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HomeMy WebLinkAboutWHITMAN STORAGE FACILITY II PDP AND APU - PDP130031 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE INVESTIGATION SEDIMENT EROSION CONTROL REPORT for WHITMAN STORAGE FACILITY II Located in the Southwest Quarter of Section 12, Township 6 North, Range 69 West of the 6' P.M. (Lot 3, Block 1, Lynn Acres) CITY OF FORT COLLINS, LARIMER COUNTY , COLORADO Prepared for: RANDY WHITMAN 209 E. SKYWAY DRIVE FORT COLLINS, COLORADO 80525 August 2013 Project No. 1032 -.GRD -13 Prepared by: DENNIS R. MES5NER P.E. Telephone: 970 461-3501 N. 1355 Cleveland Ave., Suite 1 Loveland, Colorado 80537 P below the lowest Finished Floor Elevation (5083.00). 3. Sub -Basin `OS-l', as identified on the Offsite Drainage Exhibit is comprised of 3.50 acres. The peak runoff rate during the 2-year storm is 3.28 c.f.s., the 10-year storm is 6.65 c.f.s. and the 100-year storm is 13.78 c.f.s. a. Rainfall from this basin will be conveyed in a swale located along the western property line to the existing drainage swale located along the northern boundary of the site. b. A storm drainage pipe that originates on the western side of U.S. Highway 287 that discharges into the drainage system constructed as a part of the drainage facilities for the initial Whitman Storage Facility. According to "City of Fort Collins Stone Creek Basin Hydrology Update" dated July 2008, the 100-year peak flow rate of 47 c.f.s. has been considered to discharge to the swale along the northern border of the site. c. The combined 100-year flow rate for the 36 pipe and swale system along the northern border is approximately 87.4 c.f.s. (26.6 c.f s. from Whitman Storage Facility, 118 c.f.s. from Sub -Basin `OS-1' plus 47 c.f.s. from the existing Stone Creek Basin pipe). d. The surface flow will be combined with flow from the existing pipe and be directed into the existing swale running eastward to the property line where it discharges into the natural drainage channel. V. Erosion Control: A. General Concept 1. Temporary erosion control measures will be implemented during the construction of this project. These measures will include: a. Silt fence along the east, and south property lines. b. Wattle Inlet Protection installed around the proposed outlet structure. 2. Long term erosion control measures will be implemented after the construction of this project. These measures will include: a. Landscape planting and seeding. b. Surface treatments for drives and open storage area. c. Rip rap lining the area surrounding the outlet pipe. 3. Maintenance of all erosion control devices will remain the responsibility of the developer until the completion of the project. 4. Wind erosion measures, other than watering down of the site during construction, have been neglected due to the relatively small size of the site.. 5. Water quality measures will be provided by installing a Gravel Basin at each detention facility and detaining the Excess Urban Runoff Volume for 72 hours. VL Conclusions: A. Compliance with Standards 1. All drainage design conforms to the criteria and requirements of the City of Fort Collins Storm Drainage Criteria and Construction Standards. 2. Proposed drainage improvements generally conform to the concepts and recommendations of the City of Fort Collins Master Drainage Plan. 3. Proposed erosion control measures conform to the recommendations of City of Fort Collins standards and generally accepted erosion control procedures. 4. Proposed water quality measures will be provided to remove sediment from the flow discharged from the two detention facilities. B. Drainage Concept 1. The final drainage design for the Whitman Storage Facility His. effective for the control of storm water runoff with little or no effect on the City of Fort Collins Master Drainage Plan recommendations. 2. The lowest Finished Floor Elevation (5083.00 feet), is more than 18-inches above the computed 100-year Water Surface Elevation of 4967.80 feet in the northern storm water detention facility to be constructed on site and the computed 100-year Water Surface Elevation of 4964.80 in the southern storm water detention facility to be constructed on the site. 3. Emergency overflow beyond the limits of the 100-year High Water Elevation Will spill offsite to natural drainage courses. 