According to data from the Southeast Regional Climate Change Compact Unified Sea Level Rise Projection, sea levels in South Florida are anticipated to rise six to 12 inches by the year 2030. This is an issue not only in Southern Florida, but across coastal areas around the U.S. A challenge these areas face is to assess the nature and extent of the threat of saltwater intrusion into the coastal ecosystem and the public water supply considering population growth, increasing water supply demands and sea level rise.

Saltwater intrusion into freshwater aquifers due to over-pumping has been a longtime concern among coastal water managers. This threat is exacerbated by rising sea levels along the coast. These concerns are being addressed by engineers, scientists and policy makers to ensure that coastal aquifers remain a viable source of freshwater for residents in South Florida. Following are strategies that have been implemented to manage and protect groundwater resources.

• Numerical groundwater flow models are being constructed to inform future water-use permitting and policies related to groundwater pumping in coastal aquifers. To start, spatial data on water quantity and water quality are used to establish baseline water levels and water quality in coastal aquifers. Then, future conditions can be evaluated with predictive simulations to examine the effects of different management actions.
• Integrated models are utilized to simulate both surface and groundwater systems. The models account for density differences between freshwater and saltwater and the complex interactions with surface water in the networks of drainage canals. Additionally, the models assess the response to increased sea levels and groundwater pumping. The flow of freshwater from canals into the groundwater system is vital in keeping saline water out of coastal aquifers in some areas.
• In some cases, groundwater pumping can be shifted to deeper brackish aquifers to alleviate stress on shallow freshwater aquifers. A number of utilities in South Florida have turned to deep artesian aquifer systems as a source or raw water supply. Water pumped from these wellfields does not have a significant impact on the surficial aquifer and is less affected by sea level rise or other climatic conditions.

One area facing the challenge of saltwater intrusion is the Big Cypress Basin, a coastal freshwater ecosystem that covers 2,400 square miles along Florida’s Gulf of Mexico. The basin is low-lying and the land surface is generally only several feet above sea level. To address saltwater intrusion, WSP USA staff constructed a density-dependent, 3D groundwater flow model of the basin. The model enabled the basin’s water managers to strategically define future allocations for sustainable groundwater withdrawals. The modeling and simulation GIS database developed by WSP staff has allowed the water managers to quickly review water level and water quality data, facilitating the management of water conservation strategies in the long-term.

Additionally, our team recommended strategic locations of future water quality monitoring wells to detect salinity changes in the shallow coastal aquifer and provide reliable, long-term data. Incorporating a physical and scientific understanding into planning decisions for water, as well as other infrastructure, is critical for future decision making along the nation’s coasts. WSP is contributing to this effort by developing scientific understanding of drinking water aquifers and incorporating this knowledge into planning and decision making for future water supply needs. For additional information on groundwater management, please contact scott.manahan@wsp.com