According to Shellie Habel’s opinion column in Knowable Magazine, rising coastal groundwater levels are a concern for our communities. As sea levels increase, coastal groundwater levels follow suit. This can cause flooding in important underground city infrastructure like water pipes, sewer systems, and stormwater drains. The water, often salty and corrosive, can cause infrastructure to fail. This is already causing issues such as flooded basements and water main breaks in many places.
Habel, a flood modeler based in Honolulu, uses the city as an example of the effects of rising groundwater. Honolulu has a long-operating tide gauge and a network of wells to monitor coastal groundwater. The tide gauge has recorded a sea level rise of over 20 centimeters since before World War I. In 2017, the El Niño climate pattern temporarily raised sea levels by up to 30 cm, causing a similar rise in groundwater.
Rising groundwater can also bring buried contaminants to the surface. This can interact with sewage infrastructure and old industrial spills. A 2020 study suggests that nearly 90 percent of Honolulu’s active cesspools are compromised during high tides. There are also concerns about the upward seepage of lead and hydrocarbons, and potential methane-induced explosions.