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Home My WebLink AboutSTORM WATER STUDY - Ricks College - Kimball Building - CUP for Multi-Use FacilityGREAT BASIN ENGINEERING - NORTH CONSULTING ENGINEERS P.O. Box 9307 . Ogden, Utah 84409 AND LAND SURVEYORS (801) 394-4515 • (801) 521-0222 • Fax (801) 392-7544 BYU — IDAHO MULTI - USE FACILITY BYU — IDAHO CAMPUS RF,XBURG, IDAHO STORM WATER STUDY Project No. 01N500 March 19, 2001 General Site Information: The proposed Multi -use facility located on the BYU-Idaho campus in Rexburg, Idaho. Proposed construction will consist of a building, parking lots, and landscaping. The total site consists of about 8.2 acres. The site has five drainage areas. The locations of these areas are shown on the attached figure. Area 5 is undetained and consists mostly of landscaping to the south and west of the building. The detention basins for Areas 1 and 2 are located in the parking areas. Detention basins for areas 3 and 4 are located in the landscaping and in underground pipes. The storm water is released to the existing storm water system to north of the site. This storm water system flows into the main campus storm water vault located along Viking Drive. A runoff coefficient of 0.15 was used for natural ground and landscaped areas. A runoff coefficient of 0.90 was used for asphalt, concrete, buildings, and other hard surfaced areas. The runoff coefficient for each area was calculated It was found that the runoff coefficient for the site was about 0.63. This indicates that the site has about thirty-seven percent landscaping. The remainder of the site is considered hard surface. A time of concentration for the 100 -year design storm was calculated using the method outlined by Seelye in "Design" page 18-01. The time of concentration ranged from about 5 minutes to about 25 minutes. This time is based on the largest path inside the detention area over grass, asphalt, concrete, or through a pipeline as applicable. Five minutes is the shortest time using this method. Rainfall intensities were taken from data provided by Rexburg City. A copy of this data is attached. A time of concentration for the undetained area was set to 120 minutes. The undetained peak flow from Area 5 was deducted from the net allowable flow for the entire site. This keeps the net allowable release rate at 0. 19 cubic feet per second per acre. The release rate of 0.19 cubic feet per second per acre was used to accommodate concerns that the storm water from the system not exceed the historical flow from the site. A flow rate of 0.20 cubic feet per second per acre is typical for landscaping areas. In the event that an inlet box or drainpipe becomes plugged, storm water will spill to an adjacent inlet box. The maximum depth in the parking lot if the basin spills will be about 12inches. Due to the size of the available detention area in the project, storm water flows through the 100 - year storm will be routed through the proposed detention areas and catch basins. Data showing area information, runoff coefficient, time of concentration, peak flow, required detention, and available detention for the site is provided in the attached calculations. Pipe Sizes: Storm water pipes in the project are proposed to be PVC, non -reinforced concrete (CP), and type 2 aluminized steel pipe. All pipes in the project will be sloped so that a minimum scour velocity of 2 feel per ••• -- -- --- -- -- --. ..••-,••• ..••... •.