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C-RPT-2201500-Treeline SWM rEPORT_v1 Stormwater Management Report For the Proposed: The Yard Located at: 2840 Highway 421 Wilmington, NC Prepared for: 2830 Highway 421 Owners, LLC 200 Garden City Plaza, Suite 325 Garden City, NY 11530 December 5, 2022 Prepared by: BL Companies 3420 Torringdon Way, Suite 210 Charlotte, North Carolina 28277 Phone: (704) 565-7070 Fax: (704) 565-7073 Firm NC License No. C-4082 BL Project Number: 2201500 Prepared by: Andy Mueller, P.E. 1 Table of Contents Executive Summary…………………………………………………………………..2 Existing Site Conditions and Hydrologic Conditions………………………………3 Developed Site Conditions and Hydrologic Conditions…………………….4 Hydrologic Modeling Standards……………………………………………..5 Summary………………………………………………………………………5 Appendix A: Maps · NRCS Soils Survey Map · FEMA Flood Map · USGS Location Map · Site Map Appendix B: SWM Computations · Hydraflow Modeling (1”, 1-year-24 hour and 10, 25, 100 year Storm) 2 Executive Summary This report has been prepared in support of a Major Site Plan Application for The Yard by 2830 Highway 421 Owner, LLC in Wilmington, NC. The site is an existing 80.3 acre industrial site located between Highway 421 and the Northeast Cape Fear River. The site currently consists of an existing warehouse building of approximately 108,000 sf, a large stone crushing unit on a 120,000 concrete pad, associated buildings, roadways and remnants of various former, buildings, tanks and equipment. In general, the existing topography slopes from the north and west to the east side of the site to the Northeast Cape Fear River. The majority of the site is impervious with gravel, asphalt, concrete and buildings. The northern part of the side is sandy and the east side is heavily vegetated with wetlands. The site is proposed to include 4 new warehouse/office buildings with associated parking, and laydown areas. The existing 108,000 sf warehouse building on the south side of the site will remain and is currently being retrofitted. Currently the majority of the sheet flows to various points around the perimeter. The crusher pad drains mainly to a series of headwalls and inlets that flow to an existing stormwater management pond with an oil and grease separator unit at the north west corner of the site. The pond discharged through a StormFilter device and over a metal wire into an existing drainage ditch. The drainage ditch travels to an existing sandy borrow pit. This pit has concrete foundation from a former silo structure in the bottom and an overflow weir at elevation 24 from its use as a sediment basin during the crusher pad construction. It is assumed that little to no infiltration occurs in the hole due to the concrete bottom. Based on As-built drawings provided by New Hanover County the existing pond was designed to treat the 2, 10, 25 year storm as well the 1” water quality volume for the 2.75 acre crusher pad. Analysis of currently topographic survey data shows it appears additional drainage currently gets to the pond. BL has modeled the site using the designed drainage area and the current drainage area and the pond does not currently have sufficient storage volume for the area flowing to it. Due to this the pond has been redesigned to meet the drainage flowing to it.. The proposed stormwater management system will be designed to be in compliance with the New Hanover County Stormwater Management Manual. As this site primarily impervious and is a redevelopment site only the increase in impervious must be treated. The design manual requires the treatment of the 1st inch of runoff (WQv), 85% removal of TSS and 70% of TP and attenuation of the 2, 10 and 25 year 24 hour storm as well as safely release the 100 year storm for the increase impervious area. 3 A HydraCAD model, using TR-55 and SCS methodology, was developed to evaluate the existing and proposed drainage conditions of the property. The results of the analysis show that there is an increase of 13.75 acres of impervious area on site (From 20.4 ac to 34.15 acres). However the existing water quality treatment (oil grease separator and StormFilter) are being removed so it is assumed for this analysis that all impervious area will need to be treated. Existing Site Conditions and Hydrologic Conditions General Site Information The site soil identified by the United States Department of Agriculture (USDA) Natural Resources Conservation Services (NRCS) primarily has a soil rating within the project area of Group A and D. A soils are typically well drained and consist of the sandy areas to the north of the site. D soils do not drain well. Within the disturbed area the following soils are present: Kureb Sand (HSG A), Dorovan Soils (HSG