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HomeMy WebLinkAbout06 - Stormwater Drainage ReportPage 2 of 5 The Rational Method was used to calculate peak runoff and detention requirements in accordance with City of Bozeman design standards. Storm water treatment is provided primarily by the use of above- and below-ground retention storage and infiltration, and in direct runoff areas, using biofiltration of impervious area through vegetated areas as is the case under existing conditions. Part 3 Drainage Basins Pre-development sub-basin H1 (see Figure 1) corresponds to developed sub-basins D1.1 and D1.2 (see Figure 2). The developed sub-basins are described below. Sub-basin D1.1: Sub-basin D1.1 is a narrow strip of land along the north site boundary that will be vegetated with native grasses. Runoff from this area will sheet flow through a small commercial area to the north, as it does under existing conditions. The peak runoff from this area will be less than under existing conditions. Sub-basin D1.2: Sub-basin D1.2 is part of a proposed asphalt-paved access drive. This area will drain to Dry Well #2, at the west end of this sub-basin. The dry well is sized to fully retain site runoff from this small area, in accordance with City retention requirements. During very large storms, runoff exceeding the retention volume would overflow to the north through an existing parking lot. Pre-development sub-basin H2 (see Figure 1) corresponds to developed sub-basins D2.1 through D2.11 (see Figure 2). The developed sub-basins are described below. Sub-basin D2.1: Sub-basin D2.1 includes the western end of the proposed asphalt-paved access drive of sub-basin 1.2, plus an existing, narrower north-south access drive that is partially paved. These areas will drain to Dry Well #1, near South 15th Avenue. The dry well is sized to fully retain site runoff from this small area, in accordance with City retention requirements. During very large storms, runoff exceeding the retention volume would overflow to the existing 24” storm drain inlet (flared end section) located about 60 feet west of the dry well. Sub-basins D2.2, D2.3 and D2.4: Runoff from these sub-basins drain through an existing storm drain to the existing detention pond directly north of the Detention Center. Sub-basins D2.2 and D2.3 are developed on-site areas where only a small parking addition (13 parking spaces) is proposed. The upstream end, sub-basin D2.4, is a fully developed, off-site residential area. Although the currently proposed runoff coefficients for on-site areas were calculated to be much lower, a conservatively high developed runoff coefficient of 0.80 will be used to allow flexibility for future development. This project will replace the north end of the existing storm drain with an 18-inch pipe into the detention pond, which will be re-graded (see below, under Detention Basins). Sub-basins D2.5, D2.6 and D2.7: Runoff from these sub-basins will drain through a proposed 24” storm drain to the existing detention pond directly north of the Detention Center, which will be re-graded (see below, under Detention Basins). All three of these sub-basins are developed on-site areas which could see some form of re-development in the future. Although the currently proposed runoff coefficients were calculated to be much lower, a conservatively high developed runoff coefficient of 0.80 will be used for all three of these sub-basins to allow flexibility for future development. Page 3 of 5 Sub-basins D2.8, D2.9, D2.10 and D2.11: Runoff from these sub-basins will drain through a proposed 24” storm drain to a combination of below-ground and above-ground storm water storage (see below, under Detention Basins). Sub-basins D2.8, D2.9 and D2.10 will be re-developed and sub-basin D2.11 will remain as it currently exists, as a grass/soil baseball field at the north end and the recently constructed Document Storage Building at the south end. Although the runoff coefficient for the existing sub-basin D2.11 was calculated to be much lower, a conservatively high developed runoff coefficient of 0.80 will be used for this sub-basin to allow flexibility for future development. Pre-development sub-basin H3 (see Figure 1) corresponds to developed sub-basins D3.1 and D3.2 (see Figure 2). The developed sub-basins are described