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HomeMy WebLinkAboutWEST PLUM STREET PUD - PRELIMINARY/FINAL - 10-96A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTm - 'It �77 .197 r, V, -, No Text lj--I%l:zzjlBjlTn Ul li STORM WATER DETENTION SUMMARY SITE DRAINS TO "IMPORTATION CANAL" DRAINAGE BASIN GROSS SITE AREA (including 1/2 of adjacent W. Plum Street) = 144,935 Sq. Ft. = 3.31 Acres ± NET SITE AREA = 132,858 Sq.Ft. = 3.05 Acres ± HISTORIC "C" = 0.25 DEVELOPED "C = 0.45 CRITERIA BASED DETENTION VOLUME = 9,600 Cu.Ft. ± PLAN DETENTION VOLUME = 10,750 Cu.Ft. MAXIMUM DEPTH OF DETAINED WATER = 2.50 Ft. @ Elevation 5097.75 PEAK DISCHARGE, Q = 1.74 c.f.s. ± CONCLUSIONS AND RECOMMENDATIONS 1. The proposed development will retain the "historic" drainage patterns. 2. The site is located in the IMPORTATION CANAL DRAINAGE BASIN. The site is not located within a defined floodway or flood plain. 3. All development is to be performed in accordance with City of Fort Collins criteria. A variance to the City's policies is requested from detention of adjacent street flows due to physical impracticality. 4. Onsite detention of storm water is required by the City of Fort Collins. The volume of run-off to be detained is estimated to be 9,600 cu. ft. The detention volume has been determined based upon the calculated volume of run-off from a 100 Year Storm with the site considered at the proposed conditions being released at a controlled rate of 1.74 c.f.s., the estimated rate of run-off from the site for a 2 Year Storm with the site considered in its undeveloped state. 5. The City of Fort Collins Standards for temporary erosion control measures are to be incorporated with the construction activities. Specifically, the following are to be incorporated in the site construction activities: a. A "Silt Fence" is to be placed along the northerly border of the site. b. "Straw Bale Filters" are to be placed at the the inlet end of the outfall pipe until inlet structures are in place. C. Water application is to be made to prevent dust during the site development phase of the project. d. Roughening -of the exposed earth surfaces shall take place during the site development phase of the project. n EROSION CONTROL MEASURES Erosion control considerations are based upon the short term activities that occur during construction and the long term measures that are to be placed for the life of the facility. The long term erosion control measures are the proposed methods and materials to be used to provide surface treatments for the driveways, parking areas, walkways and the landscaped open areas. Landscape materials and plantings in the open areas will provide a combination of ground covers to deter erosion. The anticipated construction schedule should have the site grading completed, within one (1) month after commencing construction. The schedule for construction activities is anticipated to be: August 1 - August 5, perform site grading; August 8 - August 20 install water and sewer lines; August 22 - August 27 construct curb, gutter and sidewalks and drainage related facilities; September 5 - September 7 place pavement; September 1 - September 10 install landscaping. The recommended short term erosion control methods to be incorporated with the construction activities consist of the following: upon completion of grading operations and at the time that the drainage outlet is installed a "Straw Bale Filter" is to be placed at the inlet; and a "Silt Fence" is to be placed along the northern boundary of the site in order to control and contain mud and debris onsite. Wind erosion measures are to consist of water application and roughening of exposed surfaces. 3 PROPOSED DEVELOPMENT The proposed development of the site is to consist of developing thirteen single family residences to be located on the northern three acres of the site. The homes are to be considered as affordable housing. The average proposed lot size is approximately 7,000 square feet. The house "foot print" is anticipated to be from 1,200 square feet to 1,500 square feet depending on the style of house to be constructed. A paved driveway and attached two -car garage are to be constructed with each home. The proposed site plan indicates that a cul de sac is to be constructed at the southerly boundary of the site. The proposed development plan indicates that the southern two and one-half acres of the site is to remain vacant with a potential for future development.The cul de sac is intended ultimately provide access to the southerly portion of the site that is to remain undeveloped. This investigation has not considered this as tributary to the development that is currently proposed. As previously stated the run-off from the site flows onto West Plum Street. There are no other drainage facilities available to accept run-off from the site. The current City policies require that the difference between the historic rate of run-off and the developed rate of run-off be detained onsite. The release rate is to be no greater than the 2 Year Storm historic rate. The City's policies normally require that the adjacent street flows be incorporated with the onsite detention requirements. This policy applies most efficiently when the street construction and onsite detention are performed concurrently. In this instance, it is not physically feasible to combine the two flows since the flow generated on the streets can not be intercepted and directed into an on -site detention facility and then routed back into the curb and gutter. The area within the southerly half of the Plum Street right-of-way has been considered as tributary to the detention facility for sizing purposes. There are long term plans for improvements to be made within the Importation Canal Drainage Basin. These improvements could provide facilities that would eliminate the need to provide onsite detention for the proposed development. Therefore, the onsite detention facility may be considered to be temporary and may be better utilized for open space purposes when its function as a drainage facility is no longer necessary. 