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Home My WebLink AboutBUCKING HORSE PARK - BDR210011 - SUBMITTAL DOCUMENTS - ROUND 4 - VARIANCE REQUEST (2) FORT COLLINS: 301 North Howes Street, Suite 100, 80521 | 970.221.4158 GREELEY: 820 8th Street, 80631 | 970.395.9880 | WEB: www.northernengineering.com ADDRESS: 200 S. College Ave. Suite 10 Fort Collins, CO 80524 PHONE: 970.221.4158 FAX: 970.221.4159 WEBSITE: www.northernengineering.com Administrative Engineering Variance Request Letter Date: March 23, 2022 Project: Bucking Horse Park Project No. 1748-002 Fort Collins, Colorado Attn: Heidi Hansen Stormwater Development Review City of Fort Collins 281 North College Avenue Fort Collins, Colorado 80524 RE: Informal Grass Buffer Dear Staff: Promoting the health, safety, welfare, and property of the City of Fort Collins and citizens through the proper control and treatment of stormwater, whether above or below surface; and, to ensure uniformity in performance with respect to design and construction of all drainage facilities are among the objectives of the Fort Collins Stormwater Criteria Manual (FCSCM) – as adopted by the City Council of the City of Fort Collins, as referenced in Section 26-500 of the Code of the City of Fort Collins December 2018. It is with those considerations in mind that this variance request letter has been prepared. This letter is provided pursuant to Chapter 2 Section 8 of FCSCM to document the site condition proposed to deviate from the current standards. The criteria in question are the requirements set forth in Chapter 7 section 6.7 of the FCSCM for “Vegetated Buffers”. Specifically, the requirements that the soils must be type A or B soils and that no cross slopes can be greater than 5% for vegetated buffers to count as LID credit. Instead, Bucking Horse Park wants to utilize Mile High Flood Control Criteria Manual 3 Chapter 4 Section T-1 Grass Buffer to size proper grass buffers that count towards LID credit. The main differences between MHFD and FCSCM when it comes to grass buffers is the soil types and the buffer slopes. MHFD does not specify that soils need to be Type A or Type B but rather that there be proper soil preparation. MHFD states; “When possible, remove, strip, stockpile, and reuse on-site topsoil.” Per the landscaping plans that is what Bucking Horse Park intends to do. However, MHFD does not specify that only soil Types A & B are suitable for effective infiltration. When it comes to vegetation requirements for grass buffers, MHFD states; “[Vegetation] is the most critical component for treatment within a grass buffer. Select durable dense, and drought tolerant grasses to vegetate the buffer. The goal is to provide a dense mat of vegetative cover. Grass buffer performance falls off rapidly as the vegetation coverage declines below 80% (Barret et al.2004). Turf grasses such as Kentucky Bluegrass are often selected due Bucking Horse Park | Variance Request | 03.23.22 P:\1748-002\Admin\Varriance Request\Old\VarianceRequest - LID Reduction.docx Page 2 of 2 ADDRESS: 200 S. College Ave. Suite 10 Fort Collins, CO 80524 PHONE: 970.221.4158 FAX: 970.221.4159 WEBSITE: www.northernengineering.com to these qualities. Dense native turf grasses may also be selected where a more natural look is desirable.” Whereas FCSCM doesn’t explicitly describe what type of vegetation is required for LID purposes, but it does state in Appendix C of FCSCM page 3-16; “Select vegetation with uniform cover characteristics. Avoid bunch type vegetation that can result in concreted flow between plants.” Therefore, irrigated sod and native turf, as shown on the landscape plans meets this requirement. Lastly, FCSCM states