below. Sub-basins D3.1 and D3.2: Sub-basins D3.1 and D3.2 are narrow strips of land along the south and west site boundaries that will be vegetated with native grasses. Runoff from these areas will flow through a grass swale to the northwest corner of the site, providing filtration through the native grasses. The peak runoff from these areas will be less than under existing conditions. Part 4 Storm Water Retention and Detention Storm water storage is proposed at six locations scattered around the site. Full retention of site runoff is provided at four locations, and a combination of retention and detention is provided as two connected surface ponds. Underground retention and detention includes the use of standard 48-inch diameter by 8’ high concrete dry wells, and of StormTech prefabricated polypropylene storage chambers installed per the manufacturer’s recommendations. The proposed retention and detention facilities are described below. Underground Retention, Dry Wells (Sub-basins D1.2, D2.1 and D2.10): For each of these relatively small drainage areas, concrete dry wells (manholes with slotted sides) and the surrounding rock fill will be used to provide full retention of storm runoff per City standards (see runoff calculations). Calculations of water storage volume above high groundwater are attached. The volume of rock fill around the dry wells will be specified on the construction drawings, and the rock fill will be fully encapsulated in geotextile to maintain its void space. Underground/Surface Retention, South Pond (Sub-basins D2.6 and D2.7): These sub-basins will drain to the “South Pond,” into two rows of fabricated underground storage chambers to store runoff from the smaller, more frequent storms. When the chambers are full, additional runoff will back up into the adjacent surface pond that meets City requirements for surface detention including a maximum water depth of 1.5 feet. The attached runoff calculations show the required retention volume, and the attached underground storage calculations show the underground and above-ground retention volumes that are provided. Retention/Detention, East Pond and West Pond (Sub-basins D2.2, D2.3, D2.4, D2.5, D2.7, D2.8, D2.9 and D2.11): The existing configuration (two connected ponds) is duplicated by the proposed East Pond and West Pond. Sub-basins D2.2, D2.3, D2.4, D2.5 and D2.7 drain directly to the East Pond, and sub-basins D2.8, D2.9 and D2.11 drain directly to the West Pond. A single discharge control structure for the connected ponds is located at the east end of the East Pond. As currently proposed, sub-basin D2.7 will drain to the South Pond as described above. It is duplicated here to allow flexibility for unspecified future improvements to the site. Page 4 of 5 Each pond incorporates its own storm water treatment, or water quality, volume. Storm runoff accumulations up to the Water Quality Storage Volume can discharge only by infiltration or evaporation. Water quality storage volumes and associated water surface elevations are set by the discharge elevations. Water quality volumes are calculated as total runoff from the first 0.5 inches of rainfall of a 24-hour storm preceded by 48 hours of no measurable precipitation, in accordance with City of Bozeman requirements. The SCS (TR-55) method was used to determine the water quality volumes; calculations are attached. During larger, less frequent storms, when site runoff exceeds the water quality storage volumes, it will discharge through the east pond’s control structure. The detention portions of the two ponds are connected by a 24-inch pipe so water elevations will equalize, and the detention storage can be treated as a single pond. The total detention volume requirement is 16,445 cubic feet; refer to the attached calculations. The additional volume provided allows flexibility for future development. Site-wide storm water storage and the discharge control structure parameters are summarized in the following table. Detailed calculations are attached. TABLE 1 - Retention/Detention Data Description Retention (Water Quality) Vol. (ft3) Detention Vol (ft3) 10-yr Max. Release Rate (cfs) Dry Wells: Dry Well #1 (sub-basin D2.1) 902 - 0 Dry Well #2 (sub-basin D1.2) 902 - 0 Dry Well #3 (sub-basin D2.10) 1,077 - 0 Retention, South Pond (sub-basins