B/D), Urban Land (HSB D). Per the FEMA Flood Insurance Rate Maps Number 3720311900K for New Hanover County, North Carolina, map revised date: August 18, 2018, the lower portion of the site resides in FEMA Flood Hazard Area AE with a flood elevation of 9. Existing Hydrologic Conditions The existing site drainage area that was analyzed totals 67.29 acres and has an existing 14.88 acres of impervious structure on the site. The majority of the site is impervious with gravel, asphalt, concrete and buildings. The northern part of the side is sandy and the east side is heavily vegetated with wetlands. The following is a brief analysis of the existing design points as shown on the Existing Drainage Mapping (ED-1) Map. Existing Drainage Area 101 (EDA-101): This drainage area consists of the the existing crusher pad in the middle of the site in addition to the offsite drainage form the north west adjacent properties. This area drainage via both underground storm drain and overland flow to the existing stormwater management pond at the northwest corner of the property. This pond currently outfalls via a manmade ditch to a sandy borrow pit to the east. Existing Drainage Area 102 (EDA-102): This drainage area generally consists of the northern portion of the site that drains to the sandy borrow pit in the center of the site. Runoff to this pit appears to generally infiltrate into the sandy soils 4 Existing Drainage Area 103 (EDA-103): This drainage area generally consists remainder of the site. This area drains via overland flow ultimately to the Cape Fear River to the east of the site. Table 1 – Pre-Development (Existing Conditions) Drainage Characteristics. Drainage Area Area (ac.) Composite C Number Impervious Cover (%) Time of Concentration (minutes) EDA-101 16.23 73 25.7% 40 EDA-102 7.48 52 4.0% 36 EDA-103 43.58 81 23.9% 57 Table 2 – Pre-Development Conditions Peak Flows (cfs) Analysis Point 24-hr SCS 2-yr 10-yr 25-yr 100-yr Design Point (SWM-1, 2 and 3) 66.08 cfs 123.82 cfs 148.59 cfs 343.07 cfs Developed Site Conditions and Hydrologic Conditions The proposed site drainage area totals 67.29 acres and is approximately 38% impervious. The intent of the proposed site drainage is to mimic existing drainage patterns to the maximum extent practicable. The site stormwater system will provide quality improvements through the installation 4 dry extended detention ponds will provide water quality treatment and attenuation of the 2-10 and 25 year storms. The Ponds have been sized per the criteria set forth by the North Carolina SWM Manual and The New Hanover County SWM Ordinance to attenuate the 2-, 10- and 25-year 24-hour storms and treat the first 1” of runoff. These measures will treat the stormwater quality flow through structural means to provide water quality treatment in conformance with the North Carolina SWM Manual and The New Hanover County SWM Ordinance. For the hydrologic analysis, the developed site retained the same Design Point as the existing model. The following drainage areas were developed to model the proposed site improvements. Proposed Drainage Area 101 (PDA-101): PDA-101 consists of the undeveloped sandy area to the north of the site. This area will bypass the Stormwater Management Ponds and discharge directly to the wetland area on the east of the site. Proposed Drainage Area 102 (PDA-102): PDA-102 consists of the middle of the site (Lots 2 and 3) in addition to the offsite drainage from the northwest adjacent properties. This area will drain 5 via both underground storm drains and overland flow to the retrofitted stormwater management pond at the northwest corner of the property. This pond outfalls to the wetlands at the east side of the site at Point of Analysis #1. Proposed Drainage Area 103 (PDA-103): PDA-103 encompasses the area north and south of PDA-102 to include the existing warehouse building at the south end of the site and the proposed warehouse building at the north of the site. This area drains to the proposed Wet Pond along the east side of the development. This pond outfalls to the wetlands at the east side of the site at Point of Analysis #1. Proposed Drainage Area 104 (PDA-104). PDA-40 generally includes the building and associated parking for proposed building #4 at the south east corner of the site. This area drains to the proposed Wet Pond along the behond Building 4. This pond outfalls to the wetlands at the east side of the site at Point of Analysis #1. Table 3 – Post Development Drainage Characteristics. Drainage Area Area (ac.) Composite C Number Impervious Cover (%) Time of Concentration (minutes) PDA-10 (Bypass) 6.91 67 4.3% 25 PDA-20 (Area to SWM-2) 20.17 82 65% 5 PDA-30 (Area to SWM-1) 32.45 89 73% 5 PDA-40 (Area to SWM-3) 5.12 