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HomeMy WebLinkAboutOAK HILL APARTMENTS PUD - PRELIMINARY - 54-87L - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE AND EROSION CONTROL STUDY FOR THE OAK HILL APARTMENTS P.U.D. FORT COLLINS, COLORADO PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY FOR THE OAK HILL APARTMENTS P.U.D. FORT COLLINS, COLORADO February 4, 1994 Prepared for: The W.W. Reynolds Companies 4909 Pearl East Circle Suite 300 Boulder, Colorado 80301 Prepared by: RBD, Inc. Engineering Consultants 209 South Meldrum Fort Collins, Colorado 80521 (303) 482-6368 RBD Job No. 088-010 February 4, 1994 Mr. Glen Schlueter City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 RE: Preliminary Drainage and Erosion Control Study for the Oak Hill Apartments P.U.D. Dear Glen: We are pleased to submit to you, for your review and approval, this Preliminary Drainage and Erosion Control Study for the Oak Hill Apartments P.U.D.. 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 � ,11+,�I• it ► j !I �!r��,, a' Roger A. Curtiss, P.E. _ z" ��•� _ "" Project Engineer 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 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 3 IV. DRAINAGE FACILITY DESIGN 3 A. GENERAL CONCEPT 3 V. STORM WATER QUALITY 4 A. GENERAL CONCEPT 4 VI. EROSION CONTROL 4 A. GENERAL CONCEPT 4 VII. CONCLUSIONS 4 A. COMPLIANCE WITH STANDARDS 4 B. DRAINAGE CONCEPT 5 C. STORM WATER QUALITY 5 D. EROSION CONTROL CONCEPT 5 REFERENCES 5 APPENDIX VICINITY MAP 1 SITE HYDROLOGY 2 DETENTION 7 DESIGN OF PIPES, INLETS, CHANNELS 10 CHARTS, GRAPHS, TABLES, REFERENCES 20 IN PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY FOR THE OAK HILL APARTMENTS P.U.D. FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location The Oak Hill Apartments P.U.D. project is located in the southeast part of Fort Collins. It is bounded on the north by Oakridge Drive and the Harmony Market development, on the east by the proposed new tennis center, and on the west by Boardwalk Drive, and The Upper Meadows at Miramont First Filing. It is a part of the Oak/Cottonwood Master plan. The site consists of approximately 12.97 acres, and is being planned as Multi -family apartment complex, with associated parking, clubhouse and pool. It can further be described as being a part of Section 1, Township 6 North, Range 69 West, 6th P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property At present the site is undeveloped, and consist mostly of native grasses. Site topography is from north to south at approximately 1.5%. To the north is retail and commercial developments, to the east is proposed recreation center, and to the west by single family development. If. DRAINAGE BASINS A. Major Basin Description The site is located within the Oak/Cottonwood Farm Overall Drainage Master Plan, and is also a part of the McClellands Master Drainage Basin. 4 4 III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. The criteria as established by the Oak/Cottonwood Farms Overall Drainage study, and the McClellands Basin Master Drainage Plan will also be used for this site. 4 B. Development Criteria Reference and Constraints This site historically drains from the north to the southeast under Lemay Avenue and through the adjacent Oakridge Development. Downstream improvements have been completed within the Oakridge Development to accept a maximum storm water runoff of 119 cfs from the entire Oak/Cottonwood Farm development. Maximum release rates for this site are 0.2 cfs/acre for the 10 year and 0.5 cfs/acre for the 100 year storms ■ events. C. Hydrological Criteria The rational method was used to determine peak developed runoff from the site. The 2 year and 100 year rainfall criteria, which was obtained from the City of Fort Collins, is the criteria used for this study. For preliminary design, the F.A.A. method was used to determine the detention requirements for this site. Per the Overall Drainage Plan for Oak/Cottonwood Farm, detention storage for this site is to be provided in detention pond 313, along with other areas outside of this site. A SWMM model was developed along with the Overall Drainage Plan, to size all the ponds within the Oak/Cottonwood Farm. Since the original report Overall plan was developed for the Oak/Cottonwood farm, the location of Pond 313 has changed. The Overall drainage plan and associated SWMM model will be updated prior to final design of this project to insure that the intent of the Overall plan is met, and to reflect the changes to the initial intent of the Overall Plan. D. Hydraulic Criteria All calculations within this study have been prepared in accordance with the City of Fort Collins Storm Drainage Criteria. 