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HomeMy WebLinkAboutDrainage Memo kimley-horn.com 250 East 96th Street, Suite 580, Indianapolis, IN 46240 317 218 9560 Drainage Memorandum To: City of Carmel From: Bryan Sheward, P.E Kimley-Horn and Associates, Inc. Original: Revised: February 28, 2025 April 11, 2025 April 25, 2025 Project Summary Project Name: Carmel Gateway East Lawn Location: Parkwood Crossing/Carmel Gateway, Carmel, IN Report Type: Drainage Memorandum Reviewing Agency: City of Carmel Basin Runoff Calculations: Rational Method Design Standards: City of Carmel Stormwater Technical Standards Manual (STSM) Project Narrative Project Scope Kimley-Horn and Associates, Inc. has been retained by Rubenstein Partners to prepare civil construction documents and provide civil engineering design services for the “Carmel Gateway East Lawn” project, a proposed amenity area and pedestrian drop off is proposed in front of Buildings 8 and 9 within the Parkwood Crossing office park development on the north side of 96th Street between College Avenue and Westfield Road. Herein the “Carmel Gateway East Lawn” project will be referred to as the Project. The Project scope includes: 1. Replacement of existing concrete drop off areas and entrance concrete sidewalks 2. Removal of asphalt and parking to create an amenity green space area 3. Installation of enhanced landscaping within the project area 4. Enhancement of stormwater conveyance system Existing Conditions In existing conditions, there are four primary inlets that drain the project area. Two are located within the project boundary, and two are located directly south of the project area. The inlets collect surface flow and directs runoff through an existing pipe network and underground detention system that exists under the existing parking lot. Page 2 kimley-horn.com 250 East 96th Street, Suite 580, Indianapolis, IN 46240 317 218 9560 In the existing conditions, the watershed area draining to the existing inlets is ~2.25 acres at a composite Rational C value = 0.79. The existing underground detention system was designed for and installed with the construction of the existing buildings and parking lot areas. Based on historical plans and the original detail below, it was comprised of three 48” diameter HI-Q Perforated Pipes running under the drive isles in the existing parking lot. However, based on survey field observations conducted in 2024, it is believed that the material was switched to Corrugated Metal Pipe. Per the existing drainage report dated December 6, 2001, the site consists of two 5-story 210,000 square feet office buildings along with associated parking, landscaping, and storm water management system as illustrated on the Development Plan dated November 30, 2001. The overall site acreage is 20.05 AC, with approximately 15.97 AC of post-developed conditions flowing to the outlet point. There is an existing underground detention system which was sized by limiting the 100- year post-development peak discharge to the 10-year pre-development peak rate at the point of discharge when first designed/installed. According to the existing drainage report, the detention system is the Hancor LandMax Sure-Lok system, which is believed to have been used in various other projects within the City of Carmel including the Fidelity Keystone offices and the Merchants Square development. There is no off-site / upstream flow specified. The allowable release rates outlined in the report are 20.78 cfs for the 100- year 24-hour condition storm event. The peak discharge was limited to approximately 20.5 cfs through an 18-inch outlet pipe. The overall volume of detention provided at the time of installation/design was approximately 3 acre-feet. See Appendix B for existing drainage report. Page 3 kimley-horn.com 250 East 96th Street, Suite 580, Indianapolis, IN 46240 317 218 9560 Proposed Conditions In the proposed conditions, the watershed area remains the same, but additional stormwater infrastructure is added due to grading adjustments. The composite