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HomeMy WebLinkAboutHANSEN (FARM) - ODP - ODP170003 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT1 Overall Drainage Report Date: July 18, 2017 Project: Hansen Overall Development Plan Fort Collins, Colorado Attn: Ms. Heather McDowell Fort Collins Utilities 700 Wood Street Fort Collins, Colorado 80524 Ms. McDowell: This letter report accompanies the submittal for the Hansen Overall Development Plan (ODP). Specifically, this letter report serves to document the overall drainage impacts associated with the proposed Hansen Development. The proposed development site is located south of the Willow Springs residential development in Fort Collins, Colorado. The site is situated south of Kechter Road, north of Zephyr Road and, west of Timberline Road. The Hansen property is bordered on the northy by the Mail Creek Ditch, on the south by an irrigation lateral, on the west by the private property and the Union Pacific Railroad, and on the east by Timberline Road. The overall Hansen site is roughly 70 acres in size. Zoning across the site includes Low-Density Mixed Use Neighborhood (LMN), Neighborhood Commercial (NC), and Medium Density Mixed-Use Neighborhood (MMN). The proposed development site is in the City of Fort Collins Fossil Creek Master Drainage Basin. Detention requirements for this basin are to detain the difference between the 100-year developed inflow rate and the historic 2-year release rate. An 18” RCP storm drain was stubbed to the site from The Timbers project. This stub is located just west of Timberline Road at Zephyr Road. The drainage report for The Timbers indicated a flow of 8 cfs allowable from the Hansen property. This is generally less than the 2-year historic for the Fossil Creek Basin. As this is the only drainage outfall for the site that does not require a drainage easement from an adjacent property, this outfall is planned to be utilized for the majority of the site. 2 This master drainage plan delineates the site into 4 basins. Approximate detention volumes are shown on the Master Drainage Plan. These volumes were calculated utilizing the Percent Imperviousness Relationship to Land Use (Table RO-14, Fort Collins Amendments to the Urban Drainage and Flood Control District Criteria Manual) and the FAA modified method. These detention volumes will be adjusted as the site further develops and proposed percent impervious are further refined with Project Development Plan submittals. Percent Impervious calculation and detention volume calculations are provided in the Appendix. Basins 1, 2, and 3 will drain into on-site detention ponds which will release into the existing 18” RCP. Basin 4 will be detained in an on-site detention pond that will release to the historic drainage route. This route will require a drainage easement from the adjacent property owner. All water quality treatment requirements and LID requirements will be satisfied with the proposed development. Means of providing for these requirements will be worked through with each respective Project Development Plan submittal. No floodplains are located on this site. In summary, this Overall Drainage Report letter adequately addresses any potential stormwater changes associated with the proposed Overall Development Plan Amendment. In general, there are no significant changes proposed at a major drainage level. The ODP complies with the governing City of Fort Collins Master Drainage Plans, and the previously approved drainage plans specific for the subject property. Please feel free to contact me with any questions you may have. Sincerely NORTHERN ENGINEERING Stephanie Thomas, PE Project Engineer Enc APPENDIX Hansen Development CHARACTER OF SURFACE 1 : Runoff Coefficient Percentage Impervious Project: Hansen LMN Zoning 0.55 60% Calculations By: S. Thomas MMN Zoning 0.65 70% Date: July 14, 2017 NC Zoning 0.95 90% Streets, Parking Lots, Roofs, Alleys, and Drives: Asphalt ……....