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Home My WebLink AboutDrainageMercedes Benz Service Center 4000 E. 96 Street Carmel, Indiana DRAINAGE REPORT Mercedes Benz Service Center 4000 E. 96 Street Carmel, Indiana Report Contents Narrative I. Design Calculations A. Pre Development Calculations B. Post Development Calculations C. Detention Calculations D. Pipe Sizing Calculations E. Water Quality II. Project Summary III. Hydrologic /Hydraulic Calculations Exhibits A. Basin Exhibits B. HydroCAD (Hydrologic) Computer Output C. Pipe Calculations D. Off-site Analyses E. Water Quality Documents Narrative This project proposes improvements to 4000 E. 96 Street, Carmel, Indiana. Improvements consist of removing existing concrete sunken dock areas, replacing the dock areas with a building addition, and reconstructing adjoining parking lot areas. All proposed improvements will outlet to a swale /ditch along the north side of the property. This swale /ditch drains approximately 34.3 acres of upland areas consisting of business /industrial uses. The effects of this swale were factored into the consideration and design of proposed storm sewers. 1. Design Calculations: A. Pre Development Calculations 1 23 4 RECEIVED UULC 1 8 2009 DOCS 0 i i II I i ''i f.. No- 1990011:3 $TArFE 01' iiiit0 This project will replace existing impervious areas with new impervious areas. New parking lot areas were limited to ensure no change in the amounts of project impervious areas. As such, the proposed impervious areas equal the existing impervious areas. See the next section (I. Design Calculations: B. Post Development Calculations) for pre and post storm run off amounts. Bordenet Civil Engineering Land Surveying, LLC 8902 Alibeck Ct. Office: 317 -536 -6181 Indianapolis, [N 46256 sbordenet a civil- Is.com Storm Event WQ Q2 Q5 Q10 Q25 Q50 Q100 Inches of Rainfall 1 2.66 3.27 3.83 4.72 5.52 6.46 On -site, cfs 0.19 0.51 0.63 0.74 0.91 1.06 1.24 Off -site, cfs 3.16 16.23 21.42 26.22 33.86 40.73 48.77 Mercedes Benz Service Center 4000 E. 96 Street Carmel, Indiana L Design Calculations: B. Post Development Calculations See section III. Hydrologic /Hydraulic Calculations Exhibit: indicating the existing and proposed impervious areas. Also, sheets indicating limits of construction. Offsite areas draining basin delineation may be seen in this section of the report. A. Basin Exhibits of this report for exhibits see the construction plans for 24" x 36" plan to the site's outlet were also assessed, and the See section III. Hydrologic /Hydraulic Calculations Exhibit: B. HydroCAD (Hydrologic) Computer Output of this report for storm run -off quantities. This project will disturb approximately 23,990 sft. of impervious areas. This area was assessed as CN =99.5. This curve number was used as required for water quality considerations, and it was used for site run -off and storm pipe sizing for conservative measure (instead of standard CN 98). The basin area and curve number in conjunction with Carmel rainfall depths and a NRCS Type II rainfall distribution were entered into hydrograph software to determine the 24 hour storm rates. Upland offsite areas draining to the site's discharge release point were also assessed in the previously described manner. The upland areas were considered urban commercial /industrial areas with 82% impervious coverage and a curve number of 91. The following table summarizes the various storm rates: L Design Calculations: C. Detention Calculations As this project will not change the site run -off rates, there is no detention proposed. See the section I. Design Calculations: D .Pipe Sizing Calculations for a discussion of on -site and off -site impacts on new and existing storm drains. L Design Calculations: D. Pipe Sizing Calculations See section III. Hydrologic /Hydraulic Calculations Exhibit: C. Pipe Calculations of this report for exhibits indicating pipe locations and labels. Also in this section are Manning pipe analyses indicating pipe capacities. The storm sewer functions as a receiving pipe that discharges to a diversion structure. The diversion structure sends an initial water quality treatment rate to an Aquaswirl and all subsequent storm discharge to the site outlet. The water quality discharge also is released to the same site outlet but downstream of the diversion structure. Though the proposed building addition discharges to the diversion structure, it is assumed for conservative measure that all proposed areas discharge to the upstream most receiving pipe. Bordenet Civil Engineering Land Surveying, LLC 8902 Alibeck Ct. Office: 317- 536 -6181 Indianapolis, IN 46256 sbordenet@civil-ls.com civil- Is.com Pipe Label Q2 Tailwater from Manning's Q2 Tailwater from HY -8 Q10 Tailwater from Manning's Q10 Tailwater from HY -8 Q100 Tailwater from Manning's Q100 Tailwater from HY -8 Diversion Structure 746.81 747.06 747.48 Water Quality Structure 746.50 746.85 747.80 Pipe Label Pipe Size Slope 10 Year Discharge 0.34 cfs 10 Year Velocity 3.0 fps Max Capacity 4.2 cfs Max Velocity 5.4 fps Pipe 1 12" 1.00% Pipe 3 12" 0.20% 0.34 cfs 1.7 fps 1.9 cfs 2.4 fps Pipe 5 12" 0.25% 0.40 cfs 1.9 fps 2.1 cfs 2.7 fps Pipe 6 12" 0.20% 0.74 cfs 2.1 fps 1.9 cfs 2.4 fps Pipe 8 12" 0.20% 0.74 cfs 2.1 fps 1.9 cfs 2.4 fps Mercedes Benz Service Center 4000 E. 96 Street Carmel, Indiana The ten year event for the proposed improvements is 0.74 cfs. This enters the upstream storm sewer receiving pipe. The diversion structure sends 0.34 cfs to the water quality structure and 0.40 cfs to the site outlet. See section I. Design Calculations: E. Erosion Control