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Home My WebLink AboutWATERGLEN SOLAR ARRAY - PDP190010 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTApril 10, 2019 DRAINAGE LETTER Waterglen Solar Array Fort Collins, Colorado Prepared for: Sandbox Solar 430 N Collage Ave, Suite 435 Fort Collins, Colorado 80524 Prepared by: 301 North Mason Street, Suite 100 Fort Collins, Colorado 80524 Phone: 970.221.4158 www.northernengineering.com Project Number: 1628-001 Drainage Letter – Waterglen Solar Array Date: April 10, 2019 Project: 150kWJ Waterglen Solar Array Project No. 1628-001 Preliminary Development Plan (PDP) Fort Collins, Colorado Attn: City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 To whom it may concern: This letter serves to address the stormwater impacts of the proposed project known as “Waterglen Solar Array”. The site is located in northeast Fort Collins and is bounded to the north and west by Larimar Weld Canal, to the south and east by an open space tract A and Rabbit Brush Park. The project site is within Tract A of the Waterglen P.U.D., which was approved in 2001, and was included in the drainage study by JR Engineering for that project. Original Drainage Patterns The original JR Engineering drainage design has Tract A and tie site area within one sub-basin, Basins E-8. In general, Basins E-8 is 7.19 acres and drained from north to south to design point 34 that outlets into two box culverts that are 3’x10’. The box culverts are sized for the 100-year storm event of 601.9 cfs and located under an emergency access road. Once captured, the flows from the basin conveyed to the south of Coopers Slough drainage. An Existing Drainage Exhibit has been provided has been provided at the back of this report for reference, along with excerpts from the original report in the appendix. Proposed Drainage Patterns The Waterglen Solar Array project conforms to the original drainage design and has proposed no change to any drainage patterns, surface slopes or imperviousness. Please see the Proposed Drainage Exhibit for more information. Site Imperviousness The total site area is approximately 25,670 SF While the drainage patterns of the proposed Waterglen solar project conform with the previously approved drainage design, access road and fencing will be installed. The emergency access road will be improved with additional road base material to meet the Poudre Fire Authority requirements. 7-foot tall fence and access gate will be installed per the City of Fort Collins requirements and security. The fence is intended to note have any negative impact on drainage flows and will allow drainage flows to pass through and positioned to minimize debris from catching on the fence. The solar panel array will be an above ground installation using helical peers. Each or the 5 rows of solar panels will have approximately 10 peers that are less than 4-inches in diameter (50 total peers = 3.5 square feet). The solar panel system will have an inverter AC combiner panel mounted on a 3’x3’ concrete pad that is outside the floodplain and 24- inches minimum above the Base Flood Elevation of 4975.49’. Since a direct comparison cannot be made between the original Final Drainage & Erosion Control Report for the Waterglen PUD and proposed solar site area, a weighted percent imperviousness has been developed. Using this approach, we