Linking climate vulnerability and inundation modeling to decision-making in Broward County, Florida

Broward County is an urban community of approximately 1.8 million people in southeast Florida. The County includes 24 miles of coastline and is situated between the Atlantic Ocean and the Everglades natural area. Drainage and flood control are actively managed using an extensive canal network operated by several drainage districts, as well as by local and regional agencies. The elaborate drainage system is composed of nearly 1,800 miles of canals, which are an important component of the broader regional water-supply system. The canals are not only a critical flood control feature, but also serve as valuable surface-water storage features for local rainfall and as a source of aquifer recharge in a region where high water-table elevations, flat topography, and limited undeveloped land preclude long-term water storage without compromising flood control. The potential for aquifer recharge is enhanced by the high transmissivity of the karstic Biscayne Aquifer, the region's primary drinking water supply, which in some parts of the county sits just below land surface.

Although the hydraulic characteristics of the Biscayne Aquifer make it a highly productive water source, they can limit the ability of the system to maintain flood control and drinking water supplies under changing climate and sea-level conditions. The Biscayne Aquifer is already vulnerable to saltwater intrusion, and several municipalities have relocated and redistributed groundwater pumpage further inland due to saltwater contamination. Increases in sea level will also impact drainage infrastructure and upstream water management systems as a result of the high transmissivity of the aquifer, which may notably reduce hydraulic gradients throughout the County. Diminished hydraulic gradients can reduce the function of coastal drainage wells and ultimately diminish the discharge capacity of coastal canals. Reduced discharge capacity could impair flood management for inland communities because drainage systems ultimately are restricted by discharge rates at the terminus of coastal canals. As such, climate change and sea-level rise could similarly impact coastal and inland communities in southeast Florida in the absence of adaptive measures. These cumulative impacts will likely be compounded by more frequent extreme weather and higher tides, which several recent events have served to underscore.

Broward County officials and local water managers are well-attuned to the challenges within the existing water-management system, and they have collaborated in the development of highly complex hydrologic models to guide water-management decisions. Historically these efforts included development of fully integrated surface-water and groundwater models using MIKE series modeling tools. To account for climate vulnerability and sea-level rise, the county recently has sought to enhance its modeling capabilities with the integration of density-dependent model components to address saltwater intrusion. Today, Broward County is collaborating with local municipalities to fund a comprehensive modeling project being developed with the United States Geologic Survey. The project includes a fully-integrated surface-water and groundwater model using MODFLOW-based tools combined with a unique surface-water process and density-dependent flow to allow for modeling the impacts of sea-level rise on groundwater elevations, flood management operations, and water quality in support of water-supply operations. The modeling effort also involves downscaling data from global climate models to evaluate the impacts of changing climatic conditions on local hydrology. High resolution modeling of a coastal and an inland community will be undertaken to serve as models for adaptive management throughout the County and the broader region of southeast Florida. Model calibration is nearly complete and scenario development has been work-shopped. The modeling efforts underway incorporate a stakeholder process involving water utility directors, municipal staff, and water managers. Model scenarios and data output will be used to identify, test, and quantify the benefits of preferred adaptation strategies for the purpose of amending regulations, guiding planning decisions and project criteria, and advancing adaptation projects. The County continues to seek ways to enhance communication of model results to decision makers and the public, and is currently investigating the development of advanced 3D visualization tools to aid in these efforts.