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HomeMy WebLinkAboutWOODRIDGE (ARAPAHOE FARM) PUD, PHASES TWO-FIVE - PRELIMINARY - 55-87E - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT PRELIMINARY/MASTER DRAINAGE STUDY FOR WOODRIDGE FORT COLLINS, COLORADO 3DNC., Engineering Consultants Ai 0 ` ' I U I PRELIMINARY/MASTER DRAINAGE STUDY FOR WOODRIDGE FORT COLLINS, COLORADO December 2, 1991 U PREPARED FOR: WOODCRAFT HOMES 1501 N. CLEVELAND AVE. LOVELAND, CO. 80538 U PREPARED BY: RBD, INC. ENGINEERING CONSULTANTS 2900 SOUTH COLLEGE AVENUE FORT COLLINS, COLORADO 80525 (303) 226-4955 U RBD Job No. 434-004 I T z` INC. III Engineering Consultants 2900 South College Avenue III Fort Collins,Colorado 80525303/226-4955 December 2, 1991 FAX 303/226-4971 01 Ms. Susan Hayes Stormwater Utility Department III City of Fort Collins 235 Matthews Street Fort Collins, CO 80522 II! RE: WOODRIDGE PRELIMINARY/MASTER DRAINAGE STUDY RBD Job No. 434-004 III Dear Susan: We are pleased to submittto you, for your review and approval, this III Preliminary/Master Drainage Study for the Woodridge development. Because the Master Drainage Study for the site was not revised, we are including the work previously done in- that study with the current work done for the preliminary in this report. Thus your ® review comments from the Master Drainage Study have been addressed within this report. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. III Thank you for your time and consideration of this submittal . Please call if you have any questions. '` Respectfully, III RBD Inc. Engineering Consultants Stun A. Myers, P.E. Project Manager `,.'0";lr ' r�//F`'4', 111 e,, -- --149"7 ' ' ,''',- evin W. Gingery, P.E. _ • IIIProject Engineer A r cc: Gary Berger , u;;stlh,t,',;" 01 John Hutchinson I 1 IIIOther offices:Denver 303/778-7338•Vail 303/476-6340•Longmont 303/678-9584 111 101 TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION 1 II. DRAINAGE BASINS AND SUB-BASINS 1 A. MAJOR BASIN CHARACTERISTICS 1 B. SUB-BASIN DESCRIPTION 1 III. DRAINAGE DESIGN CRITERIA 3 A. REGULATIONS 3 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 3 C. HYDROLOGIC CRITERIA 4 D. HYDRAULIC CRITERIA 4 E. VARIANCES FROM CRITERIA 4 IV. DRAINAGE FACILITY DESIGN 4 A. EXISTING CONDITIONS 4 111 B. SPECIFIC DETAILS 5 V. CONCLUSIONS 111 A. COMPLIANCE WITH STANDARDS 8 B. DRAINAGE CONCEPTS 8 001 REFERENCES 9 APPENDIX EXHIBIT 1 1 TIME OF CONCENTRATION 2 111 RATIONAL CALCULATIONS 2 YEAR DEVELOPED STORM EVENT 7 101 RATIONAL CALCULATIONS 100 YEAR DEVELOPED STORM EVENT 12 REGIONAL CHANNEL 17 DETENTION 22 TABLES AND FIGURES 28 !ii II] 14! II! PRELIMINARY/MASTER DRAINAGE STUDY I — FOR 1 WOODRIDGE II! I. GENERAL _LOCATION AND _DESCRIPTION The Woodridge development is located in the southwest part of Fort Collins, at the northeast corner of the intersection of Taft Hill Road and Harmony Road. Woodridge, consisting of approximately 155 acres, occupies most of the southwest quarter of Section 34, Township 7 North, Range 69 West, of the _ 6th Principal Meridian. The site is also bounded on the north by Imperial Estates, and on the east by Regency Park P.U. D. , Webber Junior High School, and Johnson Elementary School. (See Preliminary Drainage Plan in the back pocket of this report. ) ® II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Characteristics II! Numerous drainage reports have incorporated flows from this area into their studies, since this site is near the upper end of the McClellands and Mail Creek Basin, and upstream of some existing developments. The McClellands. and Mail Creek Major Drainageway Plan, prepared by Cornell Consulting Company, December, 1980, includes a hydrological analysis of the four historical drainage basins within the site. Each of these basins, 75, 77, 79, and 80, originate within this quarter section. A small portion of a fifth basin, 78, lapses over the northwest corner of the Woodridge site, but does not contribute flows to the site. According to the Major Drainageway Plan, runoff from the basins west of Taft Hill Road, 81 and 82, (refer to Exhibit 1) flow through existing culverts under Taft Hill Road and under County Road 38E, and then are routed to the north. Thus, no off-site basins contribute storm water runoff to the subject site as long as the existing culverts under Taft Hill Road and under County Road 38E are maintained on a regular basis and are not plugged up. The