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Home My WebLink About17 - Design Report - Northwestern Energy Facility Renovation - Storm S A N D E R S 0 N t!•� STEWART October 17, 2017 Project No. 17032 STORM DRAINAGE PLAN FOR C/S 157 A - NORTHWESTERN ENERGY FACILITY RENOVATION BOZEMAN, MONTANA OVERVIEW NARRATIVE The purpose of this drainage plan is to quantify storm drainage improvements required for the proposed building additions on the NorthWestern Energy property at 121 E Griffin Drive in Bozeman, Montana. The approximately 15-acre lot will include two (2) new building additions, a new customer parking area and a new employee parking area. Additional improvements will include new drive aisles, sidewalks,landscape and utilities. Generally, the storrriwater runoff within the apartment complex will be conveyed via inlets and pipes to one large infiltration basin located in the northwest corner of the property. Under a separate project a new road is being constructed from Manley Road, south of the pond, to the East Gallatin Recreation Center's parking lot. The preliminary road layout is delineated within the sheets of the attached plan set. The new road will allow new access points for Mergenthaler (NorthWestern Energy's neighbor to the west) and the City of Bozeman (NorthWestern Energy's neighbor to the north). As a result of this project, the stormwater runoff from Mergenthaler's property, a portion of Manley Road, a portion of E Griffin Drive, NorthWestern Energy's property, a portion of the property to the east of NorthWestern Energy and the City of Bozeman's property will all be diverted into the exiting infiltration basin on Northwestern Energy's property. This report presents a summary of calculations performed to quantify the stormwater runoff for the improved site. All design criteria and calculations are in accordance with The City of Bo.Zeman Design Standards and Specifications Policy, dated March 2004. The site stormwater improvements have been designed with the intent to meet the current City of Bozeman drainage regulations for the entire site to the extent feasible. To Plan and Design Fk119TFIRM IV Enduring Eommunities... www. sandersonstewart. com Specific site information and criteria are described below: I. Project Information A. Address: The physical address for the site is 121 E Griffin Drive, Bozeman, MT 59718 B. Legal Description: Tract 91-94 and COS No.157A C. Total Area: The analysis area of the site is approximately 27.55 acres. The total areas below do not align with the existing property area due to the new road configuration. North`y/estern Energy and Griffin: 14.00 acres Mergenthaler: 4.4 acres New Road &Manley: 3.46 acres City of Bozeman: 4.74 acres Property East of NWE: 0.93 acres Total: 27.55 acres D. Existing Impervious Area: Northwestern Energy and Griffin: 11.32 acres Mergenthaler: 3.83 acres New Road&Manley: 0.303 acres City of Bozeman: 4.74 acres Property East of NWE: 0.93 acres Total: 21.1 acres E. Post-Development Impervious Area (Gravel/Asphalt/Concrete/Roofs): As a result of the development, the site will exhibit the following qualities: Northwestern Energy and Griffin: 12.78 acres Mergenthaler: 3.83 acres New Road&Manley: 1.82 acres City of Bozeman: 4.74 acres Property East of NWE: 0.93 acres Total: 24.1 acres F. Type of Development: The development will be warehouses and office space. II. A. General Design 1. The existing discharge point for all five areas is the East Gallatin Recreation Center Pond. With the construction of the new road the proposed discharge V:17032_NWE_Storm_Drainage_Plan_101617_SC 2 (10/16/17)SN/jil location will be into a roadside drainage ditch that will convey flow into an existing swale that discharges into the East Gallatin River. 2. The stormwater facilities are designed to remove pollutants such as solids, silts, oils, and greases. There is no oil/water separator required on site. The infiltration basin will allow for large particles to settle and filter any smaller particles through infiltration. 3. Storm Sewers: a. Alignment between manholes is generally straight. ' b. Storm sewer systems are designed slope and pipe diameter as to ensure a velocity of 3-fps. C. Pond inlets and outlets will be protected with riprap to prevent erosion as shown on the Grading Plan. d. The storm sewers within the public access easement of the new road will be maintained by the City of Bozeman. Pipe material will either be RCP or PVC. The minimum pipe size of 12-inch for inlet structures and 15-inch for all other structures has been observed. e. The stormwater conveyance system on site is designed to convey the 25-year storm event. f. All inlets and manholes have a 9-inch sump for sediment collection as shown on the Grading Plan. 4. The redevelopment project is greater than one acre and therefore will infiltrate runoff generated from the first 0.5-inches of rainfall from a 24-hour storm. This drainage report calls to infiltrate the entire 10-year, 2-hour storm event. As part of the new road an outlet structure will be installed in the infiltration basin to discharge runoff volumes above the 0.5-inch of rainfall. B. Storm Drainage Plan 1. See the attached Figure 1 that shows the watershed delineation and area. See grading plan in attached plan set for the complete drainage plan. Figure 2 shows a more detailed breakdown of the watersheds within Northwestern Energy's property. 2. One-foot contours have been displayed on the Grading Plan of the corresponding plan set. 3. The ultimate destination of the stormwater runoff from the five areas is the East Gallatin River. It is not expected that the increased runoff from the new road and site improvements will have negative impacts on the downstream drainage facilities. 