Rational C value decreases to 0.55, as approximately 0.94 acres of pervious area is being added. The two inlets south of the project area will have reduced catchment areas, but their rational composite C value remains unchanged. The two northern inlets within the project boundary will have both reduced catchment areas and a lower rational composite C value due to the added storm infrastructure and impervious pavement removal. See Appendix A for drainage exhibits and calculations. To estimate the 10-year peak flow for the existing inlets under both existing and proposed conditions, a Time of Concentration of 5 minutes has been assumed. The summary table below compares the existing and proposed conditions for the watershed. Existing Conditions Proposed Conditions Area (ac) 2.25 acres 2.25 acres Impervious Area (ac) / Rational C 1.99 Acres / 0.90 1.05 acres / 0.90 Pervious Area (ac) / Rational C 0.26 Acres / 0.30 1.20 acres / 0.30 Composite Rational C 0.79 0.55 Rainfall Intensity (5 Min Tc) 6.12 in/hr 6.12 in/hr 10yr Q (cfs) 10.88 7.57 Emergency Flood Routing In existing conditions, should the existing inlets fail, stormwater will pond up to a point where it will spill southeastward across the existing parking lot towards the entrance off of 96th street. Refer to Appendix A for existing conditions flood routing exhibit. The highest elevation of spill point is 820.70. The finish floor elevations of Buildings 8 and 9 are 822.72 and 822.06, respectively. Therefore, Building 8 has 2.05 feet of clearance, and Building 9 has 1.36 feet of clearance between the spill point and the existing finish floor elevations. In the proposed conditions, the spill point elevation is 820.80. This reduces the clearance to 1.92 feet for Building 8 and 1.26 feet for Building 9. Stormwater Quality Under existing conditions, no stormwater quality BMPs are in place to treat runoff prior to discharge into the existing storm system. The proposed design includes a net reduction in impervious area and incorporates turf with gentle lawn slopes that will help to naturally scrub runoff before it is conveyed into the system. To further enhance water quality, FlexStorm Pure FX Inlet Filters—rated for 82% TSS removal—are proposed. BroadAcre – McCordsville, Indiana Page 6 Appendix A: Aerial Photograph Page 6 of 63 Appendix A: Drainage Calculations PA R K W O O D B U I L D I N G 9 PARKWOOD BUILDING 8 NORTH EX-1 EX I S T I N G CO N D I T I O N S EX H I B I T CA R M E L G A T E W A Y EA S T L A W N © NO T A P P R O V E D F O R CO N S T R U C T I O N SURFACE COVER SUMMARY PARKWOOD BUILDING 9 PA R K W O O D B U I L D I N G 8 96 T H S T R E E T February 25, 2025 CARMEL GATEWAY EAST LAWN EXISTING CONDITIONS FLOOD ROUTING EXHIBIT CARMEL, IN 0'60'30' SCALE: 1" = 60'NO R T H GRADING LEGEND PARKWOOD BUILDING 8 PA R K W O O D B U I L D I N G 9 PA R K W O O D B U I L D I N G 9 PARKWOOD BUILDING 8 NORTH EX-1 PR O P O S E D CO N D I T I O N S EX H I B I T CA R M E L G A T E W A Y EA S T L A W N © NO T A P P R O V E D F O R CO N S T R U C T I O N SURFACE COVER SUMMARY PARKWOOD BUILDING 9PARKWOOD BUILDING 9 PARKWOOD BUILDING 9 PA R K W O O D B U I L D I N G 8 96 T H S T R E E T April 11, 2025 CARMEL GATEWAY EAST LAWN PROPOSED CONDITIONS FLOOD ROUTING EXHIBIT CARMEL, IN 0'60'30' SCALE: 1" = 60'NO R T H GRADING LEGEND PA R K W O O D B U I L D I N G 9 PARKWOOD BUILDING 8 April 11, 2025 CARMEL GATEWAY EAST LAWN CATCHMENT AREA MAP CARMEL, IN 0'40'20' SCALE: 1" = 40' NORTH 170043003 Carmel Gateway East Lawn DATE:4/11/2025 Pervious 0.30 EX1 0.49 0.00 0.49 0.30 0.15 EX2 0.15 0.03 0.12 0.41 0.06 D1 0.29 0.22 0.07 0.72 0.21 D2 0.11 0.07 0.04 0.65 0.07 D3 0.20 0.14 0.06 0.69 0.14 D4 0.17 0.13 0.04 0.72 0.12 D5 0.14 0.07 0.07 0.58 0.08 D7 0.09 0.01 0.08 0.36 0.03 D8 0.20 0.14 0.06 0.69 0.14 D9 0.11 0.03 0.08 0.45 0.05 D10 0.29 0.16 0.13 0.60 0.18 D11 0.23 0.00 0.23 0.30 0.07 Asphalt/ Concrete/ Roof 0.85 Runoff Coefficients: NotesPROPOSED CONDITIONS ONSITE DRAINAGE AREA CALCULATIONS Drainage Area Total Area (ac) Impervious Area (ac) Pervious Area (ac) Rational Coefficient