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HomeMy WebLinkAboutFIRST CHOICE BANK - MINOR SUBDIVISION - 41-94A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTWind erosion control features will consist of the following: • The east/west irrigation channel berm along the south margin of the site. • The silt fence along the north and east margins of the site. • The temporary building.. • The main bank building. • The paved parking areas to the south and east of the temporary building. • The existing east curb of the north -bound lanes of College Avenue. • Temporary Bank Detention berm. Wind erosion control measures which will be implemented after construction will consist of mulching and seeding the bare area. Hay or straw mulch will be applied and crimped into the soil surface at a rate of 2 tons per acre after seeding of the site. INSTALLATION SCHEDULE Construction of the fill for the main bank facility is proposed to start in April 1995 and continue through September 1995 with the majority of the main bank and parking construction completed by completed July 1995. The approximate date of implementation of the erosion control measure during construction are shown on a time line spread sheet in Appendix II and on the Drainage and Erosion Control Plan. EROSION CONTROL SECURITY The erosion control security requirement for the 1ST Choice Bank main bank construction was estimated based on the specification of Section 2.0 of the Manual. The cost of the erosion control measures at the site as detailed above were estimated to cost $2,290 with a security requirement of $3,435. The estimate is detailed in Appendix II. REFERENCES 1. City of Fort Collins, Colorado, Storm Drainage Design Criteria and Construction Standards, May 1984, Revised January 1991. 1 I 1 I IPractice Factor Measures Sediment control practice measures for the 1 ST Choice Bank Construction will consist of the construction of a silt fence, gravel filter inlet and sediment trap. The location and details of the practice measures are shown on the Grading and Erosion Control Plan and Detail Sheet appended at the end of this report. Practice factor measures for the site after construction will consist of the silt fence. The silt fence will remain until the erosion controls for construction of the main bank facility are erected or until vegetation has been established. The P - Factor for the basin is presented for both the during and after construction cases on Standard Form B in Appendix II. Cover Factor Measures Cover factor measures for the site during construction will consist of the main bank building pad and the parking areas for the Temporary Bank site which will be in place at the beginning of main bank construction. The building and paved areas were assigned a C - Factor value of 0.01. Cover factor measures for the site after construction is completed will consist of the placing of sod grass and landscaping mulches. The mulched and revegetated areas were assigned C - Factor values of 0.01 as selected from the manual. Cover factor values for the paved area was not changed from during construction conditions. The calculations for the weighted C - Factor for both during and after construction are presented on Standard Form B in Appendix II. "During Construction" Effectiveness Evaluation The Net Effectiveness for the erosion control measures at the site during construction was calculated as 84.4 percent and exceeds the "During Construction" Performance Standard value of 81.0 percent. Calculations of the basin effectiveness value and the Net Effectiveness for the site are presented on Standard Form B in Appendix II. "After Construction" Effectiveness Evaluation The Net Effectiveness for the erosion control measures at the site after construction was calculated as 99.0 percent and exceeds the "After Construction" Performance Standard value of 95.3 percent. Calculations of the basin effectiveness value and the Net Effectiveness for the site are presented on Standard Form B in Appendix II. WIND EROSION ANALYSIS The surface soils at the 1 ST Choice Bank site are rated as moderately wind erodible. Construction at the site will occur during the wind season of November to May. The limited size of the construction area and the necessary access in this area will restrict the available area for placement of a wind barrier. For this reason the wind erosion features at the site will consist primarily of natural features at the site, water erosion controls and the features to be constructed. I RAINFALL EROSION ANALYSIS Site Soils The Larimer County, Soil Conservation Service Soils Report identifies the soils overlaying the site as belonging to Thedalund Loam having slight to moderate rainfall erodibility characteristics. The rainfall erosion season as detailed in the City of Fort Collins, Erosion Control Reference Manual [11 (the Manual) is between May 1 and October 31. The natural drainage of the site is from the southwest to northeast where any runoff is discharged to the south gutter flowing east along Horsetooth Road. A mixture of dryland grasses and weeds currently cover an estimated 55 percent of the site located primarily on the south side. Fifteen (15) percent of the site is covered with asphalt for the parking and access to the temporary bank site. The remaining 30 percent of the 2.17 acre property having served as a pumpkin and tree lot and parking is considered to be bare ground with sparse to no vegetation. The Manual details the site as having moderate