4. A summary of the results of the drainage calculations are provided below and the detailed calculations are included in Appendix B. V:17032_NwE_Storm_Drainage_Plan_101617_SC 3 (10/16/17)SN/jIl 5. A maintenance plan for the infiltration basins has been included in Appendix C. 6. See grading, drainage and detail plan within the plan set for details and specifications for all storm drainage improvements. C. Storage/Treatment Facilities As outlined in the geotechnical report attached, the boring closest to the infiltration basin, B-6, shows poorly graded gravel with clay and sand at approximately 4.5 feet. The bottom of the infiltration basin will key into these gravels and an infiltration rate of 3.42 inches/hour which is the average infiltration rate between GP and GC soils. The infiltration basin located in the northwest corner of NorthWestern Energy's property provides 72,126 CF of storage. Based on the runoff calculations provided in the appendix, the required storage volume needed is 47,187 CF. The infiltration basin will have three outfalls, only one outfall will be constructed under this project. Currently, there is an existing outfall structure that discharges excess runoff from the pond to the pond within the East Gallatin Recreation Center, as requested by the City, this outlet structure will be removed and the pond will be given an alternative discharge point. Until the new road is constructed, runoff that enters the pond will infiltrate, theoretically, the pond will completely infiltrate within 20 hours after the storm event. Runoff, from a storm event that produced over 72,126 CF of runoff, will overtop the pond and discharge into the pond within the East Gallatin Recreation Center. When the new road is built, a discharge structure will be constructed in the pond which will discharge water to the new roadside ditch which will convey water to the existing swale located adjacent to the park. This swale discharges water into the East Gallatin Recreation Center. 1. The proposed detention basin will be reconstructed within the existing detention basin, and will utilize the existing basin as much as possible. 2. The new infiltration pond will have 4:1 side slopes and a depth of 5 feet, however there is a fence around NorthWestern Energy's laydown yard where the pond is located. 3. The infiltration basin is located on NorthWestern Energy's property in the far northwest corner of the site. 4. Basin Characteristics a. The proposed detention basin lengths are designed to be approximately three times the width. The basin is 151 feet long and 57 feet wide. Inlet velocities to the basins will be dissipated with riprap. b. The proposed basin side slopes are designed to have a 4:1 side slope. W7032_NWE_Storm_Drainage_Plan_101617_SC 4 (10/16/17)SN/j C. Vegetated channels will be utilized to convey water for the new road, details on the new road drainage will be given in the drainage report for that project submittal. d. The detention basins on site are not located in a floodplain. e. Spill points and overflows have been designed around the site in order to limit any potential flooding damage. 5. The rational method has been used to calculate all peak flows and retention volumes. See Appendix B for detailed calculations on retention volumes. D. Discharge Structure 1. A flared end section with a trash rack is used as a discharge structure to the basin displayed in the City of Bozeman Standard Modification Storm Drain Debris Rack No.02720-11. A manhole discharge structure will be installed with the construction of the new road. 2. An orifice equation was not used for this stormwater management plan as no complex discharge structure has been proposed. 3. Failsafe a. Spill points have been designed around the site as emergency overflows in the event of a design storm exceeding the 25-year storm event. b. The discharge pipe is a minimum of 12 inches in diameter C. All stormwater systems onsite have been designed to avoid long-term standing water. However, the infiltration basin will have no real discharge structure until the completion of the new road so there is a potential for standing water. E. Runoff Estimation 1. The modified rational method was used to determine peak runoff rates. a. It was assumed the rainfall is uniformly distributed over the area for the entire duration of the storm. The rational formula provided in The City of&Zenian Standard Specifications and Policy was used to calculate the peak runoff rates on site. The rainfall intensity for the site was calculated in part by using Figure I-2 and I-3. b. The peak runoff rate occurs when the duration of the storm equals the time of concentration. The provided time of concentration tools, Table I-2, Table I-3 and Figure I-1, in The City of Bo�eman's Design Standard and Specifications Policy were used to calculate the time of concentration for each of the major watersheds. C. The runoff coefficient for a particular watershed is constant for a similar land use. The runoff coefficients provided in Table I-1 were used in calculating the peak runoff rates. V:17032_N%VE_Storm_Drainag(�_Plan_101617_SC 5 (10/16/'17)SN/jU 2. As mentioned above, runoff coefficients from Table I-1 were used to calculate runoff rates for each of the watersheds. 3. As mentioned above, time of concentration was determined, as outlined in The City of Bo:�e&lan Design Standards and Specfcatioil Policy, as a function of the ground slope, roughness, and hydraulic radius. The time of concentration included durations from sheet flow, shallow concentrated flow and channel flow. 4. The stormwater system is designed to convey the peak flows from the 25- year storm event. The infiltration basin has been designed for the 10-year, 2- hour storm event. F. Conveyance Facilities All proposed drainage facilities have been designed to accommodate the 25-year storm event. Please see sizing calculations included in the Appendix of this report for additional information. V:17032 NWE_Storm_Drainage_Plan_101617_SC 6 (10/16/17)SN/jil APPENDIX A: WATERSHEDS - EAST SIT O" b �4 3 - . 1 lb i P - O tw . � 16 � e ♦ � Mr Z _ a ,4 w 11 2 Y s�- 3 8 4 APPENDIX B: CALCULATIONS Table 1:Watershed Properties Watershed Total Area(SF) Impervious Area Pervious Area Time of 25-year (SF) (SF) Concentration Peak Runoff 1 27,909 25,131 2,778 10 min 1.44 2 13,686 13,504 182 10 min 0.76 3 13,918 1,745 12,173 10 min 0.25 4 20,579 11,724 8,855 5 min �1.04 5 14,26'1 11,385 2,876 5 min 1.05 6 4,935 4,397 538 5 min 0.39 7 2,612 2,602 10 5 min 0.03 .