125
Atlantic Ocean) but it was occurring on the western side of the island adjacent to
Bogue Sound. Since it is very difficult, if not impossible to collect adequate data to
characterize saltwater intrusion in deep aquifers, researchers typically use mathematical models to simulate the flow of groundwater and saltwater in the subsurface.
Mathematical models that simulate groundwater flow are based on principles of
physics governing the flow of water in permeable materials. As such, these models
require input parameters that capture the physical and hydrologic properties of
freshwater aquifers to run.
We acquired geological data (rock types, thicknesses of rock units, orientations
of rock units, properties of rock units, etc.) from the published literature and the
State, and water level data from the local water purveyor, to create a model of the
groundwater flow regime beneath the island. Using commercially available computer software, we built a rendering of the system beneath the island complete with
appropriate orientations and thicknesses, physical properties and flow characteristics of layers of rock and sediment in the subsurface. This process is iterative in that
we build the model and then refine it based on how well the model results match the
groundwater data that were collected by the water purveyor. If the model results do
not match the purveyor’s data, we adjust the parameters within reasonable limits
and re-run the model to generate a new set of model results. This process is called
calibration. Once the model is calibrated, that is, when the water levels generated by
the model are well aligned with the water levels collected in the field, we move on
to running the simulation to test our hypothesis.
Fig. 8.1 Map of northeastern North Carolina, USA showing locations mentioned in the text. The
yellow star indicates Bogue Banks, the location of Tale 1. The red star indicates the Emily and
Richardson Preyer Buckridge Coastal Reserve, the site of Tale 2
8 A Tale of Two Hydrogeology Problems in Coastal North Carolina
Atlantic Ocean) but it was occurring on the western side of the island adjacent to
Bogue Sound. Since it is very difficult, if not impossible to collect adequate data to
characterize saltwater intrusion in deep aquifers, researchers typically use mathematical models to simulate the flow of groundwater and saltwater in the subsurface.
Mathematical models that simulate groundwater flow are based on principles of
physics governing the flow of water in permeable materials. As such, these models
require input parameters that capture the physical and hydrologic properties of
freshwater aquifers to run.
We acquired geological data (rock types, thicknesses of rock units, orientations
of rock units, properties of rock units, etc.) from the published literature and the
State, and water level data from the local water purveyor, to create a model of the
groundwater flow regime beneath the island. Using commercially available computer software, we built a rendering of the system beneath the island complete with
appropriate orientations and thicknesses, physical properties and flow characteristics of layers of rock and sediment in the subsurface. This process is iterative in that
we build the model and then refine it based on how well the model results match the
groundwater data that were collected by the water purveyor. If the model results do
not match the purveyor’s data, we adjust the parameters within reasonable limits
and re-run the model to generate a new set of model results. This process is called
calibration. Once the model is calibrated, that is, when the water levels generated by
the model are well aligned with the water levels collected in the field, we move on
to running the simulation to test our hypothesis.
Fig. 8.1 Map of northeastern North Carolina, USA showing locations mentioned in the text. The
yellow star indicates Bogue Banks, the location of Tale 1. The red star indicates the Emily and
Richardson Preyer Buckridge Coastal Reserve, the site of Tale 2
8 A Tale of Two Hydrogeology Problems in Coastal North Carolina