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Groundwater Inundation: Doubling Community Damage from Sea Level Rise

Principal Investigator: Charles Fletcher

Graduate Student: Shellie Habel

One of the impacts of sea-level rise that is not widely known is that flooding will not only come from the sea, it will come from beneath the ground. In most coastal settings the water table lies at approximately mean sea level and rises and falls with the tides and even with weather patterns; it is intimately and immediately connected to the surface of the sea. In Honolulu and Waikīkī the water table actually lies above the height of mean sea level, very close to the ground surface. Thus, a rise in sea level means that the coastal water table will rise, possibly to the point of breaking through the ground surface and creating new wetlands, not a desirable feature in an urban setting at the foundation of a building or road, or in an ecosystem that serves as a refuge for endangered species that are unaccustomed to saturated soil and free-standing water bodies. Research indicates that as much as 70% of the flooding that will occur in Honolulu due to a 2 ft rise in sea level later this century, will be because of groundwater inundation by the rising water table. This study will collect field data, model the problem, and provide a detailed assessment of the issue as well as identify specific locations in the Honolulu corridor that are especially vulnerable to groundwater inundation.