95 81% 5 Table 4 – Post-Development Conditions Peak Flows (24-Hour) Analysis Point 24-hr SCS 2-yr 10-yr 25-yr 100-yr Design Point 1 (SWM-1, 2 and 3) 97.27 cfs 132.82 cfs 146.54 cfs 220.56 cfs 6 Table 5 –Design Point #1 Summary 2-yr 10-yr 25-yr 100-yr Design Point 1 Existing 68.28 cfs 132.11 cfs 164.67 cfs 282.37 cfs Proposed (Routed) 97.27 cfs 132.02 cfs 146.54 cfs 220.56 cfs Table 6 –SWM #1 Summary 2-yr 10-yr 25-yr 100-yr SWM Pond #1 Proposed (Inflow) 96.80 cfs 174.91 cfs 207.08 cfs 268.61 cfs Proposed (Routed Discharge) 8.65 cfs 12.07 cfs 13.59 cfs 34.09 cfs Water Surface Elevation (ft) 22.78 25.18 26.15 27.35 Water Quality Elevation (ft) 22.00 Pond Bottom (ft) 20.00 Pond Top of Dam (ft) 28.00 Table 7 –SWM #2 Summary 2-yr 10-yr 25-yr 100-yr SWM Pond #2 Proposed (Inflow) 186.59 cfs 311.55 cfs 363.51 cfs 459.38 cfs Proposed (Routed Discharge) 60.26 cfs 74.59 cfs 80.05 cfs 134.65 cfs Water Surface Elevation (ft) 12.60 14.25 14.97 15.99 Water Quality Elevation (ft) 11.00 Pond Bottom (ft) 8.00 Pond Top of Dam (ft) 16.00 7 Table 8 –SWM #3 Summary 2-yr 10-yr 25-yr 100-yr SWM Pond #3 Proposed (Inflow) 66.08 cfs 123.82 cfs 148.59 cfs 343.07 cfs Proposed (Routed Discharge) 23.29 cfs 26.17 cfs 27.54 cfs 31.38 cfs Water Surface Elevation (ft) 5.35 5.94 6.16 6.56 Water Quality Elevation (ft) 2.00 Pond Bottom (ft) 5.00 Pond Top of Dam (ft) 8.00 Hydrologic Modeling Standards The hydrologic analysis was performed to determine the stormwater discharge rates from the 2- yr, 10-yr, 25-yr and 50-year 24hr storm event. The analysis was performed using the Hydraflow stormwater modeling system computer program, version 2018 developed by Autodesk. Hydrographs for each watershed were developed using the NRCS Method. Rainfall depths and distribution per the NC DEQ Stormwater Management Manual were used for the calculation of peak flow rates and are listed in Appendix B. Pre-development and Post-development Hydraflow output can be found in Appendix B. 8 APPENDIX A MAPS Hydrologic Soil Group—New Hanover County, North Carolina Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3/1/2023 Page 1 of 4 37 9 6 7 0 0 37 9 6 8 0 0 37 9 6 9 0 0 37 9 7 0 0 0 37 9 7 1 0 0 37 9 7 2 0 0 37 9 7 3 0 0 37 9 7 4 0 0 37 9 6 7 0 0 37 9 6 8 0 0 37 9 6 9 0 0 37 9 7 0 0 0 37 9 7 1 0 0 37 9 7 2 0 0 37 9 7 3 0 0 227300 227400 227500 227600 227700 227800 227900 228000 228100 228200 228300 227200 227300 227400 227500 227600 227700 227800 227900 228000 228100 228200 228300 34° 16' 55'' N 77 ° 5 7 ' 4 7 ' ' W 34° 16' 55'' N 77 ° 5 7 ' 1 ' ' W 34° 16' 31'' N 77 ° 5 7 ' 4 7 ' ' W 34° 16' 31'' N 77 ° 5 7 ' 1 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 18N WGS84 0 250 500 1000 1500 Feet 0 50 100 200 300 Meters Map Scale: 1:5,320 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 A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D 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: New Hanover County, North Carolina Survey Area Data: Version 24, Sep 12, 2022 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Oct 5, 2020—Nov 24, 2020 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. Hydrologic Soil Group—New Hanover County, North Carolina Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3/1/2023 Page 2 of 4 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI DO Dorovan soils B/D 10.6 10.8% Kr Kureb sand, 1 to 8 percent slopes A 21.2 21.7% Ur Urban land 65.1 66.8% W Water 0.6 0.6% Totals for Area of Interest 97.4 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Hydrologic Soil Group—New Hanover County, North Carolina Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3/1/2023 Page 3 of 4 Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—New Hanover County, North Carolina Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 3/1/2023 Page 4 of 4 3/1/23, 12:30 PM 2840 US-421 - Google Maps https://www.google.com/maps/place/2840+US-421,+Wilmington,+NC+28401/@34.2793488,-77.9571552,16z/data=!4m5!3m4!1s0x89aa202532bc0603:0x3dc6b7fcaf9c589d!8m2!3d34.2781147!4d-77.9…1/1 Map data ©2023 500 ft 2840 US-421 9 APPENDIX B SWM MANAGEMENT COMPUTATIONS PDA-1 PDA-1 PDA-2 PDA-2PDA-3 PDA-3 PDA-4 PDA-4 E-WP RETRO Ex Wet PondSWM #2 PRO WET POND 2 SWM #3 PRO WET POND 1 POA Existing Wetland System Routing Diagram for C-DATA-2201500-PROPOSED ConditionsREV Prepared by {enter your company name here}, Printed 3/1/2023 HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Subcat Reach Pond Link C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 2HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Area Listing (all nodes) Area (acres) CN Description (subcatchment-numbers) 2.210 39 >75% Grass cover, Good, HSG A (PDA-1, PDA-3) 11.720 80 >75% Grass cover, Good, HSG D (PDA-1, PDA-3, PDA-4) 13.170 98 IMPERVIOUS, HSG