___... ....._...__.._...------...._._..___._, _ _.___._.___._... 8 30,608 15,617 14,991 5 min 1.G5 9 5,164 4,367 797 5 min 0.40 10 1,495 - 1,495 5 min 0.03 11 4,330 _._._.. _ 1,380 2,950 5 min 0.18 12 39,273 39,273 - 5 min 3.42 ._......._..-_......................_......---....._..._................._..._........__._._...._...._...... --.... 13 94,802 18,216 76,586 15 min 2.98 14 63,841 - 63,841 15 min 1.83. _._._15--- - y38,231 - 38,231 15 min 1.10 16 212,405 39,706 172,699 15 min 6.67 Pond 22,770 22,770 5 min 1.23 .._...._._._......_......... ._....___.. Total 610,819 Project:Northwestern Energy Addition : i Project#: 0 t Date:10/16/2017 SANDERSONW50 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E A R T Overall Watershed Design Storm Frequency= 10 years Infiltration Unit Width(ft) Unit Length(ft) Rate Discharge Rate(cfs) (in/hr) Discharge Rate,d= 0.68 cfs 57 151 3.42 0.6813875 Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 felacre) C Cf C x Cf C' C'x A Surface Type (ft') Acres =(C x C�<or=t Acres Impervious 374705 8.60 0.9 1 0.90 0.90 7.741838843 Landscape 149568 3.43 0.2 1 020 0.20 0.686721763 Gravel 675954 15.52 0.6 1 0.60 0.60 9.310661157 0 1 0.00 0.00 0 0 1 0.00 0.00 0 Totals 1200227 275534 ]7.7392 Weighted Runoff Coefficient,Cwd SCiAi _ - 0.6438 C,a x Cr= 0.64 SAi C,d x Cfx SAi= 17.74 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=7rr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =C-x SAi x i x t =d x t =Runoff Volumc-Discharge Volumc =C W x SAj x i (min) (in/hr) (h3) (ft') (ft3) (ft3/S) 1 9.16 9751.34 40.88 9710.45 162.52 5 3.22 17127.88 204.42 16923.46 57.09 10 2.05 21830.52 408.83 21421.69 36.38 15 1.58 25159.15 613.25 24545.91 27.95 20 131 27824.32 817.67 27006.66 23.19 25 1.13 30084.52 1022.08 29062.44 20.06 30 1.00 32066.87 1226.50 30840.37 17.81 35 0.91 33844.49 1430.91 32413.57 16.12 40 0.83 35463.79 1635.33 33828.46 14.78 45 0.77 36956.30 1839.75 3511655 13.69 50 0.72 38344.55 2044.16 36300.38 12.78 55 0.68 39645.24 2248.58 37396.66 12.01 60 0.64 40871.17 2453.00 38418.17 11.35 75 0.55 44191.17 3066.24 41124.93 9.82 90 0.49 47103.04 3679.49 43423.55 8.72 105 0.44 49714.19 4292.74 45421.45 7.89 120 0.41 52092.78 4905.99 47186.79 7.24 150 0.35 56324.33 6132.49 50191.84 6.26 180 031 60035.69 7358.99 52676.70 5.56 360 0.20 76519.12 14717.97 61801.15 3.54 720 0.13 97528.26 29435.94 69092.32 2.26 1440 0.08 124305.68 58871.88 47,186.79 ft3 162.52 (ft3/s) Project:Northwestern Energy Addition QVI- RATIONAL � Project#: 6/2 17 S A N D E R S O N Date:10/16/2017 METHOD FOR RUNOFF CALCULATIONS S T E WA R T Watershed 1 Design Storm Frequency= 25 years Discharge Rate,d= Ocfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 felacre) C Cf C X Cf Ct Ct X A Surface Type (ft) Acres =(c x c�<or=1 Acres Impervious 25131 0.58 0.9 1.1 0.99 0.99 0.571159091 Landscape 2778 0.06 0.2 1.1 0.22 0.22 0.014030303 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 27909 0.6407 NOW 0.5852 Weighted Runoff Coefficient,C«.d - SCiAi - - 0.8303 C�„d x Cf= 0.91 SAi CwdxCfxSAi= 0.59 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=7rr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =c.,x sA x i x t =(l3X t Runoff"Volume-Discharge Volume =cwd x sAj x i (min) (in/hr) (ft3) (ft 1 (ft) (ft3/o 1 10.72 376.32 0.00 376.32 6.27 5 3.83 671.72 0.00 671.72 2.24 10 2.46 862.10 0.00 862.10 1.44 15 1.89 997.59 0.00 997.59 1.11 20 1.58 1106.45 0.00 1106.45 0.92 25 1.37 1199.00 0.00 1199.00 0.80 30 1.22 1280.33 0.00 1280.33 0.71 35 1.10 1353.39 0.00 1353.39 0.64 40 1.01 1420.04 0.00 1420.04 0.59 45 0.94 1481.55 0.00 1481.55 0.55 50 0.88 1538.82 0.00 1538.82 0.51 55 0.82 1592.54 0.00 1592.54 0.48 60 0.78 1643.21 0.00 1643.21 0.46 75 0.68 1780.66 0.00 1780.66 0.40 90 0.60 1901.46 0.00 1901.46 0.35 105 0.55 2009.96 0.00 2009.96 0.32 120 0.50 2108.94 0.00 2108.94 0.29 150 0.43 2285.35 0.00 2285.35 0.25 180 0.39 2440.38 0.00 2440.38 0.23 360 0.25 3132.05 0.00 3132.05 0.15 720 0.16 4019.75 0.00 4019.75 0.09 1440 0.10 5159.05 0.00 2,108.94 ft3 1.44 (£t3/s) Project:Northwestern Energy Addition AM' Project 11;1703 S A N D E R S O N W40 Date:10/16/2017 17 RATIONAL METHOD FOR RUNOFF CALCULATIONS T E A R T Watershed 2 Design Storm Frequency= 25 years Discharge Rate,d= �cfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 fJ/aorc) C C, C X C f C' C'X A Surface Type (ft2) Acres =(c x ca<or=t Acres Impervious 13504 0.31 0.9 1.1 0.99 0.99 0.306909091 Landscape 182 0.00 0.2 1.1 0.22 0.22 0.000919192 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 13686 0.3142 0.3078 Weighted Runoff Coefficient,C«.d SCIAi _ = 0.8907 C'd x Cr= 0.98 SAI C_l x Cr x SAI= 0.31 Where CI is the adjusted runoff coefficient for surface type j is the area of surface type j and Ai A=7rr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =c,,,x sA;x i x t =d x t =Runoff Volume-Discharge volume =Z x sAl x (min) (in/hr) (ft) (ft) (ft) (ft'/s) 1 10.72 197.96 0.00 197.96 3.30 5 3.83 353.35 0.00 353.35 1.18 10 2.46 453.49 0.00 453.49 0.76 15 1_89 524.76 0.00 524.76 0.58 20 158 582.03 0.00 582.03 0.49 25 1.37 630.71 0.00 630.71 0.42 30 1.22 673.50 0.00 673.50 0.37 35 1.10 711.93 0.00 711.93 0.34 40 1.01 746.99 0.00 746.99 0.31 45 0.94 779.34 0.00 77934 0.29 50 0.88 809.47 0.00 809.47 0.27 55 0.82 837.73 0.00 837.73 0.25 60 0.78 864.38 0.00 86438 0.24 75 0.68 936.68 0.00 936.68 0.21 90 0.60 1000.23 0.00 1000.23 0.19 105 055 1057.30 0.00 1057.30 0.17 120 0.50 1109.37 0.00 1109.37 0.15 150 0.43 1202.16 0.00 1202.16 0.13 180 039 1283.72 0.00 1283.72 0.12 360 0.25 1647.56 0.00 1647.56 0.08 720 0.16 2114.52 0.00 2114.52 0.05 1440 0.10 2713.82 0.00 1,109.37 fe 0.76 (ft'/s) Project:Northwestern Energy Addition QVIK Project#: SANDERSON Date:10/16/2017 017 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E A R T Watershed 3 Design Storm Frequency= 25 years Discharge Rate,d= �cfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 felacre) C Cf C X C f C' C'X A Surface Type (ft) Acres =(C x Co<or=r Acres Impervious 1745 0.04 0.9 