D2.6 and D2.7): Underground (ST1) 1,090 - 0 Surface Pond 3,822 - 0 Total Retention, South Pond: 4,912 Retention/Detention, West Pond (sub-basins D2.2, D2.3, D2.4, D2.5 and D2.7): Underground Retention (ST2, to 2’ depth) 3,604 50.31 Underground Detention (ST2, above 2’ depth) 2,324 49.70 Surface Detention, to elev. 4825.00 4,289 Totals, West Pond: 3,604 6,613 Retention/Detention, East Pond (sub-basins D2.8, D2.9 and D2.11): Surface Pond, below elev. 4822.90 3,249 Surface Pond, elev. 4822.90 to 4825.00 26,393 Totals, East Pond: 3.249 26,393 The detention release structure will have the following parameters: Orifice (two alternates): circular orifice dia. 103/4” rectangular orifice 91/2” x 9 5/8” 10-yr orifice discharge elev. 4822.90 10-yr max. WSEL 4825.00 25-yr max. WSEL 4826.00 Overflow riser dia. 24” Part 5 Conveyance and Collection The proposed storm drain system is shown on Figure 2. Existing storm drain is utilized for runoff from sub-basins D2.3, D2.4 and D2.5. The proposed storm drain system was sized to convey the Page 5 of 5 25-year peak runoff. Calculations are attached for representative pipes, as required to assure pipe size is adequate for all pipes. Conveyance and collection are described below. Sub-basins D1.2 and D2.1: Runoff from these sub-basins is directed to dry wells for full retention. In the event of large, infrequent storms, overflow from the dry well for sub-basin D1.2 would flow offsite to the north through an existing parking lot, and overflow from the dry well for sub-basin D2.1 would overflow into an existing ditch and 24” storm drain inlet (flared end section). Sub-basins D2.2, D2.3 and D2.4: Runoff from sub-basin D2.2 flows directly into the east detention pond. Runoff from sub-basins D2.3 and D2.4 drains to an existing storm drain system routed around the east side of the existing Pre-release Building and Detention Center, discharging directly into the east detention pond. The pipe into the re-graded East Pond will be replaced on a different alignment. Sub-basins D2.5, D2.6 and D2.7: Runoff will drain to a 24” diameter storm drain routed between the proposed Gallatin County Courts building and the existing Detention Center. The storm drain will be installed in a casing under the connecting corridor between these two buildings. As currently proposed, runoff from sub-basins D2.6 and D2.7 will be retained in the south retention area. However, the storm drain through sub-basin D2.5 was sized to accept fully developed runoff from sub-basins D2.6 and D2.7, to allow flexibility for future development. The 24” storm drain will discharge directly into the East Pond. Sub-basins D2.8, D2.9, D2.10 and D2.11: Runoff from sub-basins D2.8 and D2.9 will drain to a 24” diameter storm drain, discharging into the West Pond. Runoff from sub-basin D2.10 is directed to a dry well for full retention. In the event of large, infrequent storms, overflow from the dry well would flow offsite to the west, into an existing grass swale. Under the currently proposed scenario, runoff from sub-basin D2.11 will discharge as it does under existing conditions, which is toward and along the west side of the property into an existing grass swale. The developed portion of this sub-basin (Document Storage Building and parking) is routed through an existing detention pond prior to discharge into the grass swale. At the time of future development, runoff from all of sub-basin D2.11 will be re-directed into the storm drain servicing sub-basins D2.8 and D2.9, thereby greatly reducing runoff to offsite areas via the west boundary grass swale. Storm drain, treatment and detention are sized adequately to accept fully developed runoff from all of sub-basin D2.11 to the west pond, and additionally sub-basin D2.7, based on a conservatively high runoff coefficient of 0.80. As is the case throughout this report, the reason is to allow flexibility for future development. Discharge to the existing system is represented by the attached “Pond Discharge Piping” backwater calculation using CulvertMaster. The maximum 10-year release rate of 4.44 cfs is only 26 percent of the 16.99 cfs capacity, and the 25-year un-detained peak runoff is only 3.94 cfs more than the 10-year un-detained peak runoff. Therefore, the limitations of the existing offsite conveyance system are offset by the