2 6Z6 The following report represents the results of a drainage investigation for a proposed single family residential development to be located in the North Half of Section 16, Township 7 North, Range 69 West of the 6th P.M.in the City of Fort Collins, Larimer County, Colorado. The investigation was performed for the project developer, Viita Building Company. The purpose of this investigation is to determine the effects of the proposed development on the area's existing drainage conditions and to determine the improvements, if any, and the appropriate sizing for the proposed improvements so that it may be incorporated with the construction of the project. The conclusions and recommendations presented in this report are based upon the proposed site development plan; proposed building construction plans; on -site observations; and the available topographic information. The analysis was performed in accordance with the City of Fort Collins "Storm Drainage Design Criteria and Construction Standards" manual. SITE DESCRIPTION The site is considered to be rectangular and contains approximately 3.05 acres, exclusive of the adjacent 2.5 acre tract to the South that is to remain undeveloped. The site's East-West dimension is approximately 395 feet and its North -South dimension is 335 feet. The site abuts the southerly right-of-way of West Plum Street and the tract that is to remain undeveloped abuts the northerly right-of-way of West Elizabeth Street. The site is located in the CANAL IMPORTATION DRAINAGE BASIN. "HISTORIC" CONDITIONS The site is vacant and has been utilized as irrigated pasture. A small depression has been dug near the Northeast corner of the site to capture surface runoff for stock watering. The ground surface has been roughly graded and a moderate ground cover of grasses is found on the parcel. The "historic" direction that the site slopes is from South to North. A small lateral ditch is situated along the crest of a hill adjacent to the southerly boundary. of the development. The site is considered to be moderate with slopes ranging from 1 % to 6 %. The major portion of the site currently drains onto West Plum Street. The run-off generated on the rear yards of the adjacent lots to the West and East flows onto the site and then flows northerly across the site to West Plum Street. The runoff from the tract to the South that is to remain undeveloped flows to the South and East toward West Elizabeth Street. An existing developed area of approximately one acre situated immediately West of the site contributes run-off to the street flow along the North side of the site. The run-off in the street flows to the East along Plum Street to the intersection with Timber Lane. The flow travels North along Timber Lane for approximately four hundred feet where it is intercepted by storm drain inlets. The run-off is directed through the inlets to an open drainage channel that flows easterly. 1 TABLE OF CONTENTS Letter of Transmittal Table of Contents Scope Site Description "Historic" Conditions Proposed Development Erosion Control Measures Conclusions and Recommendations EXHIBITS Vicinity Map "Historic" Conditions Exhibit Proposed Conditions Exhibit Calculations Drainage Summary ii Engineering May 14, 1996 Project No. PLA - 195 - 96 Mr. Doug Viita Viita Building Company P. O. Box 885 Fort Collins, Colorado 80522 Dear Mr. Viita, The enclosed report represents the results of the drainage investigation for the proposed "West Plum Street - P.U.D." to be located in the City of Fort Collins, Larimer County, Colorado. This investigation was based upon the proposed site development plan; proposed site grading plan; on -site observations; and available topographic information. The investigation was performed in accordance with the criteria established in the City of Fort Collins "Storm Drainage Design Criteria and Construction Specification Standards" manual. We sincerely appreciate the opportunity to be of service to you. If you should have any questions, please feel free to contact this office. Respectfully Submitted, MESS Engineering Associates Dennis R. Messner, P.E. DRM/mkm Enclosures Civil and Environmental Engineering Consultants 150 E. 29th Street, Suite 225 Loveland, Colorado 80538 Telephone: (970) 663-2221 DRAINAGE INVESTIGATION WEST PLUM STREET - P.U*Do CITY OF FORT COLLINS, LAREVIERR, COUNTY, COLORADO Prepared for Vista Building Company P. O. Bog 885 Fort CoUui& Colorado 80522 May 14, 1996 Project No. PLA -195 - 96 Hiilggffi,"II$ Enaineenng Associates 150 E. 29th Street, #238 Loveland, Colorado 80538 Telephone: (970) 663 - 2221