Loading...
HomeMy WebLinkAboutOAK HILL APARTMENTS PUD - FINAL - 54-87V - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE OAK HILL APARTMENTS P.U.D. FORT COLLINS, COLORADO FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE OAK HILL APARTMENTS P.U.D. FORT COLLINS, COLORADO May 2, 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 a INC. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 303/482-5922 FAX:303/482-6368 0 May 2, 1994 Mr. Glen Schlueter City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 RE: Final 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 Final 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, P� Y, RBD Inc. Engineering Consultants RogerT.rCurtiss, P.E. Project Engineer T O � � IO i,a `\\\\\\ ■ N ROther Office: Denver 303/458-5526 11 TABLE OF CONTENTS DESCRIPTION I. GENERAL LOCATION AND DESCRIPTION A. LOCATION B. DESCRIPTION OF PROPERTY IH. DRAINAGE BASINS It A. MAJOR BASIN DESCRIPTION III. DRAINAGE DESIGN CRITERIA A. REGULATIONS B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS C. HYDROLOGICAL CRITERIA D. HYDRAULIC CRITERIA E. VARIANCES FROM CRITERIA IV. DRAINAGE FACILITY DESIGN A. GENERAL CONCEPT V. STORM WATER QUALITY A. GENERAL CONCEPT VI. EROSION CONTROL A. GENERAL CONCEPT VII. CONCLUSIONS A. COMPLIANCE WITH STANDARDS B. DRAINAGE CONCEPT C. STORM WATER ,,QUALITY D. EROSION CONTROL CONCEPT REFERENCES APPENDIX VICINITY MAP SITE HYDROLOGY DETENTION REQUIREMENTS DESIGN OF CHANNELS, INLETS, CULVERTS DESIGN OF STORM SEWER SYSTEM EROSION CONTROL CHARTS, GRAPHS, TABLES, REFERENCES PA E 1 1 1 2 2 2 2 2 3 3 3 4 4 5 5 5 5 5 6 6 r Ai 1 2 8 10 40 48 55 FINAL DRAINAGE AND ■ EROSION CONTROL STUDY FOR THE J OAK HILL APARTMENTS P.U.D. FORT COLLINS, COLORADO J I. GENERAL LOCATION AND DESCRIPTION aA. Location J 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 Tennis Center, on the south by proposed Courtyards at Miramont development, and on the west by Boardwalk Drive, and The Upper Meadows at Miramont First Filing. It is a part of the IN Oak/Cottonwood Master plan. The site consists of approximately 12.97 acres, and is being planned as Multi -family apartment complex, with associated parking, IN 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 INCounty, 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 %. The project is bounded ■ to the north by retail and commercial developments, to the east by a proposed recreation center, and to the west and south by existing or proposed single family development. II. DRAINAGE BASINS ■ A. Major Basin Description The site is located within the Oak/Cottonwood Farm area, and is a part of the Oak/Cottonwood Overall Drainage Master Plan, as well as the McClellands Master Drainage Basin. 1 IN .7 IN 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 updated Oak/Cottonwood Farms Overall Drainage study, and the McClellands Basin Master Drainage Plan will also be used for this site. 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, as prescribed by the McClellands/Mail Creek Master Drainage Plan for this portion of the basin (East of College Avenue, and south of Harmony Road). 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. Per the Overall Drainage Plan for Oak/Cottonwood Farm, detention storage for this site is to be provided in detention pond 313, along with the proposed Tennis Center, and the Courtyards at Miramont development. A SWMM model was developed along with the Overall Drainage Plan, to size all the ponds within the Oak/Cottonwood Farm, and has been included in the appendix of this report. The Oak/Cottonwood Farm Overall Drainage Plan update calibrated the SWMM model per UDFCD criteria, but will be revised to reflect City of Fort Collins Criteria for SWMM modeling. The model included in the appendix of the report does reflect the revised model, and not what is currently shown in the Overall Drainage report update. 11 D. Hydraulic Criteria All calculations within this study have been prepared in accordance with the City of Fort Collins Storm Drainage Criteria. 01 2 01 0 E. Variances from Criteria ■ Two variance requests are proposed at this time, both having to do with the City of Fort Collins Criteria for providing trickle pan conveyance structures for channel sections with slopes less that 2 %. Small channel sections have been shown within Subbasins 14 and 17 that are less than 2%. Due to the relatively small amount of developed runoff from within the basins, it is requested that the requirement for trickle pans be waived for these channel sections. IV. DRAINAGE FACILITY DESIGN A. General Concept The vast majority of 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. From this point, developed flows from the site will be conveyed by storm sewer system to Detention pond 313. The average slopes across most of the pavements in the site is approximately 1.5%. A small portion of the site (Subbasin 18) together with developed flows from the proposed Tennis Center will be conveyed southerly through the proposed Courtyards at Miramont development, and to Detention Pond 313. Most of the site (Basins 1, 4, 5, 6, 7, 8, 9, 10, 11, and 13) will be conveyed by curb and gutters, sidewalk culverts, and open channels; routed to Boardwalk Drive, and conveyed by curb and gutter to a 24' curb