additional storage provided onsite in the hydraulically connected East and West detention ponds. In other words, the 25-year peak runoff will be no more than 4.44+3.94 = 8.38 cfs. Excluding the water quality volume, the total available combined detention volume to the 10-year maximum water surface elevation (25.00) is 6,693+26,393 = 33,006 cubic feet, more than double the required volume of 16,445 cubic feet. The additional attenuation will keep peak runoff from overtopping the offsite drainage improvements. (this page left blank intentionally) Gallatin County Courts Peak Runoff Calculations MODIFIED RATIONAL METHOD i = A * (Tc/60) B Qp = C i A Qp = peak runoff, cfs Design Coefficients C = runoff coefficient Storm AB i = A(Tc/60)B (Bozeman IDF curve)2-yr 0.36 -0.60 Tc = time of concentration, minutes 5-yr 0.52 -0.64 A = Area, acres 10-yr 0.64 -0.65 25-yr 0.78 -0.64 50-yr 0.92 -0.66 Retention Volume =7,200*(C)*(i)*(A), where i =0.41 in./hr 100-yr 1.01 -0.67 (Bozeman Design Standards, March 2004) Retention Sub-Basin Name Area C Tc Q2 Q5 Q10 Q25 Q50 Q100 Volume (ft.3) Basin 1 H1 1.04 0.20 5.00 0.33 0.53 0.67 0.80 0.99 1.11 D1.1 (direct) 0.41 0.20 5.00 0.13 0.21 0.26 0.31 0.39 0.44 D1.2 (ret.) 0.18 0.90 5.00 0.26 0.41 0.52 0.62 0.77 0.86 478 Basin 2 H2 14.67 0.20 15.97 2.34 3.56 4.44 5.34 6.47 7.19 D2.1 (ret.) 0.32 0.77 5.00 0.39 0.63 0.79 0.94 1.17 1.31 727 D2.2 2.00 0.44 5.00 1.41 2.25 2.83 3.37 4.17 4.70 D2.3* 3.45 0.61 11.79 2.03 3.12 3.91 4.68 5.71 6.37 D2.4 1.49 0.71 12.50 0.98 1.51 1.88 2.26 2.75 3.07 D2.3+D2.4 4.94 0.77 16.22 3.02 4.59 5.73 6.89 8.34 9.28 D2.2+D2.3+D2.4 6.94 0.68 16.22 3.71 5.65 7.04 8.47 10.26 11.41 D2.5* 4.19 0.80 10.36 3.46 5.36 6.72 8.04 9.83 10.98 D2.6* 0.78 0.80 5.00 1.00 1.59 2.01 2.39 2.96 3.33 D2.7* 1.30 0.80 5.00 1.66 2.65 3.35 3.98 4.93 5.55 D2.6+D2.7 (ret.) 2.08 0.80 5.00 2.66 4.24 5.36 6.37 7.89 8.88 4,912 D2.5+D2.6+D2.7 6.27 0.80 5.00 8.02 12.79 16.14 19.19 23.78 26.77D2.2+D2.3+D2.4+D2.5 +D2.6+D2.7 13.21 0.57 16.22 5.94 9.04 11.27 13.56 16.42 18.26 D2.8 2.44 0.64 5.00 2.51 4.01 5.06 6.01 7.45 8.38 D2.9 1.02 0.90 5.00 1.47 2.34 2.95 3.51 4.35 4.90 D2.10 (ret.) 0.40 0.90 5.00 0.58 0.92 1.16 1.38 1.71 1.92 1,063 D2.11* 1.72 0.80 5.00 2.20 3.51 4.43 5.27 6.53 7.35 D2.8+D2.9+D2.11 5.18 0.75 5.00 6.18 9.86 12.44 14.79 18.33 20.63 D2.8+D2.9+D2.10+D2.11 5.58 0.76 5.00 6.75 10.78 13.60 16.16 20.04 22.55 D2.2+D2.3+D2.4+D2.5 +D2.7+D2.8+D2.9+D2.11 17.61 0.74 16.22 10.23 15.56 19.41 23.35 28.27 31.44 Basin 3 H3 4.79 0.20 25.27 0.58 0.87 1.08 1.30 1.56 1.73 D3.1 (direct) 0.41 0.30 5.00 0.20 0.31 0.39 0.47 0.58 0.65 D3.2 (direct) 0.39 0.20 5.00 0.13 0.20 0.26 0.31 0.38 0.43 D3.1+D3.2 0.80 0.25 5.00 0.32 0.52 0.65 0.77 0.96 1.08 * A higher than proposed runoff coefficient of 0.80 was used for these subbasins to allow flexibility for future re-development Currently proposed runoff coefficients are lower, and are calculated in the coefficient table for reference Gallatin County Courts Runoff Coefficients (Rational Method) Area Area (sq. ft.) Runoff Sub-Basin (acres) Total Pervious Impervious Coefficient Basin 1 H1 1.04 45,302 45,302 0 0.20 D1.1 (direct) 0.41 17,860 17,860 0 0.20 D1.2 (ret.) 0.18 7,841 7,841 0.90 Basin 2 H2 14.67 639,025 639,025 0 0.20 D2.1 (ret.) 0.32 13,939 2,604 11,335 0.77 D2.2 2.00 87,120 57,242 29,878 0.44 D2.3* 3.45 150,282 21,400 128,882 0.80 D2.4 1.49 64,904 17,372 47,532 0.71 D2.3+D2.4 4.94 215,186 167,654 47,532 0.77 D2.2+D2.3+D2.4 6.94 302,306 96,014 206,292 0.68 D2.5* 4.19 182,516 26,150 156,366 0.80 D2.6* 0.78 33,977 4,850 29,127 0.80 D2.7* 1.30 56,628 8,100 48,528 0.80 D2.6+D2.7 (ret.) 2.08 90,605 0.80 D2.5+D2.6+D2.7 6.27 273,121 0.80 D2.2+D2.3+D2.4+D2.5+D2.6+D2.7 13.21 575,428 135,114 440,313 0.74 D2.8 2.44 106,286 38,912 67,374 0.64 D2.9 1.02 44,431 0 44,431 0.90 D2.10 (ret.) 0.40 17,424 0 17,424 0.90 D2.11* 1.72 74,923 10,700 64,223 0.80 D2.8+D2.9+D2.11 5.18 225,641 49,612 176,029 0.75 D2.8+D2.9+D2.10+D2.11 5.58 243,065 0.76 D2.2+D2.3+D2.4+D2.5+D2.7+D2.8+D2.9+D2.11 17.61 767,092 0.74 Basin 3 H3 4.79 208,652 208,652 0 0.20 D3.1 (direct) 0.41 17,860 15,360 2,500 0.30 D3.2 (direct) 0.39 16,988 16,868 120 0.20 D3.1+D3.2 0.80 34,848 0.25 * A higher than proposed runoff coefficient of 0.80 was used for these subbasins to allow flexibility for future re-development.Currently proposed runoff coefficients are