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HomeMy WebLinkAboutUTILITY SERVICES PUD PHASE 1 PRELIMINARY - 16 90C - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPrepared for: City of Fort Collins Facilities Department P.O. Box 580 Fort Collins, Colorado 80522 Attn: Mr. Jack Gianola Prepared by: Merrick & Company 2450 South Peoria Street Aurora, Colorado 80014 906 Vine Street Preliminary Drainage. Report :. _ � 12�-!li Basin PB-1 is a large basin containing the western portion of the site. This basin is 2.28 acres and consists of the remaining part of the maintenance shop, the west half of the proposed road, and the proposed 63 space parking lot and bus shelter. The basin's fully developed 10-year and 100-year runoff coefficients are 0.67 and 0.84. Drainage from the basin is expected to be 6.43 cfs and 13.82 cfs for the minor and major storms. Basin PB-1 is also subject to offsite flow from basin OS-2 that enters Basin PB-1 in the south by the maintenance shop. This flow is immediately directed into the borrow ditch of the proposed road. Flow from Basin PB-1 naturally flows eastward toward the proposed road and will be collected in its borrow ditch. The swale will carry the flow to the north edge of the site where it will enter a culvert at Design Point 2. The pipe will -carrythe:flowreastward under the -road ,to:the:detention-pond. The pipwis designed:, to carry 16.43 cfs and will be 2 ft in diameter with a 1.8% slope. Basin PC-1 is 0.07 acres and is made up mostly of the proposed asphalt road and borrow ditch. Its runoff coefficients are 0.82 for the minor storm and 1.00 for the major storm. The 10-year and 100-year peak flows of the basin are 0.32 cfs and 0.57 cfs, respectively. Drainage from this basin will flow north in the swale to Design Point 4 where it will be directed east in a swale to Wood Street. �- _ The 0.18 acres of basin PC-2 contain the remainder of the asphalt road and a channel directing flow to the detention pond. The basin's 10-year and 100-year runoff coefficients are 0.72 and 0.90. Anticipated flow from the fully developed basin will be 0.70 cfs for the minor storm and 1.15 cfs for the major storm. Drainage will be carried by a borrow ditch to the channel that will carry it to the detention pond. i -� Basin PDA contains 0.41 acres at the east side of the site. In the basin is a concrete pan that will be demolished in future phases of development. The remainder of the basin is gravelly soil. The basin has a Minor storm runoff coefficient of 0.61 and a peak flow of 1.05 cfs. The major storm runoff coefficient is 0.76 and the peak flow is 2.24 cfs. Drainage from this basin will join the drainage from Basin PC-1 in the proposed swale headed towards Wood Street. I r O!J a+ Merrick &Company 906 Vine Street Preliminary Drainage Report The 0.73 acres at the northeast corner of the site make up Basin PD-2. This basin currently consists of just gravelly soil and will experience almost no changes during development of the site. Its 10-year and 100-year runoff coefficients are 0.50 and 0.63, respectively. The minor storm flow predicted from this basin is 1.55 cfs and the major storm flow is 2.63 cfs. These flows will enter the detention pond through the eastern portion of the proposed channel which is part of Basin PC-2. E. EROSION CONTROL 1 General Concept ti A majority of the site currently drains to the onsite detention pond. After future development is completed, all drainage from the site will be directed to the detention pond. This site is excluded from wind erosion control requirements because more than 95% of its unprotected surface is covered by gravel particles larger than 2 mm in diameter. Rainfall erosion will be prevented by minimal disturbance along the shore of the Mulligan Detention Pond. Hay bales will be placed along the shore of the detention pond and the north property boundary . Overlot grading will be followed by temporary seeding, utility installation, curb and gutter placement, and street paving. During construction hay bales will protect swales. The.proposed development erosion plan will provide protection in excess of the required effectiveness. Downstream impacts of runoff will be consistent with historic patterns. I Specific Details The 906 Vine Drive site lies within Moderate Wind and Moderate to High Rain Erodabililty Zones as shown by City of Fort Collins' maps. Soils on the site include a gravelly surface underlain by clay