D (PDA-2) 2.910 80 OPEN SPACE GOOD, HSG D (PDA-2) 2.530 98 Paved parking, HSG A (PDA-3) 25.510 98 Paved parking, HSG D (PDA-1, PDA-3, PDA-4) 4.090 30 WOOD GOOD, HSG A (PDA-2) 2.510 30 Woods, Good, HSG A (PDA-1, PDA-3) 64.650 85 TOTAL AREA C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 3HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Soil Listing (all nodes) Area (acres) Soil Group Subcatchment Numbers 11.340 HSG A PDA-1, PDA-2, PDA-3 0.000 HSG B 0.000 HSG C 53.310 HSG D PDA-1, PDA-2, PDA-3, PDA-4 0.000 Other 64.650 TOTAL AREA C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 4HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Ground Covers (all nodes) HSG-A (acres) HSG-B (acres) HSG-C (acres) HSG-D (acres) Other (acres) Total (acres) Ground Cover Subcatchment Numbers 2.210 0.000 0.000 11.720 0.000 13.930 >75% Grass cover, Good PDA-1, PDA-3, PDA-4 0.000 0.000 0.000 13.170 0.000 13.170 IMPERVIOUS PDA-2 0.000 0.000 0.000 2.910 0.000 2.910 OPEN SPACE GOOD PDA-2 2.530 0.000 0.000 25.510 0.000 28.040 Paved parking PDA-1, PDA-3, PDA-4 4.090 0.000 0.000 0.000 0.000 4.090 WOOD GOOD PDA-2 2.510 0.000 0.000 0.000 0.000 2.510 Woods, Good PDA-1, PDA-3 11.340 0.000 0.000 53.310 0.000 64.650 TOTAL AREA C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 5HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Pipe Listing (all nodes) Line# Node Number In-Invert (feet) Out-Invert (feet) Length (feet) Slope (ft/ft) n Diam/Width (inches) Height (inches) Inside-Fill (inches) 1 E-WP 20.00 19.00 100.0 0.0100 0.012 15.0 0.0 0.0 2 SWM #2 8.00 7.00 138.0 0.0072 0.011 36.0 0.0 0.0 3 SWM #3 2.00 1.00 34.0 0.0294 0.011 24.0 0.0 0.0 NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 6HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Time span=0.00-120.00 hrs, dt=0.01 hrs, 12001 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=6.910 ac 4.34% Impervious Runoff Depth=0.00"Subcatchment PDA-1: PDA-1 Flow Length=1,050' Tc=24.7 min CN=67 Runoff=0.00 cfs 0.000 af Runoff Area=20.170 ac 65.29% Impervious Runoff Depth=0.11"Subcatchment PDA-2: PDA-2 Tc=5.0 min CN=82 Runoff=2.90 cfs 0.192 af Runoff Area=32.450 ac 72.63% Impervious Runoff Depth=0.28"Subcatchment PDA-3: PDA-3 Tc=5.0 min CN=89 Runoff=16.77 cfs 0.771 af Runoff Area=5.120 ac 81.45% Impervious Runoff Depth=0.56"Subcatchment PDA-4: PDA-4 Tc=5.0 min CN=95 Runoff=5.27 cfs 0.240 af Peak Elev=20.14' Storage=5,054 cf Inflow=2.90 cfs 0.192 afPond E-WP: RETRO Ex Wet Pond Outflow=0.11 cfs 0.190 af Peak Elev=9.63' Storage=0 cf Inflow=16.77 cfs 0.771 afPond SWM #2: PRO WET POND 2 Outflow=16.77 cfs 0.771 af Peak Elev=2.99' Storage=0 cf Inflow=5.27 cfs 0.240 afPond SWM #3: PRO WET POND 1 Outflow=5.27 cfs 0.240 af Inflow=22.03 cfs 1.201 afLink POA: Existing Wetland System Primary=22.03 cfs 1.201 af Total Runoff Area = 64.650 ac Runoff Volume = 1.203 af Average Runoff Depth = 0.22" 36.26% Pervious = 23.440 ac 63.74% Impervious = 41.210 ac NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 7HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Summary for Subcatchment PDA-1: PDA-1 Runoff = 0.00 cfs @ 24.12 hrs, Volume= 0.000 af, Depth= 0.00" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.01 hrs NOAA 24-hr A Custom Rainfall=1.00" Area (ac) CN Description 0.380 39 >75% Grass cover, Good, HSG A 4.630 80 >75% Grass cover, Good, HSG D 0.300 98 Paved parking, HSG D 1.600 30 Woods, Good, HSG A 0.000 77 Woods, Good, HSG D 6.910 67 Weighted Average 6.610 95.66% Pervious Area 0.300 4.34% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 11.8 100 0.0821 0.14 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 3.43" 9.3 200 0.0828 0.36 Sheet Flow, Grass: Short n= 0.150 P2= 3.43" 3.6 750 0.2462 3.47 Shallow Concentrated Flow, Short Grass Pasture Kv= 7.0 fps 24.7 1,050 Total Subcatchment PDA-1: PDA-1 Runoff Hydrograph Time (hours) 12011511010510095908580757065605550454035302520151050 Fl o w ( c f s ) 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0 0 0 0 0 NOAA 24-hr A Custom Rainfall=1.00" Runoff Area=6.910 ac Runoff Volume=0.000 af Runoff Depth=0.00" Flow Length=1,050' Tc=24.7 min CN=67 0.00 cfs NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 8HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Summary for Subcatchment PDA-2: PDA-2 Runoff = 2.90 cfs @ 12.14 hrs, Volume= 0.192 af, Depth= 0.11" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.01 hrs NOAA 24-hr A Custom Rainfall=1.00" Area (ac) CN Description * 0.000 39 OPEN SPACE GOOD, HSG A * 2.910 80 OPEN SPACE GOOD, HSG D * 0.000 98 IMPERVIOUS, HSG A * 13.170 98 IMPERVIOUS, HSG D * 4.090 30 WOOD GOOD, HSG A 20.170 82 Weighted Average 7.000 34.71% Pervious Area 13.170 65.29% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment PDA-2: PDA-2 