lower, and are calculated below for reference. Area Area (sq. ft.) Runoff Sub-Basin (acres) Total Pervious Impervious Coefficient Basin 2 (coefficients for currently proposed development) D2-3 3.45 150,282 61,351 88,931 0.61 D2-5 4.19 182,516 38,649 143,867 0.75 D2-6 0.78 33,977 23,982 9,995 0.41 D2-7 1.30 56,628 28,190 28,438 0.55 D2-11 1.72 74,923 25,400 49,523 0.66 Water Quality Runoff Volumes West Pond: D2-8,D2-9,D2-11 Event Summary Event Peak Q (cfs) Peak T (hrs) Hyd Vol (cuft) Area (ac) Method WQ 1.4356 12.0176 3,435 5.18 SCS WQ = Water Quality storm of 0.50” of rainfall. Results based on storm duration of 24.0 hours. Record Id: D2-8,D2-9,D2-11 Design Method SCS Rainfall type TYPE2.rac Hyd Intv 10.00 min Peaking Factor 484.00 Storm Duration 24.00 hrs Abstraction Coeff 0.20 Area 5.18 ac DCIA N/A CN 95.36 DC CN N/A TC 5.00 min DC TC N/A Pervious CN Calc Description SubArea Sub cn Open spaces, lawns,parks (>75% grass) 1.14 ac 86.00 Impervious surfaces (pavements, roofs, etc) 4.04 ac 98.00 Pervious Composited CN (AMC 2) 95.3591 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Paved 60.00 ft 4.17% 0.01 1.20 in 0.9081 min Shallow Paved 70.00 ft 2.14% 0.01 0.3923 min Int Channel stormpipe (n=0.012) 190.00 ft 1.0% 0.012 0.7457 min Int Channel stormpipe (n=0.012) 485.00 ft 0.72% 0.012 2.2434 min Pervious TC 4.2895 min   East Pond: D2-2,D2-3,D2-4,D2-5,D2-6,D2-7 Event Summary Event Peak Q (cfs) Peak T (hrs) Hyd Vol (cuft) Area (ac) Method WQ 2.4608 12.0905 7,832 12.43 SCS WQ = Water Quality storm of 0.50” of rainfall. Results based on storm duration of 24.0 hours. Record Id: D2-2,D2-3,D2-4,D2-5,D2-6,D2-7 Design Method SCS Rainfall type TYPE2.rac Hyd Intv 10.00 min Peaking Factor 484.00 Storm Duration 24.00 hrs Abstraction Coeff 0.20 Area 12.43 ac DCIA N/A CN 95.11 DC CN N/A TC 16.2152 min DC TC N/A CN Calc Description SubArea Sub cn Open spaces, lawns,parks (>75% grass) 2.99 ac 86.00 Impervious surfaces (pavements, roofs, etc) 9.44 ac 98.00 Composited CN (AMC 2) 95.1134 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Short prairie grass and lawns. 0.15 65.00 ft 2.0% 0.15 1.20 in 11.3358 min Int Channel Concrete gutter 300.00 ft 1.2% 0.013 1.1644 min Int Channel storm drain pipe 310.00 ft 1.97% 0.012 0.8669 min Int Channel storm drain pipe 620.00 ft 0.73% 0.012 2.8481 min Pervious TC 16.2151 min   Gallatin County Courts Sub-Basins D2.2, D2.3, D2.4, D2.5, D2.7, D2.8, D2.9, D2.11 Detention (10-yr storm) MODIFIED RATIONAL METHOD Qp = C i A POST-DEVELOPMENT PRE-DEVEL. 17.61 AC Qp (Basin H2) = 4.44 cfs 0.74 16.2 MIN D2.2 release rate = 4.44 cfs 1.50 IN/HR TIME STEP 19.41 CFS DURATION = 5.0 min. Max. Volume, Max. Volume,Required Detention Triangle Rel. (cu. ft.) Constant Rel. (cu. ft.)Volume (cu. ft.) 20247.55 12643.15 16,445 Triangle Release Constant Release DURATION INTENSITY Qp POND VOLUME POND VOLUME (MIN) (IN/HR) (CFS) (CF) (CF) 15.41 1.55 20.07 14,340 11,084 31.63 0.97 12.57 17,490 12,643 47.85 0.74 9.61 19,051 12,514 64.07 0.61 7.95 19,858 11,578 ORIFICE CALCULATIONS 80.29 0.53 6.86 20,208 10,150 MATCHING Qp = 4.44 cfs 96.51 0.47 6.09 20,248 8,385 Max. Depth = 2.10 ft 112.73 0.42 5.50 20,058 6,369 128.95 0.39 5.04 19,691 4,161 145.17 0.36 4.67 19,184 1,798 161.39 0.34 4.36 18,560 -694 CIRCULAR ORIFICE: 177.61 0.32 4.10 17,839 -3,292 DIAMETER = 10.750 inches 193.83 0.30 3.87 17,034 -5,983 Area = 0.63 ft 2 210.05 0.28 3.67 16,158 -8,753 ORIFICE FLOW = 4.40 CFS 226.27 0.27 3.50 15,219 -11,594 242.49 0.26 3.35 14,224 -14,496 258.71 0.25 3.21 13,180 -17,454 RECTANGULAR ORIFICE: 274.93 0.24 3.08 12,091 -20,462 LENGTH = 9.625 inches 291.15 0.23 2.97 10,962 -23,516 WIDTH = 9.500 inches 307.37 0.22 2.87 9,796 -26,610 Area = 0.63 ft 2 323.59 0.21 2.77 8,596 -29,742 ORIFICE FLOW = 4.43 CFS 339.81 0.21 2.69 7,366 -32,909 356.03 0.20 2.61 6,107 -36,108 372.25 0.20 2.53 4,822 -39,337 388.47 0.19 2.46 3,513 -42,594 404.69 0.19 2.40 2,181 -45,876 WEIR CALCULATIONS (not used) 420.91 0.18 2.34 827 -49,183 Coefficient = 3.33 inches 437.13 0.18 2.28 -546 -52,513 Width = 5.2500 inches 453.35 0.17 2.23 -1,939 -55,863 WEIR FLOW = 4.43 CFS 469.57 0.17 2.18 -3,349 -59,234 485.79 0.16 2.13 -4,775 -62,624 502.01 0.16 2.08 -6,218 -66,032 POST-DEV Qp = POND VOLUME CALCULATIONS: BASIN AREA POST = POST-DEV Tc = POST-DEV C = STORM INTENSITY = DURATION INTENSITY Qp POND VOLUME POND