EFFECTIVE MANAGEMENT OF COASTAL KARST AQUIFER WATER RESOURCES (Invited Presentation)

Coastal karst aquifers dominate the Mediterranean coast, are sole water sources on carbonate platforms and islands around the world, and in the United States are prominent in Florida, North Carolina, Puerto Rico, Illinois, and Wisconsin. Coupled with water demands of increasing coastal populations, rising seas, and declining recharge, the unique complexities of coastal karst aquifers pose serious technical and societal challenges to water resource management.

Past sea level fluctuations permitted the growth of conduit systems in many coastal karst aquifers. Now these can serve as submarine ground water discharge routes, as seawater entrainment sources, and/or as avenues for rapid sea water intrusion. Extreme drops in the Mediterranean Sea led to formerly coastal springs being submerged and sometimes plugged. In southeast Florida, evidence is accumulating that significant conduit systems have collapsed in some instances.

Technical challenges of managing coastal karst aquifers stem principally from difficulties in locating karst conduits, high potential flow rates in conduits that can quickly lead to seawater intrusion, density-stratified flow systems, and modeling an appropriate conduit system with relevant processes.

Cave diving expeditions reveal the exceptional complexity that can be present in cave geometry, density stratification, and tidal impacts on flow. New geophysical studies are also casting light on conduit geometries; some examples include the application of ground-penetrating-radar in France and seismic reflection in Florida.

Density-dependent and conduit modeling approaches are advancing. Simultaneous salinity and thermal effects can be important but are not often considered. Model simplification is often necessary for regional-scale application and sometimes entails use of sharp interface models. But management models that incorporate conduits and density-dependent flow simultaneously do not seem to be widely deployed.

Societal challenges affecting water management in these aquifers are related to population and demand growth, economics, legal frameworks for water extraction, and stakeholder participation. New interdisciplinary approaches are needed to sustainably utilize these resources – particularly in the face of climate change and rising sea levels.