Area * C 170043003 Carmel Gateway East Lawn 170043003 Carmel Gateway East Lawn DATE:4/11/2025 Structure ID Tributary Area A (ac) C 10-YR Peak Discharge (cfs) 100-YR Peak Discharge (cfs)Grate Max Ponding Depth H (ft) Entrance Grate Area A (sf) Entrance Loss Coefficient C Entrance Perimeter P (ft) Grate Capacity Q (cfs) 50% Clogged (cfs) EX1 0.49 0.30 0.90 1.34 R-3472 0.50 1.30 0.61 7.30 4.43 2.2 EX2 0.15 0.41 0.38 0.56 R-3472 0.50 1.30 0.61 7.30 4.43 2.2 D1 0.29 0.72 1.27 1.90 R-3287-SB10 0.50 1.50 0.61 5.50 5.11 2.6 D2 0.11 0.65 0.44 0.65 R-3286-8V 0.50 0.70 0.61 4.40 2.38 1.2 D3 0.2 0.69 0.84 1.25 R-3286-8V 0.50 0.70 0.61 4.40 2.38 1.2 D4 0.17 0.72 0.75 1.12 R-3286-8V 0.50 0.70 0.61 4.40 2.38 1.2 D5 0.14 0.58 0.49 0.73 R-3286-8V 0.50 0.70 0.61 4.40 2.38 1.2 D7 0.09 0.36 0.20 0.30 R-2750 0.50 1.80 0.61 8.30 6.13 3.1 D8 0.2 0.69 0.84 1.25 R-3286-8V 0.50 0.70 0.61 4.40 2.38 1.2 D9 0.11 0.45 0.30 0.45 R-2750 0.50 1.80 0.61 8.30 6.13 3.1 D10 0.29 0.60 1.07 1.60 R-3286-8V 0.50 0.70 0.61 4.40 2.38 1.2 D11 0.23 0.30 0.42 0.63 R-2750 0.50 1.80 0.61 8.30 6.13 3.1 Notes 1)Runoff = CIA 2)Assumed a 5 min inlet Time of Concentration Intensity 10-yr =6.12 in/hr Intensity 100-yr =9.12 in/hr 3)Grate Capacity Lesser of Q=3.3*P*H3/2 & Q=0.6*A*(2*32.2*H)1/2 4)Open Area* (sf) MH Neenah R-2750 1.80 MH Neenah R-3286-8V 0.70 MH Neenah R-3287-SB10 1.50 MH Neenah R-3472 1.30 Concrete End Section CES - *Open Area & Entrance Perimeter values obtained from Neenah 5)Casting types on STR's EX1 & EX2 are assumed. Proposed conditions will reduce the drainage area to these structures, creating more inlet capacity than the existing conditions. 5.50 7.30 - INLET CAPACITY CALCULATIONS Entrance Perimeter* (ft) 8.30 4.40 Date:Project:Storm:10-YR By:CDC Line Length Incr.Area Total Area Runoff Coeff.Inlet Time Time Conc Rnfal Int Total Runoff Adnl Flow Total Flow Capac Full Full Flow Velocity Pipe Size Pipe Slope Inv Elev Dn Inv Elev Up HGL Dn HGL Up Grnd/Rim Dn Grnd/Rim Up (ft)(ac)(ac)(C)(min)(min)(in/hr)(cfs)(cfs)(cfs)(cfs)(ft/s)(in)(%)(ft)(ft)(ft)(ft)(ft)(ft) 1 Outfall 54.817 0.11 0.31 0.65 0.07 0.21 5 5.9 5.9 1.26 0 1.26 7.43 4.20 0.013 18 0.5 815.62 815.89 816.04 816.31 819.65 820.59 D2 TO EX1 2 Outfall 54.512 0.17 0.3 0.72 0.12 0.2 5 6.1 5.9 1.18 0 1.18 7.43 4.20 0.013 18 0.5 814.81 815.08 815.21 815.49 819.72 820.48 D4 TO EX2 3 1 58.262 0.2 0.2 0.69 0.14 0.14 5 5 6.1 0.84 0 0.84 2.52 3.21 0.013 12 0.5 816.39 816.69 817.09 817.14 820.59 820.71 D3 TO D2 4 Outfall 28.763 0 0.91 0 0 0.46 0 7.5 5.6 2.57 0 2.57 10.44 5.91 0.013 18 0.99 814.61 814.89 815.12 815.5 819.72 820.31 D6 TO EX2 5 4 42.977 0.11 0.4 0.45 0.05 0.22 5 5.5 6 1.34 0 1.34 3.56 4.54 0.013 12 1 815.55 815.97 815.97 816.46 820.31 819.55 D9 TO D6 6 5 40.521 0.29 0.29 0.6 0.17 0.17 5 5 6.1 1.07 0 1.07 3.56 4.54 0.013 12 1 816.07 816.48 816.46 816.91 819.55 820.37 D10 TO D9 7 4 54.364 0.09 0.28 0.36 0.03 0.17 5 6.3 5.9 0.97 0 0.97 3.56 4.54 0.013 12 1 815.39 815.94 815.75 816.35 820.31 819.7 D7 TO D6 8 7 82.027 0.2 0.2 0.69 0.14 0.14 5 5 6.1 0.83 0 0.83 2.92 3.71 0.013 12 0.67 816.04 816.59 816.4 816.97 819.7 820.48 D8 TO D7 9 4 80.722 0.23 0.23 0.3 0.07 0.07 5 5 6.1 0.42 0 0.42 3.56 4.54 0.013 12 1 815.75 816.56 815.98 816.83 820.31 820.15 D11 TO D6 10 2 40.226 0.14 0.14 0.58 0.08 0.08 5 5 6.1 0.49 0 0.49 3.56 4.54 0.013 12 1 815.58 815.98 815.83 816.27 820.48 820.5 D5 TO D4 11 Outfall 54.12 0.29 0.29 0.72 0.21 0.21 5 5 6.1 1.28 0 1.28 47.46 3.55 0.013 48 0.11 813.26 813.32 813.71 813.77 819.65 820.16 D1 TO EX1 Program: Hydraflow Line IDTotalC x A Mannings "n" ValueLine To Line IncrC x A 4/11/2025 CARMEL GATEWAY EAST LAWN National Flood Hazard Layer FIRMette 0 500 1,000 1,500 2,000250 Feet Ü SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT SPECIAL FLOOD HAZARD AREAS Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or Depth Zone AE, AO, AH, VE, AR Regulatory Floodway 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mile Zone X Future Conditions 1% Annual Chance Flood Hazard Zone X Area with Reduced Flood Risk due to Levee. See Notes.Zone X Area with Flood