VOLUME (MIN) (IN/HR) (CFS) (CF) (CF) 518.23 0.16 2.04 -7,675 -69,458 534.45 0.15 2.00 -9,146 -72,899 550.67 0.15 1.96 -10,631 -76,356 566.89 0.15 1.93 -12,129 -79,828 583.11 0.15 1.89 -13,639 -83,313 599.33 0.14 1.86 -15,160 -86,812 615.55 0.14 1.83 -16,693 -90,324 631.77 0.14 1.80 -18,236 -93,849 647.99 0.14 1.77 -19,790 -97,385 664.21 0.13 1.74 -21,353 -100,932 680.43 0.13 1.71 -22,926 -104,491 696.65 0.13 1.68 -24,507 -108,059 712.87 0.13 1.66 -26,098 -111,638 729.09 0.13 1.64 -27,696 -115,227 745.31 0.12 1.61 -29,303 -118,825 761.53 0.12 1.59 -30,918 -122,432 777.75 0.12 1.57 -32,540 -126,048 793.97 0.12 1.55 -34,169 -129,672 810.19 0.12 1.53 -35,806 -133,304 826.41 0.12 1.51 -37,449 -136,945 842.63 0.11 1.49 -39,099 -140,593 858.85 0.11 1.47 -40,755 -144,248 875.07 0.11 1.45 -42,417 -147,911 891.29 0.11 1.44 -44,085 -151,581 907.51 0.11 1.42 -45,759 -155,257 923.73 0.11 1.40 -47,438 -158,940 939.95 0.11 1.39 -49,123 -162,630 956.17 0.11 1.37 -50,814 -166,325 972.39 0.10 1.36 -52,509 -170,027 988.61 0.10 1.34 -54,210 -173,735 1004.83 0.10 1.33 -55,915 -177,448 1021.05 0.10 1.31 -57,625 -181,167 1037.27 0.10 1.30 -59,340 -184,892 1053.49 0.10 1.29 -61,059 -188,621 1069.71 0.10 1.27 -62,783 -192,356 1085.93 0.10 1.26 -64,510 -196,097 1102.15 0.10 1.25 -66,242 -199,842 1118.37 0.10 1.24 -67,979 -203,591 1134.59 0.09 1.23 -69,719 -207,346 1150.81 0.09 1.22 -71,463 -211,105 1167.03 0.09 1.20 -73,210 -214,869 1183.25 0.09 1.19 -74,962 -218,637 1199.47 0.09 1.18 -76,717 -222,409 1215.69 0.09 1.17 -78,476 -226,186 1231.91 0.09 1.16 -80,238 -229,967 1248.13 0.09 1.15 -82,003 -233,751 1264.35 0.09 1.14 -83,772 -237,540 1280.57 0.09 1.13 -85,544 -241,333 1296.79 0.09 1.13 -87,320 -245,129 1313.01 0.09 1.12 -89,098 -248,929 1329.23 0.09 1.11 -90,879 -252,733 1345.45 0.08 1.10 -92,664 -256,541 1361.67 0.08 1.09 -94,451 -260,351 1377.89 0.08 1.08 -96,241 -264,166 1394.11 0.08 1.07 -98,034 -267,983 1410.33 0.08 1.07 -99,830 -271,804 1426.55 0.08 1.06 -101,629 -275,629 1442.77 0.08 1.05 -103,430 -279,456 1458.99 0.08 1.04 -105,234 -283,287 1475.21 0.08 1.03 -107,040 -287,120 1491.43 0.08 1.03 -108,849 -290,957 1507.65 0.08 1.02 -110,660 -294,797 Gallatin County Courts Sub-Basins D2.6+D2.7 Underground Storage Calculations (10-yr storm) StormTech Modules, Model No.SC740 (30" chamber height) Depth to top of gravel 36 in. installed storage volume 68.14 ft3 per chamber (see note) Number of chambers proposed 16 Total Volume 1,090 ft3 Installed chamber footprint (per chamber) = 5' x 7.12' Note: add 2' min. to each row, for end caps Storage Volumes: underground storage 1,090 ft3 surface retention (min.) 3,822 Total Required Retention Volume 4,912 ft3 Notes: 1. Storage volume assumes 6" of stone above and between chambers, and 40% stone porosity. Gallatin County Courts Sub-Basins D2.8+D2.10 Underground Storage Calculations (10-yr storm) StormTech Modules, Model No.SC740 (30" chamber height) Depth to top of gravel 36 in. installed storage volume 68.14 ft3 per chamber (see note) Number of chambers proposed 87 Total Volume 5,928 ft3 Installed chamber footprint (per chamber) = 5' x 7.12' Note: add 2' min. to each row, for end caps Storage Volumes: water quality storage requirement 3,507 ft3 water quality volume provided (to 2' depth) 3,604 ft3 remaining storage for detention 2,324 Underground Storage Volume Provided = 5,928 ft3 Notes: 1. Storage volume assumes 6" of stone above and between chambers, and 40% stone porosity. Gallatin County Courts Retention Volume Calculations Dry Well #1 (Sub-basin D1.2) Volume Dimension/ Description (ft3)Depth/Elev. (ft) Rim/Grate Elevation 24.70 Estimated Max. Groundwater Elevation1 14.00 Total Storage Depth to 18" Below Finished Grade2 6.50 Storage Volume in Manhole cone section volume 23.56 barrel section, storage depth (cone section to bottom of structure) 3.00 barrel section volume 37.70 Storage Volume in Manhole3 61.26 Storage Volume in Rock Fill (Void Space) Rock Fill Base Dimensions (square excavation) 6 Total Excavation Volume4 2,230.31 Subtract manhole volume to outside diameter -127.63 Rock Volume 2,102.69 Storage Volume in Rock Fill5 841.07 Total Available Retention Volume (Manhole plus Rock Voids) = 902 Required Volume for SubBasin D1.2 = 478 Notes: 1. High groundwater estimate is conservatively high (above estimated seasonal high groundwater). 