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Home My WebLink AboutFIRST ASSEMBLY OF GOD PUD - PRELIMINARY - 1-97 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT.: Preliminary Drainage Report for First Assembly of God Church City of Fort Collins, _Colorado January 13, 1997 Prepared For: First Assembly of God Church 1800 S, Lemay Ave. Fort Collins, CO 80525 Prepared By: Faucett Engineering Services 1010 Ashford Ct. Fort Collins, CO 80526 (970)223-5481 Fax(970)223-5481 Project Number: 1030 Excerpts from the Overall Drainage Plan for the Pinecone O.D.P. by Lidstone & Anderson, Inc. �r N VICINITY MAP -2000' I No Text REFERENCES 1. Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. 2: Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright McLaughlin Engineers, Denver, Colorado, March, 1969. 3. Overall Drainage Plan for the Pinecone O.D.P., Prepared by Lidstone & Anderson, dated March 7 1995 Much of this study has been based on concepts and conclusions developed by the Overall Drainage Plan for the Pinecone ODP study by Lidstone & Anderson, Inc. During final design, Faucett Engineering Services will modify the existing master plan SWMM to reflect accurately the proposed First Assembly of God Church site and the proposed detention pond. Drainage Concept The proposed drainage. concepts presented in this study and shown on the preliminary grading and drainage plans adequately provide for the conveyance and detention of developed runoff from the proposed development. If groundwater is encountered during construction, and dewatering is used to install utilities, a State of Colorado Construction Dewatering Wastewater Discharge Permit will be required. Stormwater Ouality Because water quality is important to this developer, water quality mechanisms will be incorporated into all aspects of final design of drainage systems. The proposed water quality measures in this study will require regular maintenance to remove deposits as they accumulate. The storm water quality outlet works will release the first flush of storm water runoff over a period of time in order for pollutants to settle out of the runoff. Erosion Control Concepts 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 rain and wind erosion from the site. 4 I i to determine how much flow could be released undetained from the pond. From the Pine Cone study drainage area map, the church site and CSU site make up 20.19 acres out of the total 24.6 acres of basin 60. Therefore, the undetained flow from the pond would be 3.58cfs /acre * 20.19 acres = 72 cfs. This is added to a 9 cfs release rate from detention pond 211 as shown in the Pine Cone study for a total release rate of 81 cfs. The pipe from the proposed regional detention pond -- will -need t-o be a 36" ADS. —Outlet control will -be checked during final -design. - - Specific Drainage Concepts The site has been broken into 3 basins, designated A, B and OS-L These represent the northern portion of the site, the southern portion of the site and the'off-site area which is owned by CSU. Each of the sub -basins include '/z of the proposed Timberline Road right-of-way width of 120 feet (i.e. 60 feet). The pavement, width was taken as a full 60 feet in order to be conservative when computing the impervious cover values for each of the sub -basins. A Will be conveyed by surface drainage (sheet flow) to a proposed curb cut at the east end of the parking lot. The runoff will then be carried in a 30" ADS to the proposed detention pond. B - Will be conveyed by surface drainage to two proposed curbs at the south end of the parking lots. The runoff will then be carried directly to the proposed detention pond. OS -I - The CSU property sheet flows onto the western end of the sub -basin B. From there this runoff will be conveyed along with a portion of sub=basin B surface runoff to the curb cut in the south east end of the parking lot which leads directly to the detention pond. IV. EROSION CONTROL The First Assembly of God Church lies within the Moderate Rainfall Erodibility Zone, and the Moderate Wind Erodibility Zone, per the City of Fort Collins zone maps. At the time of final design, per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, the erosion control performance standard will need to be calculated, and appropriate measures designed to control rain and wind 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 discharge permit will be required before any construction grading can begin. V. CONCLUSIONS Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. 3 III. DEVELOPED DRAINAGE . Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual, and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been used for the Preliminary Drainage Study. The Overall Drainage Plan for the Pinecone O.D.P., by Lidstone & Anderson was also used for this study, and copies of pertinent excerpts have been included in this study. Hydrologic Criteria The Rational Method was used to estimate peak stormwater runoff from the proposed site. The 10 year storm and the 100 year storm event were used to evaluate the proposed drainage system. Rainfall intensity data for the Rational method was taken from the City of Fort Collins Stormwater Utility Intensity curves (Figure 3-1). Hydraulic Criteria J• City of Fort Collins Storm Drainage Criteria has been used for all hydraulic calculations. Preliminary Drainage Concents This site was analyzed as partof the Pine Cone O.D.P. A regional detention facility has been planned on this site, and is referred as pond 211 in the Pine Cone report. In the Pine Cone study a conceptual 2-point rating curve was developed to limit the discharge to 9 cfs from pond 211. The results of the Pine Cone study also show a volume requirement of 2.3 acre-feet for pond 211. However, this volume requirement was based on an impervious value of no greater than 40% for this site. As shown in the Appendix the actual overall site impervious value is 62%. Because of the difference between the impervious values the site has been graded to include a 4.61 ac-ft detention pond. In addition, a preliminary sizing was done using Hydro Pond. This analysis showed a required volume of 3.27 ac-ft. During final design the SWMM will be modified to reflect the actual site impervious values in order to verify that 4.61 ac-ft is adequate. t. In the Pine Cone study the site was broken into two sub -basins which were labeled 59 and 60. Sub -basin 59 which was the northern portion of the site was 20.7 acres and sub -basin 60 which was the southern portion of the site was 24.6 acres. According to the Pine Cone study sub -basin 60 which also included the property owned by CSU (which lies on the west side of the Church site) and a portion of the apartments which are on the southern side of the Foothills channel, was allowed to release undetained into the Foothills channel. The total undetained release from sub - basin 60 was set at 88 cfs (see page 14 of the Pine Cone study). This translates to 3.58 cfs/acre over the entire basin 60. With the way the site has been graded all of the runoff will go through the proposed detention pond, including the runoff from the CSU site. Because of this we needed i] 0 FartEng-C4 6nWSevvfce* January 13, 1997 ---Mr. Glen Schleuter ----- _— -- - - - — City of Fort Collins Stormwater Utility 235 Mathews Fort Collins, Colorado 80522 RE: First Assembly of God Church Fort Collins, Colorado ;. Project Number: 1030.00 Dear Glen: Faucett Engineering Services is pleased to submit this Preliminary Drainage Report for the First Assembly of God Church for your review. It'represents an analysis of existing and proposed stormwater characteristics of the project site. This report was prepared in compliance with technical criteria set forth in the, City of Fort Collins, Storm Drainage Design Criteria and Construction Standards manual If you should have any questions or comments as you review this report, please feel free to contact me at your convenience. Sincerely, FAUCETT ENGINEERING SERVICES kHilCnkll`^ ��Nlze 4L'�t"FJ Andrea H. Faucett, RE: 101OAsh(ord,CC. *ForrCoUixw, Coiorado-80526 * (9,70)223-5481 * Fc w(970)223-5481