find that the existing drainage conditions have a Composite Percent Imperviousness of 28.21% while the proposed project will have a Composite Percent Imperviousness of 28.18%. This is an 210kW Page | 3 overall imperviousness change of less than of 0.05%, which will result in no change in runoff from the project than the original report anticipated. Detention As shown in the analysis of overall Site Imperviousness, the proposed project will not change the imperviousness of the project site when compared to the originally approved project, thereby there will be no change to the runoff from the project site. This sites imperviousness and runoff also results do not change the required detention volume identified in the original JR Engineering report. Since detention was accounted for in the original drainage report, no additional detention is required as a part of this project, and no changes to the existing facilities are proposed. Erosion and Sediment Control During construction, the Contractor will follow the appropriate and applicable City of Fort Collins standards for erosion and sediment control. Since more less than 10,000 sf will be disturbed as a part of this project, a comprehensive Stormwater Management Plan will not be required for this project at final design. Post construction water quality and erosion control will be achieved by a fully established and stabilized site. All areas disturbed during construction will receive permanent hardscape, landscape, or building structure. Floodplains This project site is within the floodplain on FEMA FIRM map 08069C098SF dated 1/19/2006. The site area within the floodplain is in zone AE. A floodplain use permit will be required for the project. Conclusions The proposed grading matches the original drainage patterns without an overall increase to site imperviousness, so additional detention is proven to be unnecessary. Stormwater quality has been provided and meets the city requirements for Low Impact Development treatment. Therefore, it is my professional opinion that Waterglen Solar Array satisfies all applicable stormwater criteria and will effectively limit potential damage associated with stormwater runoff. Please do not hesitate to contact me if you have questions or require additional information. Sincerely, Isaac Tiley Project Engineer, PE ATTACHMENT 1 PREVIOUS REPORT – FINAL DRAINAGE AND EROSION CONTROL REPORT – WATERGLEN, P.U.D. By JR Engineering, Ltd. Dated August 11, 1997 (revised November 6, 1998) ATTACHMENT 2 DRAINAGE CALCULATIONS & DRAINAGE EXHIBITS X X X X X X X X X X 1 077 UICV -Utility.Irrigation.Control Valve 4977.72 1095 UICV -Utility.Irrigation.Control Valve 4977.60 1096 UICV -Utility.Irrigation.Control Valve 4976.94 1105 UICV -Utility.Irrigation.Control Valve 4976.96 1737 UICV -Utility.Irrigation.Control Valve 4974.19 1738 UICV -Utility.Irrigation.Control Valve 4974.17 6" 3" 6" 6" 24" 1818 LWT1 B 4981.63 1819 LWT1 RBRK1 1820 4981.67 LWT1 RBRK1 4981.66 1821 LWT1 4981.65 24HX48W" RCP I.E.= 4979.01 D RIM=4982.61 I.E.