and well -graded sand. This information is detailed in the 1995 Geotechnical Engineering Report by Empire Laboratories, Inc. Erosion is a potential problem during construction and after until exposed soils are revegetated. Erosion control performance standards were calculated according to crlteria.presented in the City of Fort Collins Erosion Control Reference manual for Construction Sites. Temporary seeding will be used for areas that are overlot graded and permanent seeding will follow final grading. Straw bales will be placed in all erosion -prone swales before permanent seeding takes place. Outfall velocities will be low enough to prevent erosion.. Rip -rap or other protection will be provided to prevent scour and bank and swale erosion. Merrick & Company Page 9 906 Vine Street Preliminary Drainage Report F. CONCLUSIONS •Il �. l.. '-• -Il- The designs and calculations included in this report comply with the 1984 City of Fort Collins Storm Drainage Design Criteria. Hydrologic and hydraulic calculations were based on accepted practices for the Rational Method as contained in the City of Fort Collins Storm Drainage Criteria and in the Urban Drainage and Flood Control District Criteria Manual. Calculations of the runoff rates for this project are included in Appendices 1 and 2 of this report. I Summant of Drainage ConeW The existing site currently drains to the northeast to an onsite existing detention pond. Further development within the subbasin will require that the outfall pipes of both ponds be enlarged. The proposed development drainage plan will continue that pattern. Downstream impacts will be consistent with historic flow rates and volumes, and will meet the requirements of the City of Fort Collins criteria. A Drainage Plan has been prepared and is included in this report. Included in the Appendices are calculations to support the channels, and culverts. l 11 • • • 1 • •K4T-T1X:1-611 A majority of the site drains to the onsite Mulligan Detention Pond. Sediment control barriers will protect the pond from siltation during construction. Rainfall induced erosion into the pond will be prevented by trapping of any sediments in the proposed detention facility. Overlot grading will be followed by temporary seeding, utility installation and paving. Hay bales will protect swales. The proposed development erosion plan will provide protection in excess of the required effectiveness and with downstream impacts consistent with historic patterns. The erosion control plan meets the requirements of the City of Fort Collins criteria. Respectfully submitted, MERRICK & COMPANY Amy D. nkell, EIT Design Engineer Reviewed and Approved by, Barney J. Fix, PE Project Manager Merrick & Company Page 10 906 Vine Street Preliminary Drainage -Report G. REFERENCES 1. City of Fort Collins, Colorado Storm Drainage Design Criteria and Construction Standards, 1984 EDITION. 2. Urban Drainage and Flood Control District - Urban Storm Drainage Criteria Manual, 1990 Revisions. 3. G_ eotechnical Engineering Report for Proposed 906 West Vine Drive Parking and Drive Area Improvements, Fort Collins, Colorado prepared by Empire Laboratories, Inc. May 1995 4. _: Mulligan Property;D.etention.Pond Drainage Analysis:and Design prepared by Lidstone & Anderson, Inc. November 1994 & Company Page 11 906 Vine Street Preliminary Drainage Report APPENDIX 1 HYDROLOGIC CALCULATIONS & Company Page 12 TABLE OF CONTENTS A. INTRODUCTION ............................................... PAGE Location................................................... 1 Property Description .........................6.............. 1 2 Proposed Development ...................................... vicinityMap ................................................ 3 B. HISTORIC DRAINAGE ................................. .......... 4 Overall Basin Descri ions ................................... 4 Dralnaae Pattems Through Propefy ........................... 5 . �....... _C. _...._.DESIGN„CRITERIA_�...;.�....�.........:. ..........,.... ...,...::.......... 5 References and -Regulations .................................. 6 Hydrologic Criteria .......................................... HydraulicCrlter1............................................ 6 D. DRAINAGE PLAN ......................... ..... ............. 6 6 General Concept ............................................ Specific_Details............................................ .7 E. EROSION CONTROL PLAN ........................................ . 9 GeneralConcept ........................................... .9 Specific Details .......... .... ........................ . 9 F. CONCLUSIONS .................................................. 10 Compliance with Standards ................................. 10 summary of Drainage Concept ............................... 10 rnmary of Erosion ControlConcept......................... 10 G. REFERENCES ................................................... 11 H. APPENDICES.................................................... Appendix 1 - Hydrologic Calculations .......................... 12 Appendix 2 - Hydraulic Calculations ........................... 13 Appendix 3 - Erosion Control Calculations ..................... 14 906 Vine Street Preliminary Drainage Report A. INTRODUCTION This report analyzes the drainage impacts of the proposed 906 Vine Drive improvements. The design considerations for this project are to provide a drainage system capable of handling runoff generated on the proposed site. In order to accomplish this, the offsite and onsite drainage areas are studied as they are impacted by the proposed project. This report was prepared following guidelines and criteria presented in the "Fort Collins Storm Drainage Criteria and Construction Standards", 1984 and the "Urban Storm Drainage Criteria Manual" (USDCM), 1992. L Location Tahe::projectis,-located in'-the7SW,quarter.of Section:.2 Township 7 North,-Range.69, West, of the Sixth Principal Meridian, City of Fort Collins, Larimer County, State of Colorado. (See Figure 1, page 3 - Vicinity Map) The project site is bounded on the south by West Vine Drive and on the east by Wood Street. A tributary of the Arthur irrigation ditch runs north along the western boundary of the property. It is then piped along the north property line. The site is approximately 4.55 acres. The 906 West Vine Drive site contains 4.55 gross acres. The site consists of an existing City of Fort Collins' maintenance and storage yard facility. An asphalt driveway adjacent to the maintenance shop provides access to West Vine Drive. Presently, this driveway is the only access to the site. Two wood fram. e buildings are located within the central portion of the site. An irrigation ditch borders the west side. Most of the site is overlain by a gravel surface material. Existing vegetation primarily consists of native grasses and weeds and scattered deciduous and coniferous trees. The soil on the site is a natural sandy lean clay. The site has moderate wind and moderate to high rain erodability, is relatively flat except for a drop off on the north side and exhibits drainage in the north direction. The majority of the property presently drains into the existing Mulligan Detention Pond at the northeast corner of the site. Although it was designed for full retention, the Mulligan Pond has an outfall pipe that drains to the recently constructed Vehicle Maintenance Facility (VMF) Detention Pond to the northeast of the site. The VMF Detention Pond has an outfall pipe which drains to the Poudre River. NOTE. The Vehicle Maintenance Facility referred to here is different from the Maintenance Shop to be remodeled in Phase 1. The VMF is located off the project site to the north: Merrick & Company Page 1 906 Vine Street Preliminary Drainage Report The proposed site improvements included in Phase 1 are remodeling the existing maintenance shop and installing a 25 space parking lot adjacent to it. The asphalt access driveway will be removed and landscaping will be installed. Also in the Phase 1 development, an asphalt road will be built running directly north from the new parking lot to the north property line where it will be connected to the Vehicle Maintenance Facility's parking lot. There is a wood frame building accompanied by a concrete pad in the path of this proposed road that will therefore be demolished. In future phases, a bus shelter, a 63 space police car parking lot, and storage facilities will all be constructed. Also in future phases, two drives will be built off of the development's road to the east where they will provide access to Wood Street. (See Site Plan) The developed site will have 10-year and 100-year composite runoff coefficients of 0.63 and 0.79, respectively. Merrick & Company Page 2 906 Vine Street Preliminary Drainage Report Scale: 1 ". = 2000' ACA-MULMAW Figure 1 Page 3 Merrick & Company 906 Vine Street Preliminary