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(340) 473-0131 info@islanddesignsllc.com 7200 Regatta Point 8D | St. Thomas, USVI 00802 FIFA Soccer Field Hydrology Report Prepared for USVI Soccer Federation By Island Designs LLC 3/23/2026 (340) 473-0131 info@islanddesignsllc.com 7200 Regatta Point 8D | St. Thomas, USVI 00802 Hydrology Study Report Pre-development versus post-development analysis for the 5-acre site located at N-1 Estate Nazareth, St. Thomas, VI. Introduction The FIFA soccer field is a proposed soccer field including tiered seating areas and potential concession stands. The project will also include the construction of driveways and parking areas. The plan is to construct a regulation sized soccer field along the west side of the property with tiered seating for spectators immediately surrounding the field. Potential to add concession and/or locker room buildings will be included in the northeast corner of the parcel, with parking and driveways in the already graded and cleared southeastern corner of the lot. The stormwater management BMP’s will be designed and constructed with the assumption that buildings are being constructed, although there is no definitive design regarding the size or placement at this time. As such, when the concessions stands are constructed, the stormwater management BMP’s will have already been designed and constructed. Existing (Pre-Development) and Proposed (Post-Development) Conditions The drainage for the property slopes from north to south and mainly discharges into an existing swale that traverses also west to east across the south border of the property. The ground cover for the existing conditions for the property is a mixture of woods/grass combination and newly graded area. The post development conditions considered that both the field and buildings were being constructed, including all the parking and driveway areas for all areas. The post development conditions considered the soccer field and parking lot as permeable surfaces, as discussed in previous meetings with the Soccer Federation, and driveway and building areas as impervious surfaces. The other disturbed surfaces will be covered with grass beyond the buildings, parking and driveways. The design point for the pre-and-post development conditions was taken at the southeast corner of the site where the exiting swale leaves the property. Stormwater Management BMP The project area’s land cover was digitized into categories including grass cover, newly graded area, impervious area, and woods/grass combination. Since there is not an oƯicial design of the site available at this time, it was estimated that an approximate area of 1 acre was to be impervious due to driveway or building structures. Stormwater runoƯ 3/23/2026 (340) 473-0131 info@islanddesignsllc.com 7200 Regatta Point 8D | St. Thomas, USVI 00802 for the site was delineated from the interpretation of topographic data, including elevation contours, derived from topographical survey datasets. Time of Concentration lines, the longest hydrological flow path, was estimated. A Hydrologic & Hydraulic model was developed in WinTR-55 version 1.00.10, to estimate peak flows for the site, size proposed best management practices (BMPs) and to assess the peak flow reduction benefits of the current conditions (pre-development) compared to utilizing BMPs in the proposed condition (post development). The models were prepared using several spatial input layers, including the manually digitized land cover, Natural Resource Conservation Service (NRCS) soils data, and National Oceanic and Atmospheric Administration (NOAA) rainfall data. Rainfall data was obtained from the NOAA Atlas 14 Point Precipitation Frequency Estimates. The proposed BMP, a permeable soccer field and parking area with overflows into the existing swale, was sized to maximize peak discharge reduction benefits during the 1- year storm event and to provide water quality treatment for the 1.1” rainfall event, the 90th percentile rainfall event. A peak flow comparison can be seen in Table 1 below. The modeling results support that the proposed BMP is adequately