site will also use grass -lined swales to enhance water quality where possible. Erosion potential on the site is expected to be moderate to high, according to City of Fort ID Collins erosion zone maps. Use of silt fence, sediment traps, gravel or hay mulches, and filter inlets will reduce transport of erosion downstream to the existing wetlands, or further rdownstream to the natural area. As flows through the existing 30-inch pipe under College will be restricted to the 2-year historic storm event, discharge into the natural area will be less than it has been in the past. Thus downstream erosion potential will also be minimized. .a 0 Denver 3031458-5526 Rob Wilkinson 14 December 1994 Page 2 Exhibits showing the area and delineating the flow path are attached. The complete site, utility, and drainage plans for above project will be submitted to the City of Fort Collins on December 19, 1994. If you have any questions regarding this request, please contact me. Sincerely, RBD, Inc. David K. Delan y, P.E. Project Engineer cc: File 638-OOIA