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HomeMy WebLinkAbout2300 W. ELIZABETH, EBERL / SIMPSON - PDP - 22-04 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT�f in the final landscaping to cover the soil. Re -seeded areas should be mulched with straw or hay to protect exposed soil until vegetation is established. ' Controlled Runoff Across Exposed Areas: Where practical, construction may include constructing temporary swales to intercept and direct storm water around exposed areas. Swales can be constructed to control surface water, which collects on exposed areas and prevent gross erosion in the form of gullies. Riprap, straw bale dikes, or other temporary erosion control devices ' may be installed to control storm water velocities across exposed areas. Sediment Control: Temporary and/or permanent sediment control devices ' may be installed at the major drainage structures and flow concentration points shown on the Drainage Exhibit. Such structures shall be used to intercept and trap sediment once it is produced and prevent it from being M conveyed offsite onto downstream property. C. Erosion and Sediment Control Plan ' The following summarizes the overall erosion control plan for this project. The details will be shown on the construction drawings. 1. Inlet protection will be used on the detention pond outlet box. 2. Other erosion control measures will be used as necessary to help minimize erosion for this project such as vehicle tracking control and silt fence. ' VHL References Final Grading and Drainage Report for Jefferson Commons PUD, by Ayres & Associates, Inc., August 2, 1996 11 6 pond is 0.27 cfs (0.39 cfs historical release minus 0.12 cfs of undetained runoff). The top of berm is at elevation 5087 with the 100-year water surface f elevation at elevation 5086.69. The outlet structure will be designed with an orifice plate to limit the flows to the release rate. The outlet pipe will be sized for the entire developed 100-year flow. The outlet level spreader design is shown in the Appendix. The difference between the 100-year developed and historic runoff for I Subbasin B is 0.01 cfs. This difference assumes that the driveway from the proposed right-of-way to West Elizabeth Street will be paved in the future. Because of the negligible difference in 100-year runoff, no detention is being proposed for Subbasin B. f A water quality plate is being proposed for this development, and the required water quality volume is included as part of the total required detention pond volume. VII. Erosion and Sediment Control This section describes methods recommended to control wind erosion, soil erosion, and sediment from storm runoff during and after the construction of drainage structures, and site grading. This development of erosion control criteria establishes the methods and guidelines used to perform the erosion analysis and develop the erosion control plan. A. Discussion ' The clearing and stripping of land for site grading, overlot grading, or for the construction of drainage structures, and swales, may cause high -localized ' erosion rates with subsequent deposition and damage to offsite properties. Uncontrolled, such erosion could destroy the aesthetic and practical values of individual sites, and cause damage to downstream property. In general, erosion and sediment control measures may consist of minimizing soil exposure, controlled runoff across exposed areas, and sediment control at ' drainage structures. Each of these measures is described below and shall be utilized by the developer and/or the contractor during any construction activity occurring at this site. B. General Erosion and Sediment Control Measures o Minimizing Soil Exposure: Where practical, the construction area and duration of soil exposure should be kept to a minimum. All other areas should have a good cover of vegetation or mulch. Grading should be completed as soon as possible after it is begun. A temporary cover crop, a permanent vegetative cover crop, or other landscaping should be established in disturbed areas. Re -vegetation may consist of native grasses, lawn grasses, or various winter wheat. Decorative rock, flower gardens, or shrubs may also be utilized Subbasin C Subbasin C is undetained runoff around the perimeter of Subbasin A. The 100-year developed runoff will be subtracted from the release rate. B. Specific Details The Final Grading and Drainage Report for Jefferson Commons PUD states that the 100-year peak discharge for Gutter 130 is 9 cfs and the total area for Basin 60 is 1.501 acres. The northern portion of this site is part of Basin 60. Therefore, based on the paved and rooftop areas for all area in Basin 60, we estimated the historic release from this site as 0.39 cfs. The calculations are shown in the Appendix. 