1.1 0.99 0.99 0.039659091 Landscape 12173 0.28 0.2 1.1 0.22 0.22 0.061479798 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 13918 0.3195 0.1011 Weighted Runoff Coefficient,Cwd - SCiAi - - - 0.2878 Cwd x C f= 0.32 SAi Cwd xCfxSAi= 0.10 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=7rr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =Cvd x SA;x i x t =d X t =Runoff Volume-Discharge Volume =Cwd x SAj x i (rain) (in/hr) (ft3) (ft3) (ft3) (ft3/s) 1 10.72 65.04 0.00 65.04 1.08 5 3.83 116.09 0.00 116.09 0.39 10 2.46 149.00 0.00 149.00 0.25 15 1.89 172.41 0.00 172.41 0.19 20 1.58 191.23 0.00 191.23 0.16 25 1.37 207.22 0.00 207.22 0.14 30 1.22 221.28 0.00 22128 0.12 35 1.10 233.91 0.00 233.91 0.11 40 1.01 245.43 0.00 245.43 0.10 45 0.94 256.06 0.00 256.06 0.09 50 0.88 265.96 0.00 265.96 0.09 55 0.82 275.24 0.00 275.24 0.08 60 0.78 284.00 0.00 284.00 0.08 75 0.68 307.75 0.00 307.75 0.07 90 0.60 328.63 0.00 328.63 0.06 105 0.55 347.38 0.00 347.38 0.06 120 0.50 364.49 0.00 364.49 0.05 150 0.43 394.98 0.00 .394.98 0.04 180 0.39 421.77 0.00 421.77 0.04 360 0.25 541.31 0.00 541.31 0.03 720 0.16 694.74 0.00 694.74 0.02 1440 0.10 891.64 0.00 364.49 ft3 0.25 (ft3/s) Project:Northwestern Energy Addition L �r Project#:17032.0 S A N D E R S O N t '� Date:10/16/2017 RATIONAL METHOD FOR RUNOFF CALCULATIONS GI E A Watershed 4 Design Storm Frequency= 25 years Discharge Rate,d= �cfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 fry/acre) C Cf C x Cf C' C'x A Surface Type (ft) Acres =(C x C�<or=t Acres Impervious 11724 0.27 0.9 1.1 0.99 0.99 0.266454545 Landscape 885 0.02 0.2 1.1 0.22 0.22 0.004469697 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 12609 0.2895-A 0.2709 Weighted Runoff Coefficient,C_1 SCii - A - 0.8509 Cwd x Cf= 0.94 SAi C,..d a Cfx SAi= 0.27 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface tape j A=rrrz Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =C,�.sA x's t =d x t =Runoff Volume-Discharge Volume =Cwd x SAj x i (min) (in/hr) (ft) (ft3) (ft) (ft3/s) 1 10.72 174.23 0.00 174.23 2.90 5 3.83 310.99 0.00 310.99 1.04 10 2.46 399.13 0.00 399.13 0.67 15 1.89 461.85 0.00 461.85 0.51 20 1.58 512.25 0.00 512.25 0.43 25 1.37 555.10 0.00 555.10 0.37 30 1.22 592.75 0.00 592.75 0.33 35 1.10 626.58 0.00 626.58 0.30 40 1.01 657.43 0.00 657.43 0.27 45 0.94 685.91 0.00 685.91 0.25 50 0.88 712.43 0.00 712.43 0.24 55 0.82 737.29 0.00 737.29 0.22 60 0.78 760.76 0.00 760.76 0.21 75 0.68 824.39 0.00 824.39 0.18 90 0.60 880.31 0.00 880.31 0.16 105 0.55 930.55 0.00 930.55 0.15 120 0.50 976.37 0.00 976.37 0.14 150 0.43 1058.04 0.00 1058.04 0.12 180 0.39 1129.82 0.00 1129.82 0.10 360 0.25 1450.04 0.00 1450.04 0.07 720 0.16 1861.02 0.00 1861.02 0.04 1440 0.10 2388.48 0.00 976.37 ft3 1.04 (ft3/s) Project:Northwestern Energy Addition t�' Project#h 17032.0 SANDERS O N �IA Date:10/16/2017 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E WA R T Watershed 5 Design Storm Frequency= 25 years Discharge Rate,d= Ocfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 ft'/acre) C Cf C X C f Ct Ct X A Surface Type (fr) Acres =(C x Q<or=t Acres Impervious 11385 0.26 0.9 1.1 0.99 0.99 0.25875 Landscape 2876 0.07 0.2 1.1 0.22 0.22 0.014525253 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 14261 0.3274 0.2733 Weighted Runoff Coefficient,C,d - SCiAi - - SAi 0.7588 Cwd x C f= 0.83 Cwd x Cfx SAi= 0.27 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=7rr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =c,'x sA x i x t =d X t =Runoff Volume-Discharge Volumc =Cwd x SAj x i (min) (tn/hr) (0 (0 (ft3) (ft3/s) 1 10.72 175.74 0.00 175.74 2.93 5 3.83 313.68 0.00 313.68 1.05 10 2.46 402.59 0.00 402.59 0.67 15 1.89 465.86 0.00 465.86 0.52 20 1.58 516.69 0.00 516.69 0.43 25 1.37 559.91 0.00 559.91 0.37 30 1.22 597.90 0.00 597.90 0.33 35 1.10 632.02 0.00 632.02 0.30 40 1.01 663.14 0.00 663.14 0.28 45 0.94 691.86 0.00 691.86 0.26 50 0.88 718.61 0.00 718.61 0.24 55 0.82 743.69 0.00 743.69 0.23 60 0.78 767.36 0.00 767.36 0.21 75 0.68 831.54 0.00 831.54 0.18 90 0.60 887.95 0.00 887.95 0.16 105 0.55 938.62 0.00 938.62 0.15 120 0.50 984.85 0.00 984.85 0.14 150 0.43 1067.22 0.00 1067.22 0.12 180 039 1139.62 0.00 1139.62 0.11 360 0.25 1462.62 0.00 1462.62 0.07 720 0.16 1877.17 0.00 1877.17 0.04 1440 0.10 2409.20 0.00 984.85 ft3 1.05 (ft3/s) Project:Northwestern Energy Addition AM Project#: 0 S A N D E R S O N AF Date:10/16/2016/2017 RATIONAL METHOD FOR RUNOFF CALCULATIONS T E WA R T Watershed 6 Design Storm Frequency= 25 years Discharge Rate,d= Ocfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 fry/acre) C Cf C X C f C' C'X A Surface Type (ft) Acres =(C x Ca<or=1 Acres Impervious 4397 0.10 0.9 1.1 0.99 0.99 0.099931818 Landscape 538 0.01 0.2 1.1 0.22 0.22 0.002717172 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 4935 0.1133 EMU 0.1026 Weighted Runoff Coefficient,C«.d SCiAi _ - 0.8237 C,d x Cf= 0.91 SAi C,.d x CI x SAi= 0.10 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=rrr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =CWd x SA,x'x t =d3x t =Runoff Volume-Discharge Volumc =C vd x SAj x i (min) (in/hr) (ft) (ft) (fr3) (ft3/s) 1 10.72 66.01 0.00 66.01 1.10 5 3.83 117.83 0.00 117.83 0.39 10 2.46 151.22 0.00 151.22 0.25 15 1.89 174.99 0.00 174.99 0.19 20 158 194.08 0.00 194.08 0.16 25 1.37 210.32 0.00 210.32 0.14 30 1.22 224.59 0.00 224.59 0.12 35 1.10 237.40 0.00 237.40 0.11 40 1.01 249.09 0.00 249.09 0.10 45 0.94 259.88 0.00 259.88 0.10 50 0.88 269.93 0.00 269.93 0.09 55 0.82 279.35 0.00 279.35 0.08 60 0.78 288.24 0.00 288.24 0.08 75 0.68 312.35 0.00 312.35 0.07 90 0.60 333.54 0.00 333.54 0.06 105 055 352.57 0.00 352.57 0.06 120 0.50 369.93 0.00 369.93 0.05 150 0.43 400.88 0.00 400.88 0.04 180 0.39 428.07 0.00 428.07 0.04 360 0.25 549.40 0.00 549.40 0.03 720 0.16 705.11 0.00 705.11 0.02 1440 0.10 904.96 0.00 369.93 ft3 0.39 (ft3/s) Project:Northwestern Energy Addition Project :0 S A N D E R S O N t III Date:10/16/2016/2017 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E A R T Watershed 7 Design Storm Frequency= 25 years Discharge Rate,d= OCfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560£?here) C Cf C x C f C' C'x A Surface Type (ft) Acres =(C x CO<or=t Acres Impervious 10 0.00 0.9 1.1 0.99 0.99 0.000227273 Landscape 1602 0.04 0.2 1.1 0.22 0.22 0.008090909 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 1612 0.0370 0.0083 Weighted Runoff Coefficient,Cwd - SCiAi - - 0.2043 Cwd x CF= 0.22 SAi C«,d x CF x SAi= 0.01 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=7rr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =c,.