4. With the implementation of the proposed detention facilities and controlled release rates, the development of this site will not result in an increase of runoff compared to the historic rates. The total released runoff during the 100-year storm events will equal the 100-year historic release rate as prescribed by the City of Fort Collins Storm Drainage Criteria and Construction Standards. VII. References: A. City of Fort Collins Storm Drainage Criteria and Construction Standards B. City of Fort Collins Master Drainage Plan C. City of Fort Collins Development Standards D. Soil Survey of Larimer County Area, Colorado E. Urban Drainage and Flood Control District Drainage Criteria Manuals, Volumes 1, 2 and 3. F. Larimer County Urban Area Street Standards 8 EI�IT'S WHITMAN FACILITY vlcUNlTY MA."` SCALE: 1 "=500' 209 East Skyway Drive Fort Collins, Colorado Dennis A. Messner. P. E. Consulting Civil Engineer August 26, 2013 Project No. 1032-GRD-13 Stormwater Utility Service Center 700 Wood Street Fort Collins, Colorado 80522-0580 Re: Final Drainage Investigation and Erosion Control Report for Whitman Storage Facility II - P. D. P:; Fort Collins, Colorado Gentlemen: I am pleased to submit; for your review and comment, this "Final Drainage Investigation and Erosion Control Report for Whitman Storage Facility II - P. D. P., Fort Collins, Colorado." This investigation was based upon the proposed site development plan; on -site observation; and available topographic information. The investigation and design within this report have been performed according to the criteria established in the City of Fort Collins' Storm Drainage Criteria. I sincerely appreciate your time and consideration in the review of this project. if you should have any questions, pleage feel free to contact this office. M Submitted, ,,7 R. Messner, P.E. cb: Randy Whitman I hereby state that the attached "Final Drainage Investigation and Erosion Control Report for Whitman Storage Facility II - P. D. P., Fort Collins, Colorado' was prepared by me or under my direct supervision in accordance with the provisions of the City o"rt Collins' Drainage Criteria for the owners thereof. Dennis State ofCo� No�2f4 g 7-13 1355 N. Cleveland Ave., Ste#1 Telephone: (9`70) 461-3501 Loveland, Colorado 80537 s TABLE OF CONTENTS Pam_ Description LETTER OF TRANSMITTAL 1 TABLE OF CONTENTS & I GENERAL LOCATION AND DESCRIPTION l A. Location 1 B. Description of Property I DRAINAGE BASINS 2 Major Basin Description 2 Sub -basin Description III DRAINAGE DESIGN CRITERIA 2 A. Development Regulations 2 B. Development Criteria Reference and Constraints 3 C. Hydrologic Criteria 3 D. Hydraulic Criteria I DRAINAGE FACILITY DESIGN 4 General Concept 4 Specific Details - Detention Facility V EROSION CONTROL 5 General Concept VI CONCLUSIONS 6 A. Compliance with Standards 6 B. Drainage Concept 7 VII REFERENCES 11 TABLE OF CONTENTS (CONTINUED): EXHIBITS Vicinity Map Existing Conditions Exhibit Proposed Conditions Exhibit Offsite Conditions Exhibit Grading & Drainage Plan Stormwater Detention Plan Erosion Control Plan APPENDIX I Drainage Calculations APPENDIX II Charts, Graphs, Figures and Details iii I. General Location and Description: A. Location 1. The proposed Whitman Storage Facility H is located in the Southwest Quarter of Section 12, Township 6 North, Range 69 West of the 6' P.M. in the City of Fort Collins, Larimer County, Colorado. 2. The site is more specifically located south of Skyway Drive and east of South College Avenue. (Refer to the included Vicinity Map.) 3, The Whitman Storage Facility borders the site along its north boundary. To the west of the site lies commercial properties and US Highway 287. The Discovery Montessori School is located directly to the east. Immediately south of the site is undeveloped Cherelyn Street and the Prairie Dog Meadows Natural Area to the south of . B. Description of property 1. The Whitman Storage Facility II - R D. P. site consists of approximately 3.21 acres and is undeveloped. 2. The existing ground cover consists mainly of sparse non -irrigated grasses and native vegetation. 3. The "Soil Survey of Larimer County Area, Colorado" prepared by the U.S. Department of Agriculture, Soil Conservation Service, indicates that the surface soils consist of"Midway clay loam." The soil typical of this series is described as a shallow, well -drained soil that formed in material from clay shale. The "Soil Survey" identifies the runoff potential as rapid, and the hazard of erosion as severe. The soil type is classified in the `D' hydrologic group. 