2. Structure depth is 8 feet. Total Storage Depth is from bottom of structure to 18" below finished grade. 3. Storage Volume in Manhole is the air volume within the concrete dry well structure. 4.Total excavation volume calculated as a pyramid with 11/2:1 side slopes. 5. Water storage volume in the washed rock backfill based on a 40% void ratio. Gallatin County Courts Retention Volume Calculations Dry Well #2 (Sub-basin D2.1) Volume Dimension/ Description (ft3)Depth/Elev. (ft) Rim/Grate Elevation 24.70 Estimated Max. Groundwater Elevation1 14.00 Total Storage Depth to 18" Below Finished Grade2 6.50 Storage Volume in Manhole cone section volume 23.56 barrel section, storage depth (cone section to bottom of structure) 3.00 barrel section volume 37.70 Storage Volume in Manhole3 61.26 Storage Volume in Rock Fill (Void Space) Rock Fill Base Dimensions (square excavation) 6 Total Excavation Volume4 2,230.31 Subtract manhole volume to outside diameter -127.63 Rock Volume 2,102.69 Storage Volume in Rock Fill5 841.07 Total Available Retention Volume (Manhole plus Rock Voids) = 902 Required Volume for SubBasin D2.1 = 727 Notes: 1. High groundwater estimate is conservatively high (above estimated seasonal high groundwater). 2. Structure depth is 8 feet. Total Storage Depth is from bottom of structure to 18" below finished grade. 3. Storage Volume in Manhole is the air volume within the concrete dry well structure. 4.Total excavation volume calculated as a pyramid with 11/2:1 side slopes. 5. Water storage volume in the washed rock backfill based on a 40% void ratio. manhole to outside diameter. Based on 6' square bottom of dry well excavation and 11/2:1 excavation side slopes. Gallatin County Courts Retention Volume Calculations Dry Well #3 (Sub-basin D2.10) Volume Dimension/ Description (ft3)Depth/Elev. (ft) Rim/Grate Elevation 28.40 Estimated Max. Groundwater Elevation1 19.00 Total Storage Depth to 18" Below Finished Grade2 6.50 Storage Volume in Manhole cone section volume 23.56 barrel section, storage depth (cone section to bottom of structure) 3.00 barrel section volume 37.70 Storage Volume in Manhole3 61.26 Storage Volume in Rock Fill (Void Space) Rock Fill Base Dimensions (square excavation) 8 Total Excavation Volume4 2,665.81 Subtract manhole volume to outside diameter -127.63 Rock Volume 2,538.19 Storage Volume in Rock Fill5 1,015.27 Total Available Retention Volume (Manhole plus Rock Voids) = 1,077 Required Volume for SubBasin D2.10 = 1,063 Notes: 1. High groundwater estimate is conservatively high (above estimated seasonal high groundwater). 2. Structure depth is 8 feet. Total Storage Depth is from bottom of structure to 18" below finished grade. 3. Storage Volume in Manhole is the air volume within the concrete dry well structure. 4.Total excavation volume calculated as a pyramid with 11/2:1 side slopes. 5. Water storage volume in the washed rock backfill based on a 40% void ratio. 5. Water storage volume in the washed rock backfill is the volume of void space in the backfill, based on a 40% void ratio. Gallatin County Courts Pipe Calculations (25-yr storm) MODIFIED RATIONAL METHOD Qp = C i A Qp = 25-yr peak runoff, cfs C = runoff coefficient i = 0.78(Tc/60)-0.64 (Bozeman IDF curve) Tc = time of concentration, minutes A = Area, acres Basin Name Flow Entry Point Area1 C Tc Qpipe2 Pipe Dia.3 Basin 1 D1.2 (ret.) Total to curb inlet #3 0.18 0.90 5.00 0.62 12" Basin 2 D2.4 total offsite, College St. to south site boundary) 1.49 0.71 12.50 2.26 12" D2.3+D2.4 total to curb inlet #2 4.94 0.77 16.22 6.89 18" D2.5, south half total to curb inlet #7 2.10 0.80 5.00 6.41 15" D2.6+D2.7 (ret.) total to SD MH #10 2.08 0.80 5.00 6.37 18" D2.5+D2.6+D2.7 total to SD MH #6 6.27 0.80 5.00 19.19 24" D2.11* total to end cap south of SD MH #17 1.72 0.80 5.00 5.27 18" D2.8+D2.9+D2.11 total to underground storage at north parking lot 5.18 0.75 5.00 14.79 24" * Pipe size increased to 18"dia. to allow flexibility for future development. NOTES: 1. Contributing drainage area (conservatively high in some cases) 2.Qpipe is the total 25-year peak runoff (direct surface runoff plus flows from upstream pipes) to the pipe draining the indicated structure/flow entry point. 3. Discharge pipe for the indicated flow entry point. Calculations are attached for pipes in bold text. Other pipe sizes are evident based on subbasin areas and flow rates in the above table. Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.012 Channel Slope 0.70 % Normal Depth 1.00 ft Diameter 12.00 in Discharge 3.23 ft³/s Results Discharge 3.23 ft³/s Normal Depth 1.00 ft Flow Area 0.79 ft² Wetted Perimeter 3.14 ft Hydraulic Radius 0.25 ft Top Width 0.00 ft Critical Depth 0.77 ft Percent Full 100.0 % Critical Slope 0.00794 ft/ft Velocity 4.11 ft/s Velocity Head 0.26 ft Specific Energy 1.26 ft Froude Number 0.00 Maximum Discharge 3.47 ft³/s Discharge Full 3.23 ft³/s Slope Full 0.00700 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % 12" PVC - capacity at 0.70% 5/2/2022 11:12:11 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.012 Channel Slope 1.00 % Normal Depth 1.25 ft Diameter 15.00 in Discharge 7.00 ft³/s Results Discharge 7.00 ft³/s Normal Depth 1.25 ft Flow Area 1.23 ft² Wetted Perimeter 3.93 ft Hydraulic Radius 0.31 ft Top Width 0.00 ft Critical Depth 1.06 ft Percent Full 100.0 % Critical Slope 0.00945 ft/ft Velocity 5.70 ft/s Velocity Head 0.51 ft Specific Energy 1.76 ft Froude Number 0.00 Maximum Discharge 7.53 ft³/s Discharge Full 7.00 ft³/s Slope Full 0.01000 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % 15" PVC - capacity at 1.00% 5/2/2022 11:15:37 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.012 Channel Slope 0.70 % Normal Depth 1.50 ft Diameter 18.00 in Discharge 9.52 ft³/s Results Discharge 9.52 ft³/s Normal Depth 1.50 ft Flow Area 1.77 ft² Wetted Perimeter 4.71 ft Hydraulic Radius 0.38 ft Top Width 0.00 ft Critical Depth 1.19 ft Percent Full 100.0 % Critical Slope 0.00743 ft/ft Velocity 5.39 ft/s Velocity Head 0.45 ft Specific Energy 1.95 ft Froude Number 0.00 Maximum Discharge 10.24 ft³/s Discharge Full 9.52 ft³/s Slope Full 0.00700 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % 18" PVC - capacity at 0.70% 5/2/2022 11:16:48 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page Project Description Friction Method Manning Formula Solve For Full Flow Capacity Input Data Roughness Coefficient 0.012 Channel Slope 0.70 % Normal Depth 2.00 ft Diameter 24.00 in Discharge 20.50 ft³/s Results Discharge 20.50 ft³/s Normal Depth 2.00 ft Flow Area 3.14 ft² Wetted Perimeter 6.28 ft Hydraulic Radius 0.50 ft Top Width 0.00 ft Critical Depth 1.62 ft Percent Full 100.0 % Critical Slope 0.00712 ft/ft Velocity 6.53 ft/s Velocity Head 0.66 ft Specific Energy 2.66 ft Froude Number 0.00 Maximum Discharge 22.06 ft³/s Discharge Full 20.50 ft³/s Slope Full 0.00700 ft/ft Flow Type SubCritical GVF Input Data Downstream Depth 0.00 ft Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % 24" PVC - capacity at 0.70% 5/2/2022 11:17:42 AM Bentley Systems, Inc. Haestad Methods Solution CenterBentley FlowMaster V8i (SELECTseries 1) [08.11.01.03] 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 2of1Page Culvert Calculator Report Pond Discharge Piping Title: Bozeman Public Safety Center n:\...\04 design\civil\drainage\pipes.cvm 10/25/22 08:41:23 AM Morrison Maierle Inc © Bentley Systems, Inc. Haestad Methods Solution Center Watertown, CT 06795 USA +1-203-755-1666 Project Engineer: MHickman CulvertMaster v3.3 [03.03.00.04] Page 1 of 1 Solve For: Discharge Culvert Summary Allowable HW Elevation 26.00 ft Headwater Depth/Height 2.89 Computed Headwater Eleva 26.00 ft Discharge 16.99 cfs Inlet Control HW Elev. 25.46 ft Tailwater Elevation 21.80 ft Outlet Control HW Elev. 26.00 ft Control Type Outlet Control Grades Upstream Invert 21.66 ft Downstream Invert 20.16 ft Length 111.00 ft Constructed Slope 1.3514 % Hydraulic Profile Profile PressureProfile Depth, Downstream 1.64 ft Slope Type N/A Normal Depth N/A ft Flow Regime N/A Critical Depth 1.44 ft Velocity Downstream 9.62 ft/s Critical Slope 1.9424 % Section Section Shape Circular Mannings Coefficient 0.012 Section MaterialCorrugated HDPE (Smooth Interior) Span 1.50 ft Section Size 18 inch Rise 1.50 ft Number Sections 1 Outlet Control Properties Outlet Control HW Elev. 26.00 ft Upstream Velocity Head 1.44 ft Ke 0.20 Entrance Loss 0.29 ft Inlet Control Properties Inlet Control HW Elev. 25.46 ft Flow Control Submerged Inlet Type Groove end w/headwall Area Full 1.8 ft² K 0.00180 HDS 5 Chart 1 M 2.00000 HDS 5 Scale 2 C 0.02920 Equation Form 1 Y 0.74000 (this page left blank intentionally)