Coastal regions such as Florida and the Netherlands are susceptible to various impacts of climate change, although sea level rise is arguably the greatest concern for these low coastal regions. Several studies have examined recent historical, and projected future, sea level rise resulting from melting glaciers and thermal expansion of the oceans as they become warmer (Levitus et al. 2000; USGS 2000; Meehl et al. 2005). This issue is familiar to areas such as Miami-Dade County, which has measured a twelve-inch rise in sea level since 1848. If the historical average rate continues, sea level will increase another three inches by 2025. Global warming will accelerate the rate of sea level change. Miami-Dade County has responded to this possibility by anticipating an increase of five inches by 2025, and a comparable rise in sea level over the remainder of the century. Likewise, the Netherlands is considering increases in sea level that, if realized, would significantly affect the nation’s freshwater supply.
Sea level rise can have several impacts on coastal utilities. The most visible effect is damage to freshwater infrastructure caused by flooding, but also significant is saltwater intrusion into coastal aquifers, such as the Biscayne Aquifer that supplies Miami-Dade’s 2.2 million inhabitants. To assess these issues, in 2002 the South Florida Regional Planning Council began mapping effects of sea level rise for coastal counties. These maps reveal that an increase in sea level of only five inches would be enough to inundate some of Miami’s freshwater facilities. Key among the decisions Miami’s water department must make in the near future will be whether to invest in protecting vulnerable facilities through flood control and drainage infrastructure or abandon them. In October 2003, the County established a task force to identify technically sound and economically viable responses in infrastructure planning to cope with sea level rise and other regional climate change impacts in the 21st century.
The second impact of sea level rise, saltwater intrusion, has been apparent long before climate change became a recognized threat. At the beginning of the twentieth century, saltwater did not intrude into the Biscayne Aquifer beyond the coast, but extensive construction of drainage canals provided an inlet for saltwater into the aquifer. Construction of control structures to hold back saltwater began in the 1940s, and more recently saltwater intrusion has been partially stabilized. However, groundwater is still contaminated several miles inland of the coast. This intrusion has driven the location of well fields and treatment facilities inland. Many of Miami’s wells are located far enough inland that a rise of several inches in sea level will result in the loss of several inches at the base of the aquifer, which is small considering that the depth of the aquifer ranges between 100 to 150 feet. However, constructing wells inland has come at the cost of competing with the Everglades for fresh water. Environmental regulations protect the Everglades, especially since recent efforts have begun to restore the region’s ecology. Therefore, the groundwater supply for Miami’s water utilities will be constrained by both encroaching saltwater from the coast and limits on the utility’s ability to continue moving its well fields inland due to the environmental needs of the Everglades. Additional constraints are the inability to maintain high enough water levels at the salinity control structures during droughts, and the need to open the salinity control structures and release water to prevent inland floods during high rainfall periods.
Saltwater intrusion will be confined within several miles of the coast in Florida, but regions that are already below sea level, such as parts of the Netherlands, will face more drastic impacts from contaminated groundwater. In the Netherlands, enhanced saltwater intrusion will result from both sea level rise and a shortage of fresh surface water to maintain water levels in polder (reclaimed, low-lying) areas during extreme dry summers. This may result in saltwater contamination of fresh groundwater aquifers. Since sixty-five percent of the Dutch drinking water supply comes from groundwater, it is obvious that climate change and saltwater intrusion may affect drinking water supply over the course of this century. Twenty-five percent of the Netherlands’ 200 drinking-water facilities are situated just above or below sea level. At many of these sites, groundwater is vulnerable to saltwater contamination. Fifteen percent of the 200 facilities are estimated to be threatened due to saltwater intrusion and up-coning of saltwater from deeper (fossil) marine aquifers, and fifteen of the country’s 200 freshwater production sites have already closed because of saltwater contamination. Such a possible drastic reduction in available groundwater in the future will make the Netherlands much more dependent on surface water, which currently accounts for only thirty-five percent of freshwater production.
The Netherlands does have an ample supply of surface water, but it is often polluted. The Netherlands’ surface supply originates from Belgium, Germany and France via the rivers Rhine and Meuse, so contaminants from other countries’ industry, agriculture, and urban regions inevitably end up in the Netherlands’ water. Because the source of much of the water pollution lies outside of the Netherlands, it is rarely feasible to prevent contamination through regulations, although tackling such pollution is a goal of the EU Water Framework Directive (adopted in 2000). Therefore, the Dutch water utilities will need to incur the expense of sanitizing surface water. If a fifteen percent decrease in groundwater supply (including riverbank filtrate) occurs during this century, Dutch utilities will be required to filter over 100 billion liters of additional surface water per year to meet current demands. Purifying such a large quantity will be an expensive task and one that will take some time to implement, particularly if warmer water temperature and variable river flows further impair the already poor quality of the country’s surface water. For this reason, the Dutch utilities carry out research on the production of drinking water from brackish groundwater using reverse osmosis membranes and on prevention of saltwater contamination of fresh aquifers by experimental well field design.