sized to reduce stormwater flows associated with 1-year 24hour storm event (2.82 inches). The stormwater flow is controlled by the permeable field and parking area with gravels bases and potential underground graywater storage capabilities, with overflows piped directly into the existing drainage swale along the road. Table 1. The peak flows for various sized storm events have been modeled using WinTR-55. In Each storm event, the post development flow is lower, as the BMP has been appropriately sized to attenuate flow. STORM EVENT PEAK FLOW (PRE-DEVELOPED) PEAK FLOW (POST-DEVELOPED) 1-YEAR 6.22 cfs 2.17 cfs 5-YEAR 19.32 cfs 12.47 cfs 10-YEAR 24.64 cfs 17.24 cfs 100-YEAR 44.71 cfs 36.48 cfs Conclusion The hydrologic analysis performed using WinTR-55 demonstrates that the proposed FIFA Soccer Field development results in a net reduction of peak discharge for the 1, 5, 10, and 100-year storm events. These results reflect high initial abstraction from a storage layer (gravel base) under the field and parking area that acts like a detention basin. Consequently, the project as designed meets DPNR requirements for stormwater attenuation, as it will not increase downstream runoƯ rates. WinTR-55 Current Data Description --- Identification Data --- User: CSIDES Date: 3/23/2026 Project: FIFA Soccer Field Units: English SubTitle: Existing Condition Areal Units: Acres State: Virgin Islands County: St. Thomas-E Filename: C:\Users\cside\AppData\Roaming\WinTR-55\Fifa N-1.w55 --- Sub-Area Data --- Name Description Reach Area(ac) RCN Tc N-1 Existing Condition Outlet 5.03 78 0.1 Total area: 5.03 (ac) --- Storm Data -- Rainfall Depth by Rainfall Return Period 2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in) 4.3 6.2 7.4 9.0 10.4 11.9 3.1 Storm Data Source: User-provided custom storm data Rainfall Distribution Type: Type III Dimensionless Unit Hydrograph: <standard> WinTR-55, Version 1.00.10 3/23/2026 7:27:16 PM CSIDES FIFA Soccer Field Existing Condition St. Thomas-E County, Virgin Islands Storm Data Rainfall Depth by Rainfall Return Period 2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in) 4.3 6.2 7.4 9.0 10.4 11.9 3.1 Storm Data Source: User-provided custom storm data Rainfall Distribution Type: Type III Dimensionless Unit Hydrograph: <standard> WinTR-55, Version 1.00.10 3/23/2026 7:27:16 PM CSIDES FIFA Soccer Field Existing Condition St. Thomas-E County, Virgin Islands Watershed Peak Table Sub-Area Peak Flow by Rainfall Return Period or Reach 5-Yr 10-Yr 100-Yr 1-Yr Identifier (cfs) (cfs) (cfs) (cfs) SUBAREAS N-1 19.32 24.64 44.71 6.22 REACHES OUTLET 19.32 24.64 44.71 6.22 WinTR-55, Version 1.00.10 3/23/2026 7:27:16 PM CSIDES FIFA Soccer Field Existing Condition St. Thomas-E County, Virgin Islands Hydrograph Peak/Peak Time Table Sub-Area Peak Flow and Peak Time (hr) by Rainfall Return Period or Reach 5-Yr 10-Yr 100-Yr 1-Yr Identifier (cfs) (cfs) (cfs) (cfs) (hr) (hr) (hr) (hr) SUBAREAS N-1 19.32 24.64 44.71 6.22 12.11 12.11 12.11 12.12 REACHES OUTLET 19.32 24.64 44.71 6.22 WinTR-55, Version 1.00.10 3/23/2026 7:27:16 PM CSIDES FIFA Soccer Field Existing Condition St. Thomas-E County, Virgin Islands Sub-Area Summary Table Sub-Area Drainage Time of Curve Receiving Sub-Area Identifier Area Concentration Number Reach Description (ac) (hr) N-1 5.03 0.100 78 Outlet Existing Condition Total Area: 5.03 (ac) WinTR-55, Version 1.00.10 3/23/2026 7:27:16 PM CSIDES FIFA Soccer Field Existing Condition St. Thomas-E County, Virgin Islands Sub-Area Time of Concentration Details Sub-Area Flow Mannings's End Wetted Travel Identifier/ Length Slope n Area Perimeter Velocity Time (ft) (ft/ft) (sq ft) (ft) (ft/sec) (hr) N-1 SHEET 100 0.0600 0.130 0.081 SHALLOW 100 0.0600 4.3 0.007 CHANNEL 100 0.0175 Time of Concentration 0.1 WinTR-55, Version 1.00.10 3/23/2026 7:27:16 PM CSIDES FIFA Soccer Field Existing Condition St. Thomas-E County, Virgin Islands Sub-Area Land Use and Curve Number Details Sub-Area Hydrologic Sub-Area Curve Identifier Land Use Soil Area Number Group (ac) N-1 Newly graded area (pervious only) C 1.53 91 Woods - grass combination (fair) B 1.3 65 Woods - grass combination (fair) C 2.2 