0.39 cfs minus undetained runoff was used as the release rate for the detention pond. The spreader design that distributes this flow is also shown in the Appendix. There is no storm pipe proposed for this site except for the outlet and pipe from the building to the pond. There is an existing storm pipe underneath the existing gravel driveway access to West Elizabeth Street. Because West Elizabeth Street will be widened in the near future, we are not proposing to pave from the proposed right-of-way to the northern existing edge -of -asphalt of West Elizabeth Street. Therefore, this existing storm pipe will not be replaced as part of this project V. Request for Variance This report is a formal request for a variance from the standards noted in the City of Fort Collins' Strom Drainage Design Criteria and Construction Standards concerning the required detention pond freeboard. Specifically, the request is for a variance from the minimum 1.0-foot freeboard requirement. This request is made because the detention pond was sized as large as possible t and the developed 100-year runoff to the pond is minimal (less than 2 cfs). The calculated freeboard is 0.31 feet VI. Conclusions A. Compliance with Standards All storm drainage calculations followed the guidelines provided by the City of Fort Collins Storm Drainage Design Criteria except for detention freeboard requirements. B. Drainage Concept The drainage system has been designed to convey the runoff to the designated detention pond in a manner as safe as possible. The detention pond will be designed to hold approximately 888 cubic feet plus an additional 201 cubic feet for water quality for a total of 1,089 cubic feet. The release rate of the ' areas in Jefferson Commons are labeled as utility, public access, and drainage easements on the final plat. The grass swale and landscaped area along the ' western and southern Jefferson Commons property boundaries are labeled as a drainage and utility easements. The capacity of the detention pond will include the contribution of the 100- year runoff produced by the northern Subbasins (Al and A2). The release rate for the ponds will be the 0.39 cfs minus 100-year developed undetained runoff. The 0.39 cfs release is described below under "Specific Details." The runoff generated by the site will be conveyed by swales, pans, and the ' parking lot to the pond. IV. Drainage Facility Design ' A. General Concept There is one proposed detention pond in the development that runoff will be conveyed to. The runoff will be released at a predetermined rate to the north. There are two additional proposed subbasins that will not be detained. In the existing condition, the site consists of Subbasin A and B. Subbasin A is the northern subbasin that historically directs runoff northeasterly towards Jefferson Commons. Subbasin B is the southern subbasin that directs runoff southeasterly to West Elizabeth Street. There is a small ditch located near the southern property boundary that may also collect flows from Subbasin B. With the development of Jefferson Commons, the outfall for this ditch appears to be West Elizabeth Street and a 15-inch storm pipe located in the southwest comer of Jefferson Commons. The four proposed subbasins will include the following: ' Subbasins Al and A2 Subbasins Al and A2 consists rooftop, pavement, and landscape. The runoff from these two subbasins are directed to a detention pond located near the northern property boundary. The detained runoff will be released at a predetermined rate, as explained below under "Specific Details." Subbasin B Subbasin B consists rooftop, pavement, and landscape. Runoff is directed southeasterly to West Elizabeth Street. Subbasin B is not detained, however, the area has been reduced so that the difference in developed and historic 100- year runoff is only 0.01 cfs. IB. Sub -Basin Description ' As mentioned above, the drainage for the site is split (approximately at the location of the residence) and flows are directed northeasterly to Jefferson Commons PUD or southeasterly to West Elizabeth Street. There appears to ' be no offsite runoff onto the site itself except for the flows from West Elizabeth Street and portions of the lots north of West Elizabeth Street. The ., offsite flows do no effect the proposed detention pond. ■ In the developed condition, there will be one onsite detention pond that detains runoff from the northern portion of the site. The onsite subbasin ' contributing runoff to the pond consists of ground covered by rooftop, pavement, and landscape. The onsite runoff will be conveyed through the site to the detention pond and to a concrete outlet structure that releases detained runoff through an orifice plate and a level spreader. The level spreader will evenly distribute the runoff northerly to Jefferson Commons PUD as sheet flow. III. Drainage Design Criteria A. Regulations The design criteria for this study are directly from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards Manual. B. Development Criteria Reference and Constraints ' The developed site will convey runoff to the detention pond and West Elizabeth Street in a safe and effective manner. C. Hydrological Criteria In accordance with the Fort Collins policy, a minor and major storm for the Fort Collins area is identified as the 2-year and 100-year storms, respectively. A major storm for the Fort Collins area has a recurrence interval of 100 years and a total rainfall depth of 3.67 inches for a 2-hour design storm, with a peak intensity of 9.95 in/hr. These storms have been used as a basis for planning and system design. The peak flow