Advanced Hydrologic Modeling
Hydrologic models can’t predict the future, but they can generate scenarios illustrating the likely impacts of sea level rise and extreme flooding on the region’s water supply and flood control systems. We expect the 3D models in particular to capture the attention of policymakers and residents and generate a lot of discussion about adaptation choices.Dr. Jennifer Jurado, Director, Broward County Environmental Planning and Community Resilience Division
In 2006, Broward County partnered with the U.S. Geological Survey (USGS) to develop a numerical model tracking the movement of saltwater inundation in the northern third of the county. The initial results established that the model accurately represented the historic movement of the saltwater front, while sensitivity analyses identified how various factors contributed to the front’s migration. Results showed that the influence of sea level rise was minimal by itself, but when coupled with other stressors like wellfield withdrawals, the combined effects were significant.
Several years later, in 2013, Broward County and USGS undertook a new project to model the central and southern portions of Broward and to link to the already-completed northern model. As with the earlier model, the expanded model was tested and calibrated to ensure it would accurately represent the historic record of saltwater intrusion. Sensitivity analyses were designed to isolate various manmade and natural stresses—everything from potable water withdrawals and canal elevations to drought and sea level rise. The model sought to incorporate predictive scenarios to give insight into future conditions and the best management practices for protecting potable water supplies.
While substantial, these saltwater intrusion groundwater models represented only an initial phase of work. The next steps involved linking coastal variable density models with more expansive models of the combined surface/groundwater system in Broward County to evaluate interactions between sea level rise, surface waters, and groundwater, including reductions in soil storage and changes to overland flows. This expanded model is now being calibrated to match historical data before applying the Compact’s unified sea level rise projection and downscaled precipitation data from global climate models and analyzing the combined impacts of sea level rise, high tides, and storm events on water management systems and flood protection. The model allows for testing of proposed adaptation measures, such as increased pump capacity, relocation of water control structures, raising of sea walls, and regional water storage options in lessening the impacts of climate change. Modeled changes in wet and dry season groundwater elevations are also expected to provide updated guidance for the design and licensing of water management systems.
Despite the predictive power of these numerical models, their results can be difficult to present to less-technical audiences. Understanding that these scenarios need to be communicated in more effective ways, Broward County has partnered with the National Environmental Modeling and Analysis Center (NEMAC) at the University of North Carolina – Asheville on a project to develop 3D visualizations of the groundwater/surface water models. The project is being conducted in four phases, with the first two focused on the creation of a climate impacts database from available GIS data, model outputs, and the construction of 3D models and visualizations. The third and fourth phases will focus on developing narratives to accompany the 3D models and workshops for Broward County staff, planners, and stakeholders, both to teach the techniques that can be employed throughout the region and to communicate the final results for community feedback.
These modeling efforts provide water managers, municipal utilities, planners, and elected officials with valuable tools that develop scenarios illustrating the range of possible impacts of climate change and sea level rise on Broward County’s groundwater and surface water systems, and an initial assessment of the types of measures that could be employed to adapt to the risks posed by climate impacts.
Implementation has moved forward via individual and collaborative efforts by Broward County staff, USGS, and NEMAC.
By investing in this modeling, Broward County stakeholders gain a powerful tool for evaluating the likely influence of sea level rise on saltwater intrusion and the performance of drainage and flood control systems with higher sea levels and more intense storm events. In addition, the models facilitate information sharing relating to the potential benefits of adaptation measures, such as the replacement of gravity drainage systems with pumps, movement of control structures, and raising of sea walls. These modeling tools have the potential of being linked to models being developed for Miami-Dade County and other jurisdictions in the future, supporting scenario analysis on an even larger scale.