……………...……….....…...……………….………………………………………………………….0.95 100% . Concrete …….......……………….….……….………………..….…………………………………………………….0.95 90% . Gravel (packed) ……….…………………….….…………………………..………………………………………….0.50 40% . Roofs …….…….………………..……………….……………………………………………………………………… 0.95 90% Pavers…………………………...………………..……………………………………………………………………… 0.40 22% Lawns and Landscaping Sandy Soil Flat <2% ……………………………………………………………………………………………………………… 0.10 0% Average 2% to 7% ………………………………………………………………………………………………….0.15 0% . Steep >7% …………………………………………………………………………………………………………… 0.20 0% Clayey Soil Flat <2% ……………………………………………………………………………………………………………… 0.20 0% Average 2% to 7% ………………………………………………………………………………………………….0.25 0% . Steep >7% …………………………………………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year Cf = 1.25 Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11 Sub-Basin ID Sub- BasinBasin Area (ac) Area of LMN Area of MMN Area of NC 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. 1 49.21 45.50 3.70 0.00 0.56 0.56 0.70 61% 2 14.22 1.02 12.55 0.64 0.66 0.66 0.82 70% 3 3.29 0.00 0.07 3.22 0.94 0.94 1.00 90% 4 3.10 0.00 0.00 3.10 0.95 0.95 1.00 90% 1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis Composite Runoff Coefficient with Adjustment PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS 7/14/2017 4:07 PM D:\Projects\911-015\Drainage\Hydrology\911-015_MP_Rational_Calcs.xlsx\Composite C Hansen Development 911-015 Fort Collins, Colorado S. Thomas Date: 7/14/2017 Pond No.: 1 Pond 1 100-yr 0.70 WQCV 37830 ft3 Area (A)= 49.21 acres Quantity Detention 411714 ft3 Max Release Rate = 6.2 cfs Total Volume 449544 ft3 Total Volume 10.320 ac-ft Time Time Fort Collins 100-yr Intensity Q100 Inflow (Runoff) Volume Outflow (Release) Volume Storage Detention Volume (mins) (secs) (in/hr) (cfs) (ft3) (ft3) (ft3) 5 300 9.95 342.7 102824 1860 100964 10 600 7.72 265.9 159559 3720 155839 15 900 6.52 224.6 202135 5580 196555 20 1200 5.60 192.9 231484 7440 224044 25 1500 4.98 171.5 257319 9300 248019 30 1800 4.52 155.7 280261 11160 269101 35 2100 4.08 140.5 295142 13020 282122 40 2400 3.74 128.8 309196 14880 294316 45 2700 3.46 119.2 321804 16740 305064 50 3000 3.23 111.3 333791 18600 315191 55 3300 3.03 104.4 344436 20460 323976 60 3600 2.86 98.5 354666 22320 332346 65 3900 2.72 93.7 365414 24180 341234 70 4200 2.59 89.2 374714 26040 348674 75 4500 2.48 85.4 384429 27900 356529 80 4800 2.38 82.0 393523 29760 363763 85 5100 2.29 78.9 402307 31620 370687 90 5400 2.21 76.1 411090 33480 377610 95 5700 2.13 73.4 418221 35340 382881 100 6000 2.06 71.0 425765 37200 388565 105 6300 2.00 68.9 434032 39060 394972 110 6600 1.94 66.8 441059 40920 400139 115 6900 1.89 65.1 449223 42780 406443 120 7200 1.84 63.4 456354 44640 411714 Detention Pond Calculation | FAA Method Project Number: Project Location: Calculations By: Input Variables Results Design Point Design Storm Required Detention Volume Developed "C" = 7/14/2017 4:08 PM D:\Projects\911-015\Drainage\Detention\911-015_Detention Pond Concept_Pond 1.xlsm\FAA_LarmCnty idf Hansen Development 911-015 Fort Collins, Colorado S. Thomas Date: 7/14/2017 Pond No.: 2 Pond 2 100-yr 0.82 WQCV 13967 ft3 Area (A)= 14.22 acres Quantity Detention 143677 ft3 Max Release Rate = 1.5 cfs Total Volume 157644 ft3 Total Volume 3.619 ac-ft Time Time Fort Collins 100-yr Intensity Q100 Inflow (Runoff) Volume Outflow (Release) Volume Storage Detention Volume (mins) (secs) (in/hr) (cfs) (ft3) (ft3) (ft3) 5 300 9.95 116.0 34806 450 34356 10 600 7.72 90.0 54011 900 53111 15 900 6.52 76.0 68423 1350 67073 20 1200 5.60 65.3 78358 1800 76558 25 1500 4.98 58.1 87103 2250 84853 30 1800 4.52 52.7 94869 2700 92169 35 2100 4.08 47.6 99906 3150 96756 40 2400 3.74 43.6 104664 3600 101064 45 2700 3.46 40.3 108931 4050 104881 50 3000 3.23 37.7 112989 