• I . llUl 1W. UVIJVLIJYY 1,UJ/ 1L second is maintained when the pipes are flowing full. The pipes and inlet boxes have sufficient capacity to convey the 10 -year storm without surcharging. Orif9ce Plates: Orifice plates will be used to control the rate of discharge from each area. Each plate will have a diameter of no less than 4 inches. The locations and sizes of the orifice plates are shown on the attached figure. Each orifice plate will be constructed as indicated on the attached detail. Each plate will be mounted concentric with the outlet pipe as indicated. Detention Pond: The detention pond will be used to hold the storm water as it drains into the storm sewer. The pond has a maximum depth of 2.56 feet before storm water spills out at the inlet lox. Small flows will pass through the pipes without detention. As the flows increase, the orifice plate will restrict the flow and the detention pond will begin to fill. As indicated above, detention for Areas 1 and 2 will be in the parking lot. Detention in Area 3 will be in the detention pond and in a series of 48" diameter pipes. The detention for Area 4 will be in a series of 36" diameter pipes. 100 -Year Storm Flow Routin¢: As indicated above, the 100 -year storm will be routed through the proposed inlet boxes, catch basins, and detention pond. The elevation of the building is set so that no flooding will take place during the 100 -year storm. Great Basin Engineering, Inc. Prepared by David R Waldron, P.E. Project Manager JIM [IV. UULJQC-fJ44 F1 U4/ Ic �,%Ixl Yj\ N flo'dr w it VI Area "Xi .1 .0 "o .'I A A X iAl IV !Area /Platd ..... ..... . . . . . . J� Area ---- --- --- --- - --------- - --------- --------------------------------------------------------------------- - - ---- ---------------- -- -------- 7.7 jl 1 4 A rp/PWI I I V .'I A A X iAl IV !Area /Platd ..... ..... . . . . . . J� Area ---- --- --- --- - --------- - --------- --------------------------------------------------------------------- - - ---- ---------------- -- -------- 7.7 ••• �• •�- ..•+ •• u•••..••• �uvrn gnu MA IYV• oul3urID44 Y•UO/1Z ,u -� v• ,vv ��. vv ,u unw„ v,wau waw 11111 RV, UVIJVLIJYY 1, VV/ IL Total Area Area (sf) Area 1 35,988 Area 2 9,820 Area 3 211,398 Area 4 37,714 Area 5 63,348 358,268 Note Area 5 is Undetained BYU-Idaho Multi -Use Facility Landscaping Rexburg Idaho Area Area 6 -Feb -01 (acres) (acres) Storm Water Study 0.551 6 Drainage Areas 5 Detention Ponds Hard Surface Landscaping Total Area Area Area (st) (sf) (acres) 24,012 11.976 0.826 8,514 1,306 0.225 158,083 53,315 4.853 21,340 16,374 0.866 26,210 37,138 1.454 238,159 120,109 8.225 Runoff Coefficient C=0.16 for natural ground and landscaping C=0.90 for hard surfaces Le. asphalt, concrete, etc. Hatt) Surface Landscaping Runoff Area Area Coefficient (acres) (acres) 870' over asphalt @ s=3.0% avg 0.551 0.275 0.650 0.195 0.030 0.800 3.629 1.224 0.711 0.490 0.376 0.574 0.602 0.853 0.460 5.467 2.757 0.649 Time of Concentration use "Design" by Seeye Area 1 85' over grass @ s= 12.2% 8.5 min. Area 2 60' over asphalt @ s= 1.67% 5 min. Area 3 145' over grass @ s=5.8% 12 min. 870' over asphalt @ s=3.0% avg 8.5 min. 20 min. Area 4 90' over roof 5 min. Area 5 800' over gross @ s=4.5% 25 min Rainfall Intensities Use data from Rexburg City 10 Year Storm Area 1 @ tc=8 min., Intensity = 2.75 Inches per hour Area 2 @ tc=5 min., Intensity = 3.40 inches per hour Area 3 @ tc=20 min., Intensity = 2.75 inches per hour Area 4 @ tc=5 min., Intensity = 3.40 inches per hour Area 5 @ tc=25 min., Intensity = 2.40 inches per hour Peak Flow Use "Rational Method" Note Area 5 at 120 min. storm Allowable Discharge Rate = 0.19 cis per acre 1 Area Q Area C (in/hr) (acres) (cfs) Area 1 0.650 2.75 0.83 1.48 Area 2 0.800 3.40 0.23 0.61 Area 3 0.711 2.75 4.85 9.49 Area 4 0.574 3.40 0.67 1.69 Area 5 0.460 0.70 1.45 0.47 Note Area 5 at 120 min. storm Allowable Discharge Rate = 0.19 cis per acre Total Allowable Discharge = 1.563 cfs Net Allowable Discharge = 1.094 cis Net Allowable Discharge = 0.162 ofs per acre Area 1 100 Year Storm