�x sn x i x t =d x t =Runoff Volume-Discharge Volume =Cwd x SAj x i ( ) (in/hr) (ft) (0 (ft) (ft3/s) 1 10.72 5.35 0.00 5.35 0.09 5 3.83 9.55 0.00 9.55 0.03 10 2.46 12.25 0.00 12.25 0.02 15 1.89 14.18 0.00 14.18 0.02 20 1.58 15.73 0.00 15.73 0.01 25 1.37 17.04 0.00 17.04 0.01 30 1.22 18.20 0.00 18.20 0.01 35 1.10 19.24 0.00 19.24 0.01 40 1.01 20.19 0.00 20.19 0.01 45 0.94 21.06 0.00 21.06 0.01 50 0.88 21.87 0.00 21.87 0.01 55 0.82 22.64 0.00 22.64 0.01 60 0.78 23.36 0.00 23.36 0.01 75 0.68 25.31 0.00 2531 0.01 90 0.60 27.03 0.00 27.03 0.01 105 0.55 28.57 0.00 28.57 0.00 120 0.50 29.98 0.00 29.98 0.00 150 0.43 32.49 0.00 32.49 0.00 180 039 34.69 0.00 34.69 0.00 360 0.25 44.52 0.00 44.52 0.00 720 0.16 57.14 0.00 57.14 0.00 1440 0.10 73.33 0.00 29.98 ft3 0.03 (ft3/s) Project:Northwestern Energy Addition Project#: 0 Date:10/16/2016/2017 S A N D E R S O N t'10 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E A R T Watershed 8 Design Storm Frequency= 25 years Discharge Rate,d= Ocfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 ftr/acrc) C CC C x C f C' C'x A Surface Type (ft) Acres =(c x cr)<or=t Acres Impervious 15617 0.36 0.9 1.1 0.99 0.99 0.354931818 Landscape 14991 0.34 0.2 1.1 0.22 0.22 0.075712121 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 30608 0.7027 0.4366 Weighted Runoff Coefficient,C,,.d SCiAi - _ - 0.5572 C,d x CC= 0.61 SAi C,,d x CC x SAj= 0.43 Where Ci is the adjusted runoff coefficient for surface type f and Ai is the area of surface type j A =rrr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =Cod x st;x i x t =d x t =Runoff Volume-Discharge Volumc =Cwd x SAj x i (min) (113/hr) (ft) (ft3) (ft3) (ft3/S) 1 10.72 276.94 0.00 276.94 4.62 5 3.83 494.32 0.00 494.32 1.65 10 2.46 634.43 0.00 634.43 1.06 15 1.89 734.13 0.00 734.13 0.82 20 1.58 814.24 0.00 814.24 0.68 25 1.37 882.35 0.00 882.35 0.59 30 1.22 942.20 0.00 942.20 0.52 35 1.10 995.97 0.00 995.97 0.47 40 1.01 1045.02 0.00 1045.02 0.44 45 0.94 1090.28 0.00 1090.28 0.40 50 0.88 1132.43 0.00 1132.43 0.38 55 0.82 1171.96 0.00 1171.96 0.36 60 0.78 1209.25 0.00 1209.25 0.34 75 0.68 1310.40 0.00 1310.40 0.29 90 0.60 1399.29 0.00 1399.29 0.26 105 0.55 1479.14 0.00 1479.14 0.23 120 050 1551.98 0.00 1551.98 0.22 150 0.43 1681.80 0.00 1681.80 0.19 180 0.39 1795.89 0.00 1795.89 0.17 360 0.25 2304.89 0.00 2304.89 0.11 720 0.16 2958.15 0.00 2958.15 0.07 1440 0.10 3796.57 0.00 1,551.98 ft3 1.65 (ft3/s) Project:Northwestern Energy Addition 40M Project#: S A N D E R S O N 400 Date:10/16/2017 017 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E WA R T Watershed 9 Design Storm Frequency= 25 years Discharge Rate,d= Ocfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 fJ/acre) C Cf C x Cf C' C'x A Surface Type (fr2) Acres =(c x c�<or=t Acres Impervious 4367 0.10 0.9 1.1 0.99 0.99 0.09925 Landscape 797 0.02 0.2 1.1 0.22 0.22 0.004025253 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 5164 0.1185 MESON 0.1033 Weighted Runoff Coefficient,C,..d - SCiAI SAi - 0.7920 Cwd x C f= 0.87 C«.d x Cfx SAI= 0.10 Where Cl is the adjusted runoff coefficient for surface type j and AI is the area of surface type j A=rrrz Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =CWd x sA x i x t =d x t =Runoff Volume-Discharge Volume =Cwd x SAj x i (-in) (in/hr) (ff) (ft3) (ft3) (ft3/S) 1 10.72 66.41 0.00 66.41 1.11 5 3.83 118.55 0.00 118.55 0.40 10 2.46 152.15 0.00 152.15 0.25 15 1.89 176.06 0.00 176.06 0.20 20 1.58 195.27 0.00 195.27 0.16 25 1.37 211.60 0.00 211.60 0.14 30 1.22 225.96 0.00 225.96 0.13 35 1.10 238.85 0.00 238.85 0.11 40 1.01 250.61 0.00 250.61 0.10 45 0.94 261.47 0.00 261.47 0.10 50 0.88 271.57 0.00 271.57 0.09 55 O.S2 281.05 0.00 281.05 0.09 60 0.78 290.00 0.00 290.00 0.08 75 0.68 314.25 0.00 314.25 0.07 90 0.60 335.57 0.00 335.57 0.06 105 0.55 354.72 0.00 354.72 0.06 120 0.50 372.19 0.00 372.19 0.05 150 0.43 403.32 0.00 40332 0.04 180 0.39 430.68 0.00 430.68 0.04 360 0.25 552.75 0.00 552.75 0.03 720 0.16 709.41 0.00 709.41 0.02 1440 0.10 910.48 0.00 372.19 ft3 0.40 (ft3/s) Project:Northwestern Energy Addition : �j Project#: 0 Date:10/16/2017 SANDERSONW40 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E WA R T Watershed 10 Design Storm Frequency= 25 years Discharge Rate,d= �cfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 ft,/acre) C Cf C x C f C' C'x A Surface Type (ft) Acres =(c x CO<or=t Acres Impervious 0 0.00 0.9 1.1 0.99 0.99 0 Landscape 1495 0.03 0.2 1.1 0.22 0.22 0.007550505 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 1495 0.0343 0.0076 Weighted Runoff Coefficient,C«.d SCiAi _ - 0.2000 C,d x Cf= 0.22 SAi C_1xCfxSAi= 0.01 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=rrr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =c,,x SAi x i x t =d X t =Runoff Volumc-Discharge Volumc =Cwd x SAj x i (min) (tn/hr) (ft3) (ft3) 1 10.72 4.86 0.00 4.86 0.08 5 3.83 8.67 0.00 8.67 0.03 10 2.46 11.12 0.00 11.12 0.02 15 1.89 12.87 0.00 12.87 0.01 20 1.58 14.28 0.00 14.28 0.01 25 137 15.47 0.00 15.47 0.01 30 1.22 16.52 0.00 1652 0.01 35 1.10 17.46 0.00 17.46 0.01 40 1.01 18.32 0.00 18.32 0.01 45 0.94 19.12 0.00 19.12 0.01 50 0.88 19.85 0.00 19.85 0.01 55 0.82 20.55 0.00 20.55 0.01 60 0.78 21.20 0.00 21.20 0.01 75 0.68 22.98 0.00 22.98 0.01 90 0.60 24.53 0.00 24.53 0.00 105 0.55 25.93 0.00 25.93 0.00 120 0.50 27.21 0.00 27.21 0.00 150 0.43 29.49 0.00 29.49 0.00 180 0.39 31.49 0.00 31.49 0.00 360 0.25 40.41 0.00 40.41 0.00 720 0.16 51.87 0.00 51.87 0.00 1440 0.10 66.57 0.00 27.21 ft3 0.03 (ft3/s) Project:Northwestern Energy Addition 40-W-2 Project#: S A N D E R S O N wip Date:10/16/2017 6/2 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E