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Home My WebLink AboutDrainage Reports - 04/09/2003I 1 1 1 1 L 1 1 1 1 SEAR -BROWN April 9, 2003 Mr. Basil Hamdan City of Ft. Collins Stormwater Utility Department 700 Wood Street Ft. Collins, Colorado 80521 ARCHITE URI- FNGINEFUNF PLANNING CONSTRUCTION 209 South Meldwrn FOR Collin;CO 8OS21 970.4825922 phone 970.482,6368 fax www.searbrownxom RE: Addendum to Final Drainage & Erosion Control Report for the City of Ft. Collins Service Center Warehouse Storage Area, Ft. Collins, Colorado Dear Basil: We are pleased to submit for your review and approval this letter addendum. This addendum regards the design and construction of a new meter shop building at the City of Fort Collins Ufility Service Center campus as an element of a Minor Amendment submittal to the City. All computations within the original report have been completed in accordance with the City of Ft. Collins Storm Drainage Design Criteria Manual. There is no material change in the hydrologic or hydraulic design for the currently proposed improvements, and this addendum describes these improvements in more detail. We appreciate your time and consideration in reviewing this submittal. Feel free to call if you have questions regarding the findings of this addendum or the original study. ' Respectfully, The Sear -Brown Group Prepared by: Michael T. Carr, P.E. Project Manager 1 1 1 I ADDENDUM TO THE FINAL DRAINAGE AND EROSION CONTROL REPORT ' City of Fort Collins, Service Center Warehouse Storage Area Improvements, Fort Collins, Colorado April, 2003 ' I. INTRODUCTION This letter report is an Addendum to the Final Drainage Report for City of Fort Collins, Service Center Warehouse Storage Area Improvements dated August, 2002 by Sear -Brown (SB). This addendum is intended to address changes to the proposed drainage improvements represented in the approved construction plans for the City of Fort Collins, Service Center Warehouse Storage Area Improvements as represented in ' the construction plans for Fort Collins Utilities Facility Meter Shop Improvements. The project is located in the City of Fort Collins Service Center P.U.D., north of ' Elm Street, east of Wood Street in Ft. Collins, and west of Lee Martinez Park. The current project area is located in the northwestern corner of the Utilities Service Center campus. The site location can also be described as situated in the Northwest ' 1/4 of Section 11 and the Southwest '/< of Section 2, Township 7 North, Range 69 West of the 6th P.M., City of Fort Collins, Latimer County, Colorado. The project site is shown on the attached vicinity map. II. GENERAL PROJECT DESCRIPTION ' The current project consists of the removal of the existing meter shop buildings to the north of existing building B, the construction of a new meter shop building near the west property line and south of the north entrance off of Wood Street, and ' construction of asphalt parking areas where the meter shop buildings currently stand. The area where the proposed new building will be located is currently a paved parking area. A copy of the original Storm Drainage Plan showing the ' current study area is included for reference. ' The area comprised of demolition and removals and proposed building area is currently completely impervious, covered by existing buildings or paved parking/storage areas. The proposed improvements will create a small addition of ' permeable ground surface, approximately 0.13 acres or about 2% of the sub -basin 17.1 in which this area lies, thereby slightly reducing the amount of runoff. No significant changes to site topography or drainage patterns are proposed with this ' project. 1 ' Page I of 3 All previously approved and constructed improvements on this site have been in ' conformance with applicable regulations, hydrologic and hydraulic criteria, and appear to be in good condition, functioning as intended. ' III. DRAINAGE FACILITY DESIGN ASSOCIATED WITH METER SHOP IMPROVEMENTS The majority of runoff from this site of proposed improvements currently flows overland in a northeasterly direction where it is intercepted at a curb inlet and in ' conveyed the storm drainage system to the east and north and subsequently discharged to the Poudre River. This drainage regime will not be substantially changed with the proposed improvements. The area where existing buildings are ' located will be graded to match the paved parking areas to the north and east, and runoff will flow to the northeast to the existing curb inlet. An exhibit drawing, showing existing features and storm drainage piping and proposed improvements, is included with this Addendum for reference. ' A 15-inch HDPE storm drain pipe currently conveys runoff from the southwestern portion of sub -basin 17.1 through the new building. This be proposed piping will reconfigured to circumvent the proposed building. This reconfiguration does not t materially affect the function of the existing storm drainage system. A drawing, showing proposed storm drain plan and profile, is included with this Addendum for reference. ' IV. EROSION CONTROL ' The great majority of the area of proposed improvements will be covered