Drainage. Report B. HISTORIC DRAINAGE • r• •r i_,_ •' ' 1 ', The site is found in the North Tributary Subbasin of the major historic Old Town Basin in the area described as Sub -basin 10 in the Old Town Basin Drainage Master Plan. The portion of the major drainage basin in which this project is located is presently nearly fully developed. Major basin drainage is generally to the north and the east. The Old Town Basin drains to the Poudre River. The slopes vary across the site from very shallow to as steep as 17%,. Elevations range from 5005 It on the south to 4988 ft at the north property line. The site and the drainage basin lie entirely under the jurisdiction of the City. of Fort Collins. No flows enter the site from the north. The existing drainage pattern of most of the site is surface flow draining to the existing Mulligan Detention Pond. No drainage leaves the site to the south (Refer to the Historic Drainage Basin Map). (See Appendix 1 - Historic Runoff Calculation). Offsite Basins The proposed project will be affected by three small offsite basins. Offsite basins OS-1 and OS-2 are located to the west of the southwest comer of the project site, just west of the maintenance building. These basins presently house single family residences. Both have a developed 10-year runoff coefficient of 0.50, and a 100-year runoff coefficient of 0.63. Basin OS-3 includes the area of Vine Drive beginning at the existing onsite driveway and running west 900 feet. Basin OS-1 is 0.16 acres and has 10 and 100-year peak flows of 0.37 and 0.72 cfs. This runoff flows to the east onto the project site just south of the maintenance building. Basin OS-2 has an area of 0.96 acres. The 10 and 100-year peak flows of Basin OS-2 are 173 and 3.90 cfs. The runoff of the basin enters the site from the west side to the north of the maintenance building. Basin OS-3's surface consists completely of asphalt and therefore has a developed 10-year runoff coefficient of 0.95, and a 100-year runoff coefficient of 1.00. The 10-year and 100-year peak flows of the basin are 2.21 cfs and 3.74 cfs, respectively. Flow from this basin travels east on Vine Drive and enters the site through the existing asphalt driveway. Merrick & Company Page 4 906 Vine Street Preliminary -Drainage Report The site can be divided into two historic basins and three offste historic basins. Onsite historic basins are designated with an H, and the offsite historic basins are labeled with OS, (See Figure 1, Appendix 1 - Historic Basin Map). Historic Basin H-1 contains 2.86 acres and slopes to the north and east. The basin is defined by natural high point located in its southwest comer. An irrigation ditch runs along the west side. An asphalt.storage area. enclosed in a 7foot high chain link fence is located in the west side of the basin along with a 7 foot high dirt pile. Basin H-1 also -th-gs and concrete pon�surrounding=ahem:.:These:aretall.;. to be removed in future phases of development. The basin has a 10-year and a 100- year runoff coefficient of 0.54 and 0.68 respectively. The minor storm peak flow is 5.48 cis and the major storm flow is 12.51 cfs. Historic Basin H-2 is 1.71 acres and contains the existing maintenance shop and asphalt driveway. There are also two concrete pans in this basin. This basin has a. 10- year runoff coefficient and peak flow of 0.64 and 3.43 cfs. The 100-year runoff coefficient and peak flow are 0.80 and 8.49 cfs, respectively. Drainage from this basin flows to the north to the Mulligan Detention Pond. Currently existing on the property is the Mulligan Detention Pond. The pond's volume is 1.94 acre-feet and its surface area is 0.80 acres. This pond has been designed for full retention but has an 18 inch outfall pipe to the existing VMF Detention Pond with a. historic release rate of 5.00 cfs. This pipe has no orifice plate on it. The VMF Detention Pond has a 12" outfall pipe to the Poudre River. Runoff volume to the Mulligan Pond was predicted assuming full development of Subbasin 10. The detention pond is large enough to handle runoff from proposed development on the 906 Vine Drive site. Further development within the subbasin will require that the outfall pipes of both ponds be enlarged. C. DESIGN CRITERIA a. This report and the analysis and design of the storm drainage facilities for the 906 Vine Drive site are based upon regulations outlined in the City of Fort Collins Page 5 Merrick & Company 906 Vine Street