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Home My WebLink About13633 Carey Road Drainage Report 5.13.2020May 13, 2020 Alex Jordan City of Carmel Engineering City Hall, One Civic Square Carmel, IN 46032 RE: 13633 Carey Road – Plot Plan Drainage Summary Dear Mr. Jordan: I am submitting the enclosed plot plan for approval of the above referenced project located at 13633 Carey Road. Included within this project is the construction of a ± 5330 square foot building for single family residential use, parking lot, sidewalk improvements, and a dry detention basin to accommodate the stormwater runoff. The roof drainage from the proposed building will be routed to the detention facility via the proposed roof drain outlet pipes, with the majority of the site sheet flowing to basin. The outlet pipe for the basin will connect to a proposed inlet before directing drainage south and connecting into an existing structure located in the northeast quadrant of the Carey Road and Smoky Row Road roundabout. The total impervious area for the site is ±9370 square feet. Detention Calculation Summary As you can see from the included drainage calculations, the modified rational method was used to calculate the additional storage needed to meet the allowable release rates where the post 100-year release rates is less or equal to the pre 10-year release rate, and the post 10-year release rate is less than or equal to the pre-2 year release rate. It was determined based on the post 100/pre 10-year scenario that 0.02 acre-feet of storage is required to meet these release rates. This equates to 871.2 cubic feet of storage. Based on the detention basin shown on the plot plan, the required volume of 871.2 cubic feet is met at an elevation of 846.40. See Exhibit 1 & 2 for the modified rational method detention calculations. See Exhibit 3 for the rational method runoff coefficient calculations. See Exhibit 4 for the calculation showing that the required storage volume is met at an elevation of 846.40. The outlet control orifice is a 6” pipe that will be utilized to meet the allowable discharge requirements. The pre-developed 10-year runoff rate shown in Exhibit 2 is 1.84 cfs. The outlet flow calculations illustrating that the 100-year scenario is less than the pre 10-year scenario are as follows: Q=CdA√2gH Q = 0.76 < 1.84 cfs Cd = 0.6 A = 0.196 sft (area of 6” pipe) g = 32.2 ft/s2 H = 0.65 ft (from critical storage elevation to center of pipe) A 4.5-foot-wide weir is proposed as the emergency spillway on the south side of the detention basin to convey 4.7 cfs, which is 1.25 times the maximum inflow of 3.76 cfs shown on Exhibit 2. This will also alleviate flooding conditions if the detention outlet pipe becomes plugged or overwhelmed. The spillway will drain south and follow existing drainage patterns. The verification of weir calculations are as follows: Q=CdLH1.5 Bottom of Weir Elevation = 846.40 Q = 5.25 cfs > 4.7 cfs Cd = 3.3 H = 0.5 feet L = 4.5 feet Pipe Sizing Summary A small watershed area of 0.08 acres made up entirely of grass/turf on the west side of the proposed building will be routed to the new inlet (STR 1) in the southwest corner of the site. The runoff flow rate calculations for this watershed area are as follows: Q=CIA Q = 0.22 cfs C = 0.45 (Impervious Soils with