Risk due to Levee Zone D NO SCREEN Area of Minimal Flood Hazard Zone X Area of Undetermined Flood Hazard Zone D Channel, Culvert, or Storm Sewer Levee, Dike, or Floodwall Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of Study Jurisdiction Boundary Digital Data Available No Digital Data Available Unmapped This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 11/25/2024 at 11:01 PM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time. This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for unmapped and unmodernized areas cannot be used for regulatory purposes. Legend OTHER AREAS OF FLOOD HAZARD OTHER AREAS GENERAL STRUCTURES OTHER FEATURES MAP PANELS 8 B 20.2 The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location. 1:6,000 86°8'56"W 39°55'55"N 86°8'19"W 39°55'28"N Basemap Imagery Source: USGS National Map 2023 Agricultural Organic Soil Subsidence—Hamilton County, Indiana Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/25/2024 Page 1 of 5 44 2 0 0 4 0 44 2 0 0 7 0 44 2 0 1 0 0 44 2 0 1 3 0 44 2 0 1 6 0 44 2 0 1 9 0 44 2 0 2 2 0 44 2 0 0 4 0 44 2 0 0 7 0 44 2 0 1 0 0 44 2 0 1 3 0 44 2 0 1 6 0 44 2 0 1 9 0 44 2 0 2 2 0 573030 573060 573090 573120 573150 573180 573210 573240 573270 573300 573330 573030 573060 573090 573120 573150 573180 573210 573240 573270 573300 573330 39° 55' 44'' N 86 ° 8 ' 4 3 ' ' W 39° 55' 44'' N 86 ° 8 ' 3 0 ' ' W 39° 55' 37'' N 86 ° 8 ' 4 3 ' ' W 39° 55' 37'' N 86 ° 8 ' 3 0 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 16N WGS84 0 50 100 200 300 Feet 0 20 40 80 120 Meters Map Scale: 1:1,450 if printed on A landscape (11" x 8.5") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons Severe subsidence Moderate subsidence Low subsidence Mineral soil Not rated or not available Soil Rating Lines Severe subsidence Moderate subsidence Low subsidence Mineral soil Not rated or not available Soil Rating Points Severe subsidence Moderate subsidence Low subsidence Mineral soil Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:15,800. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Hamilton County, Indiana Survey Area Data: Version 25, Aug 27, 2024 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jun 15, 2022—Jun 21, 2022 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Agricultural Organic Soil Subsidence—Hamilton County, Indiana Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/25/2024 Page 2 of 5 Agricultural Organic Soil Subsidence Map unit symbol Map unit name Rating Component name (percent) Rating reasons (numeric values) Acres in AOI Percent of AOI UbaA Urban land- Brookston complex, 0 to 2 percent slopes Not rated Urban land (60%) 3.2 48.1% UcfA Urban land- Crosby silt loam complex, fine-loamy subsoil, 0 to 2 percent slopes Not rated Urban land (60%) 0.2 2.5% UkbB2 Urban land- Miami silt loam complex, 2 to 6 percent slopes, eroded Not rated Urban land (60%) 3.3 49.4% Totals for Area of Interest 6.7 100.0% Rating Acres in AOI Percent of AOI Null or Not Rated 6.7 100.0% Totals for Area of Interest 6.7 100.0% Agricultural Organic Soil Subsidence—Hamilton County, Indiana Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/25/2024 Page 3 of 5 Description SOH - Soil Health Agricultural Organic Soil Subsidence Soil health is primarily influenced by human management, which is not captured in soil survey data at this time. These interpretations provide information on inherent soil properties that influence our ability to build healthy soils through management. Organic soils used in agricultural production are subject to a loss of volume and depth of organic material due to oxidation caused by above normal microbial activity resulting from excessive water drainage, soil disturbance, or extended drought. Microbial mediated oxidation is the primary driver of volume reduction once excess water is removed. Soil shrinkage and compaction due to dewatering is considered to be secondary. Any drawdown resulting in water levels below soil surface can result in increased subsidence rates. The subsidence rate can also be influenced by