4500 108489 55 3300 3.03 35.3 116592 4950 111642 60 3600 2.86 33.3 120055 5400 114655 65 3900 2.72 31.7 123694 5850 117844 70 4200 2.59 30.2 126842 6300 120542 75 4500 2.48 28.9 130130 6750 123380 80 4800 2.38 27.8 133208 7200 126008 85 5100 2.29 26.7 136182 7650 128532 90 5400 2.21 25.8 139155 8100 131055 95 5700 2.13 24.8 141569 8550 133019 100 6000 2.06 24.0 144123 9000 135123 105 6300 2.00 23.3 146921 9450 137471 110 6600 1.94 22.6 149300 9900 139400 115 6900 1.89 22.0 152063 10350 141713 120 7200 1.84 21.5 154477 10800 143677 Detention Pond Calculation | FAA Method Project Number: Project Location: Calculations By: Input Variables Results Design Point Design Storm Required Detention Volume Developed "C" = 7/14/2017 4:09 PM D:\Projects\911-015\Drainage\Detention\911-015_Detention Pond Concept_Pond 2.xlsm\FAA_LarmCnty idf Hansen Development 911-015 Fort Collins, Colorado S. Thomas Date: 7/14/2017 Pond No.: 3 Pond 3 100-yr 1.00 WQCV 4795 ft3 Area (A)= 3.29 acres Quantity Detention 41426 ft3 Max Release Rate = 0.3 cfs Total Volume 46221 ft3 Total Volume 1.061 ac-ft Time Time Fort Collins 100-yr Intensity Q100 Inflow (Runoff) Volume Outflow (Release) Volume Storage Detention Volume (mins) (secs) (in/hr) (cfs) (ft3) (ft3) (ft3) 5 300 9.95 32.7 9821 90 9731 10 600 7.72 25.4 15239 180 15059 15 900 6.52 21.5 19306 270 19036 20 1200 5.60 18.4 22109 360 21749 25 1500 4.98 16.4 24576 450 24126 30 1800 4.52 14.9 26767 540 26227 35 2100 4.08 13.4 28189 630 27559 40 2400 3.74 12.3 29531 720 28811 45 2700 3.46 11.4 30735 810 29925 50 3000 3.23 10.6 31880 900 30980 55 3300 3.03 10.0 32897 990 31907 60 3600 2.86 9.4 33874 1080 32794 65 3900 2.72 8.9 34900 1170 33730 70 4200 2.59 8.5 35789 1260 34529 75 4500 2.48 8.2 36716 1350 35366 80 4800 2.38 7.8 37585 1440 36145 85 5100 2.29 7.5 38424 1530 36894 90 5400 2.21 7.3 39263 1620 37643 95 5700 2.13 7.0 39944 1710 38234 100 6000 2.06 6.8 40664 1800 38864 105 6300 2.00 6.6 41454 1890 39564 110 6600 1.94 6.4 42125 1980 40145 115 6900 1.89 6.2 42905 2070 40835 120 7200 1.84 6.1 43586 2160 41426 Input Variables Results Design Point Design Storm Required Detention Volume Developed "C" = Detention Pond Calculation | FAA Method Project Number: Project Location: Calculations By: 7/14/2017 4:10 PM D:\Projects\911-015\Drainage\Detention\911-015_Detention Pond Concept_Pond 3.xlsm\FAA_LarmCnty idf Hansen Development 911-015 Fort Collins, Colorado S. Thomas Date: 7/14/2017 Pond No.: 4 Pond 4 100-yr 1.00 WQCV 4518 ft3 Area (A)= 3.10 acres Quantity Detention 38909 ft3 Max Release Rate = 0.3 cfs Total Volume 43427 ft3 Total Volume 0.997 ac-ft Time Time Fort Collins 100-yr Intensity Q100 Inflow (Runoff) Volume Outflow (Release) Volume Storage Detention Volume (mins) (secs) (in/hr) (cfs) (ft3) (ft3) (ft3) 5 300 9.95 30.8 9254 90 9164 10 600 7.72 23.9 14359 180 14179 15 900 6.52 20.2 18191 270 17921 20 1200 5.60 17.4 20832 360 20472 25 1500 4.98 15.4 23157 450 22707 30 1800 4.52 14.0 25222 540 24682 35 2100 4.08 12.6 26561 630 25931 40 2400 3.74 11.6 27826 720 27106 45 2700 3.46 10.7 28960 810 28150 50 3000 3.23 10.0 30039 900 29139 55 3300 3.03 9.4 30997 990 30007 60 3600 2.86 8.9 31918 1080 30838 65 3900 2.72 8.4 32885 1170 31715 70 4200 2.59 8.0 33722 1260 32462 75 4500 2.48 7.7 34596 1350 33246 80 4800 2.38 7.4 35414 1440 33974 85 5100 2.29 7.1 36205 1530 34675 90 5400 2.21 6.9 36995 1620 35375 95 5700 2.13 6.6 37637 1710 35927 100 6000 2.06 6.4 38316 1800 36516 105 6300 2.00 6.2 39060 1890 37170 110 6600 1.94 6.0 39692 1980 37712 115 6900 1.89 5.9 40427 2070 38357 120 7200 1.84 5.7 41069 2160 38909 Detention Pond Calculation | FAA Method Project Number: Project Location: Calculations By: Input Variables Results Design Point Design Storm Required Detention Volume Developed "C" = 7/14/2017 4:11 PM D:\Projects\911-015\Drainage\Detention\911-015_Detention Pond Concept_Pond 4.xlsm\FAA_LarmCnty idf