76 Total Area / Weighted Curve Number 5.03 78 ==== == WinTR-55, Version 1.00.10 3/23/2026 7:27:16 PM WinTR-55 Current Data Description --- Identification Data --- User: CSIDES Date: 3/23/2026 Project: FIFA Soccer Field Units: English SubTitle: Post-Developed Condition Areal Units: Acres State: Virgin Islands County: St. Thomas-E Filename: C:\Users\cside\Documents\Island Designs\Soccer Field\Fifa N-1 Post.w55 --- Sub-Area Data --- Name Description Reach Area(ac) RCN Tc N-1 Developed Land Use Outlet 5.03 64 0.1 Total area: 5.03 (ac) --- Storm Data -- Rainfall Depth by Rainfall Return Period 2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in) 4.3 6.2 7.4 9.0 10.4 11.9 3.1 Storm Data Source: User-provided custom storm data Rainfall Distribution Type: Type III Dimensionless Unit Hydrograph: <standard> WinTR-55, Version 1.00.10 3/23/2026 7:28:04 PM CSIDES FIFA Soccer Field Post-Developed Condition St. Thomas-E County, Virgin Islands Storm Data Rainfall Depth by Rainfall Return Period 2-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1-Yr (in) (in) (in) (in) (in) (in) (in) 4.3 6.2 7.4 9.0 10.4 11.9 3.1 Storm Data Source: User-provided custom storm data Rainfall Distribution Type: Type III Dimensionless Unit Hydrograph: <standard> WinTR-55, Version 1.00.10 3/23/2026 7:28:04 PM CSIDES FIFA Soccer Field Post-Developed Condition St. Thomas-E County, Virgin Islands Watershed Peak Table Sub-Area Peak Flow by Rainfall Return Period or Reach 5-Yr 10-Yr 100-Yr 1-Yr Identifier (cfs) (cfs) (cfs) (cfs) SUBAREAS N-1 12.47 17.24 36.48 2.17 REACHES OUTLET 12.47 17.24 36.48 2.17 WinTR-55, Version 1.00.10 3/23/2026 7:28:04 PM CSIDES FIFA Soccer Field Post-Developed Condition St. Thomas-E County, Virgin Islands Hydrograph Peak/Peak Time Table Sub-Area Peak Flow and Peak Time (hr) by Rainfall Return Period or Reach 5-Yr 10-Yr 100-Yr 1-Yr Identifier (cfs) (cfs) (cfs) (cfs) (hr) (hr) (hr) (hr) SUBAREAS N-1 12.47 17.24 36.48 2.17 12.12 12.12 12.11 12.13 REACHES OUTLET 12.47 17.24 36.48 2.17 WinTR-55, Version 1.00.10 3/23/2026 7:28:04 PM CSIDES FIFA Soccer Field Post-Developed Condition St. Thomas-E County, Virgin Islands Sub-Area Summary Table Sub-Area Drainage Time of Curve Receiving Sub-Area Identifier Area Concentration Number Reach Description (ac) (hr) N-1 5.03 0.100 64 Outlet Developed Land Use Total Area: 5.03 (ac) WinTR-55, Version 1.00.10 3/23/2026 7:28:04 PM CSIDES FIFA Soccer Field Post-Developed Condition St. Thomas-E County, Virgin Islands Sub-Area Time of Concentration Details Sub-Area Flow Mannings's End Wetted Travel Identifier/ Length Slope n Area Perimeter Velocity Time (ft) (ft/ft) (sq ft) (ft) (ft/sec) (hr) N-1 SHEET 100 0.0600 0.150 0.091 SHALLOW 100 0.0600 0.025 0.006 CHANNEL 100 0.0175 Time of Concentration 0.1 WinTR-55, Version 1.00.10 3/23/2026 7:28:04 PM CSIDES FIFA Soccer Field Post-Developed Condition St. Thomas-E County, Virgin Islands Sub-Area Land Use and Curve Number Details Sub-Area Hydrologic Sub-Area Curve Identifier Land Use Soil Area Number Group (ac) N-1 Open space; grass cover 50% to 75% (fair) B .84 69 Open space; grass cover > 75% (good) A 1.78 39 Paved parking lots, roofs, driveways C 1 98 Newly graded area (pervious only) A .41 77 Woods - grass combination (fair) B 1 65 Total Area / Weighted Curve Number 5.03 64 ==== == WinTR-55, Version 1.00.10 3/23/2026 7:28:04 PM Newly Graded Area (Pervious) Woods - Grass Combination (Fair, C) Woods - Grass Combination (Fair, B) SHEET NUMBER: 1.1 Pre-Development Conditions PROJECT: FIFA Soccer Field St. Thomas, VI DRAWN BY: CS REVIEWED BY: DZ REV DATE DESCRIPTION 7200 Regatta Pt Unit 8D St. Thomas VI 00802 March 24, 2026 Designed by Dave Zimmerman Professional Landscape Designer CCPI, CSRWI, PDCC Newly Graded Area (Pervious) Open Space; Grass Cover > 75% Paved driveways, roofs Open Space; Grass Cover 50% to 75% Woods - Grass Combination (Fair, B) SHEET NUMBER: 1.2 Post-Development Conditions PROJECT: FIFA Soccer Field St. Thomas, VI DRAWN BY: CS REVIEWED BY: DZ REV DATE DESCRIPTION 7200 Regatta Pt Unit 8D St. Thomas VI 00802 March 24, 2026 Designed by Dave Zimmerman Professional Landscape Designer CCPI, CSRWI, PDCC