agricultural practices. The type of tillage operation, such as plowing, disc harrowing and switch plowing, moldboard plowing increase the oxidation rate. The use of no-till practice is recommended to slow the subsidence. Any aggressive tillage measure increases microbiological activity and decreases carbon sequestration. Drainage water management can be implemented to control water tables to help slow the subsidence rate. Several soil and site properties influence the rate of organic matter oxidation and subsidence. Organic soils are generally found in cooler climates, thus, farmed organic soils in warmer climates are vulnerable. Periodic saturation of the organic soil with water tends to decrease the rate of oxidation since anaerobic decomposition is slower than aerobic decomposition. The pre-existing degree of decomposition is also a factor in the subsidence rate since as organic matter is decomposed, the remaining material becomes more resistant to decay. Acidity in soils tends to slow microbial growth so acid soils are less prone to subsidence. The degree to which each of the soil properties considered promotes oxidation is rated. The average degree of accelerating microbial oxidation of organic matter is taken as the overall rating. The ratings are both verbal and numerical. Numerical ratings indicate the suitability of the individual soil properties. The ratings are shown in decimal fractions ranging from 0.01 to 1.00. They indicate gradations between the point at which a soil feature has the most severe propensity for subsidence (1.00) and the point at which the soil has no propensity for subsidence, such as a mineral soil (0.00). Rating class terms indicate the rate at which the soils are likely to subside considering all the soil features that are examined for this rating. "Severe subsidence" indicates that the soil has features that are very favorable for the aerobic soil organisms that cause subsidence. Very careful management will be needed to slow the subsidence rate. "Moderate subsidence" indicates that the soil has features that are moderately favorable for aerobic soil organisms. The soil can be made more sustainable by careful management. "Low subsidence" Agricultural Organic Soil Subsidence—Hamilton County, Indiana Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/25/2024 Page 4 of 5 indicates that the soil has one or more features that are unfavorable for aerobic soil organisms. With careful management the soil can be used for crop production and be nearly sustainable. Soils that are not organic are rated "Mineral soil". These soils do not subside due to organic matter oxidation. The map unit components listed for each map unit in the accompanying Summary by Map Unit table in Web Soil Survey or the Aggregation Report in Soil Data Viewer are determined by the aggregation method chosen. An aggregated rating class is shown for each map unit. The components listed for each map unit are only those that have the same rating class as listed for the map unit. The percent composition of each component in a particular map unit is presented to help the user better understand the percentage of each map unit that has the rating presented. Other components with different ratings may be present in each map unit. The ratings for all components, regardless of the map unit aggregated rating, can be viewed by generating the equivalent report from the Soil Reports tab in Web Soil Survey or from the Soil Data Mart site. Onsite investigation may be needed to validate these interpretations and to confirm the identity of the soil on a given site. This interpretation is being provided for review and comment by the user community. Please forward any feedback to the Soils Hotline soilshotline@lin.usda.gov. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Agricultural Organic Soil Subsidence—Hamilton County, Indiana Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/25/2024 Page 5 of 5 BroadAcre – McCordsville, Indiana Page 6 Appendix A: Aerial Photograph Page 6 of 63 Appendix A: Drainage CalculationsB