by either the building or pavement, with the small remainder, approximately 0.13 acres, landscaped primarily with landscaping rock and shrubbery. Following ' construction, there will be no more potential for erosion than that which currently exists, which is virtually nil. ' During construction, erosion controls measures including vehicle tracking control pads, inlet filters and silt fencing will be utilized to minimize erosion. Soils exposed during construction surrounding the new building will be covered with'/4" ' to 1" washed gravel to a minimum depth of 1-1/2 inches. ' All construction activities must comply with the State of Colorado permitting process for Stormwater Discharge Associated with Construction Activity. If any dewatering is required during construction, a construction dewatering permit issued ' by the Colorado Department of Public Health and Environment will be required. 1 ' - Page 2 of 3 I 1 1 1 1 1 1 1 1 VI. 2. 0 CONCLUSION The design presented in this report and shown on the Drainage and Erosion Control Plan are in compliance with the City of Fort Collins drainage criteria and is adequate to address the stormwater management needs of the project area. REFERENCES Final Drainage & Erosion Control Report City of Fort Collins, Service Center Warehouse Storage Area Improvements, Ft. Collins, Colorado, August 2002 Update to: Final Drainage & Erosion Control Study, Ft. Collins Utility Center, PUD, 5 h Filing, Ft. Collins, Colorado, Sept. 1997 (Rev. Jan. 2000). Final Drainage & Erosion Control Study, Ft. Collins Utility Center, PUD, 51s Filing, Ft. Collins, Colorado, September 1997. Flood Insurance Rate Map Panel No. 080102-0001, FEMA, February 1984. Flood Insurance Study, City of Ft. Collins, Larimer County, FEMA, February 1984. Page 3 of 3 RAINFALL PERFORMANCE STANDARD EVALUATION 183053 Project: Fort Collins Meter Shop Utility Bldg. STANDARD FORM A Calculated By: AGW Date: 4/81200:> DEVELOPED ERODIBILITY Asp Lab Ssb Lb Sip PS SUBBASIN ZONE (ac) (ft) (%) (ft) (%) (%) 1 Moderate 0.67 240 2,63 240.0 2.6 Total 0.67 240.00 2.63 80.9 EXAMPLE CALCULATIONS Lb = sum(AiLi)/sunn(Al) = (0.10 x 10 + 0.46 x 200 + 0.13 x 230)/ 0.68 = 240.0 n Sb = sum(AiSp/sum(Ai) = (0.10 x 2.00 + 0.46 x 1.10 + 0.13 x 2.00)/ 0.68 = 2.63 % PS (during construction) = 80.9 (from Table 8A) PS (after construction) - 80.9 /0.85 = 95.1 ' 183053 EFFECTIVENESS CALCULATIONS 1 1 1 1 1 1 1 1 Project: Fort Collins Meter Shop Utility Bldg. STANDARD FORM B Calculated By. AGW Date: 4/82003 Erosion Control C-Factor P-Factor Comment Number Method Value Value 3 Bare Soil - Rough Irregular Surface 1 0.9 5 Gravel Filter 1 0.8 8 Silt Fence Barrier 1 0.5 38 Gravel Mulch 0.05 1 SUB PS AREA BASIN (%) (ac) Site 80.86 0.67 SUB SUB AREA Practice C"A P'A Remarks BASIN AREA (ac) DURING CONSTRUCTION 1 Pervious 0.27 3 0.27 0.24 Bare Soil - Rough Irregular Surface 1 Pervious 0.40 38 0.02 0.40 Gravel Mulch Cnet = 10.06x0.03+„ +0.06x0.13]/0.68 Cnet = 0.43 Pnet = [1.00x0.03+...+I.00x0.13110.68 Pnet = 0.39 EFF = (1-C-P)l00 EFF = 83.2 > 80.9 PS Before 1 I 1 ' EFFECTIVENESS CALCULATIONS 183053 1 1 1 1 1 1 Project Fort Collins Meter Shop Utility Bldg. STANDARD FORM B Calculated By: AGW Date: 4/a/2003 Erosion Control C-Factor P-Factor Comment Number Method Value Value 6 Gravel Filter 1 0.8 8 Silt Fence Barrier 1 0.5 9 Asphalt/Concrete Pavement 0.01 1 20 Sod Grass 0.01 1 SUB PS AREA BASIN (%) (ac) Site 95.13 0.67 SUB SUB AREA Practice C.A P'A Remarks BASIN AREA (ac) AFTER CONSTRUCTION 1 Impervious 0.54 9 0.0054 0.54 Asphalt/Concrete Pavement 1 Pervious 0.13 20 0.0013 0.13 Sod Grass Cnet = [0.06x0.03+...+0.06x0.13]10.68 Cnet = 0.01 Pnet = [1.00x0.03+...+1.00x.13Y0.68 Pnet = 0.43 EFF = (1-C-P)l00 EFF = 99.6 > 95.1 PS After 1 I 1 1 1 1 1 1 1 EROSION CONTROL COST ESTIMATE Project: Fort Collins Meter Shop Utility Bldg. 183053 Prepared By: AGW Date: 4/8/2003 CITY RESEEDING COST Unit Total Method Quantity Unit Cost Cost Notes Reseed/mulch 0.67 ac $655 $436.89 See Note 1. Subtotal $437 Contingency 50% $218 Total $655 Notes: 1. Ar_5 ac=$655lac; A>5 ac=$615/ac. EROSION CONTROL MEASURES Unit Total Number Method Quantity Unit Cost Cost Notes 6 Gravel Filter 2 ea $400 $800 8 Silt Fence Barrier 250 LF $3 $750 20 Sod Grass 0.13 ac $0 $0 38 Gravel Mulch 0.54 ac $1,350 $729 Subtotal $2.279 Contingency 50% $1,140 Total $3,419 Total Security $3,419 1 EROSION CONTROL CONSTRUCTION SEQUENCE STANDARDFORMIC Whimsy AGW IENCE FOR 2003 ONLY to by use of a bar line or symbols when erosion Control measures will be installed modifications to an approved schedule may require submitting a new schedule for dal by the City Engineer. YEAR 1 20W WIND EROSION CONTROL Straw Mulch Penmetor Bamer Additional Samers Vege1a0ve Methods Soil Sealant Oyler RAINFALL EROSION CONTROL STRUCTURAL'. Sediment Trap/Basin Inlet Filters Straw Banters Sit[ Fence Bamer. Sand Bags Bare Boll Preparation Contour Furrows, Terraang A.PhaIVCoovela Paving Omer - VEGETATIVE Permanent Seed Planting MulchinglSealant Temporary Seed Planlmg Sod Installation N rmargallaalslBlarakel. Other STRUCTURES. INSTALLED BY VEGETATIONIMULCHING CONTRACTOR DATE SUBMITTED 20" N I D I J I F MAINTAINED BY APPROVED BY CITY OF FORT COLLINS ON q