()(0" xxx)=4982.6 1838 UICV -Utility.Irrigation.Control Valve 4980.53 1845 UICV -Utility.Irrigation.Control Valve 4981.14 1858 INV 4979.27 5741 SI -Sign.Information 4984.50 5742 SI -Sign.Information 4984.42 5743 SI -Sign.Information 4984.56 5744 SI -Sign.Information 4984.46 5745 SI -Sign.Information 4984.41 5746 SI -Sign.Information 4984.38 5747 SI -Sign.Information 4984.38 5748 SI -Sign.Information 4984.36 5201 WATER ELEV 4973.59 5618 LCS1 B -Landscape.Concrete.Slab 4982.08 5619 LCS1 -Landscape.Concrete.Slab 4982.44 5620 LCS1 -Landscape.Concrete.Slab 4982.37 5621 LCS1 CL -Landscape.Concrete.Slab 4981.97 5648 UICV -Utility.Irrigation.Control Valve 4982.465649 UICV -Utility.Irrigation.Control Valve 4982.35 5666 UICV -Utility.Irrigation.Control Valve 4982.93 5672 UICV -Utility.Irrigation.Control Valve 4984.98 6" 6" 6" 6" 5564 UICV -Utility.Irrigation.Control Valve 4984.30 5588 UICV -Utility.Irrigation.Control Valve 4982.43 5591 UICV -Utility.Irrigation.Control Valve 4981.09 5594 UICV -Utility.Irrigation.Control Valve 4980.53 5596 UICV -Utility.Irrigation.Control Valve 4980.42 5597 UICV -Utility.Irrigation.Control Valve 4980.19 200 MCP -Monument.Control Point 4981.59 G G G G X X X X OHE OHE OHE OHE 1941 UWV -Utility.Water.Valve 4973.93 1943 UWFH UWU1 -Utility.Water.Fire Hydrant 4974.72 1953 UPSL UEU1 -Utility.Pole.Street Light 4972.92 1954 UPSL UEU1 -Utility.Pole.Street Light 4972.92 1959 UGU1 B 4973.88 1960 UGU1 4974.43 1961 UGU1 4974.69 1964 UGU1 4974.64 1965 UGU1 4974.80 S 2055 UGU1 4974.96 2056 UGU1 UGU2 B 4974.95 2057 UGU2 4975.78 2058 UGU1 4974.58 2059 UGU1 4975.19 2060 UGU1 UGU2 B 4975.21 2061 UGU2 4975.85 2062 UGU1 4974.20 2063 UGU1 4974.52 2064 UGU1 4974.37 2065 UGU1 4974.78 2066 UGU1 4973.98 W 2074 UWM UWU1 -Utility.Water.Meter W 2076 4975.57 UWM -Utility.Water.Meter 4975.06 3" 12" 15" 15" 5513 LCS1 -Landscape.Concrete.Slab 4979.02 5514 LCS1 LCS2 -Landscape.Concrete.Slab 4979.07 S RIM=4977.84 I.E.()(0" PVC)=4965.6 I.E.()(0" PVC)=4965.7 6" 6" 6" 12" 5817 18" VOID 4977.38 18" SS SS SS SS SS SS SS SS 2557 LWT1 B 4981.63 2558 LWT1 RBRK1 2559 4981.67 LWT1 RBRK1 4981.66 2560 LWT1 4981.65 2586 MF 1IN ALCAP ILL -Monument.Found 4980.05 2589 MF 1IN ALCAP 24307 -Monument.Found 4979.99 2590 MF 1IN ALCAP 24307 -Monument.Found 4976.87 5929 LCS1 B -Landscape.Concrete.Slab 4982.08 5930 LCS1 -Landscape.Concrete.Slab 4982.44 5931 LCS1 -Landscape.Concrete.Slab 4982.37 5932 LCS1 CL -Landscape.Concrete.Slab 4981.97 2615 MF 1.5 IN ALCAP ILL -Monument.Found 4976.89 2655 UGU1 B 4973.88 2656 UGU1 4974.43 2657 UGU1 4974.69 2660 UGU1 4974.64 2661 UGU1 4974.80 2665 UGU1 4974.96 2666 UGU1 UGU2 B 4974.95 2667 UGU2 4975.78 2668 UGU1 4974.58 2669 UGU1 4975.19 2670 UGU1 UGU2 B 4975.21 2671 UGU2 4975.85 2672 UGU1 4974.20 2673 UGU1 4974.52 2674 UGU1 4974.37 2675 UGU1 4974.78 2676 UGU1 4973.98 6184 LCS1 -Landscape.Concrete.Slab 4979.02 6185 LCS1 LCS2 -Landscape.Concrete.Slab 4979.07 OHE OHE OHE OHE OHE OHE X X X X X X X X X X 1 077 UICV -Utility.Irrigation.Control Valve 4977.72 1095 UICV -Utility.Irrigation.Control Valve 4977.60 1096 UICV -Utility.Irrigation.Control Valve 4976.94 1105 UICV -Utility.Irrigation.Control Valve 4976.96 1737 UICV -Utility.Irrigation.Control Valve 4974.19 1738 UICV -Utility.Irrigation.Control Valve 4974.17 6" 3" 6" 6" 24" 1818 LWT1 B 4981.63 1819 LWT1 RBRK1 1820 4981.67 LWT1 RBRK1 4981.66 1821 LWT1 4981.65 24HX48W" RCP I.E.= 4979.01 D RIM=4982.61 I.E.