Loading...
HomeMy WebLinkAboutDrainage Reports - 04/19/1974V) w w ,A J "T LLL; D T L N 1/5 April 19, 1974 File No. 39-8-20 Wheeler Realty 1331 8th Street Greeley, Colorado 80631 Re: Drainage Study - Brown Farm 2nd Filing Gentlemen: At your request, we have prepared a storm drainage study for Brown Farm 2nd Filing, Fort Collins, Colorado. Brown Farm 2nd Filing is a residential subdivision located in Section 21, T7N, R69W of the 6th Principal Meridian. The topography of this tract is gently rolling hills, formerly irrigated crop land. The Lake Canal irrigation ditch flows generally through the project from North to South. This irrigation canal will receive partial runoff waters from the development. Coordination and approval have been made with the Lake Canal Company in this regard. This tract lies at the high point of a ridge with drainage to the North and South of this high - point. A small portion of this subdivision will drain directly to the Canal while the majority of the subdivision will drain overland and by way of street flow and channel flow to a retention pond located to the Northeast Corner of the Brown Farm Subdivision. A portion of the tract will drain South into the existing irrigation Swale. DESIGN CRITERIA The rational method of design as outlined in "Design and Construction of Sanitary and Storm Sewers" prepared by a Joint Committee of Water Pollution Control Federation and the American Society of Civil Engineers is the basis of computation used in this study. This method is based on the formula Q = CIA explained as follows: Q = The discharge of storm water in cubic feet per second. C = A runoff factor - the runoff factor is a coefficient that approximates the amount of rainfall running off of a particular area and takes into consideration various factors that effect this runoff such as soil features and type of improvement. For this report, a runoff factor of 0.5 was used for all land that is to be developed as single family residences. Wheeler Realty File No. 39-8-20 Page 2 April 19, 1974 I - Intensity rate of rainfall - for this study we have used an intensity frequency curve developed by Black and Veach developed for the Fort Collins area for storms with frequencies of 50 years or less. Additional rainfall data was needed in order to determine an intensity curve for a storm of 100 year frequency. This data was obtained from the Colorado State University recording station in Fort Collins. The 100 year rainfall intensities as plotted on Exhibit No. 3 are within 10 percent of data taken from the U.S. Department of Commerce, Weather Bureau, Technical Paper No. 40, repaginated and reprinted January 1963. Therefore, the 100 year intensity curve was used as the design basis throughout this report. The 100 year curve was used to determine capacities of pans in easements, drainage swales and street sections. A - The area contributing storm water runoff to any particular point in the design considerations. EXHIBITS The exhibits accompanying this study are: 1. Location Map 2. A set of 4 plan sheets indicating the drainage areas used, detail sections and general development of the Tract. 3. Rainfall intensity frequency curves. 4. Calculations. STORM DRAINAGE DESIGN This tract is divided into four design study areas. Area A Romeldale Lane Area B Ryland Lane Area C Hampshire Road North of the High Point Area D Hampshire Road South of the High Point Area A - Romeldale Lane has a high point at Zenith Court. Zenith Court is on the East side of Stuart Street and the drainage from this area crosses Stuart Street in a drainage pan at Romeldale Lane and flow is generally westerly to the cul-de-sac at the west end of Romeldale Lane at which point flows are directed overland in the drainage easement between Lots 18 and 19, Block 8. A drainage pan carries the 10 year storm flows to the open space and drainage Swale west of the subdivided Lots. The drainage swale runs northerly to an existing drainage swale in Brown Farm First Filing. Wheeler Realty File No. 39-8-20 Page 3 April 19, 1974 The design of this area considers a 100year storm flow to pass through the easement at the West end of the cul-de-sac on Romeldale Lane with a drainage swale to the North along the open green area West of the subdivided portion. A drainage pan in the easement between Lots 18 and 19, Block 4, was designed to handle a 100year storm. Area B - Ryland Lane. The high point is to the West of the boundary of the Brown Farm 2nd Filing. The flow is overland by way of street flow to a low point on Ryland Lane between Lots 6 and 7, Block 4, at which point overland flow is by way of a drainage pan generally Southeasterly to the Lake Canal Ditch. The design shows that storm flows can be carried between the two houses on Lots 6 and 7, Block 4. The drainage pan was designed to carry the 100year storm flows by way of a drainage pan to the existing irrigation ditch to the Southeast of these two properties. Area C - Hampshire Road, from a high point between Marianna Court and Panama Court. The flow for this area is generally Northerly to the boundary of Brown Farm First Filing. These flows will be overland by street flow and continue overland through the Brown Farm First Filing until they enter the drainage retention pond at the Northeast corner of the entire tract. Area D - Hampshire Road, South from the high point previously described. The flows are generally overland by way of street flow to a point at the south boundary of Brown Farm 2nd Filing at which point flows will enter an existing irrigation ditch. For Areas C and D the design was based on a100 year storm with all the flows going to Hampshire Road and a cross section of Hampshire Road is shown indicating the maximum capacity at the top of the curb and compared to the design flow of these particular areas. CONCLUSIONS It is observed that storm flow from the Brown Farm 2nd Filing can be adequately handled either by overland flow along proposed streets or through constructed drainage swales as noted on the attached exhibits. RECOMMENDATIONS It is recommended: 1. That storm water swales be constructed in accordance with the details shown on the drawings, Wheeler Realty File No. 39-8-20 Page 4 April 19, 1974 2. That minimum street grades of .4% be maintained, 3. That minimum overlot grading standards of the Federal Housing Administration be observed in the construction of residences. Very truly yours, HOGAN & OLHAUSEN, P.C. Max A. Karner MAK/car