rates for design points have been calculated based on the rational method as described in the Storm Drainage Design Criteria with storm duration set equal to the time of concentration for each subbasin. D. Hydraulic Criteria The runoff produced by the site will be conveyed to the proposed detention pond within the development. The pond will outfall to northerly towards Jefferson Commons. As mentioned above, the parking lots and driveway 0 I. General Location and Description A. Location The 2300 West Elizabeth site is located in the South Half of the Northeast Quarter of Section 16, Township 7 North, Range 69 West of the 6th P.M., the County of Larimer, State of Colorado. The site is bounded on the north by Jefferson Commons PUD, on the east and west by private residences, and on the south by West Elizabeth Street. B. Description of Property The site consists of approximately 0.34 acres and contains an existing residence, garage, and shed and a gravel driveway. Historically, the drainage for the site is split (approximately at the location of the residence) and flows are directed northeasterly to Jefferson Commons PUD at about 2% slope and southeasterly to West Elizabeth Street at about 1.4% slope. As part of this project, the garage and shed will be removed and an additional building with paved parking will be added. H. Drainage Basins and Sub -Basins A. Major Basins Description The north portion of the site has been included in the Final Grading and Drainage Report for Jefferson Commons PUD by Ayres & Associates, Inc. According to this Report, the site was located in the West Plum Street Basin (1995). The site is currently located in the Canal Importation Basin. According to the Final Plat for Jefferson Commons PUD, the parking lots and driveway areas are labeled as utility, public access, and drainage easements. The landscaped area along the western and southern Jefferson Commons PUD property boundaries are labeled as a drainage and utility easements. There is an existing ditch that runs west -east along the north side of West Elizabeth, or along the southern property boundary of this site. It is our understanding this irrigation ditch is no longer utilized by upstream interests and will not be maintained as part of this project. There is also a 15-inch storm located east of the residence adjacent to this site. According to the Final Grading and Drainage Report for Jefferson Commons PUD, this 15- inch storm was designed to direct a portion of stormwater runoff from West Elizabeth Street and portions of the lots north of West Elizabeth Street (refer to the references in the Appendix) to the central detention pond in Jefferson Commons. Based on the flow stated in the report, we calculated that this storm sewer does not have additional capacity for runoff. We have therefore minimized the additional runoff to this storm pipe (only 0.01 cfs increase for the 100-year storm). VICINITY MAP TABLE OF CONTENTS SECTION I - GENERAL PROJECT LOCATION AND DESCRIPTION Page No. Location 1 Description of Property 1 SECTION II - DRAINAGE BASINS & SUB -BASINS Major Basin Description 1 Sub -Basin Description 2 SECTION III - DRAINAGE DESIGN CRITERIA Regulations 2 Development Criteria Reference and Constraints 2 Hydrological Criteria 2 Hydraulic Criteria 2 SECTION IV - DRAINAGE FACILITY DESIGN General Concept 3 Specific Details 4 SECTION V — REQUEST FOR VARIANCE 4 SECTION VI - CONCLUSIONS Compliance with Standards 4 Drainage Concept 4 SECTION VII — EROSION AND SEDIMENT CONTROL Discussion 5 General Erosion and Sediment Control Measures 5 Erosion and Sediment Control Plan 6 SECTION VIII — REFERENCES 6 APPENDIX EXHIBIT A - Final Grading Plan .Erosion Control Plan Drainage Plan PROFESSIONAL ENGINEER'S CERTIFICATION I hereby certify that this Final Drainage Plan and Report for 2300 West Elizabeth was prepared by me or under my direct supervision in accordance with the provisions of the City of Fort Collins Storm Drainage Design Criteria for the owners thereof. Loonan and Associates, Inc. James R. Loonan Registered Professional Engineer State of Colorado No. 19195 Michele L. White Registered Professional Engineer State of Colorado No. 35428 zooa" & �"oc. 19"C' 1630 S. 6Wege ,4 - ia. 0. 64 270952 �aat (J,d4", 626 80527 (970) 493-2808 9,42 (970) 495- 9735 April 2, 2004 City of Fort Collins Stormwater Utility . 700 Wood Street �. Fort Collins, CO 80526 RE: 2300 West Elizabeth Dear Sirs: Loonan and Associates, Inc. is pleased to submit this Final Drainage Report and -Plan for the proposed 2300 West Elizabeth site located south of Jefferson Commons PUD and north of West Elizabeth Street. Please review this Final Drainage Report and Plan at your earliest convenience. We look forward to your comments and ultimate approval of the Final Drainage Report. Please feel free to contact me at (970) 493-2808, if you have additional questions. Sincerely, Loonan and Associates, Inc. { James R. Loonan Michele White FOR 2300 •WEST ELIZABETH ■ PREPARED FOR;.. JIM SIMPSON 801 HIGHLAND COURT FORT: COLLINS, CO 80528 ... " r DATE APRIL 2004 PROJECT; NO.1.26 " CONSULTING ENGINEER ` + LOONAN AND ASSOCIATES, INC 1630 SOUTH. COLLEGE AVE. P.O BOX 270852 ` FORT'COLLINS, CO 80527,.' ) 1 V i