that for LID credit slopes cannot be greater than 5%. For the most part Bucking Horse Park has cross slopes of 1.5%, specifically, where the soccer field is going, but some locations within the park are closer to 10:1 which is still acceptable per MHFD. To offsite this increase in slope Bucking Horse Park is proposing much wider widths of grass buffers than the minimum requirements. This increase in grass buffer widths along with slopes no greater than 10:1 will offset the FCSCM requirement of a max of 5% cross slope. These increased widths with greatly increase the time that runoff is sheet flowing across these buffers. A similar project that was recently approved by the City of Fort Collins utilizing the same philosophy that Bucking Horse Park is using is Trail Head Park. Trail Head Park also did not utilize any other form of LID whereas Bucking Horse Park is also installing a Rain Garden to treat an area that has a higher concentration of impervious area (basketball court, ping-pong court, and associated sidewalks). Bucking Horse Park plans on treating 69% of the sites impervious area via LID methods. The proposed alternative design will not reduce the design life of the proposed park and will also reduce the footprint of additional alternative LID systems such as rain gardens, infiltration basins, contrasted wetlands, etc. that take up useable and desirable space within the park for community members to utilize. All the grass buffers greatly exceed the minimum grass buffer widths, see Appendix D of the Final Drainage Report Bucking Horse Park for sizing calculations. These larger widths will bolster the effectiveness of these grass buffers to promote healthy and sustainable infiltration. The landscape plans have also specified a soil amendment that will promote healthy growth for both the native sod and irrigated sod. Lastly, Bucking Horse Park has no vehicular traffic which dramatically reduces the concentrations of pollutants that migrate onto the site. Therefore, what Bucking Horse Park is proposing meets the requirements set forth by the FCSCM with regards to LID measures. Sincerely, Northern Engineering Blaine Mathisen, PE Project Engineer Attachments: - LID EXHIBIT - DRAINAGE EXHIBIT X MILES HOUSE AVE . C.O. STORM DRAIN (TYP.) SWALE (TYP.) RAIN GARDEN 11 FLAT AREA = 206 SQ. FT. MIN. AREA = 146 SQ. FT. LID EXHIBIT RAIN GARDEN AND GRASS BUFFER SUMMARY FORT COLLINS, CO BUCKING HORSE PARK E N G I N E E R N GI EHTRON R N 03.22.2022 P:\1748-002\DWG\DRNG\PARK\1748-002_PARK_LID-V2.DWG NORTH PROPOSED CONTOUR PROPOSED STORM SEWER PROPOSED SWALE EXISTING CONTOUR PROPOSED INLET LID SUMMARY: PROPERTY BOUNDARY BASIN 4 GRASS BUFFER NOTES 1.FOR LID, RAIN GARDEN, AND GRASS BUFFER CALCULATIONS PLEASE REFER TO THE FINAL DRAINAGE REPORT BUCKING HORSE PARK DATED MARCH 30, 2022. 2.REFER TO UTILITY PLANS FOR BUCKING HORSE PARK FOR ADDITIONAL GRADING AND UTILITY INFORMATION. 3.REFER TO LANDSCAPE PLANS FOR ADDITIONAL INFORMATION ON HARDSCAPES. 4.REFER TO LANDSCAPING PLANS FOR SOIL AMENDMENT NOTES. ( IN FEET ) 0 1 INCH = 100 FEET 100 100 BASIN 1 GRASS BUFFER Basin ID LID Treatment Impervious Area (i%>=90%)(sq. ft.) Impervious Area Treated By LID (sq. ft.) Percent of Impervious Treated by LID 1 Grass Buffer 2957 2586 87% 4 Grass Buffer 3688 3688 100% 5 Grass Buffer 583 583 100% 6 Grass Buffer 1923 866 45% 11 Rain Garden 6781 6781 100% 12 Grass Buffer 3127 3127 100% Total Site 25492 17631 69% LEGEND: * TOTAL PERCENT IMPERVIOUS FOR ONSITE BASINS ONLY (i) = 13% BASIN 1 IMPERVIOUS (i>=90%) AREA TREATED BY GRASS BUFFER BASIN 4 IMPERVIOUS (i>=90%) AREA TREATED BY GRASS BUFFER BASIN 5 GRASS BUFFERBASIN 5 IMPERVIOUS (i>=90%) AREA TREATED BY GRASS