WA R T Watershed 11 Design Storm Frequency= 25 years Discharge Rate,d= Ocfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 ftr/acre) C Cf C X Cf Ct Ct X A Surface Type (fr) Acres =(c x Co<or=t Acres Impervious 1380 0.03 0.9 1.1 0.99 0.99 0.031363636 Landscape 2950 0.07 0.2 1.1 0.22 0.22 0.01489899 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 4330 0.0994 0.0463 Weighted Runoff Coefficient,C,d SCiAi - - - 0.4231 Cwd x Cf= 0.47 SAi C,d x Cc x SAi= 0.05 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=7rrz Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =C.,x s,;x i x t =d X t =Runoff Volume-Discharge Volume =Cwd x SAj x i (min)( ) (m/hr) (ft) (0 (fi) (ft3/o 1 10.72 29.75 0.00 29.75 0.50 5 3.83 53.10 0.00 53.10 0.18 10 2.46 68.15 0.00 68.15 0.11 15 1.89 78.87 0.00 78.87 0.09 20 1.58 87.47 0.00 87.47 0.07 25 1.37 94.79 0.00 94.79 0.06 30 1.22 101.22 0.00 101.22 0.06 35 1.10 106.99 0.00 106.99 0.05 40 1.01 112.26 0.00 112.26 0.05 45 0.94 117.12 0.00 117.12 0.04 50 0.88 121.65 0.00 121.65 0.04 55 0.82 125.90 0.00 125.90 0.04 60 0.78 129.91 0.00 129.91 0.04 75 0.68 140.77 0.00 140.77 0.03 90 0.60 150.32 0.00 150.32 0.03 105 0.55 158.90 0.00 158.90 0.03 120 0.50 166.72 0.00 166.72 0.02 150 0.43 180.67 0.00 180.67 0.02 180 0.39 192.93 0.00 192.93 0.02 360 0.25 247.61 0.00 247.61 0.01 720 0.16 317.78 0.00 317.78 0.01 1440 0.10 407.85 0.00 166.72 ft3 0.18 (ft3/s) Project:Northwestern Energy Addition 0�r Project 0 S A N D E R S O N W49 Date:10/16/2016/2017 RATIONAL METHOD FOR RUNOFF CALCULATIONS g E ART Watershed 12 Design Storm Frequency= 25 years Discharge Rate,d= Ocfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 f?/acre) C Cf C X Cf Ct Ct X A Surface Type (ft) Acres =(C x C�<of=t Acres Impervious 39273 0.90 0.9 1.1 0.99 0.99 0.892568182 Landscape 0 0.00 0.2 1.1 0.22 0.22 0 Gravel 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 39273 0.9016 0.8926 Weighted Runoff Coefficient,C,,.d SCiAI - _ - 0.9000 C,�d s Cf= 0.99 SAi C,,.d x Cc SAi= 0.89 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=rrrZ Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =c x sn x i x t =d X t =Runoff Volume-Discharge Volume =Cwd x SAi x i (min) (in/hr) (ft3) (ft) (ft3) 1 10.72 573.99 0.00 573.99 9.57 5 3.83 1024.55 0.00 1024.55 3.42 10 2.46 1314.93 0.00 1314.93 2.19 15 1.89 1521.59 0.00 1521.59 1.69 20 1.58 1687.62 0.00 1687.62 1.41 25 1.37 1828.78 0.00 1828.78 1.22 30 1.22 1952.84 0.00 1952.84 1.08 35 1.10 2064.28 0.00 2064.28 0.98 40 1.01 2165.94 0.00 2165.94 0.90 45 0.94 2259.75 0.00 2259.75 0.84 50 0.88 2347.11 0.00 2347.11 0.78 55 0.82 2429.04 0.00 2429.04 0.74 60 0.78 2506.33 0.00 2506.33 0.70 75 0.68 2715.98 0.00 2715.99 0.60 90 0.60 2900.22 0.00 2900.22 0.54 105 0.55 3065.72 0.00 3065.72 0.49 120 0.50 3216.69 0.00 3216.69 0.45 150 0.43 3485.76 0.00 3485.76 0.39 180 0.39 3722.22 0.00 3722.22 0.34 360 0.25 4777.19 0.00 4777.19 0.22 720 0.16 6131.18 0.00 6131.18 0.14 1440 0.10 7868.91 0.00 3,216.69 ft3 3.42 (ft3/s) Project:Northwestern Energy Addition duo Project#:17032.0 SANDERS O N Q14 Date:10/16/2017 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E WA R T Watershed 13 Design Storm Frequency= 25 years Discharge Rate,d= Ocfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 felacre) C Cf C x C f C' C'x A Surface Type (ft) Acres =(c x c�<or=t Acres Impervious 18216 0.42 0.9 1.1 0.99 0.99 0.414 Landscape 0 0.00 0.2 1.1 0.22 0.22 0 Gravel 76586 1.76 0.6 1.1 R66 0.66 1.160393939 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 94802 2.1764 1.5744 Weighted Runoff Coefficient,C va - SCiAi - - 0.6576 C,a x Cf= 0.72 SAi C,,a x Cfx SAi= 1.57 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=Trr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t In/tensity,i =cq,x sM x'x r =d x t =is �offvomme-nischargc von e =cwa/x sA1 x (lllltl) ( / ) (fr3) (ft3) (fi3) (ft3/S) 1 10.72 1012.46 0.00 1012.46 16.87 5 3.83 1807.20 0.00 1807.20 6.02 10 2.46 2319.40 0.00 2319.40 3.87 15 1.89 2683.92 0.00 2683.92 2.98 20 1_58 2976.78 0.00 2976.78 2.48 25 1.37 3225.78 0.00 3225.78 2.15 30 1.22 3444.61 0.00 3444.61 1.91 35 1.10 3641.17 0.00 3641.17 1.73 40 1.01 3820.48 0.00 3820.48 1.59 45 0.94 3985.96 0.00 3985.96 1.48 50 0.88 4140.05 0.00 4140.05 1.38 55 0.82 4284.56 0.00 4284.56 1.30 60 0.78 4420.90 0.00 4420.90 1.23 75 0.68 4790.69 0.00 4790.69 1.06 90 0.60 5115.68 0.00 5115.68 0.95 105 0.55 5407.60 0.00 5407.60 0.86 120 0.50 5673.90 0.00 5673.90 0.79 150 0.43 6148.50 0.00 6148.50 0.68 180 039 6565.60 0.00 6565.60 0.61 360 0.25 8426.46 0.00 8426.46 0.39 720 0.16 10814.73 0.00 10814.73 1 0.25 1440 0.10 13879.91 0.00 5,673.90 ft3 2.98 (ft3/s) Project:Northwestern Energy Addition AW2- Projectt: 0 Date:10/16/2017 SANDERSON tP _RATIONAL METHOD FOR RUNOFF CALCULATIONS t/�� '� Watershed 14 Design Storm Frequency= 25 years Discharge Rate,d= �cfs Input values For runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 felacre) C Cf C X Cf C' C'X A Surface Type (ft) Acres =(C x c,)<or=i Acres Impervious 0 0.00 0.9 1.1 0.99 0.99 0 Landscape 0 0.00 0.2 1.1 0.22 0.22 0 Gravel 63841 1.47 0.6 1.1 0.66 0.66 0.967287879 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 63841 1.4656 MEN 0.9673 Weighted Runoff Coefficient,Cwd SCir1i - _ - 0.6000 C,d X CC= 0.66 SAi C_1 x CC SAi= 0.97 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=Rr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t In/tensity,i =c.