attached preliminary drainage plan also shows the locations of these historical basins. !IF B. Sub-Basin Description Since flows from the four main historic basins will be directed in three different directions, the following 1!! discussion deals with the separate basins accordingly, as �.. Qk 111 shown on Exhibit 1 in the appendix. Basin 75 The Final Drainage_ Report for Regency Park P.U.D. , by Parsons and Associates, Consulting Engineers, dated March 30, 1987, states that 100-year developed runoff from basin 75 will be routed through Regency Park in an open channel along the north side of Harmony Road. Basin 77 The following information was acquired from the "Final Drainage Report for Poudre School District R-1 Elementary School", dated April 1987, and prepared by Engineering Professionals, Inc. A regional detention facility is planned for Basins 77, 78, 83, and 84, by the City of Fort Collins Stormwater Utility. This facility would ultimately provide detention for.these undetained basins, when the necessary downstream improvements have been made to handle the additional flows. On-site improvements at the elementary school were designed to handle 100-year historic flows from Basin 77 upstream of the school site. The peak flow rate for these historic flows is 13 .8 cfs, which was 011 taken from the Parsons and Associates preliminary report for the elementary school site. These off-site flows are not to be detained on the school site, but are routed through the school's on-site detention pond. Flows from �!_ upstream of the school exceeding the 100-year historic rate will weir flow into Seneca Street, and enter the catch basin at the low point in Seneca Street. They will then be released to the area on the east side of Seneca Street, opposite from the elementary school. Basin 78 Consistent with the McClellands and Mail Creek Major Drainageway Plan, the developed conditions for the very northwest corner of the site will direct flows to the north, which is the historical drainage pattern. In order for runoff from Basins 81 and 82 to be directed into Basin 78, the existing culverts under Taft Hill Road and under County Road 38E must be maintained on a regular basis and not allowed to plug. !II_ Basins 79 and 80 Based on the Preliminary Drainage Report for the 1990 Junior High School, dated February 5, 1988, and prepared by RBD, Inc. , provisions for the developed flows from 2 basins 79 and 80 were made in the design of the improvements at the junior high site. y 1 According to the Final Drainage Report for Poudre School District R-1_ Elementary School, dated April 1987, by Engineering Professionals, Inc. , the channel along the ®_ north side of Seneca Street and the east side of Regency Drive was sized for undetained on-site as well as undetained off-site developed runoff from Basins 79, 80, and 85. In summary, for basins 75, 79, and 80, the downstream 11, improvements were designed to provide for the undetained conveyance of the originally anticipated developed flows into Regional Detention Pond No. 1, (located east of Regency Drive and south of Wake Robin Lane) . For basin 77, however, the downstream limprovements will only accommodate the historic flow rate. III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. ® B. Development Criteria Reference and Constraints -J From The Final Drainage Report for Regency Park P.U..D. , P100 year developed runoff from Basin 75 will be routed through the Regency Park subdivision in an open channel along the north side of Harmony Road. A 42 inch culvert lies under Regency Drive. During the summer of 1991, a channel was constructed from the outlet of the 42 inch culvert (immediately east of Regency Drive) north to the . existing Regional Detention Pond No. 1. From the Preliminary Drainage Report for the 1990 Junior High School, the channel and culvert system along the north side of Seneca Street and the east side of Regency Drive was sized for undetained on-site as well as undetained off-site 100 year developed runoff from Basins 79, 80 and 85. The existing 42 inch culverts under the service drive at the west side of the Junior High were originally designed to carry 57 cfs each, with 120 cfs weir flowing into Seneca Street, for a total of 234 cfs. This information was taken from the June 7, 1988 letter �l from RBD, Inc. to the City of Fort Collins, relating to the "100 Year Developed and Historic Flows