BUFFER BASIN 6 GRASS BUFFERBASIN 6 IMPERVIOUS (i>=90%) AREA TREATED BY GRASS BUFFER BASIN 11 RAIN GARDENBASIN 11 IMPERVIOUS (i>=90%) AREA TREATED BY RAIN GARDEN BASIN 12 GRASS BUFFERBASIN 12 IMPERVIOUS (i>=90%) AREA TREATED BY GRASS BUFFER S S S S S S S S S SWWWWW CMWWSSSSSSSSSSSSSSSS S S SS SS SS SSEWWWWWXXXX X X X X X X X X XXXX T F EXISTING DETENTION POND 215 C.O. 1 2 4 5 100' ROW GREAT WESTERN RAIL ROAD CO CO CO CO CO S S S S SSSSSSSSSSSSSCO CO CO CO COS S S S S S S SSSSSSSHYD EMILES HOUSE AVENUEPALOMINO COURT1 0.58 ac 4 0.79 ac 3 0.16 ac 5 0.40 ac 6 0.95 ac 7 0.43 ac 9 0.14 ac 10 0.39 ac 11 0.37 OS1 0.65 ac 2 0.38 ac PROPERTY BOUNDARY POUDRE RIVER 500-YR FLOODPLAIN (PER RiskMAP) PROPERTY BOUNDARY PROPERTY BOUNDARY PROPERTY BOUNDARY PROPOSED AREA DRAIN PROPOSED AREA DRAIN PROPOSED AREA DRAIN PROPOSED AREA DRAIN PROPOSED AREA DRAIN PROPOSED AREA DRAIN RE-ALIGN EXISTING SWALE 10: 1 EDGE OF WETLANDS AA8 0.56 ac 6 12 0.99 9 10 RAIN GARDEN 11 FLAT AREA = 206 SQ. FT. MIN. AREA = 146 SQ. FT. EXISTING 36" RCP CULVERT SWALE OVERTOPPING LOCATION SWALEMA X Q I N SW A L E = 3 4 1 . 1 C F S 10:1 GRASS BUFFERGRASS BUFFER GRASS BUFFER GRASS BUFFER DR1 DRAINAGE EXHIBIT18 NORTH ( IN FEET ) 1 inch = ft. Feet05050 50 100 150 SECTION A-A SWALE SUMMARY (NORMAL DEPTH): 1.REFER TO THE FINAL DRAINAGE REPORT BUCKING HORSE PARK DATED MARCH 30, 2022 FOR ADDITIONAL INFORMATION. 2.THIS PROPERTY IS CURRENTLY LOCATED IN THE FEMA MODERATE RISK FLOOD HAZARD AREA FOR THE CACHE LA POUDRE RIVER. BUT THE PROPOSED REMAPPING FROM RISKMAP WILL REMOVE ALL FLOODPLAIN DESIGNATIONS FROM THE PROJECT AREA. 3.REFER TO THE LANDSCAPE PLANS BY CITY OF FORT COLLINS FOR ADDITIONAL LANDSCAPING INFORMATION. LEGEND: PROPOSED CONTOUR PROPOSED STORM SEWER PROPOSED SWALE EXISTING CONTOUR PROPOSED CURB & GUTTER PROPERTY BOUNDARY PROPOSED INLET ADESIGN POINT FLOW ARROW DRAINAGE BASIN LABEL GRASS BUFFER PROPOSED SWALE SECTION AA CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU DIG, GRADE, OR EXCAVATE FOR THE MARKING OF UNDERGROUND MEMBER UTILITIES. CALL UTILITY NOTIFICATION CENTER OF COLORADO Know what'sbelow. before you dig.Call R SheetBUCKING HORSE PARKThese drawings areinstruments of serviceprovided by NorthernEngineering Services, Inc.and are not to be used forany type of constructionunless signed and sealed bya Professional Engineer inthe employ of NorthernEngineering Services, Inc.NOT FOR CONSTRUCTIONBLDG PERMITENGINEERNGIEHTRONRNFORT COLLINS: 301 North Howes Street, Suite 100, 80521GREELEY: 820 8th Street, 80631970.221.4158northernengineering.comof 18 10 0.37 ac BASIN DESIGNATION BASIN AREA (AC) NOTES: Design Point Basin ID Total Area (acres) C2 C100 2-Yr Tc (min) 100-Yr Tc (min) Q2 (cfs) Q100 (cfs) 1 1 0.58 0.29 0.37 6.21 6.21 0.45 2.03 2 2 0.38 0.26 0.32 7.72 7.72 0.24 1.07 3 3 0.16 0.31 0.38 5.00 5.00 0.14 0.63 4 4 0.79 0.30 0.37 11.22 11.22 0.50 2.18 5 5 0.40 0.24 0.30 11.22 11.22 0.21 0.90 6 6 0.95 0.25 0.31 11.28 11.28 0.50 2.19 7 7 0.43 0.28 0.35 10.56 10.56 0.26 1.15 8 8 0.56 0.31 0.39 10.56 10.56 0.38 1.65 9 9 0.14 0.31 0.38 5.00 5.00 0.12 0.52 10 10 0.39 0.21 0.27 5.43 5.43 0.24 1.03 11 11 0.37 0.53 0.66 5.00 5.00 0.56 2.44 12 12 0.99 0.25 0.32 11.00 11.00 0.54 2.43 os1 OS1 0.65 0.29 0.36 7.68 7.68 0.46 2.04 LID SUMMARY: MIN. TW (FT)MIN. BW (FT)MIN. D (FT)MAX D (FT)S1 S2 40 13 2.83 4.22 4 4 Basin ID LID Treatment Impervious Area (i%>=90%)(sq. ft.) Impervious Area Treated By LID (sq. ft.) Percent of Impervious Treated by LID 1 Grass Buffer 2957 2586 87% 4 Grass Buffer 3688 3688 100% 5 Grass Buffer 583 583 100% 6 Grass Buffer 1923 866 45% 11 Rain Garden 6781 6781 100% 12 Grass Buffer 3127 3127 100% Total Site 25492 17631 69% DRAINAGE SUMMARY: DRAINAGE BASIN BOUNDARY