4. The site is generally considered moderate, with slopes between 3% and 6%. 5. The Whitman Storage Facility II - R D. P. will involve the construction of an outdoor storage area. The proposed outdoor storage area is to be approximately 2.59 acres. IL Drainage Basins and Sub -basins: A. Major Basin Description 1. The subject area is located on Lot 3, Block 1 of the Lynn Acres Subdivision. 2. The site is located within the Stone Creek sub -basin of the Fossil Creek Drainage Basin as identified by the City of Fort Collins' Master Drainage Plan. The site is not located within a designated flood way or flood plain. B. Sub -basin Description 1. The historic drainage pattern of the property flows from west to east. Runoff is directed to Stone Creek at the southeast corner of the site. 2. The northern 2.03. acres of the site drains to the northeast corner of the site where runoff is directed into the northern branch of Stone Creek. 3 The southern 1.18 acres of the site drains to the southeast comer of the site where runoff is directed into Stone Creek. III. Drainage Design Criteria: A. Development Regulations 1. Design criteria from the current City of Fort Collins Storm Drainage Criteria and Constriction Standards, the Urban Storm Drainage Manuals, Volumes I, II, and III and the Larimer County Urban.Area Street Standards were utilized. B. Development Criteria Reference and Constraints 1 The historic drainage pattern will be affected by the development of the site in that flow will be concentrated and channelized. The development of this site will produce more runoff than the historic amount, however, the historical runoff from the property will be maintained through the use of detention facilities and flow control devices. a. Stormwater will be released according to the historic peak flow rate as established in the City of Fort Collins Storm Drainage Design Criteria. b. The storm water is to be released at controlled rates onto the adjacent property in the historic drainage way. 2. The drainage impact of this site will not adversely affect streets or utilities. C. Hydrological Criteria 1. The Rainfall -Intensity -Duration curve for the City of Fort Collins (Larimer County Area II) was used in conjunction with the Rational Method for determining peak flows at various concentration points. 2 a. Spreadsheets from the Urban Storm Drainage Criteria Manual were used to first determine the weighed imperviousness for a contributing sub - basin, and then to calculate the peak runoff rates. (See the Drainage Calculation Section of this report.) b. Table RO-3 from the Urban Storm Drainage Criteria Manual was used for recommended imperviousness values for various land cover. c. The hydrological group `D' was used in the Urban Storm Drainage Criteria Spreadsheets for the on -site soils. 2. The 10-year and 100-year storms were analyzed in the design of the storm water management infrastructure in accordance with the City of Fort Collins Storm Drainage Criteria and Construction Standards. 3. The proposed detention facility was sized for the 100-year storm event. The maximum release rates are based on the Fort Collins Storm Drainage Criteria and Construction Standards, which prescribes a unit release rate equal to the historic release rate for the 100-year storm. The release rates were determined by the U.D.F.C.D. Full Spectrum Method as well as the on -site storage volumes for the proposed detention facilities. D. Hydraulic Criteria 1. A stormwater quality structure was designed for the project based upon the requirements found in Volume III of the Urban Storm Drainage Criteria Manual. a. Sizing of structures are based on the design figures and spreadsheets provided in Volume III of the Urban Storm Drainage Criteria Manual. 2. Proposed storm drain pipes onsite are designed using smooth interior wall High Density Polyethylene (HDPE) pipe. a_ A Mannings `n' value of 0.013 is to be used for all storm pipe according to Sec.4.4.2 of the City of Fort Collins Storm Drainage Design Criteria. 