Runoff Hydrograph Time (hours) 12011511010510095908580757065605550454035302520151050 Fl o w ( c f s ) 3 2 1 0 NOAA 24-hr A Custom Rainfall=1.00" Runoff Area=20.170 ac Runoff Volume=0.192 af Runoff Depth=0.11" Tc=5.0 min CN=82 2.90 cfs NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 9HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Summary for Subcatchment PDA-3: PDA-3 Runoff = 16.77 cfs @ 12.13 hrs, Volume= 0.771 af, Depth= 0.28" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.01 hrs NOAA 24-hr A Custom Rainfall=1.00" Area (ac) CN Description 1.830 39 >75% Grass cover, Good, HSG A 2.530 98 Paved parking, HSG A 0.910 30 Woods, Good, HSG A 6.140 80 >75% Grass cover, Good, HSG D 21.040 98 Paved parking, HSG D 0.000 77 Woods, Good, HSG D 32.450 89 Weighted Average 8.880 27.37% Pervious Area 23.570 72.63% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment PDA-3: PDA-3 Runoff Hydrograph Time (hours) 12011511010510095908580757065605550454035302520151050 Fl o w ( c f s ) 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 NOAA 24-hr A Custom Rainfall=1.00" Runoff Area=32.450 ac Runoff Volume=0.771 af Runoff Depth=0.28" Tc=5.0 min CN=89 16.77 cfs NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 10HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Summary for Subcatchment PDA-4: PDA-4 Runoff = 5.27 cfs @ 12.12 hrs, Volume= 0.240 af, Depth= 0.56" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-120.00 hrs, dt= 0.01 hrs NOAA 24-hr A Custom Rainfall=1.00" Area (ac) CN Description 0.950 80 >75% Grass cover, Good, HSG D 4.170 98 Paved parking, HSG D 0.000 98 Roofs, HSG D 5.120 95 Weighted Average 0.950 18.55% Pervious Area 4.170 81.45% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Subcatchment PDA-4: PDA-4 Runoff Hydrograph Time (hours) 12011511010510095908580757065605550454035302520151050 Fl o w ( c f s ) 5 4 3 2 1 0 NOAA 24-hr A Custom Rainfall=1.00" Runoff Area=5.120 ac Runoff Volume=0.240 af Runoff Depth=0.56" Tc=5.0 min CN=95 5.27 cfs NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 11HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Summary for Pond E-WP: RETRO Ex Wet Pond Inflow Area = 20.170 ac, 65.29% Impervious, Inflow Depth = 0.11" for Custom event Inflow = 2.90 cfs @ 12.14 hrs, Volume= 0.192 af Outflow = 0.11 cfs @ 16.80 hrs, Volume= 0.190 af, Atten= 96%, Lag= 279.4 min Primary = 0.11 cfs @ 16.80 hrs, Volume= 0.190 af Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.01 hrs Peak Elev= 20.14' @ 16.80 hrs Surf.Area= 35,096 sf Storage= 5,054 cf Plug-Flow detention time= 1,028.6 min calculated for 0.190 af (99% of inflow) Center-of-Mass det. time= 1,023.2 min ( 1,907.6 - 884.4 ) Volume Invert Avail.Storage Storage Description #1 20.00' 355,865 cf Custom Stage Data (Prismatic) Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 20.00 34,764 0 0 21.00 37,057 35,911 35,911 22.00 39,410 38,234 74,144 23.00 41,819 40,615 114,759 24.00 44,285 43,052 157,811 25.00 46,920 45,603 203,413 26.00 49,255 48,088 251,501 27.00 52,247 50,751 302,252 28.00 54,980 53,614 355,865 Device Routing Invert Outlet Devices #1 Primary 20.00'15.0" Round Culvert L= 100.0' Ke= 0.300 Inlet / Outlet Invert= 20.00' / 19.00' S= 0.0100 '/' Cc= 0.900 n= 0.012, Flow Area= 1.23 sf #2 Primary 26.00'2.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s) #3 Primary 27.00'20.0' long x 10.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.49 2.56 2.70 2.69 2.68 2.69 2.67 2.64 Primary OutFlow Max=0.11 cfs @ 16.80 hrs HW=20.14' (Free Discharge) 1=Culvert (Barrel Controls 0.11 cfs @ 2.04 fps) 2=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs) 3=Broad-Crested Rectangular Weir ( Controls 0.00 cfs) NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 12HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Pond E-WP: RETRO Ex Wet Pond Inflow Primary Hydrograph Time (hours) 12011511010510095908580757065605550454035302520151050 Fl o w ( c f s ) 3 2 1 0 Inflow Area=20.170 ac Peak Elev=20.14' Storage=5,054 cf 2.90 cfs 0.11 cfs NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 13HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Summary for Pond SWM #2: PRO WET POND 2 Inflow Area = 32.450 ac, 72.63% Impervious, Inflow Depth = 0.28" for Custom event Inflow = 16.77 cfs @ 12.13 hrs, Volume= 0.771 af Outflow = 16.77 cfs @ 12.13 hrs, Volume= 0.771 af, Atten= 0%, Lag= 0.0 min Primary = 16.77 cfs @ 12.13 hrs, Volume= 0.771 af Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.01 hrs Peak Elev= 9.63' @ 12.13 hrs Surf.Area= 34,954 sf Storage= 0 cf Plug-Flow detention time= 0.0 min calculated for 0.771 af (100% of inflow) Center-of-Mass det. time= 0.0 min ( 837.5 - 837.5 ) Volume Invert Avail.Storage Storage Description #1 8.00' 0 cf Forebay (Irregular) Listed below (Recalc) 28,681 cf Overall x 0.0% Voids #2 8.00' 0 cf Permanent Storage (Irregular) Listed below (Recalc) 73,452 cf Overall x 0.0% Voids #3 11.00' 299,314 cf Temporary Storage (Irregular) Listed below (Recalc) 299,314 cf Total Available Storage Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 8.00 3,785 1,271.0 0 0 3,785 9.00 7,662 1,296.0 5,611 5,611 9,051 10.00 11,579 1,315.0 9,553 15,164 13,209 11.00 15,552 1,333.0 13,517 28,681 17,226 Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 8.00 19,256 1,147.0 0 0 19,256 9.00 22,724 1,166.0 20,966 20,966 22,939 10.00 26,249 1,184.0 24,465 45,431 26,505 11.00 29,830 1,203.0 28,020 73,452 30,306 Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 11.00 29,831 1,204.0 0 0 29,831 12.00 56,024 1,349.0 42,245 42,245 59,317 13.00 60,101 1,368.0 58,051 100,296 63,644 14.00 64,236 1,387.0 62,157 162,453 68,031 15.00 68,428 1,406.0 66,321 228,774 72,479 16.00 72,674 1,425.0 70,540 299,314 76,987 Device Routing Invert Outlet Devices #1 Primary 8.00'36.0" Round Culvert L= 138.0' RCP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 8.00' / 7.00' S= 0.0072 '/' Cc= 0.900 n= 0.011, Flow Area= 7.07 sf #2 Primary 11.00'3.0" Vert. Orifice/Grate C= 0.600 #3 Primary 15.00'1.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s) NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 14HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC #4 Primary 15.50'50.0' long x 10.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Coef. (English) 2.49 2.56 2.70 2.69 2.68 2.69 2.67 2.64 Primary OutFlow Max=16.76 cfs @ 12.13 hrs HW=9.63' (Free Discharge) 1=Culvert (Barrel Controls 16.76 cfs @ 6.19 fps) 2=Orifice/Grate ( Controls 0.00 cfs) 3=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs) 4=Broad-Crested Rectangular Weir ( Controls 0.00 cfs) Pond SWM #2: PRO WET POND 2 Inflow Primary Hydrograph Time (hours) 12011511010510095908580757065605550454035302520151050 Flo w ( c f s ) 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=32.450 ac Peak Elev=9.63' Storage=0 cf 16.77 cfs16.77 cfs NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 15HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Summary for Pond SWM #3: PRO WET POND 1 Inflow Area = 5.120 ac, 81.45% Impervious, Inflow Depth = 0.56" for Custom event Inflow = 5.27 cfs @ 12.12 hrs, Volume= 0.240 af Outflow = 5.27 cfs @ 12.12 hrs, Volume= 0.240 af, Atten= 0%, Lag= 0.0 min Primary = 5.27 cfs @ 12.12 hrs, Volume= 0.240 af Routing by Stor-Ind method, Time Span= 0.00-120.00 hrs, dt= 0.01 hrs Peak Elev= 2.99' @ 12.12 hrs Surf.Area= 7,021 sf Storage= 0 cf Plug-Flow detention time= (not calculated: outflow precedes inflow) Center-of-Mass det. time= (not calculated: outflow precedes inflow) Volume Invert Avail.Storage Storage Description #1 2.00' 0 cf Forebay (Irregular) Listed below (Recalc) 15,317 cf Overall x 0.0% Voids #2 2.00' 0 cf Permanent Storage (Irregular) Listed below (Recalc) 11,233 cf Overall x 0.0% Voids #3 5.00' 59,606 cf Temporary Storage (Irregular) Listed below (Recalc) 59,606 cf Total Available Storage Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 2.00 1,913 633.0 0 0 1,913 3.00 4,084 687.0 2,931 2,931 7,624 4.00 6,179 706.0 5,095 8,026 9,842 5.00 8,462 739.0 7,291 15,317 13,705 Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 2.00 1,457 495.0 0 0 1,457 3.00 2,971 514.0 2,170 2,170 3,064 4.00 4,542 532.0 3,729 5,898 4,651 5.00 6,169 551.0 5,335 11,233 6,375 Elevation Surf.Area Perim. Inc.Store Cum.Store Wet.Area (feet) (sq-ft) (feet) (cubic-feet) (cubic-feet) (sq-ft) 5.00 6,169 552.0 0 0 6,169 6.00 20,976 792.0 12,840 12,840 31,846 7.00 23,380 810.0 22,167 35,007 34,277 8.00 25,838 829.0 24,599 59,606 36,887 Device Routing Invert Outlet Devices #1 Primary 2.00'24.0" Round Culvert L= 34.0' RCP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 2.00' / 1.00' S= 0.0294 '/' Cc= 0.900 n= 0.011 Concrete pipe, finished, Flow Area= 3.14 sf #2 Primary 5.00'6.0" Vert. Orifice/Grate C= 0.600 #3 Primary 6.00'2.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s) #4 Primary 7.00'20.0' long x 10.