through the Proposed 1990 Junior High Site. " The current SWMM model analysis for Basins 79 and 80, as P �,. I recently obtained from the City of Fort Collins, indicates that the existing 42 inch culverts under the 14 service drive at the west side of the Junior High as well as Seneca Street (downstream of the subject site) will receive greater 100 year developed runoff than was Ii! originally anticipated. The SWMM model has indicated the 100 year developed runoff at this point to be 318 cfs. The City of Fort Collins is currently reviewing this matter and has indicated that the downstream existing improvements are not adequate to transport the entire 100 year developed runoff (318 cfs) that could be produced from the subject site and leave at the east property line onto Seneca Street. Therefore the City of Fort Collins - has asked that the subject site detain as much runoff as the site layout can accommodate and the City would II! acquire this property as another regional detention pond of which they would maintain along with their other regional detention ponds. C. Hydrologic Criteria The Rational Method for determining surface runoff was used for the project site. The 2 and 100 year storm event criteria, obtained from the City of Fort Collins, was utilized in calculating runoff values. These calculations and criteria are included in the Appendix. D. Hydraulic Criteria II!, 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. II[ E. Variances from Criteria No variances are being sought for the proposed project site. IV. DRAI-NAGE FACILITY DESIGN A. Existing Conditions MO The existing site is covered with native grasses, with MIL little vegetation otherwise. Except for a Fort Collins- Loveland Water District water line through the site, there are no improvements, except for several field roads '. crossing through the area. Most of the site drains naturally to the east, with most slopes averaging from less than one percent to over three percent. A natural drainage swale through the center of the quarter section intercepts much of the stormwater flows, and transports the flows toward the east boundary of the site. 11 4 �- I 49 Once runoff from the subject site leaves the east property line at Seneca Street, the runoff flows through the Webber Junior High School property. Through three separate segments of double 42 inch culverts and various types of open channels, runoff from the subject site and runoff from the Junior High are transported from the Junior High school to the Regional Detention Pond No. 1. This pond is located south of Wake Robin Lane, east of Regency Drive, and west of Pleasant Valley and Lake ® Canal. Regional Detention Pond No. 1 is designed for flows from basins 75, 79, 80, and 85. The southeast portion of the Woodridge site drains toward an existing swale running along the north side of Harmony Road, adjacent to the Regency Park development. A 42" culvert carries the flows under Regency Drive where the flows then enter a recently constructed open channel which takes the flows north into Regional Detention Pond No. 1. A small portion of the quarter section drains to the very northeast corner, and then along the north side of Johnson Elementary School, located directly north of the junior high school. The flows are routed through the site and then released into a detention area on the east side of Seneca Street, opposite the school. `= The very northwest corner of the site, lying within historic basin 78, drains to the northeast and off-site, through Imperial Estates. The southwest corner of the site has a distinctive ridge line. With grades over ten percent sloping toward Harmony Road, this corner drains away from the area under study, and is in an entirely separate drainage basin from ® the rest of the site, i.e. Fossil. Creek. Basin. B. Specific Details The Woodridge site is planned as a single-family residential housing development, with ultimately 432 lots. Harmony Road will be realigned to pass through the center of the site, and connect with West Horsetooth Road ® (County Road 38E) at Taft Hill Road. Seneca Street, I '= which currently stops at the east boundary of Woodridge, will be extended across the southeast corner of the site. The existing drainage swale through the center of the site will be used as the primary means of storm water conveyance through the site and for delivery of flows to the proposed on-site regional detention pond which will — outlet into the existing drainage improvements at Webber Junior High School. 