Turf) I = 6.12 (based on assumed Tc of 5 minutes) A = 0.08 acres The proposed 12” RCP leaving the site and connecting in the existing inlet was designed at a minimum slope of 0.31% to produce the required minimum velocity of 2.5 ft/s. This equates to a flow capacity of 1.98 cfs. If you should have any questions or comments concerning this project, feel free to contact me at (317) 780-1555 ext 112. Sincerely, CrossRoad Engineers, PC Gregory J. Ilko, P.E. Vice President DETENTION STORAGE CALCULATIONS Project:13633 Carey Road Designer:GJI Date:rev 4/29/2020 Release Rate Return Period 2 yrs Design Return Period 10 yrs Watershed Area, (AU)0.69 acres Watershed Area, (AD)0.69 acres (Undeveloped Watershed)(Developed Watershed) Time of Concentration 10.00 min.Developed Runoff 0.598 (Undeveloped Watershed)Coefficient, (CD) Rainfall Intensity, (iU)3.95 in./hr Undeveloped Runoff 0.51 Coefficient, (CU) Undeveloped Runoff Rate, (O)1.39 cfs (O = CU*iU*AU) Storm Rainfall Inflow Outflow Storage Required Duration Intensity Rate Rate Rate Storage td id I(td) =O =I(td)-O [I(td)-O]*td/12 (CD*id*AD)(CU*iU*AU) (hrs)(in./hr)(cfs)(cfs)(cfs)(acre-ft) 0.08 6.12 2.53 1.39 1.14 0.01 0.17 5.22 2.15 1.39 0.76 0.01 0.25 4.55 1.88 1.39 0.49 0.01 0.50 3.25 1.34 1.39 -0.05 0.00 1.00 2.03 0.84 1.39 -0.55 -0.05 2.00 1.11 0.46 1.39 -0.93 -0.16 3.00 0.84 0.35 1.39 -1.04 -0.26 6.00 0.50 0.21 1.39 -1.18 -0.59 12.00 0.29 0.12 1.39 -1.27 -1.27 24.00 0.16 0.07 1.39 -1.32 -2.65 DETENTION STORAGE CALCULATIONS Project:13633 Carey Road Designer:GJI Date:rev 4/29/2020 Release Rate Return Period 10 yrs Design Return Period 100 yrs Watershed Area, (AU)0.69 acres Watershed Area, (AD)0.69 acres (Undeveloped Watershed)(Developed Watershed) Time of Concentration 10.00 min.Developed Runoff 0.598 (Undeveloped Watershed)Coefficient, (CD) Rainfall Intensity, (iU)5.22 in./hr Undeveloped Runoff 0.51 Coefficient, (CU) Undeveloped Runoff Rate, (O)1.84 cfs (O = CU*iU*AU) Storm Rainfall Inflow Outflow Storage Required Duration Intensity Rate Rate Rate Storage td id I(td) =O =I(td)-O [I(td)-O]*td/12 (CD*id*AD)(CU*iU*AU) (hrs)(in./hr)(cfs)(cfs)(cfs)(acre-ft) 0.08 9.12 3.76 1.84 1.93 0.01 0.17 7.78 3.21 1.84 1.37 0.02 0.25 6.77 2.79 1.84 0.96 0.02 0.50 4.84 2.00 1.84 0.16 0.01 1.00 3.03 1.25 1.84 -0.59 -0.05 2.00 1.87 0.77 1.84 -1.07 -0.18 3.00 1.42 0.59 1.84 -1.25 -0.31 6.00 0.85 0.35 1.84 -1.49 -0.74 12.00 0.48 0.20 1.84 -1.64 -1.64 24.00 0.27 0.11 1.84 -1.73 -3.45 ELEVATION A FT^2 H (FT) STORAGE VOLUME (FT^3) 845.50 790 0.00 0.0 845.83 924 0.33 282.8 846.17 1064 0.67 621.0 846.18 1068 0.68 631.8 846.19 1073 0.69 642.6 846.20 1077 0.70 653.5 846.21 1081 0.71 664.4 846.22 1086 0.72 675.3 846.23 1090 0.73 686.3 846.24 1095 0.74 697.4 846.25 1099 0.75 708.5 846.26 1104 0.76 719.6 846.27 1108 0.77 730.8 846.28 1112 0.78 742.0 846.29 1117 0.79 753.2 846.30 1121 0.80 764.5 846.31 1126 0.81 775.9 846.32 1130 0.82 787.3 846.33 1135 0.83 798.7 846.34 1139 0.84 810.2 846.35 1143 0.85 821.7 846.36 1148 0.86 833.3 846.37 1152 0.87 844.9 846.38 1157 0.88 856.6 846.39 1161 0.89 868.3 846.40 1166 0.90 880.1 846.41 1170 0.91 891.8 846.42 1174 0.92 903.7 846.43 1179 0.93 915.6 846.44 1183 0.94 927.5 846.45 1188 0.95 939.5 846.46 1192 0.96 951.5 846.47 1197 0.97 963.5 846.48 1201 0.98 975.6 846.49 1205 0.99 987.8 846.50 1210 1.00 1000.0