A Resilient Stormwater and Coastal Management Plan for Hollywood Florida

INTRODUCTION & BACKGROUND The City of Hollywood, Florida, developed a Stormwater Master Plan (SWMP) to evaluate and model the City's watersheds and identify resilient stormwater and flood prevention capital investments for today, tomorrow, and decades to come. The master plan includes modeling the effects of sea level rise (SLR), rising groundwater tables, and increased rainfall intensities. It also considers anticipated development growth and climate change data, providing the tools necessary for the City to create a forward-thinking capital plan that anticipates and prioritizes funding and infrastructure needs. Program goals were established to create a vision and metrics for the future. Topics include:

*Flood control

*Water quality protection

*Aquifer recharge and water supply

*Conservation and stormwater harvesting

*Operation and maintenance

*Long-term financing

*Community acceptance The City of Hollywood encompasses approximately 45 square miles (Figure 1). The stormwater service area is divided naturally by elevation, topography, and infrastructure into three major basins. These basins interact with Broward County, Central Broward Water Control District (CBWCD), South Broward Drainage District (SBDD), Florida Department of Transportation (FDOT), City of Hallandale Beach, City of Dania Beach, and South Florida Water Management District (SFWMD) stormwater systems. APPROACH Using the United States Environmental Protection Agency's (EPA) Storm Water Management Model (SWMM), the SWMP hydrologic and hydraulic models were developed for the City's primary stormwater management system (PSMS). The models included a study area of 29,000 acres, 2,228 sub-basins, consideration of offsite basin and major canal contributions, 80 backflow preventers, 12 stormwater pump stations, 217 miles of stormwater pipes, 29 miles of canals, 15 bridges, 33 miles of exfiltration trench, 250 outfalls, and a one-year tidal stillwater elevation of 2.5 feet North American Vertical Datum (NAVD). The SWMP involved coordinating the City's geographic information system (GIS) to update the existing stormwater atlas, populating an asset management database. Simultaneously, a city-wide stormwater model was developed, accounting for pervious and impervious areas in the urban landscape. The data collection effort included a survey of stormwater structures and the development of a Digital Elevation Model (DEM) based on Light Detection and Ranging (LiDAR) topographic data. The data collected was validated with the City's existing infrastructure and bathymetric data to develop a City-wide model for the major watersheds that accounts for varying rainfall events, tidal and groundwater influences, and future SLR impacts in coordination with Broward County, SBDD, CBWCD, Dania Beach, Hallandale Beach, FDOT, and SFWMD stormwater systems. Modeling inputs and parameters required extensive manipulation and analyses using GIS tools such as the Geographic Watershed Information System (GWIS) schema and ArcHydro. The modeling provides a comprehensive basin-by-basin analysis of the flood control level of service (LOS) for existing and proposed stormwater systems. It also considers the effects of projected climatological conditions for the future. The City conducted a series of public meetings for citizens to provide locations of reported problems. The input, combined with the City's stormwater complaint system records and Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRM), defined flooding problem locations and system connectivity (Figure 2). The project team used SWMM to estimate flood stages and inundation maps (Figure 3). They evaluated the flow rates and volumes for storage, conveyance, exfiltration, recharge wells, and potential pumping. The plan included conditions for the April 2023 flood event, ranging from a five-to-1,000-year event. Individual neighborhood capital improvement projects were tailored, specifically in areas most susceptible to flooding. Swales, detention systems, and exfiltration systems were evaluated, along with time-varying storage operations and recharge wells. The team is also considering seawall height extensions for the City's 140 miles of shoreline and backflow prevention for the 250 outfalls. SUMMARY This paper will present the results of the SWMP focusing on coastal resilience. It encompasses hydrologic and hydraulic models, historical storm tidal surge evaluations, LOS evaluations, cost-effective alternatives assessments, and associated Capital Improvement Program (CIP). This presentation includes a summary discussion on stakeholder coordination and prioritization strategies.