5 iir Stormwater flows from the northeast corner of the I development will, as historically, flow along the north ill side of the elementary school. The southeast corner of the site will continue to flow to the drainage channel along the north side of Harmony Road. PIThe accompanying preliminary drainage map shows the boundaries of the developed basins, based on proposed 111 street layout and consistency with historical basins. The times of concentration were based on approximate design slopes for the proposed streets, or else on velocities derived from a channel rating computer program itfor sub-basins through the regional drainage channel. The appropriate street encroachment criteria was used for II the various types of streets through the site. The arterial standards were used for Harmony Road, collector standards for Seneca Street, and local street standards for all other streets in the development. 101 Where the developed runoff exceeds the standards for street encroachment for the initial storm, a storm sewer I system has been defined. Inlets were located where the _ street capacity was exceeded, and outlet pipes were sized by the Manning's equation. IThe required portions of storm drain system, i.e. , P crosspans, inlets a:nd pipe systems, are shown on the Preliminary Drainage Plan. The pipe systems outlet into the regional drainage channel and the regional on-site I detention pond through the center of the development. A box culvert will be installed where Harmony Road crosses II over the regional drainage channel. A pedestrian underpass will be incorporated into the design of the culvert crossing. II Two of the on-site historical basins, numbered 79, and 80, will drain into the proposed on-site regional detention pond at the east property line and immediately north of Seneca Street. Flows in excess of the regional 11_ ponds capacity will exit the regional pond via the existing 42" culverts along the east property line or via earthen overflow weir being proposed along the east Ian property line. Ideally the discharging of storm water runoff onto Seneca Street at the east property line is not desirable by the City of Fort Collins. The ® discharging of storm water runoff across the south side !_ of the Webber school site and then overflowing onto Seneca Street further downstream of the subject site is II more desirable from the downstream flow restrictions. _ A preliminary analysis was completed as to the proposed II6 Pl_ I . MI on-site regional detention pond sizing. In order to ' F detain the developed runoff from the subject site and. II release the runoff at the capacity of the existing 42 inch culverts at the east property line, a pond of approximately 6.3 acre-feet in size would be required. `® A preliminary grading plan was prepared for the proposed regional detention pond in order to determine the approximate volume available. From the computations, the approximate volume available for a regional on-site MIdetention pond is 2.55 acre-feet. Thus approximately 3. -feet of storm water runoff release75acre by an overflow weir at some locationwillneed alongto the S eastern property line of the subject site. The regional drainage channel and regional on-site detention pond will be a Basin Master Planned facility and will be II eligible for basin reimbursement through the Developer Repay Program. It should be pointed out, when sub-basins 7A, 7B, 7C and 1111 17 are fully developed, the developed peak discharge rate, 54.3 cfp, exceeds the capacity of the existing downstream channel, adjacent to Regency Park P.U.D. . Per NI the report titled "Final Drainage Report for Regency Park P.U.D. " it states "the channel north of Harmony Road is sized to carry 42 cfs at a depth of 1.4 feet. " Since the original concept from the Major Drainageway Plan was for j developed flows from Basin 75 to flow undetained to the Regional Detention Pond No.1, minor improvements will be required to upgrade the channel capacity in the future. a Sub-basins 24, 25, 26 and 27 in historic basin 77, will III require their own on-site temporary detention facility. The release rate will need to match the 100-year historic release rate, 13.8 cfs, as given in the Engineering Professionals final report for the elementary school site. The outlet pipe should discharge into