�/x SAj x i x t -d X t =Runoff Volum/c-Discharge Volume =Cwd x SAj x i (min) (lri/hr) (ft3) (ft3) (ft3) (ft3/S) 1 10.72 622.04 0.00 622.04 10.37 5 3.83 1110.32 0.00 1110.32 3.70 10 2.46 1425.01 0.00 1425.01 2.38 15 1.89 1648.96 0.00 1648.96 1.83 20 1.58 1828.90 0.00 1828.90 1.52 25 1.37 1981.88 0.00 1981.88 1.32 30 1.22 2116.32 0.00 2116.32 1.18 35 1.10 2237.09 0.00 2237.09 1.07 40 1.01 2347.25 0.00 2347.25 0.98 45 0.94 2448.92 0.00 2448.92 0.91 50 0.88 2543.59 0.00 2543.59 0.85 55 0.82 2632.38 0.00 2632.38 0.80 60 0.78 2716.14 0.00 2716.14 0.75 75 0.68 2943.34 0.00 2943.34 0.65 90 0.60 3143.01 0.00 3143.01 0.58 105 055 3322.36 0.00 3322.36 0.53 120 050 3485.97 0.00 3485.97 0.48 150 0.43 3777.56 0.00 3777.56 0.42 180 0.39 4033.82 0.00 4033.82 0.37 360 0.25 5177.11 0.00 5177.11 0.24 720 0.16 6644.44 0.00 6644.44 0.15 1440 0.10 8527.64 0.00 3,485.97 ft3 1.83 (ft3/s) Project:Northwestern Energy Addition 40° Project#: S A N D E R S O N 41F Date:10/16/2017 017 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E WA R T Watershed 15 Design Storm Frequency= 25 years Discharge Rate,d= Ocfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 fr'/acre) C Cf C X Cf C' C'X A Surface Type (ft) Acres =(c x C�<or=t Acres Impervious 0 0.00 0.9 1.1 0.99 0.99 0 Landscape 0 0.00 0.2 1.1 0.22 0.22 0 Gravel 38231 0.88 0.6 1.1 0.66 0.66 0.579257576 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 38231 0.8777 0.5793 Weighted Runoff Coefficient,C«.d - SCIAI - - - 0.6000 Cwd x Cf= 0.66 SAI Cwd x Cfx SAI= 0.58 Where CI is the adjusted runoff coefficient for surface type j and AI is the area of surface type j A=rrr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =c„,x SA;x i x t =d X t =Runoff Volume-Discharge Volume =Cwd x SAj x i (fin) (in/hr) (fr) (ft) (fr3) (ft3/S) 1 10.72 372.51 0.00 372.51 6.21 5 3.83 664.91 0.00 664.91 2.22 10 2.46 853.36 0.00 853.36 1.42 15 1.89 987.48 0.00 987.48 1.10 20 1.58 1095.23 0.00 1095.23 0.91 25 1.37 1186.84 0.00 1186.84 0.79 30 1.22 1267.35 0.00 1267.35 0.70 35 1.10 1339.67 0.00 1339.67 0.64 40 1.01 1405.65 0.00 1405.65 0.59 45 0.94 1466.53 0.00 1466.53 0.54 50 0.88 1523.22 0.00 1523.22 0.51 55 0.82 1576.39 0.00 1576.39 0.48 60 0.78 1626.56 0.00 1626.56 0.45 75 0.68 1762.61 0.00 1762.61 0.39 90 0.60 1882.18 0.00 1882.18 0.35 105 0.55 1989.59 0.00 1989.59 0.32 120 0.50 2087.56 0.00 20S7.56 0.29 150 0.43 2262.18 0.00 2262.18 0.25 180 0.39 2415.64 0.00 2415.64 0.22 360 0.25 3100.30 0.00 3100.30 0.14 720 0.16 3979.00 0.00 3979.00 0.09 1440 0.10 5106.75 0.00 23087.56 ft3 1.10 (ft3/s) Project:Northwestern Energy Addition Lo"M Project q:17032.0 S A N D E R S O N t '� Date:10/16/2017 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T EWART Watershed 16 Design Storm Frequency= 25 years Discharge Rate,d= �cfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 ft,/acre) C Cf C X C f Ct Ct X A Surface Type (ft) Acres =(C x C�<or=1 Acres Impervious 39706 0.91 0.9 1.1 0.99 0.99 0.902409091 Landscape 0 0.00 0.2 1.1 0.22 0.22 0 Gravel 172699 3.96 0.6 1.1 0.66 0.66 2.616651515 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 212405 4.8761 3.5191 Weighted Runoff Coefficient,Cwd SCiAi _ - 0.6561 Cwd X Cr= 0.72 SAi Cwd X Cf X SAi= 3.52 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=lrr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,1 =C,,,x SAj x i x t =d X t =Runoff Volume-Discharge Volume =Cwd x SAj x i (min) (in/hr) (ft3) (ft3) (0 (ft3/s) 1 10.72 2263.03 0.00 2263.03 37.72 5 3.83 4039.42 0.00 4039.42 13.46 10 2.46 5184.29 0.00 5184.29 8.64 15 1.89 5999.05 0.00 5999.05 6.67 20 1.58 6653.65 0.00 6653.65 5.54 25 1.37 7210.21 0.00 7210.21 4.81 30 1.22 7699.33 0.00 7699.33 4.28 35 1.10 8138.68 0.00 8138.68 3.88 40 1.01 8539.47 0.00 8539.47 3.56 45 0.94 8909.35 0.00 8909.35 3.30 50 0.88 9253.77 0.00 9253.77 3.08 55 0.82 9576.79 0.00 9576.79 2.90 60 0.78 9881.52 0.00 9881.52 2.74 75 0.68 10708.08 0.00 10708.08 2.38 90 0.60 11434.49 0.00 11434.49 2.12 105 0.55 12086.97 0.00 12086.97 1.92 120 0.50 12682.20 0.00 12682.20 1.76 150 0.43 13743.02 0.00 13743.02 1.53 180 0.39 14675.32 0.00 14675.32 1.36 360 0.25 18834.68 0.00 18834.68 0.87 720 0.16 24172.92 0.00 24172.92 0.56 1440 0.10 31024.15 0.00 3 12,682.20 ft 6.67 (ft3/s) Project:Northwestern Energy Addition tom% Project##:17032.0 SANDERS O N MM Date:10/16/2017 RATIONAL METHOD FOR RUNOFF CALCULATIONS S T E WA R T Pond Design Storm Frequency= 25 years Discharge Rate,d= �cfs Input values for runoff coefficients from appropriate tables. Runoff Frequency Calculation Area Area Coefficient Factor Value A A/(43560 ft'/acre) C Cf C x C f C' C'x A Surface Type (ftZ) Acres =(C x C�<er=1 Acres Impervious 0 0.00 0.9 1.1 0.99 0.99 0 Landscape 22770 0.52 0.2 1.1 0.22 0.22 0.115 Gravel 0 0.00 0.6 1.1 0.66 0.66 0 0 1.1 0.00 0.00 0 0 1.1 0.00 0.00 0 Totals 22770 0.5227 0.1150 Weighted Runoff Coefficient,Cud - SCiAI - 0.2000 Cw d x Cf= 0.22 SAS Cwd x Cfx SA = 0.12 Where Ci is the adjusted runoff coefficient for surface type j and Ai is the area of surface type j A=7rr2 Rainfall Rainfall Runoff Volume Discharge Volume Site Detention Peak Flow Duration,t Intensity,i =C_x SA,x i x t =d3x�t =Runoff Volume-Discharge Volume =Cwd x SAj x i (min) (tn/hr) (ft3) (ft J (ft) (ft3/s) 1 10.72 73.95 0.00 73.95 1.23 5 3.83 132.00 0.00 132.00 0.44 10 2.46 169.42 0.00 169.42 0.28 15 1.89 196.04 0.00 196.04 0.22 20 1.58 217.44 0.00 217.44 0.18 25 1.37 235.62 0.00 235.62 0.16 30 1.22 251.61 0.00 251.61 0.14 35 1.10 265.97 0.00 265.97 0.13 40 1.01 279.06 0.00 279.06 0.12 45 0.94 291.15 0.00 291.15 0.11 50 0.88 302.41 0.00 302.41 0.10 55 0.82 312.96 0.00 312.96 0.09 60 0.78 322.92 0.00 322.92 0.09 75 0.68 349.93 0.00 349.93 0.08 90 0.60 373.67 0.00 373.67 0.07 105 0.55 394.99 0.00 394.99 0.06 120 0.50 414.44 0.00 414.44 0.06 150 0.43 4-49.11 0.00 449.11 0.05 180 0.39 479.58 0.00 479.58 0.04 360 0.25 615.50 0.00 615.50 0.03 720 0.16 789.95 0.00 789.95 0.02 1440 0.10 1013.84 0.00 414.44 ft3 1.23 (ft3/5) Project:Northwestern Energy Addition Project#:17032.0 Date:10/16/2017 TABLE 1-1:Runoff Coefficients for Use in the Rational Method LAND USE RUNOFF COEFFICIENTS,C Open Land 0.2 Low to Medium Density Residential 0.35 Dense Residential 0.5 Commercial Neighborhood 0.6 Commercial Downtown 0.8 Industrial 0.8 Project:Northwestern Energy Addition Project#i:17032.0 Date:10/16/2017 Design Standards and Specifications Policy City of Bozeman,March 2004 as Amended RAINFALL INTENSITY-DURATION CURVES(Figures 1-2,1-3) Storm Recurrence Interval Time 2 5 10 ZS 54 100 (min) (in/hr) (in/hr) (in/hr) (in/hr) (i"r) (in/hr) 1 4.20 7.15 9.16 10.72 13.72 15.69 5 1.60 2.55 3.22 3.83 4.74 5.34 10 1.05 1.64 2.05 2.46 3.00 3.35 15 0.83 1.26 1.58 1.89 2.30 2.56 20 0.70 1.05 1.31 1.58 1.90 2.11 25 0.61 0.91 1.13 1.37 1.64 1.82 30 0.55 0.81 1.00 1.22 j 1.45 1.61 35 0.50 0.73 