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 16HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Coef. (English) 2.49 2.56 2.70 2.69 2.68 2.69 2.67 2.64 Primary OutFlow Max=5.26 cfs @ 12.12 hrs HW=2.99' (Free Discharge) 1=Culvert (Inlet Controls 5.26 cfs @ 3.39 fps) 2=Orifice/Grate ( Controls 0.00 cfs) 3=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs) 4=Broad-Crested Rectangular Weir ( Controls 0.00 cfs) Pond SWM #3: PRO WET POND 1 Inflow Primary Hydrograph Time (hours) 12011511010510095908580757065605550454035302520151050 Fl o w ( c f s ) 5 4 3 2 1 0 Inflow Area=5.120 ac Peak Elev=2.99' Storage=0 cf 5.27 cfs5.27 cfs NOAA 24-hr A Custom Rainfall=1.00"C-DATA-2201500-PROPOSED ConditionsREV Printed 3/1/2023Prepared by {enter your company name here} Page 17HydroCAD® 10.00-26 s/n 01334 © 2020 HydroCAD Software Solutions LLC Summary for Link POA: Existing Wetland System Inflow Area = 64.650 ac, 63.74% Impervious, Inflow Depth = 0.22" for Custom event Inflow = 22.03 cfs @ 12.13 hrs, Volume= 1.201 af Primary = 22.03 cfs @ 12.13 hrs, Volume= 1.201 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-120.00 hrs, dt= 0.01 hrs Link POA: Existing Wetland System Inflow Primary Hydrograph Time (hours) 12011511010510095908580757065605550454035302520151050 Fl o w ( c f s ) 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=64.650 ac 22.03 cfs22.03 cfs NOAA Atlas 14, Volume 2, Version 3 Location name: Wilmington, North Carolina, USA*Latitude: 34.2763°, Longitude: -77.9596°Elevation: 28.42 ft*** source: ESRI Maps** source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley NOAA, National Weather Service, Silver Spring, Maryland PF_tabular | PF_graphical | Maps_&_aerials PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1 Duration Average recurrence interval (years) 1 2 5 10 25 50 100 200 500 1000 5-min 0.519(0.485‑0.560)0.617(0.575‑0.665)0.722(0.671‑0.777)0.804(0.745‑0.864)0.907(0.838‑0.974)0.985(0.905‑1.06)1.07(0.974‑1.15)1.15(1.04‑1.23)1.25(1.12‑1.35)1.33(1.19‑1.44) 10-min 0.830 (0.774‑0.894) 0.987 (0.920‑1.06) 1.16 (1.08‑1.24) 1.29 (1.19‑1.38) 1.45 (1.34‑1.55) 1.57 (1.44‑1.69) 1.69 (1.55‑1.82) 1.82 (1.65‑1.95) 1.98 (1.78‑2.13) 2.10 (1.87‑2.27) 15-min 1.04(0.968‑1.12)1.24(1.16‑1.34)1.46(1.36‑1.57)1.63(1.51‑1.75)1.83(1.69‑1.97)1.99(1.83‑2.13)2.14(1.96‑2.30)2.29(2.08‑2.46)2.49(2.23‑2.68)2.64(2.35‑2.85) 30-min 1.42(1.33‑1.53)1.71(1.60‑1.85)2.08(1.93‑2.24)2.36(2.18‑2.53)2.72(2.51‑2.91)2.99(2.75‑3.21)3.28(3.00‑3.52)3.57(3.24‑3.84)3.96(3.56‑4.27)4.27(3.80‑4.61) 60-min 1.77 (1.65‑1.91) 2.15 (2.00‑2.32) 2.66 (2.48‑2.87) 3.07 (2.84‑3.30) 3.62 (3.34‑3.88) 4.06 (3.73‑4.36) 4.51 (4.13‑4.85) 5.00 (4.54‑5.38) 5.68 (5.10‑6.12) 6.24 (5.55‑6.73) 2-hr 2.10(1.94‑2.30)2.56(2.36‑2.80)3.27(3.01‑3.56)3.85(3.54‑4.19)4.69(4.29‑5.11)5.41(4.92‑5.89)6.20(5.61‑6.74)7.06(6.34‑7.67)8.34(7.40‑9.07)9.43(8.31‑10.3) 3-hr 2.25 (2.08‑2.46) 2.74 (2.53‑3.00) 3.50 (3.23‑3.83) 4.16 (3.81‑4.55) 5.14 (4.68‑5.60) 6.00 (5.43‑6.54) 6.95 (6.25‑7.57) 8.01 (7.14‑8.70) 9.62 (8.47‑10.5) 11.0 (9.60‑12.0) 6-hr 2.78(2.57‑3.05)3.39(3.13‑3.72)4.34(3.99‑4.76)5.17(4.73‑5.65)6.41(5.83‑6.98)7.49(6.77‑8.16)8.71(7.82‑9.48)10.1(8.94‑11.0)12.2(10.7‑13.2)14.0(12.1‑15.3) 12-hr 3.26(2.98‑3.60)3.97(3.62‑4.38)5.12(4.67‑5.65)6.13(5.56‑6.74)7.65(6.88‑8.39)9.00(8.05‑9.86)10.5(9.35‑11.5)12.3(10.8‑13.4)14.9(12.9‑16.4)17.3(14.8‑18.9) 24-hr 3.81 (3.46‑4.26) 4.62 (4.20‑5.18) 5.98 (5.42‑6.69) 7.18 (6.49‑8.01) 9.02 (8.07‑10.0) 10.7 (9.45‑11.9) 12.5 (11.0‑14.0) 14.7 (12.7‑16.3) 17.9 (15.2‑20.1) 20.9 (17.3‑23.5) 2-day 4.49(4.09‑4.98)5.42(4.95‑6.03)6.95(6.33‑7.73)8.29(7.52‑9.21)10.3(9.27‑11.5)12.1(10.8‑13.5)14.1(12.4‑15.8)16.4(14.2‑18.4)19.9(16.9‑22.5)23.0(19.2‑26.1) 3-day 4.77 (4.36‑5.30) 5.76 (5.26‑6.40) 7.34 (6.68‑8.15) 8.70 (7.90‑9.66) 10.8 (9.67‑12.0) 12.5 (11.2‑14.0) 14.5 (12.8‑16.2) 16.8 (14.6‑18.8) 20.2 (17.3‑22.8) 23.2 (19.5‑26.3) 4-day 5.06(4.62‑5.61)6.10(5.57‑6.77)7.72(7.04‑8.57)9.12(8.27‑10.1)11.2(10.1‑12.4)13.0(11.6‑14.4)15.0(13.2‑16.7)17.2(15.0‑19.2)20.5(17.6‑23.1)23.4(19.8‑26.5) 7-day 5.83(5.37‑6.38)7.02(6.48‑7.69)8.82(8.12‑9.66)10.3(9.48‑11.3)12.5(11.4‑13.7)14.4(13.0‑15.8)16.4(14.7‑18.1)18.6(16.5‑20.5)21.9(19.1‑24.3)24.6(21.2‑27.5) 10-day 6.57 (6.08‑7.16) 7.87 (7.27‑8.58) 9.75 (8.98‑10.6) 11.3 (10.4‑12.3) 13.6 (12.5‑14.8) 15.5 (14.1‑17.0) 17.6 (15.9‑19.2) 19.8 (17.7‑21.8) 23.1 (20.3‑25.5) 25.8 (22.4‑28.7) 20-day 8.81(8.20‑9.51)10.5(9.78‑11.3)12.8(11.9‑13.8)14.7(13.6‑15.8)17.4(16.1‑18.8)19.6(18.0‑21.2)22.0(20.0‑23.8)24.5(22.1‑26.7)28.1(25.0‑30.8)31.0(27.2‑34.2) 30-day 10.8 (10.2‑11.6) 12.9 (12.1‑13.8) 15.5 (14.5‑16.6) 17.6 (16.5‑18.8) 20.5 (19.1‑21.9) 22.8 (21.2‑24.4) 25.2 (23.3‑27.1) 27.7 (25.4‑29.8) 31.1 (28.2‑33.8) 33.9 (30.3‑36.9) 45-day 13.5(12.8‑14.4)16.0(15.1‑17.0)19.0(17.9‑20.2)21.4(20.1‑22.8)24.7(23.1‑26.3)27.3(25.5‑29.1)30.0(27.8‑32.1)32.8(30.2‑35.2)36.6(33.3‑39.4)39.6(35.7‑42.9) 60-day 16.3(15.4‑17.3)19.1(18.1‑20.3)22.4(21.2‑23.8)25.0(23.5‑26.5)28.4(26.7‑30.2)31.1(29.2‑33.1)33.8(31.5‑36.1)36.5(33.9‑39.1)40.1(36.9‑43.1)42.8(39.1‑46.3) 1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequencyestimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimatesat upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top PF graphical Back to Top Maps & aerials Small scale terrain Large scale terrain Large scale map + – 3km 2mi + – 100km 60mi Large scale aerial Back to Top US Department of Commerce National Oceanic and Atmospheric Administration