C = 0.650 Release Rate = 0.848 ds/acre Area = 0.826 Total Release Rate = 0.701 ds Rainfall Accumulated Allowable Needed Time Intensity Volume Release Detention (min.) (in/hr) (CF) (CF) (CF) 5 5.95 959.179 210.171 749.008 10 4.05 1305.774 420.342 885.432 15 3.25 1571.764 630.513 941.251 Peak Detention 20 2.75 1773.273 840.684 932.669 30 2.05 1982.841 1261.026 721.815 40 1.76 2256.893 1681.368 575.524 50 1.54 2482.582 2101.710 380.672 60 1.40 2708.271 2522.052 186.219 90 0.90 2611.547 3783.078 -1171.531 120 0.70 2708.271 5044.104 -2335.833 180 0.54 3133.857 7566.156 -4432.300 •..... ..••.., , u rnn nV UV IJOC 1044 Areas 182 100 Year Storm C = 0.683 Release Rate = 0.708 cWacre Area = 1.052 Total Release Rate = 0.745 cis Rainfall Accumulated Allowable Needed Time intensity Volume Release Detention (min.) (inlhr) (CF) (CF) (CF) 5 5.95 1281.205 223,471 1057.733 10 4.05 1744.161 440.943 1297.218 15 3.25 2099.453 670.414 1429.039 20 2.75 2368.614 MAN 1474.728 Peak Detention 30 2.05 2648.541 1340.828 1307.713 40 1.75 3014.599 1787.770 1226.829 50 1.64 3318.059 2234.713 1081.346 60 1.40 3617.519 2681.656 935.863 90 0.90 3488.322 4022.483 -534.162 120 0.70 3617.519 5363.311 -1745.792 180 0.54 4185.980 8144.967 -3868.981 240 0.44 4547.738 10726.623 -6178.884 300 0.36 4651.096 13408.278 -8757.182 360 0.32 4961.169 16069.934 -11128.765 720 0.185 5736.352 32179.888 -28443.516 Areas 1-3 100 Year Storm r uo/i(, C = 0.706 Release Rate = 0.162 cfslacre Area = 5.905 Total Release Rate - 0.954 cls Rainfall Accumulated Allowable Needed Time Intensity Volume Release Detention (min.) (in/hr) (CF) (CF) (CF) 5 5.95 7439.043 286.257 7162,786 10 4.05 10127.100 572.514 9554.586 15 3.25 12190.028 858.771 11331.257 20 2.75 13752.852 1145.029 12607.824 30 2.05 15378.189 1717.543 13660.646 40 1.75 17503.630 2290.057 15213.573 50 1.54 19253.993 2862.572 16391.422 60 1.40 21004.366 3436.086 17569.270 Peak Detention 90 0.90 20264.201 5152.629 15101.572 120 0.70 21004,356 6670.172 14134.184 180 0.54 24305.041 10305.258 13999.783 240 0.44 26405.476 13740.344 12665.133 300 0.36 27005.601 17175.430 9830.171 360 0.32 28805.974 20610.516 8195.458 720 0.105 33306.908 41221.032 -7914.124 r uo/i(, Area 4 100 Year Storm C = 0.574 Release Rate = 0.162 cfs/acre Area = 0.866 Total Release Rate = 0.140 CIS Rainfall Accumulated Allowable Needed Time Intensity Volume Release Detention (min.) (in/hr) (CF) (CF) (CF) 5 5.95 887.669 42.078 845.591 10 4.05 1208.423 84.155 1124.268 15 3.25 1454.583 126.233 1328.350 20 2.75 1641.068 168.310 1472.758 30 2.05 1835.013 252.466 1682.547 40 1.75 2088.632 336.621 1752.011 50 1.54 2297.495 420.776 1876.719 60 1.40 2506.359 504.931 2001.427 Peak Detention 90 0.90 2416.846 757397 1659.449 120 0.70 2506.359 1009.662 1496.496 100 0.54 2900.215 1614.704 1385.421 240 0.44 3150.851 2019.725 1131.126 300 0.36 3222.461 2524.656 697.805 360 0.32 3437.292 3029.687 407.704 720 0.185 3974.369 6059.175 -2084.806 Detention Pond Calculations Area Required Available Detention Detention Area 1 941.3 1,794.0 OK Areas 1&2 1,474.7 2,375.0 OK Areas 1-3 17,569.3 17,697.0 OK Area 2,001A 2,015.0 OK Orifice Plate Calculations Orifice Plate Equation 0-cd'Area"sgrt(2.9'head), cd=0.62 Top Water Flow Line Pipe Size Head Q Area Diameter Diameter Area (feet) (feet) (inches) (feet) (cis) (FeetA2) (feet) (inches) Area 1 110.01 106.99 10 2.603 0.701 0.087 0.333 4.00 Area 2 106.67 103.31 10 2.943 0.745 0.087 0.333 4.00 Area 3 98.56 94.14 10 4.003 0.954 0.096 0.349 4.19 Area 4 68.7 82.36 10 5.933 1.094 0.090 0.339 4.07 H M ,o VERL.AND � I . 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PRX N0, 8013927544 P-12112 7lvanized Ste Bolls Galvanized Steel Plate (Dia. Varies, See Sheet C3) Catch Basin Restriction P/ate Detai/ Catch Basin OPLAT£