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Home My WebLink AboutAMIGOS AT SOUTH COLLEGE PUD - 31 91 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE REPORT & EROSION CONTROL PLAN FOR THE AMIGOS P.U.D. PARSONS & ASSOCIATES , CONSULTING ENGINEERS 0 a PRELIMINARY DRAINAGE REPORT & EROSION CONTROL PLAN FOR THE AMIGOS P.U.D. JUNE 3, 1991 PREPARED BY: S 432 LINK LANE FORT COLLINS, COLORADO 80524 (303) 22:1-2400 PROJECT NUMBER: 91.09 AMI PRELIMINARY DRAINAGE REPORT & EROSION CONTROL PLAN FOR THE AMIGOS P.U.D. INTRODUCTION This report was completed as part of the preliminary design of improvements for the Amigos P.U.D. It is our intent to complete the proper hydrologic and hydraulic analysis for this site in accordance with the City of Fort Collins' Storm Drainage Design Criteria. This analysis will identify the drainage requirements for the site, calculate the proposed runoff and suggest improvements which will convey the proposed runoff. Every effort will be made to address the needs of the Amigos site and those adjacent sites affected by its development. This report then will provide the following. 1._ General project information. 2. Description of the specific site to be developed. 3. The criteria used to develop the drainage information & runoff. 4. Development of flows and detention requirements. 5. Proposed Drainage Improvements. 6. Erosion Control 7. Design Calculations 8. Preliminary Grading and Drainage Plan The proposed Amigos P.U.D. is located along the east side of South College Avenue just north of its intersection with Harmony Road. Specifically this site is located in the westhalf of the southwest quarter of Section 36, Township 7 North, Range 69 West, of the Sixth Principal Meridian, City of Fort Collins, Larimer County Colorado. It is bounded by South College Avenue on the west, a service station to the south (unplatted parcel owned by Schrader), a motel to the north (unplatted parcel owned by Holter) and residential homes and a trailer court to the east (unplatted parcels owned by Fort Collins Assemblage. (See Figure 1). This site will be broken into two commercial sites. The Amigos site will cover approximately the western one-half of the site and a car wash and an auto lube center will occupy the eastern on -half of the site. A summary of the individual areas follows. M Tract "A" (Amigos) Tract "B" (Auto Wash & Lube) Right -Of -Way (South 1/2 of Street) TOTAL Pared Utility & Access Easement 20 foot wide East of site 0.73 Acres 0.64 Acres 0.24 Acres 1.61 Acres 0.11 Acres This parcel is also part of the South College Properties Superblock #1 Plan prepared by Robert Sutter and approved by the Fort Collins Planning and Zoning Board on May 26, 1981. This site is within a BP zoning designation. SITE DESCRIPTION This 1.61 acre site is currently undeveloped, fairly level and is used as an informal parking area. The West one-half of the site is composed of broken asphalt and gravel surfacing while the East one-half of the site is mostly gravel surfaced. South College Avenue forms a barrier to the West, an motel exists to the North, a service station exists to the South and a mobile home park and various residential structures exist to the East. This site slopes from South College Avenue to the East at about 1%. Runoff from this site and adjacent sites runs to the East where it is intercepted by the Larimer #2 Canal. It is intended that this pattern will be maintained. Irrigation lines run along the Westerly and Southerly edges of the site. It is uncertain whether these lines are presently in use. They ultimately discharge into the Larimer #2 Canal. Water and sewer lines are present in Pavilion Road approximately 350 foot to the North and will be extended South at the East edge of the site. Phone, gas, and electrical will be supplied from existing lines in South College Avenue. DESIGN CRITERIA This report is based on guidelines established in the City of Fort Collins Storm Drainage Design criteria dated May 1984. Because of the size of this site, the Rational Method of determining runoff was used in the drainage analysis. All variables used in this analysis were developed using Fort Collins Storm Drainage Design Criteria. Offsite flows in College Avenue will be maintained and will not be allowed to enter the site. Likewise, flows from the motel to the North and flows from the service station to the South will not be changed and will continue to flow Easterly into the Larimer #2 Canal. With no offsite drainage affecting this site it is expected that each tract will be responsible for releasing water from their site at a historic two year rate. Both tracts will provide detention in parking areas to detain larger storm events. Historical discharge will be released via a storm sewer system into an'existing drainage swale at the Southerly boundary of the site. FLOWS AND DETENTION The Amigos Site (Tract "A") contains .86 acres. Tract "A" itself contains .73 acres and the adjacent Right -Of -Way to the North contains .13 acres. This area drains towards the South edge of the site where it is intercepted by catch basins. The 100 year developed runoff is calculated to be 6.58 cfs. The 2 year historic discharge is calculated to be .82 cfs. Using these numbers, approximately 5,760 cubic feet of detention will be required. This detention will be provided in the parking lot. Outlet flows will be metered by an orifice plate located in the catch basins. The car wash and lube site (Tract "B") also contains .86 acres. Tract "B" itself contains .64 acres. The adjacent Right - Of -Way to the North adds .11 acres to the total and the adjacent 20 aaccessnand..utili.ty easement—to_the_Eas.t-addsaanother—.11—ac-r-es to the total. This site is the same shape and size of Tract "A", has identical slope and runoff lengths. The same calculations that apply to Tract "A" will therefore also be accurate for Tract "B". PROPOSED DRAINAGE IMPROVEMENTS The proposed drainage improvements for both sites will involve curb and gutters to convey water though the parking areas. Catch Basins will capture this water and direct it to culverts where it will discharge into an open surface and ultimately into the Larimer #2 Canal. Orifice plates in the catch basin will limit release into these culverts and storm events larger than the two-year storm will back up into same areas created in the parking lots. EROSION CONTROL A. EROSION HAZARD Any construction site such as this is exposed to increased erosion hazard as a result of grading. Since the grading removes the protective vegetative blanket, exposing soil particles to the forces of wind and water, we must consider both protective devices and timing of construction. B: GENERAL TYPE OF EROSION CONTROL WATER EROSION - This site is fairly well suited to staged filtration of soil particles being carried by water erosion. Although this project is not very large it is exposed on the West where it is adjacent to College Avenue. We anticipate installing a snow fence along the West boundary to reduce the impact of this exposure. WIND EROSION - On this project, timing of construction will be a large factor in controlling wind erosion. Additionally, it is not a very large site in the northwest to southeast direction, which reduces the potential for wind erosion. However, after grading operations, we are considering roughening the soil through tillage and planting rapid germination grasses to reduce or eliminate what wind erosion might occur. This project is expected to be under construction in September or October of 1991. 'The overlot grading will be the first item of construction and is expected to take approximately 1 week. In terms of erosion control, this is ideal timing since it is during the low wind season. Additionally, there is still enough precipitation expected after the grading is complete to allow germination of grasses prior to the winter wind season. Prepared under the direct supervision of: Donald M. Parsons, P.E. Colorado License # 13131 I I