2 a L:� E. Variances from Criteria No variances are anticipated at this time. IV. DRAINAGE FACILITY DESIGN A. General Concept Developed runoff from the Oak Hill Apartment site will be conveyed to the southwesterly corner of the project by way of curb and gutter, and open channels. The average slopes across most of the pavements in the site is approximately 1.5%. Runoff from the site will be collected in an open channel _ parallel to Boardwalk Drive, and conveyed south approximately 350 feet south of the site to a permanent detention pond (Pond 313). Detention for the project will be provided within this pond. Detained release from Detention Pond 313 will be piped easterly towards Lemay Avenue, and tied in by a junction box to the existing 3 -36" RCP pipes crossing Lemay Avenue. The _ ultimate location of this outlet pipe is still being negotiated with the proposed projects between this pond and Lemay. Detention Pond 313 will also provide storage for irrigation waters. Per the Overall Drainage Plan for Oak/Cottonwood Farms, developed runoff ■from adjacent Boardwalk will be conveyed southerly to an existing curb inlet — across from Highcastle Drive, then by open channel parallel to Boardwalk Drive to Detention Pond 340, located at the Northwesterly corner of Lemay Avenue and Boardwalk Drive. The inlets, open channel and pond 340 have already been constructed, and have accounted for this portion of Boardwalk adjacent to this project. • The part of Oakridge Drive adjacent to this project is a part of Basin 204 of the Overall Drainage Plan for Oak/Cottonwood Farm. Developed runoff from ■ Oakridge Drive will be conveyed by curb and gutter to Lemay Avenue. — Detention for basin has been provided in the southeast corner of basin 204 at Lemay Avenue, and will be released south and parallel Lemay Avenue. A SWMM model was developed as a part of the Overall Drainage Plan for Oak/Cottonwood Farm. Prior to final design of this project, this Overall Plan and SWMM model will be revised and updated to reflect any and all changes — to the original concept of the model. 3 V. STORM WATER QUALITY A. General Concept Beginning in October of 1992, water quality of storm water runoff was required to be addressed on all final designs. The Oak Hill Apartments _ project is anticipating construction beginning in the summer of 1994. Therefore for this study, we have sought to find various Best Management Practices for the treatment of storm water runoff at the preliminary design phase which could be implemented in the final design process. The Oak Hill Apartment project has been designed with a number of open channel and swales to transport developed flows to offsite detention pond 313. The major channel connecting the site to pond 313 will have a relatively flat slope, which is ideal from a water quality standpoint, as flat slopes allow storm water to filter out pollutants in the grass as the stormwater is transported. The permanent detention pond 313 will also be a permanent water feature, utilizing space below the detention storage as storage for irrigation waters. Vl. EROSION CONTROL • A. General Concept ■ The Oak Hill Apartment development lies within the Moderate Rainfall Erodibility Zone and the Moderate wind erodibility Zone per the City of Fort Collins zone maps. Per the City of Fort Collins Erosion Control Reference rManual 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 erosion during and after construction. 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 permit will be required before any construction grading can occur. r VII. CONCLUSIONS A. Compliance with Standards All computations within this report have been completed with the City of Fort Collins Storm Drainage Design Criteria. 4 L Ei B. Drainage Concept The proposed drainage concepts presented in this study and shown on the preliminary grading and drainage plan, adequately provide for the conveyance and detention of developed runoff for this project. The preliminary size of the detention ponds will enable this site to develop in conformance with the Overall Drainage Plan for Oak/Cottonwood Farms and the McClellands Basin Master Plan. The ultimate pond 313 will be provided with a minimum of 1' of freeboard and an emergency overflow outlet in the event the outlet structure and pipe become plugged. In the event groundwater is encountered during construction of any portion of the site and dewatering is used to install utilities, a State of Colorado Construction Dewatering Wastewater Discharge permit will be required. C. Storm Water Quality Because Storm water quality has become a requirement, the site will need to address this storm water aspect during final design. MD. Erosion Control Concept 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 erosion from the site. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984, revised March 1991. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. 3. McClellands Basin Master Drainage Plan, by Greenhorn and O'Mara, Inc. 1986. r4. Overall Drainage Study for the Oak/Cottonwood Farm and Preliminary Drainage Study for the Upper Meadow at Miramont First Filing, Fort Collins, Colorado, by RBD, Inc., May 4, 1992. 9 APPENDIX ■ ■ VICINITY MAP SrAI F- 1 "- gnnn'