Methods for a discussion of water quality treatment rates. The following table summarizes the characteristics of the ten year flow rates in the pipes and the pipes' maximum capacities: See section III. Hydrologic /Hydraulic Calculations Exhibit: Off -site Analyses of this report for HY -8 offsite pipe analysis for the culvert carrying the offsite swale (proposed construction's site outlet) under Lakeshore Drive. Also see the same section for a Manning's analysis of the swale leading into the culvert. Currently the site's outlet, the swale on the north side of the building addition, backs up into the existing site during heavy storms. It is recognized that the storm sewer improvements will limit the flooding of the proposed parking lot but it will eliminate flooding entirely. The proposed storm sewer discharges into the swale at two points. One is at the diversion structure, and the second is at the water quality structure. When the storm sewer is inundated at these locations, off -site storm water will flow back into the proposed storm sewer and site. Flow back into the site is analyzed by projecting a Manning's channel head from the diversion structure outlet and an HY -8 Lakeshore drive culvert headwater at the Lakeshore Drive culvert from the water quality structure. This was done for the two, ten and on- hundred year events. The highest resulting head was accepted as the depth of parking lot inundation in the northwest portion of the proposed lot construction. The following table summarizes the results: As shown in the table, the two year event will not back up into the lower parking lot. The ten year event will inundate the parking lot by 0.06' (3/4 The on- hundred year event will inundate into the parking lot by 0.80' (9.5 8902 Alibeck Ct. Indianapolis, IN 46256 Bordenet Civil Engineering Land Surveying, LLC Office: 317 -536 -6181 sbordenet @civil- ls.com Mercedes Benz Service Center 4000 E. 96 Street Carmel, Indiana L Design Calculations: E. Water Quality Note in the HY -8 culvert analysis (see profile section diagram) that culvert under Lakeshore Drive has sufficient capacity to convey all storm events including the one hundred year event. See section III. Hydrologic /Hydraulic Calculations Exhibit: Water Quality Documents for the site CN -wq, BMP structure sizing chart, and Structure O &M Manual. As previously discussed, the proposed water quality curve number was determined to be 99.5. By hydrograph analysis and previously indicated in this report, the water quality treatment rate was determined to be 0.19 cfs (minimum). An AS -2 offline Aquaswirl was selected to treat a rate of 0.34 cfs. Therefore, the depth flowing into and through the Aquaswirl is (746.05 +0.30, see Manning's pipe calculation sheet for 12" RCP at 0.20 746.35. Based on the HY -8 Analysis, the depth at the structure outlet is 746.19. Therefore, the required rate will flow through unaffected by the off -site Tailwater and the required rate is achieved. The diversion structure was designed by setting the diversion pipe's outlet (upstream invert of Pipe 5) at a depth of 0.3 feet (resulting depth from 0.34 cfs in 12" RCP at 0.2 see Manning's analysis sheet) above the upstream invert of Pipe 3 (discharge pipe into the water quality structure. As previously indicated in this section of the report, the Tailwater of the water quality structure is below the structure's designed flow rate depth during the onsite /offsite water quality discharges. After the this initial discharge (ie. first flush), the offsite swale will inundate the diversion structure's outlet and water quality outlet. This equal head on the system inlet and outlet will effectively "shut off" flow through this section of storm sewer. The swale depths will back above the diversion structure into the northwest parking lot as previously discussed. IL Project Summary This project does not propose detention. Since discharge from the site is not increased and downstream facilities (swale along the north side of the project and culvert under Lakeshore Drive) are more than adequate to handle discharges from the site, they are not necessary. The project will address water quality requirements. The main focus of this project is to provide a building addition for the site. New parking lots will be constructed and be drained by new storm sewers. The new storm sewers and grading will provide limited improvement in flooding. The parking lot flooding is manageable and safe under high flow events (9.5" during the one hundred year event). It should be noted that the cover on the proposed pipe is 1' at a minimum. This cover is in a non -paved area and is deemed acceptable. If the project were to raise the site as much as possible and provide inlet type pipe collection, inlets would necessarily be in pavement areas. The inlet storm sewer pipes would then have covers of approximately 6 Project improvements are limited by the site outlet (pipe under Lakeshore Drive) and existing finished floors. The proposed solution provides acceptable (but not preferred) cover and manageable parking lot inundation from off -site drainage. Bordenet Civil Engineering Land Surveying, LLC 8902 Alibeck Ct. Office: 317 536 -6181 Indianapolis, IN 46256 sordenet @civil- Is.com Mercedes Benz Service Center 4000 E. 96 Street Carmel, Indiana III. Hydrologic /Hydraulic Calculations Exhibit: A. Basin Exhibit Bordenet Civil Engineering Land Surveying, LLC 8902 Alibeck Ct. Office: 317 -536 -6181 Indianapolis, IN 46256 sordenet @civil- ls.com ii/ ifil 08 Vg 1 1 :7°,..i.t. /27—, /Q 7.---. 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