3. Recommended Channel Design Roughness Coefficients are per Table MD-1 of the Urban Storm Drainage Criteria Manual Volume I. IV. Drainage Facility Design: A. General Concept 1. During a large rainfall event; storm water will be conveyed to two detention facilities for the site. The western, southern and eastern edges of the site will be conveyed in drainage swales around the perimeter of the site and into the two detention facilities. The open areas located at the northeast and the southeast comers of the property will be utilized as a stormwater quality/detention facilities to capture and temporarily store stormwater from the remainder of the site that otherwise would be routed directly off site. B. Specific Details - Detention Facility 1. Sub -Basin `A', as identified on the Proposed Drainage Exhibit, comprises the northern portion of the site that contains 2.03 acres. The peak runoff rate during the 2-year storm is 1.23 c.f.s., the 10-year storm is 3.118 c.f.s. and the 100- year peak runoff rate is 7.71 c.f.s. a. Surface run-off will be conveyed as sheetflow across the gravel drives and open storage area of this basin and is to be directed to the detention facility located in the northeast corner of the site. The area will be utilized as a stormwater quality/detention facility to capture and temporarily store stormwater that otherwise would be routed directly off site. b. A proposed drainage swale along the east edge of the site will prevent runoff from passing off site and will direct flow to the detention facility to be located at the northeast corner of the site. c. An 8-inch diameter HDPE storm drain will extend east from the inlet and discharge into the existing drainage course., e. A multi -stage outlet structure will be constructed at the inlet to the proposed 8-inch diameter HDPE storm drain. The outlet structure will incorporate a perforated steel orifice plate to allow for a 72-hour drain time of the WQCV. A steel restrictor plate is to be installed over the outlet pipe to act as a flow regulator for the detention area during a 100-year storm event. f. The 100-year maximum release rate from the detention facility will be 2.03c.f.s. Based on this outflow rate, the detention facility will require 0.13 acre-feet (0.06 acre-feet of storage + 0.07 acre-feet of EURV). g. Proposed rip rap at the pipe outlet will reduce erosion and scouring along the side of the ditch. h. In the event the outlet structure or storm pipe becomes blocked, the detention area will overflow at the 100-year Water Surface Elevation through an emergency overflow spillway and discharge to the adjacent 4 drainage course. i. The 100-year Water Surface Elevation (4967.80) is more than 18-inches below the lowest Finished Floor Elevation (5083.00). 2. Sub -Basin `B7, as identified on the Proposed Drainage Exhibit, comprises the southern portion of the site that contains 1.18 acres. The peak runoff fate during the 2-year storm is 0.66 c.f.s., the 10-year storm is 1.89 c.f.s. and the 100-year peak runoff rate is 4.80 c.f s. a. Surface run-off will be conveyed as sheetflow across the gravel drives and open storage area of this basin and be directed to the Detention Facility located in the southeast comer of the site.. The open area will be utilized as a stormwater quality/detention facility to capture and temporarily store stormwater that otherwise would be routed directly offsite. b. Proposed drainage swales along the south and east edges of the site will prevent runoff from passing offsite and will direct flow to the detention facility. c. A proposed 8-inch diameter HDPE storm drain will extend east from the inlet and discharge into the existing drainage course. e. A proposed multi -stage outlet structure will be constructed at the inlet to the proposed 8-inch diameter HDPE storm drain. The outlet structure will incorporate a perforated steel orifice plate to allow for a 72-hour drain time of the WQCV. A steel restrictor plate will be installed over the outlet pipe to act as a flow regulator for the detention area during a 100-year storm event. f. The 100-year maximum release rate from the Detention Facility will be 1.18 c.f.s. Based on this outflow rate, the detention facility will require 0.06 acre-feet (0.03 acre-feet of storage + 0.03 acre-feet of EURV). g. Proposed rip rap at the pipe outlet will reduce erosion and scouring along the side of the ditch. h. In the event the outlet structure or storm pipe becomes blocked, the detention area will overflow at the 100-year Water Surface Elevation through an emergency overflow spillway and discharge to the natural drainage course offsite. i. The 100-year Water Surface Elevation (4964.80) is more than 18-inches