0.91 1.10 1.31 1.45 40 0.46 0.67 0.83 1.01 1.20 1.33 45 0.43 0.63 0.77 0.94 1.11 1.22 50 0.40 0.58 0.72 0.88 1.04 1.14 55 0.38 0.55 0.68 0.82 0.97 1.07 60 0.36 0.52 0.64 1 0.78 0.92 1.01 75 0.31 0.45 0.55 0.68 0.79 0.87 90 0.28 0.40 0.49 0.60 0.70 0.77 105 0.26 0.36 0.44 0.55 0.64 0.69 120 0.24 0.33 0.41 0.50 0.58 0.63 150 0.21 0.29 0.35 0.43 0.50 0.55 180 0.19 0.26 0.31 0.39 0.45 0.48 360 0.12 0.17 0.20 0.25 0.28 0.30 720 0.08 0.11 0.13 0.16 0.18 0.19 1440 1 0.05 0.07 0.08 0.10 0.11 0.12 Project:Northwestern Energy Addition Project#:17032.0 Date:10/16/2017 Design Standards and Specifications Policy City of Bozeman, March 2004 as Amended Zoning District/Design Storm Requirement Design Rainfall Zoning i a Frequency Open Land 2-year Residential 10-year Commercial 10-year (p.28,Table I-3) Project:Northwestern Energy Addition Project#:17032.0 Date:10/16/2017 STORMWATER MANAGEMENT MANUAL TABLE 2-5 FREQUENCY FACTORS FOR THE RATIONAL FORMULA Recurrence Interval Adjustment Factor !. (Years) Cf 2 1.00 5 1.00 10 1.00 25 1.10 50 1.20 100 1.25 *C X Crshould not exceed 1.0 S,, m Drain Pipe Flow Watershed 1 Inlet Qin 1.44 cfs n 0.012 RCP Mannings Roughness Coefficient d 12 inches Pipe Diameter S 0.0022 ft/ft Pipe Slope Q 1.815 cfs Flow Capacity Watershed 2 Inlet Qin 2.2 cfs n 0.012 RCP Mannings Roughness Coefficient d 15 inches Pipe Diameter S 0.0022 ft/ft Pipe Slope Q 3.291 cfs Flow Capacity Watershed 3 Inlet Qin 2.45 cfs n 0.012 RCP Mannings Roughness Coefficient d 15 inches Pipe Diameter S 0.0022 ft/ft Pipe Slope Q 3.291 cfs Flow Capacity Watershed 4 Inlet Qin 3.49 cfs n 0.012 RCP Mannings Roughness Coefficient d 15 inches Pipe Diameter S 0.0026 ft/ft Pipe Slope Q 3.578 cfs Flow Capacity (75% full) Watershed 6,7, 9 & 10 Inlet Qin 0.85 cfs n 0.012 RCP Mannings Roughness Coefficient d 12 inches Pipe Diameter S 0.0022 ft/ft Pipe Slope Q 1.815 cfs Flow Capacity Watershed 8 Inlet Qin 1.65 cfs n 0.012 RCP Mannings Roughness Coefficient d 12 inches Pipe Diameter S 0.0022 ft/ft Pipe Slope Q 1.815 cfs Flow Capacity Watershed 5 Inlet Qin 2.7 cfs n 0.012 RCP Mannings Roughness Coefficient d 15 inches Pipe Diameter S 0.0022 ft/ft Pipe Slope Q 3.291 cfs Flow Capacity Manhole Qin 7.04 cfs n 0.012 RCP Mannings Roughness Coefficient d 18 inches Pipe Diameter S 0.005 ft/ft Pipe Slope Q 8.068 cfs Flow Capacity Watershed 11 Inlet Qin 7.22 cfs n 0.012 RCP Mannings Roughness Coefficient d 18 inches Pipe Diameter S 0.005 ft/f Pipe Slope Q 8.068 cfs Flow Capacity Watershed 13 Inlet Qin 2.98 cfs n 0.012 RCP Mannings Roughness Coefficient d 12 inches Pipe Diameter S 0.006 ft/ft Pipe Slope Q 2.998 cfs Flow Capacity Manhole Qin 10.2 cfs n 0.012 RCP Mannings Roughness Coefficient d 18 inches Pipe Diameter S 0.0086 ft/ft Pipe Slope Q 10.582 cfs Flow Capacity Watershed 14 Inlet Qin 1.83 cfs n 0.012 RCP Mannings Roughness Coefficient d 12 inches Pipe Diameter S 0.003 ft/ft Pipe Slope Q 2.120 cfs Flow Capacity Manhole Qin 12.03 cfs n 0.012 RCP Mannings Roughness Coefficient d 24 inches Pipe Diameter S 0.0086 ft/ft Pipe Slope Q 22.789 cfs Flow Capacity Watershed 15 Inlet Qin 1.1 cfs n 0.012 RCP Mannings Roughness Coefficient d 12 inches Pipe Diameter S 0.0022 ft/ft Pipe Slope Q 1.815 cfs Flow Capacity Outfall Qin 13.13 cfs n 0.012 RCP Mannings Roughness Coefficient d 24 inches Pipe Diameter S 0.005 ft/ft Pipe Slope Q 17.376 cfs Flow Capacity APPENDIX C: MAINTENANCE PLAN SANDERSON V STEWART October 17, 2017 Project No. 17032 STORM DRAINAGE FACILITY MAINTENANCE PLAN FOR NORTHWESTERN ENERGY BUILDING ADDITION BOZEMAN, MONTANA OVERVIEW NARRATIVE The purpose of this maintenance plan is to outline the necessary details needed to determine who is responsible for the maintenance of the facilities, when the facilities need to be maintained and who owns the storm drainage facilities. The City of Bo.Zeman Design Standards and Specifications Policy, dated March 2004. The site stormwater improvements have been designed with the intent to meet the current City of Bozeman drainage regulations for the entire site to the extent feasible. Specific site information and criteria are described below: I. Ownership of all facilities Northwestern Energy II. Schedule: Infiltration Basin: Inspection: Every 6 months Dredge Pond: Every 2 years or as needed based on inspection Inlets &Manholes: Inspection: Every 6 months Vacuum: Every 2 years or as needed based on inspection III. Responsible Party: Northwestern Energy rtHO FIRM To Plan and Design -_� Enduring Communities... www.sa ndersonstewa rt. com APPENDIX D: GEOTECH REPORT Project No.:4531.12044.01 LOG OF BOREHOLE B-6 Sheet 1 of 1 CLIENT PROJECT NorthWestern Energy Bozeman Service Center Expansion BORING LOCATION SITE Pro osed Access Road-See Fi ure 2 Bozeman Montana SAMPLES TESTS M.C. o wU MATERIAL DESCRIPTION J Z L w W a ADDITIONAL O O a a u� p W a w PL LL DATA/ a ¢ W O m w�r Y W REMARKS W Surface Elevation:4,717 J o m 00 N VALUE ❑ BLOWS/FT C7 w m o m z z ?? IL I__ 10 20 30 40 0 3-inches Asphalt Pavement, black 5 13 Surface Elevation from 0.3 "716.I 7 4/18 Google Earth 2-inches Road Base, Well Graded Gravel wit6 1 1 8% ❑ 7s/° Sand, GW; moist, brown, subrounded to subangular, fine to coarse grained sand3 6 Lab#17-16 0.4 "716. 3 13/16 Nat.Moisture=16.4% Fill, Sandy Lean Clay with Gravel, CL; moist3 2 72% ❑ • 3.s to slightly moist, stiff, black to dark brown, rounded to subangular, fine to coarse grained7-17 sand, organic roots 21 3s Lab#oistu °2.1 "71q 11/18 Nat.Moisture=9.9/°Fill, Sandy Lean Clay, CL; moist, medium stiff1s 3 61% black to dark brown, occasional rounded gravel, fine to coarse grained sand, metal wire 5 4712. 7 Poorly Graded Gravel with Clay and Sand, GP-GC; moist, dense, light brown to light gray to multi-colored, rounded to subangular, fine to coarse grained sand 5.5 4711.5. Boring terminated at 5.5 feet 10.5 No groundwater observed 14 17.5 21 24.5 DOWL STARTED 7/31/2017 FINISHED 7/31/2017 2090 Stadium Drive DRILL CO. O'Keefe DRILL RIG MobileB-61 Bozeman, Montana 59715 D Q W L Telephone: (406) 586-8834 DRILLER M.Simmons HAMMER Auto www.dowl.com LOGGED BY D. Barrick APPROVED BY G. Underhill