National Weather ServiceNational Water Center1325 East West Highway Silver Spring, MD 20910Questions?: HDSC.Questions@noaa.gov Disclaimer + – 100km 60mi + – 100km 60mi NOAA Atlas 14, Volume 2, Version 3 Location name: Wilmington, North Carolina, USA*Latitude: 34.2763°, Longitude: -77.9596°Elevation: 28.42 ft*** source: ESRI Maps** source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley NOAA, National Weather Service, Silver Spring, Maryland PF_tabular | PF_graphical | Maps_&_aerials PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches/hour)1 Duration Average recurrence interval (years) 1 2 5 10 25 50 100 200 500 1000 5-min 6.23(5.82‑6.72)7.40(6.90‑7.98)8.66(8.05‑9.32)9.65(8.94‑10.4)10.9(10.1‑11.7)11.8(10.9‑12.7)12.8(11.7‑13.7)13.7(12.5‑14.8)15.0(13.5‑16.2)16.0(14.3‑17.3) 10-min 4.98 (4.64‑5.36) 5.92 (5.52‑6.38) 6.94 (6.45‑7.46) 7.71 (7.15‑8.29) 8.68 (8.01‑9.31) 9.41 (8.65‑10.1) 10.2 (9.28‑10.9) 10.9 (9.88‑11.7) 11.9 (10.7‑12.8) 12.6 (11.2‑13.6) 15-min 4.15(3.87‑4.47)4.96(4.62‑5.35)5.85(5.44‑6.29)6.50(6.03‑6.99)7.33(6.77‑7.87)7.95(7.30‑8.54)8.56(7.82‑9.20)9.16(8.31‑9.85)9.95(8.94‑10.7)10.5(9.40‑11.4) 30-min 2.84(2.65‑3.07)3.43(3.19‑3.69)4.15(3.86‑4.47)4.71(4.37‑5.07)5.43(5.01‑5.83)5.99(5.50‑6.43)6.56(5.99‑7.04)7.13(6.47‑7.67)7.92(7.11‑8.54)8.54(7.61‑9.22) 60-min 1.77 (1.65‑1.91) 2.15 (2.00‑2.32) 2.66 (2.48‑2.87) 3.07 (2.84‑3.30) 3.62 (3.34‑3.88) 4.06 (3.73‑4.36) 4.51 (4.13‑4.85) 5.00 (4.54‑5.38) 5.68 (5.10‑6.12) 6.24 (5.55‑6.73) 2-hr 1.05(0.970‑1.15)1.28(1.18‑1.40)1.63(1.50‑1.78)1.92(1.77‑2.10)2.35(2.14‑2.55)2.71(2.46‑2.94)3.10(2.80‑3.37)3.53(3.17‑3.83)4.17(3.70‑4.54)4.72(4.15‑5.15) 3-hr 0.749 (0.692‑0.820) 0.911 (0.841‑0.998) 1.17 (1.07‑1.27) 1.39 (1.27‑1.51) 1.71 (1.56‑1.87) 2.00 (1.81‑2.18) 2.31 (2.08‑2.52) 2.67 (2.38‑2.90) 3.20 (2.82‑3.48) 3.67 (3.20‑4.00) 6-hr 0.465(0.429‑0.510)0.566(0.522‑0.621)0.725(0.666‑0.794)0.863(0.790‑0.944)1.07(0.973‑1.17)1.25(1.13‑1.36)1.45(1.31‑1.58)1.68(1.49‑1.83)2.03(1.78‑2.21)2.34(2.03‑2.55) 12-hr 0.270(0.247‑0.299)0.330(0.301‑0.363)0.425(0.388‑0.469)0.508(0.462‑0.559)0.635(0.571‑0.697)0.747(0.668‑0.818)0.874(0.776‑0.957)1.02(0.894‑1.11)1.24(1.07‑1.36)1.44(1.23‑1.57) 24-hr 0.159 (0.144‑0.178) 0.193 (0.175‑0.216) 0.249 (0.226‑0.279) 0.299 (0.270‑0.334) 0.376 (0.336‑0.419) 0.444 (0.394‑0.494) 0.522 (0.458‑0.581) 0.611 (0.528‑0.681) 0.748 (0.633‑0.839) 0.869 (0.723‑0.980) 2-day 0.093(0.085‑0.104)0.113(0.103‑0.126)0.145(0.132‑0.161)0.173(0.157‑0.192)0.215(0.193‑0.239)0.252(0.225‑0.281)0.294(0.259‑0.329)0.342(0.297‑0.384)0.415(0.352‑0.468)0.479(0.399‑0.543) 3-day 0.066 (0.061‑0.074) 0.080 (0.073‑0.089) 0.102 (0.093‑0.113) 0.121 (0.110‑0.134) 0.149 (0.134‑0.166) 0.174 (0.155‑0.194) 0.202 (0.178‑0.226) 0.233 (0.203‑0.261) 0.281 (0.240‑0.316) 0.322 (0.270‑0.365) 4-day 0.053(0.048‑0.058)0.064(0.058‑0.071)0.080(0.073‑0.089)0.095(0.086‑0.105)0.117(0.105‑0.129)0.135(0.121‑0.150)0.156(0.138‑0.174)0.179(0.156‑0.200)0.214(0.183‑0.241)0.244(0.206‑0.276) 7-day 0.035(0.032‑0.038)0.042(0.039‑0.046)0.053(0.048‑0.058)0.062(0.056‑0.067)0.075(0.068‑0.082)0.086(0.078‑0.094)0.098(0.088‑0.107)0.111(0.098‑0.122)0.130(0.114‑0.145)0.146(0.126‑0.164) 10-day 0.027 (0.025‑0.030) 0.033 (0.030‑0.036) 0.041 (0.037‑0.044) 0.047 (0.043‑0.051) 0.057 (0.052‑0.062) 0.065 (0.059‑0.071) 0.073 (0.066‑0.080) 0.083 (0.074‑0.091) 0.096 (0.085‑0.106) 0.107 (0.093‑0.120) 20-day 0.018(0.017‑0.020)0.022(0.020‑0.024)0.027(0.025‑0.029)0.031(0.028‑0.033)0.036(0.033‑0.039)0.041(0.037‑0.044)0.046(0.042‑0.050)0.051(0.046‑0.056)0.058(0.052‑0.064)0.065(0.057‑0.071) 30-day 0.015 (0.014‑0.016) 0.018 (0.017‑0.019) 0.021 (0.020‑0.023) 0.024 (0.023‑0.026) 0.028 (0.027‑0.030) 0.032 (0.029‑0.034) 0.035 (0.032‑0.038) 0.038 (0.035‑0.041) 0.043 (0.039‑0.047) 0.047 (0.042‑0.051) 45-day 0.013(0.012‑0.013)0.015(0.014‑0.016)0.018(0.017‑0.019)0.020(0.019‑0.021)0.023(0.021‑0.024)0.025(0.024‑0.027)0.028(0.026‑0.030)0.030(0.028‑0.033)0.034(0.031‑0.037)0.037(0.033‑0.040) 60-day 0.011(0.011‑0.012)0.013(0.013‑0.014)0.016(0.015‑0.017)0.017(0.016‑0.018)0.020(0.019‑0.021)0.022(0.020‑0.023)0.023(0.022‑0.025)0.025(0.024‑0.027)0.028(0.026‑0.030)0.030(0.027‑0.032) 1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS). Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (fora given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are notchecked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top PF graphical Back to Top Maps & aerials Small scale terrain Large scale terrain Large scale map + – 3km 2mi + – 100km 60mi Large scale aerial Back to Top US Department of Commerce National Oceanic and Atmospheric Administration National Weather ServiceNational Water Center1325 East West Highway Silver Spring, MD 20910Questions?: HDSC.Questions@noaa.gov Disclaimer + – 100km 60mi + – 100km 60mi