()(0" xxx)=4982.6 1838 UICV -Utility.Irrigation.Control Valve 4980.53 1845 UICV -Utility.Irrigation.Control Valve 4981.14 1858 INV 4979.27 5741 SI -Sign.Information 4984.50 5742 SI -Sign.Information 4984.42 5743 SI -Sign.Information 4984.56 5744 SI -Sign.Information 4984.46 5745 SI -Sign.Information 4984.41 5746 SI -Sign.Information 4984.38 5747 SI -Sign.Information 4984.38 5748 SI -Sign.Information 4984.36 5201 WATER ELEV 4973.59 5618 LCS1 B -Landscape.Concrete.Slab 4982.08 5619 LCS1 -Landscape.Concrete.Slab 4982.44 5620 LCS1 -Landscape.Concrete.Slab 4982.37 5621 LCS1 CL -Landscape.Concrete.Slab 4981.97 5648 UICV -Utility.Irrigation.Control Valve 4982.465649 UICV -Utility.Irrigation.Control Valve 4982.35 5666 UICV -Utility.Irrigation.Control Valve 4982.93 5672 UICV -Utility.Irrigation.Control Valve 4984.98 6" 6" 6" 6" 5564 UICV -Utility.Irrigation.Control Valve 4984.30 5588 UICV -Utility.Irrigation.Control Valve 4982.43 5591 UICV -Utility.Irrigation.Control Valve 4981.09 5594 UICV -Utility.Irrigation.Control Valve 4980.53 5596 UICV -Utility.Irrigation.Control Valve 4980.42 5597 UICV -Utility.Irrigation.Control Valve 4980.19 200 MCP -Monument.Control Point 4981.59 G G G G X X X X OHE OHE OHE OHE 1941 UWV -Utility.Water.Valve 4973.93 1943 UWFH UWU1 -Utility.Water.Fire Hydrant 4974.72 1953 UPSL UEU1 -Utility.Pole.Street Light 4972.92 1954 UPSL UEU1 -Utility.Pole.Street Light 4972.92 1959 UGU1 B 4973.88 1960 UGU1 4974.43 1961 UGU1 4974.69 1964 UGU1 4974.64 1965 UGU1 4974.80 S 2055 UGU1 4974.96 2056 UGU1 UGU2 B 4974.95 2057 UGU2 4975.78 2058 UGU1 4974.58 2059 UGU1 4975.19 2060 UGU1 UGU2 B 4975.21 2061 UGU2 4975.85 2062 UGU1 4974.20 2063 UGU1 4974.52 2064 UGU1 4974.37 2065 UGU1 4974.78 2066 UGU1 4973.98 W 2074 UWM UWU1 -Utility.Water.Meter W 2076 4975.57 UWM -Utility.Water.Meter 4975.06 3" 12" 15" 15" 5513 LCS1 -Landscape.Concrete.Slab 4979.02 5514 LCS1 LCS2 -Landscape.Concrete.Slab 4979.07 S RIM=4977.84 I.E.()(0" PVC)=4965.6 I.E.()(0" PVC)=4965.7 6" 6" 6" 12" 5817 18" VOID 4977.38 18" SS SS SS SS SS SS SS SS 2557 LWT1 B 4981.63 2558 LWT1 RBRK1 2559 4981.67 LWT1 RBRK1 4981.66 2560 LWT1 4981.65 2586 MF 1IN ALCAP ILL -Monument.Found 4980.05 2589 MF 1IN ALCAP 24307 -Monument.Found 4979.99 2590 MF 1IN ALCAP 24307 -Monument.Found 4976.87 5929 LCS1 B -Landscape.Concrete.Slab 4982.08 5930 LCS1 -Landscape.Concrete.Slab 4982.44 5931 LCS1 -Landscape.Concrete.Slab 4982.37 5932 LCS1 CL -Landscape.Concrete.Slab 4981.97 2615 MF 1.5 IN ALCAP ILL -Monument.Found 4976.89 2655 UGU1 B 4973.88 2656 UGU1 4974.43 2657 UGU1 4974.69 2660 UGU1 4974.64 2661 UGU1 4974.80 2665 UGU1 4974.96 2666 UGU1 UGU2 B 4974.95 2667 UGU2 4975.78 2668 UGU1 4974.58 2669 UGU1 4975.19 2670 UGU1 UGU2 B 4975.21 2671 UGU2 4975.85 2672 UGU1 4974.20 2673 UGU1 4974.52 2674 UGU1 4974.37 2675 UGU1 4974.78 2676 UGU1 4973.98 6184 LCS1 -Landscape.Concrete.Slab 4979.02 6185 LCS1 LCS2 -Landscape.Concrete.Slab 4979.07 OHE OHE OHE OHE OHE OHE LANDSCAPE CONCRETE GRAVEL SURFACE AREA (SF) % IMPERV. IMPERV. AREA (SF) 0 0 9,095 2% 90% 40% TOTALS 42,500 TOTAL= 11,989 LANDSCAPE CONCRETE GRAVEL SURFACE AREA (SF) % IMPERV. IMPERV. AREA (SF) 25,168 20 17,312 TOTALS 42,500 TOTAL= 11,977 EXISTING PROPOSED P:\1628-001\DWG\ENGINEER\ISAAC\1628-001_IMPERVIOUS.DWG WATERGLEN SOLAR SITE FORT COLLINS COLORADO 301 N. Howes Street, Suite 100 Fort Collins, Colorado 80521 E NGINEER ING N O R T H E RN PHONE: 970.221.4158 www.northernengineering.com DESCRIPTION EXISTING VS. PROPOSED IMPERVIOUS AREA DRAWN BY I. TILEY DATE APRIL 10, 2019 PROJECT 1628-001 SK-C1 SCALE DRAWING 1"=80' NATIVE DIRT 33,405 25% NATIVE DIRT 0 2% 90% 40% 25% 0 0 0 5,034 18 3,638 6,925 8351 COMPOSITE IMPERVIOUSNESS = 28.21% COMPOSITE IMPERVIOUSNESS = 28.18%