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HomeMy WebLinkAbout1990 JUNIOR HIGH SCHOOL - SITE PLAN ADVISORY REVIEW - 20-87A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE REPORT for POUDRE SCHOOL DISTRICT R-1 ELEMENTARY AND JUNIOR HIGH SCHOOLS S.E. 1/4, SECTION 34-7-69 ENGINEERING PROFESSIONALS INC. 2000 Vermont Dr. Fort Collins, CO 80525 (303) 226-3852 Wk PRELIMINARY DRAINAGE REPORT for POUDRE SCHOOL DISTRICT R-1 ELEMENTARY AND JUNIOR HIGH SCHOOLS S.E. 1/4, SECTION 34-7-69 January 1987 Project No.: 206.21 Prepared by: Engineering Professionals, Inc. 2000 Vermont Drive Fort Collins, CO 80525 Prepared for: WJM Associates 146 W. Harvard, Ste. 302 Fort Collins, CO 80526 LOCATION AND SITE DESCRIPTION This site for the location of an elementary school and junior high school to be constructed by the Pouder School District R-1 is located in the Southeast quarter of Section 34, Township 7 North, Range 69 West of the 6th P.M., in the City of Fort Collins, Colorado. The site is located on the west side of Seneca Street immediately south of a proposed future City Park, approximately one-half mile west of South Shields Street and one - quarter mile north of Harmony Road. The site has been used historically as dry land pasture and slopes gently from west to east at approximately 1:3%. There are no improvements on -site at this time except for an excavated storm drainage channel along the southern most boundary. This channel was constructed as part of the improvements for Belair P.U.D. PROPOSED USE As mentioned above, the Poudre School District R-1 is planning to develope this site for an elementary school and a junior high school. The elementary school will be located at the north end of the site with construction being planned to commence in March of 1987. Along with the school building will be the associated parking lots and playground facilities. The junior high school will be situated at the south end of the site with construction being planned to commence in the year 1988. As well as parking facilities, the junior high school will have a running track enclosing a football field, a soccer field and several baseball fields. Drainage improvements for the two projects will be phased with the respective site improvements for the two projects. HISTORIC CONDITIONS AND EXISTING REPORTS The site is tributary to Basins 77, 79, 80 and 85 of the "McClellands and Mail Creek Major Drainageway Plan" prepared by Cornell Consulting Company and John S. Griffith, P.E. in December, 1980. The site is also part of the "Preliminary Drainage Report for the Villages at Harmony West P.U.D., 2nd Filing" prepared by Parsons and Associates Consulting Engineers in July 1983. The latter report addressed detention as it pertains to the site in its developed state. The portion of the site tributary to Basins 79, 80, and 85 of the "McClellands" report will not detain any runoff on -site but will direct all runoff to the regional detention facility located on the south side of Wakerobin Lane west of the Pleasant Valley and Lake Canal. Runoff will be transported to the detention pond via an open channel along the north side of Seneca Street and the east side of Regency Drive, which was partially constructed with Belair P.U.D. The channel configuration was sized for undetained on -site as well as undetained off -site developed runoff from Basins 79, 80 and 85. DEVELOPED CONDITIONS AND PROPOSED IMPROVEMENTS Basin 77 - As indicated with the above mentioned Parsons and Associates Prleiminary Drainage Report, developed improvements occuring within historic basin 77 would require that runoff be detained and released at the rate of the historic 100-year intensity storm. It was indicated in that report that this runoff would then be discharge into the "upgraded Pleasant Valley and Lake Canal." The City of Fort Collins Storm Water Utility is currently studying the possibility of constructing a regional detention facility for historic basin 77 as well as baisns 78, 83 and 84 (as indicated in the aforementioned McClellands and Mail Creek Plan) which would allow the release of storm runoff at the 100- year historic rate. Until such time as the necessary improvements are made to handle the additional runoff from the 100-year historic flows, the portion of basin 77 currently being developed will detain storm runoff and release it at the rate of the historic 2-year intensity storm which is the currently accepted practice within the City of Fort Collins. Onsite runoff from basin 77 (developed basins D-1 thru D-5) will be detained along the west side of Seneca Street and released at the historic 2-year rate into a catch basin at the low point on Seneca Street. The catch basin and necessary culvert crossing Seneca Street will be constructed with the street improvements and is being designed by others. Provisions will be made at the release structure for the detention pond to allow for the higher 100-year historic release rate at a time when suitable downstream improvements are made to handle the additional flows. At such time as downstream improvements are made, a new oriface plate will be fitted to the release structure and the developer may also at that time reclaim portions of the detention pond for other uses. Onsite improvements will also be made to incorporate the handling of the 2-year historic flows from the offsite portion of basin 77 flowing through the site. These flows will not be detained onsite but will be routed through the detention pond. The pond will be constructed such that during a 100-year intensity storm, it will detain the onsite runoff and release it at the 2-year historic rate while any additional runoff will spill over onto Seneca Street and enter the catch bains as indicated previously. Basins 79, 80, and 85 - As mentioned previously in this report and in the Parsons and Associates Preliminary Report, developed runoff from basins 79, 80 and 85 will be directed to the regional facility located south of Wakerobin Lane and west of the Pleasant Valley and Lake Canal. Onsite runoff from these basins (developed basins D-6 thru D-8) will be directed to a proposed crossing of Seneca Street immediately north of the intersection of Regency Drive. Onsite improvements will be made to accept runoff from Basin 79, as it enters basin D-6, at the 2-year historic rate and routed through the site to the Seneca Street crossing. OVERSIZING As mentioned above, onsite improvements for both basins 77 and 79 will be sized to properly handle runoff for the historic 2-year intensity storms for the offsite portions of those basins. The cost of oversizing these facilities for anything will be considered as over and above said 2-year historic flows a basin improvement and it will be expected that the cost for those improvements will be considered as oversizing and reimbursement made to the developer under the City Oversizing Policy. CALCULATIONS All calculations and proposed improvements are indicated on the Preliminary Drainage and Grading Plan enclosed in the pocket at the end of this report. All formulae used for calculations are indicated in the Appendix. All improvements shall meet or exceed the requirements as set forth in the "City of Fort Collins Storm Drainage Design Criteria and -•Construction Standards" and any other applicable criteria in effect at the time of construction. ENGINEERING PROFESSIONALS, INC. Kenneth L. Rabbers Michael N. Schmid, P.E. APPENDIX FORMULAE Time of Concentration: _ 1 87(1.1 - Ccf)D'5 Where: C = Runoff Coefficient D = Distance in feet Tc S•33 S = Slope in percent cf = Antecedent precipitation factor 1.0 for 2-year and 10-year 1.25 for 100-year Velocity and Capacity: V = 1.487 X R•67 X S'5 Where: n = Manning's roughness coefficient n A = Cross -sectional area in square feet R = Hydraulic radius Q 1.486 X A X R'67 X S'S S = Slope in feet per foot n Runoff Quantities: Where: C = Runoff Coefficient Q = CIAcf I = Rainfall intensity, inches per hour A = Area in acres cf = Antecedent precipitation factor 1.0 for 2-year and 10-year 1.25 for 100-year Runoff -Volume: V = Q.X Tc X 60 Where: Q = Runoff in cubic feet per second Tc = Time of concentration Orifice Plate: Q = 0.65A 29h Where: A = Cross-section area in square feet g = Acceleration due to gravity, 32 feet/sec.Z h = Height of water above center of opening Detention: Volume is computed by means of a program, using the Modified Rational Method which varies the rate of flow in, while dis- charging at a constant rate.