Preliminary Drainage Report "Storm Drainage Design Criteria and Construction Standards Manual" May 1984 and Urban Drainage and Flood Control District's "Urban Storm Drainage Criteria Manual", 1989. b. "Mulfiigan Property Detention Pond Drainage Analysis and Design" prepared by Lidstone & Anderson, Inc, 1994, was reviewed to assess the condition of the existing onsite detention pond. C. Various data sheets and soils reports were used in preparation of this preliminary drainage report. Hydrologic Criteria s. The design rainfalls were determined using the "Rainfall - Intensity - Frequency for the City of Fort Collins, Colorado" (Graph included in Appendix 1) from the City's Storm Drainage Design Criteria Manual. b_ . The Rational Method was used for calculation of storm runoff associated with this development. Overland flow time of concentrations were calculated based on the "Overland Time Of Flow Curves" (included in Appendix 1) from UD&FCD's Drainage Criteria Manual. Travel times for channelized flow were calculated using the "Estimate Of Average Flow Velocity" (included in Appendix A) also from the UD&.FCD's Criteria Manual. C. The City of Fort Collins Criteria specifies detention of the 100-year (major) storm and release at the 2-year historic rate. d. The Initial (Minor) storm was calculated using the 10-year recurrence interval. for Light Industrial Land Use as required by the City of Fort Collins' Design Criteria. The Major storm was calculated using the 100-year recurrence interval. 3. Hydraulic Criteria a. The culvert pipe hydraulic capacities and swale capacities and design depths were calculated using Manning's equation. Procedures referred to in UD&FCD's Drainage criteria Manual were followed_. D. DRAINAGE PLAN General Concept This drainage design is based on the 10-year recurrence interval storm for the initial storm, and the 100-year recurrence interval storm for the major storm. Proposed site Merrick & Company Page 6 906 Vine Street Preliminary Drainage Report improvements will direct the offsite flows through the site by means of culverts and graded channels. The developed onsite flows will be directed into the graded channels where they will flow to the Mulligan Detention Pond. Disturbance and grading around the irrigation ditch and the detention pond will be minimal. 2, fipPcifiaDetails The site has been divided into seven primary onsite basins and three offsite basins. (See included Preliminary Drainage Plan). Primary basins are designated with a P, and the offsite basins are labeled with OS. Basin PA-1 consists of the southeastern pari of the site 5y Vine Drive. Basin PA-, contains 0.84 acres and contains part of the maintenance shop that is to be remodeled. Also, the 25 space parking lot with curb and gutter and landscaping are proposed for development in Basin PA-1. The proposed 10-year and 100-year runoff coefficients for the basin are 0.64 and 0.80. The basin is anticipated to create a developed peak flow for the minor storm of 2.21 cfs and 4.82 cfs for the major storm. The parking Lot will slope in from the sides to a cross pan that will run northward with a 1 % grade. This cross pan will carry flow generated in Basin PA-1 as well as flow entering the site from Offsite Basin. s OS-1 and OS-3. Flow from Basin OS-1 will be directed eastward through a small swale between the maintenance shop and a berm running east along Vine Drive. Drainage from Basin OS-3 will enter Basin PA-1 from Vine Drive, be piped under the berm, and continue to flow north to join the flow in the crosspan of the parking lot. The flow collected in the cross pan will be directed into the curb and gutter along the parking lot entrance and then into a swale at Design Point 1 that will flow eastward to Wood Street. The existing swale to the west of Wood Street will carry the flow to the detention pond. Basin PA-2 Basin PA-2 contains 0.040 acres and has 10-year and 100-year runoff coefficients of 0.84 and 1.00, respectively. The 10-year developed flow for this basin is oil cfs and the 100-year flow is 0.29 cfs at Design Point 5. The basin will be developed as a road leading west from the new parking lot to the proposed road. The road will have a 2% crown and flow will be directed from its center into a graded swale along the north side of the basin. The drainage collected in the swale will flow eastward into the swale carrying the flow of Basin PA-1 to Wood Street. I Merrick & Company Page 7