the existing drainage channel on the north side of the elementary school. The City has identified a tentative site for regional detention pond/park north of the elementary school. Flows from developed sub-basin 24, 25, 26 and 27 could be routed through the school site and/or through the future regional detention pond/park. When these anticipated downstream improvements have been made to handle the 100-year developed flows from sub-basins 24, 25, 26 and 27, this temporary detention facility will no longer be needed. Exhibit 1 indicates that historically a portion of basin 78 crossed the northwest corner of the subject site. Runoff from the historic basins west of Taft Hill Road, 81 and 82, flow through existing culverts under Taft Hill 7 ti Road and under County Road 38E, and then the runoff is routed to the north. For the subject site, a high point in proposed Harmony Road has been provided near the northwest corner of the site to force any overflow runoff from historic basins 81 and 82, to the north. By creating the high point in Harmony Road and subsequent grading along the west property line of the subject site, it is the intent that no off-site runoff enter the subject site and be transported southeast along Harmony Road. V. CONCLUSIONS A. Compliance with Standards All computations that have been completed within this report are in compliance with the City of Fort Collins Storm Drainage Design Criteria Manual. B. Drainage Concepts The proposed drainage concepts adequately provide the 111 transmission of developed on-site runoff to the existing drainage devices at the eastern property line of the 4v_ subject site. The proposed storm sewer system will collect the 2 year runoff generated within the site, except for Seneca Street at the east property line where some runoff carries over along the street. The storm sewer system will discharge into the regional channel and on-site regional detention pond. The 100 year runoff is proposed to be conveyed by streets, swales, regional. channel, and regional on-site detention pond to the 11111 eastern property line of the subject site. From the eastern property line of the subject site, runoff is proposed to be carried to Regional Detention Pond No. 1 east of Regency Drive and south of Wake Robin via the series of off-site culverts, open channels and streets. The City of Fort Collins in conjunction with RBD Inc. , are currently studying the possible reconfiguration of the existing 42 inch culverts at Webber Junior High { School adjacent to Seneca Street. Depending on the outcome of this analysis, the existing 42 inch culverts may or may not be 'reconfigured. On the preliminary drainage plan the existing 42 inch culverts at the east property line are shown in their existing location. Also the designated weir, overflow point for the on-site regional detention pond is being studied at this time. In addition to the 42 inch culvert study, the City of Fort Collins is also evaluating the capacity of downstream existing improvements in regards to the new 8 SWMM runoff flows which exceed the previously used R'` downstream criteria. Upon the outcome of this analysis, recommendations will be made as to the configuration and "'{ hydraulics which should be utilized in the on-site 4tti,H regional detention pond design. IIIN At the time of construction, if for some unforeseen reason ground water is encountered during construction, IV a Colorado Department of Health Construction Dewatering IIIPermit would be required. At the time of preparation of tz '� ' ° any final drainage reports, for the subject site, erosion 6 - control methods will need to be analyzed and provided with the utility drawings for future phases of Woodridge. per the Erosion Control Reference Manual for Construction ° _. sites by the City of Fort Collins, Colorado, January III 1991. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by 'f" - the City of Fort Collins, Colorado, May 1984 . 2 . The McClellands and Mail Creek Major Drainageway Plan by Cornell Consulting Company, December 1980. a' - 3 . Final Drainage Report for Regency Park P.U.D. by Parsons & III Associates Consulting Engineers, March 30, 1987. 4 . Preliminary Drainage Report for the 1990. Junior High School by RBD, Inc. , February 5, 1988. „ 5. Final Drainage Report for Poudre School District R-1 Elementary School by Engineering Professionals, Inc. , April 1987. ill . 'y `r IIII 9 • P1!