wind erodibility characteristics. The Manual states the predominant wind direction is from the west-northwest in this area. The wind erosion season as detailed in the manual is between November 1 st and May 31 st. Construction at the site is estimated to begin in April 1995 and continue through September 1995, with the majority of the grading and fill work completed by March 1995 with the Box Culvert Installation. This schedule places the project in the rainfall season for this area and out the wind erosion season. Performance Standard The estimated "During Construction" and "After Construction" Performance Standard for the 1 ST Choice Bank Main site are 81.0 and 95.3, respectively. For the purpose of estimating the site's Performance Standard the entire site was evaluated as one, ' 2.17 acre basin. The Performance Standard for the site was estimated using the methods detailed in the Manual and the estimated, average slope length and slope for the basin. Flow lengths and slopes developed for calculation of the "During Construction" Performance Standard is presented on Standard Form A in Appendix 11. The Performance Standard I was taken from Table 5.1 of the Manual. The "After Construction" Performance Standard is calculated by dividing the "During Construction" Performance Standard by 0.85. I J I I I Details Support for the following discussion will be found in the calculations in Appendix I. The total drainable area of the historic site, the area of the compacted earth and the grassed area were measured. A composite runoff coefficient was calculated using base coefficients of 0.35 for the compacted earth and 0.20 for grassed areas. Using a time of concentration taken from overland flow curves, discharge was calculated for a 2-year event under historic conditions. A peak discharge from a two year storm was calculated to be 0.83cfs at Design Point A. As shown, Basin A includes the interior of the developed site and Basin B includes the widened portions of College Avenue and Horsetooth Road and Mitchell Drive Extension to its centerline. Except for the paved surfaces included in Basin A, the culvert over the canal along the south boundary of the site contributes little if any runoff to the site as drainage holes in the culvert roof allow seepage to flow directly into the canal. Runoff coefficients were determined for both Basin A and Basin B using base coefficients of 0.25 for grassed areas and 0.95 for impervious surfaces. A mass balance was calculated for Basin A for the 100 year event using a release rate of 0.83cfs. It was determined that this would require a pond volume of 11,239 cubic feet. Mass balances were also calculated for Basin B alone and Basin A and B combined fora 100 year event using a release rate of 0.83cfs. It was determined that Basin B alone would require a detention volume of 2135 cubic feet and the combination of Basins A and B would require a pond volume of 15,849 cubic feet. The pond volume provided by site grading is 14,454 cubic feet (calculated by the trapezoidal method). The pond volume required by adding the results of analyzing Basin A and Basin B separately, equals 13,374 cubic feet. The difference between this and the mass balance for the combination of Basin A and B results from release the effect of differing release rates. While the layout and grading of the site provides the volume to theoretically detain all the runoff from a 100 year event from Basin A and all or most of the runoff from Basin B, depending on the analytical approach, it is difficult to actually route runoff from the adjacent streets into the site and through the detention system. Therefore, the runoff from College, Horsetooth and Mitchell Drive will flow undetained to Warren Lake. To offset this the runoff from Basin A, the site interior, will be released at a maximum rate of 0.15cfs, less than the 0.83cfs historic release rate. This will be done using a 2 inch orifice and will theoretically allow the capacity of the pond to be utilized during the first three hours of a 100 year event. The detention system as designed accounts for development within the site and all or at least 90% of the adjacent street work depending on the approach to analyzing the combination of Basins A and B. Thus, it does not appear that downstream stormwater runoff conditions have been adversely impacted by the development of the 1 st Choice Bank site. The following does not have a direct impact on the foregoing. The flow in the east gutter of College Avenue south of its intersection with Horsetooth Road to its high point near Boardwalk Drive, was analyzed. The 5 foot inlet in the bridge over Canal No.2 takes about 3cfs and about 11 cfs continues to Horsetooth during a 100 year event. I ® m m i m m � � ! � � � � ® � � � � � -N V PTV V. • .. -• -- 26LL25 35 36 �P� a 1. ILI is u --------------------------------- EAST NORSETOOTH ROAD --------------------------------- OWN 1o1 CHOICE BANK OF FORT COLLINS BASIN A EXISTING tof CHOICE BANK OF FORT COLLINS DRAINAGE STUDY AND EROSION CONTROL PLAN UTILITY PLAN APPROVAL M[rID lI:�R�a� MC4o ar:�V HATER [ wwsre 5 of 12 " —.