inlet located on the north side of the project entry road. From this curb inlet, and combined with developed flows from the remainder of the basins, with the exception of Basins 2, 3 and 18, conveyed to Detention Pond 313 by a storm sewer system. a portion of this storm sewer system has previously been designed by Shear Engineering and submitted as a part of the Courtyards at Miramont Utility Plans. Per the Overall Drainage Plan for Oak/Cottonwood Farms, developed runoff from adjacent Boardwalk south of the project entry road (Basin 2) 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 (Basin 3) 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 204 has been provided in the southeast corner of basin 204 3 ■ 0 at Lemay Avenue, and will be released south and parallel Lemay Avenue. Developed flows from Basin 18 will be conveyed easterly and to an open channel and then conveyed southerly through the proposed Courtyards at Miramont development. These developed flows will be combined with the developed flows from the proposed Tennis Center, through a previous agreement with the owner of Oak Hill Apartments, and also conveyed southerly through the proposed Courtyards at Miramont development to Detention pond 313 (also by previous agreement with the owner of the Courtyards at Miramont. A permanent drainage easement will be conveyed by the plat for Oak Hill for all upstream drainage through this project. A SWMM model was developed as a part of the Overall Drainage Plan for Oak/Cottonwood Farm. This SWMM model has been be revised and updated to reflect any and all changes to the original concept of the model. A copy of the updated SWMM model is included in the appendix of this report. (Subject to further review by the City of Fort Collins Stormwater Utility). 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 op en pen channel and swales to transport developed flows to offsite detention pond 313. The small open channels connecting the site are 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. The pond, as shown on these plans, is actual field verified contours. All volumes shown for the pond included in this report have been based on actual field measurements. It 14 VI. 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 Standards, the performance standard during construction for this site was calculated to be 79.5 %. The actual performance standard for this site as specified on the Drainage and Erosion Control plan will be 80.2 %, complying with the City of Fort Collins requirements. After the overlot grading has been completed, all disturbed areas, not located within a building pad, sidewalk, or roadway/parking area shall have a temporary vegetation seed applied per the specifications shown on the Drainage and Erosion control plan (a copy is included in the back of this report). After seeding, a hay or straw mulch shall be applied over the seed at a rate of 2 tons/acre, minimum. The mulch shall be adequately anchored, tacked, or crimped onto the soil per the methods shown on the Drainage and erosion Control plan. After the utilities have been installed, the road and parking areas shall have the pavement base course installed as soon as practical. After installation of the curb inlets and sidewalk culverts, they shall be filtered with a combination of concrete blocks, 1/2" wire screen and course gravel (3/4"), according to the detail shown on the Utility plans. Straw bale checks dams are also to be installed after the channel sections have been graded. 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. VH. CONCLUSIONS A. Compliance with Standards All computations within this report have been completed with the City of Fort Collins Storm Drainage Design Criteria. B. Drainage Concept The proposed drainage concepts presented in this study and shown on the grading, drainage and erosion control plan, adequately provide for the conveyance and detention of developed runoff for this project. The ultimate size of the detention ponds will enable this site to develop in conformance with the Overall Drainage 5 2 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. Final design of Pond 313, and the associated outlet structure will be performed by Shear Engineering, which is being submitted to the City for review and comment within the same time frame as this project submittal. 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. The measures incorporated into this plan have given consideration to water quality issues. The open channel presented in this plan, particularly if the variance is granted for the elimination of concrete trickle pans, will help with water quality. D. Erosion Control Concept This site will comply with or exceed the requirements as specified per the City of Fort Collins Erosion Control Criteria. 1. Storm Drainage Design Criteria and Construction Standards b the City of Fort g g Y tY Collins, Colorado, May 1984, revised March 1991. 2. Erosion Control Reference Manual for Construction Sites by h' the City of Fort Collins Colorado, January 1991. 3. McClellands Basin Master Drainage Plan, by Greenhorn and O'Mara, Inc. 1986. 4. 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. 0.1--] 0 4 4 4 Lj APPENDIX 1-7 �; 4 0 4 0 11 ■ 4 i/ IN VICINITY MAP ,Al F• 1 "=,?nnn'