WRRC Seminar
November 21, 3:00pm - 4:15pm
Mānoa Campus, POST 126
Modeling specific groundwater problems in Hawaii: Borehole flow and groundwater inundation
Two specific problems involving localized groundwater flow processes are presented
as examples of groundwater models at different scales and different approximations:
Vertical flow of groundwater through monitor wells and increased coastal flooding from
groundwater-table rise with sea level.
The Pearl Harbor aquifer in southern Oahu is one of the most important sources of
freshwater in Hawaii. Salinity profiles collected from uncased deep monitor wells
(DMWs) commonly are used to monitor freshwater-lens thickness. However, vertical
flow in DMWs can cause the measured salinity to differ from salinity in the adjacent
aquifer. Substantial borehole flow and displacement of salinity in DMWs over several
hundred feet have been observed in the Pearl Harbor aquifer. A numerical modeling
approach incorporated hydraulic characteristics and flux rates representative of the
Pearl Harbor aquifer. Borehole flow caused by vertical hydraulic gradients associated
with both the natural regional flow system and groundwater withdrawals was simulated.
Model results indicate that, with all other factors being equal, greater withdrawal rates,
closer withdrawal locations, or higher hydraulic conductivity of the well cause greater
borehole flow and displacement of salinity in the well. Borehole flow caused by the
natural groundwater-flow system is five orders of magnitude greater than vertical flow in
a homogeneous aquifer.
In the wake of climate change, sea-level rise will impact many coastal areas in Hawaii.
Global mean sea level may rise about 1 ft by 2050 and 3 ft by 2100, and cause
substantial coastal erosion and flooding. However, it is widely unrecognized that low-
lying coastal areas may also be vulnerable to groundwater inundation, which is flooding
due to a rise of the groundwater table with sea level. Vulnerability to groundwater
inundation in southern Oahu was assessed and results indicate that 0.6 m of potential
sea level rise causes significant flooding. In fact, the flooded area considering
groundwater inundation more than doubles previous predictions of flooding with future
sea-level rise. Groundwater inundation has wide-reaching consequences for decision-
makers, resource managers and urban planners, and requires a revised approach to
adapt to climate change.
Event Sponsor
Water Resources Research Center, Mānoa Campus
More Information
Philip Moravcik, 808-956-3097, morav@hawaii.edu