-- v.tx`x�x Road, Landings Drive and Stanford Road to Warren Lake. Some runoff from the east side of College Avenue from its high point opposite Shopko also enters this system. A part of this College Avenue runoff enters Canal No.2 where College bridges the canal . (this will be discussed separately under Drainage Design Details). The runoff from the present level of development in the area served by the described system causes flooding from time to time at the intersection of Horsetooth, Landings Drive and Stanford Road. Hydrologic Criteria The Rational Method was used to analyze the impact of the runoff from the site of interest. Calculations All calculations for this report have been made in accordance with criteria established by the City of Fort Collins. Calculations are included in Appendix I. Variances No variance is requested. DRAINAGE DESIGN Conceot The tendency for downstream flooding, as described under Development Constraints, suggests that future development in the contributing area should not aggravate this condition any more than absolutely necessary. To this end the 1 st Choice Bank site has been graded to collect runoff in the northeast corner. A part of the runoff from the street pavement and the shoulder construction along College Avenue, Horsetooth Road and Mitchell Drive adjacent to the site has also been accounted for. Water detained on site will be released to the south flow line of Horsetooth Road at less than the peak rate that would theoretically occur from the two year historic storm falling on Basin A (Basin A, Basin B and Design Point A are located on the enclosed figure and are shown at a larger scale on the Drainage Study and Erosion Control Plan contained with the Utility Drawings). The volume that will be provided in the site detention pond exceeds the volume required by established criteria (the required volume should provide for the difference in runoff from Basin A between a 100 year storm under developed conditions and a 2 year storm under historic conditions released at the historic rate). This additional volume will be utilized during the first three hours of a 100 year storm by reducing the release rate to less than the historic 2 year rate. This will be done by restricting the flow with an orifice of minimum practical size. This reduced release rate and the excess detained volume have the effect of offsetting some of the runoff that would be contributed to the system downstream by the adjacent streets in Basin B during a 100 year event: W W z z z w W > ¢ d w � � d a � a W- o a v SITE EAST HORSETOOTH ROAD [Cm .11 0 �. WARREN LAKE 1p Q \ I \ RESERVOIR Cn J � W / z l w ¢ w JHARMONY a 1 WATER FIGURE 1 Date: FEB 1995 IVASTE 1st CHOICE BANK OF FORT COLLINS SITE LOCATION MAP Project: LAND 9441 21 00 INC. FINAL DRAINAGE AND EROSION CONTROL REPORT FOR THE 1 ST CHOICE BANK PERMANENT FACILITY FORT COLLINS, COLORADO DEVELOPMENT LOCATION AND DESCRIPTION Location A new two story building is planned for a site at the southeast corner of College Avenue and Horsetooth Road as shown on the enclosed Site Location Map. The building will contain the permanent banking office of the 1st Choice Bank of Fort Collins and several retail outlets. The project is scheduled for completion in 1995. A site layout at a larger scale is shown on the Utility Drawings. The site lies in the Northeast Quarter of Section 36, Township 7 North, Range 69 West of the Sixth Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. Prooerty Description The property that the new building will occupy currently contains a trailer that the 1 st Choice Bank is using as a temporary facility to conduct business until the new building is completed. The remainder of the site is presently partially covered with grasses and is partially covered with compacted earth resulting from earlier use as a fall pumpkin and Christmas tree sales location. The site slopes from the southwest to the northeast at a gradient of approximately 2%. Runoff historically entered the south gutter area of Horsetooth Road and eventually flowed into Warren Lake Reservoir. DRAINAGE BASIN IDENTIFICATION Description The site lies in the Foothills Drainage Basin. DRAINAGE DESIGN CRITERIA Regulations The City of Fort Collins Storm Drainage Design Criteria (1 ] is being used as the basis for this report. Development Constraints The system that presently conveys and will continue to convey runoff from the site to downstream storage includes the gutters in Horsetooth Road, the piped drainage system conveying runoff from part of Horsetooth Road and from the Marriot Hotel area to Warren Lake and the piping that conveys runoff from the intersection of Horsetooth WATER WASTE & LAND INC. February 7, 1995 2629 Redwing Rd. Suite 200, Fort Collins, Colorado 80526-2879 (303)226-3535 fax (303) 226-6475 Mr.Glen D. Schlueter City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 RE: 1 ST CHOICE BANK OF FORT COLLINS PERMANENT FACILITY - FINAL DRAINAGE AND EROSION CONTROL REPORT Dear Mr. Schlueter: Transmitted herewith is a copy of the referenced report for your review and approval. The report has been prepared in accordance with the requirements of the City of Fort Collins. If you have any questions or require any modifications please call me. Thank you. Sincerely, WATER, WASTE & LAND, INC. Ma rice H. Lutkin, P.E. Manager, Civil Engineering Division Consulting Engineers and Scientists FINAL DRAINAGE AND EROSION CONTROL REPORT FOR 1 ST CHOICE BANK OF FORT.COLLINS PERMANENT FACILITY FORT COLLINS, COLORADO Prepared for: 1 st Choice Bank of Greeley 2162 35th Avenue Greeley, CO 80634 Prepared by: Water, Waste & Land, Inc. 2629 Redwing Road, Suite 200 Fort Collins, Colorado 80526 • � i ' ° %%r^ "`:�,•' February 7, 1995 =, . :`• — n� FINAL DRAINAGE AND EROSION CONTROL REPORT FOR 1ST CHOICE BANK OF FORT. COLLINS PERMANENT FACILITY FORT COLLINS, COLORADO y�ll • R III � LAND