124
wedge-like feature in the subsurface, owing to density differences between freshwater and seawater at the coast (seawater is denser than freshwater). The interface
between freshwater and saltwater is neither sharp nor static. It is a diffuse zone
(known as the freshwater-saltwater transition zone) where mixing between freshwater and saltwater occurs.
The location of the transition zone in the subsurface depends on drivers such as
sea-level, subsidence, and groundwater withdrawals. Some of these processes occur
on short and intermediate timescales (days to weeks) whereas other processes occur
on long timescales (months to years). An increase in sea level, and/or or land subsidence would move the transition zone further inland thereby causing saltwater intrusion. Groundwater withdrawals would reduce the flow of freshwater that
counterbalances saltwater and as a result would cause saltwater to migrate further
inland. The extent and magnitude of saltwater intrusion in coastal aquifers may
therefore be caused by natural and/or anthropogenic drivers.
Surface water bodies are also threatened by saltwater intrusion. Sea-level rise
and wind-tides are examples of drivers that may push saltwater into fresh surface
water bodies. The saltwater in these bodies may then infiltrate into adjacent aquifers
thereby making groundwater more saline. Studying and mitigating the effects of
saltwater intrusion therefore depends on the causal mechanism (e.g., sea-level rise
vs. groundwater withdrawals) as well as the type of water body affected by intrusion
(i.e., groundwater vs. surface water). My research interests focus on investigating
saltwater intrusion drivers in both surface water and groundwater in coastal North
Carolina.
Tale 1: Saltwater Intrusion into Groundwater on a North
Carolina Barrier Island
A recent project that my research team and I undertook involved using groundwater
modeling techniques to understand how groundwater withdrawals were causing
saltwater intrusion in a limestone aquifer beneath Bogue Banks, NC (Fig. 8.1). The
Castle Hayne aquifer is the source of domestic water supply for thousands of permanent residents on the island and tens of thousands of holiday makers that frequent
Bogue Banks during the summer. The threat from saltwater contamination is therefore taken very seriously by water managers on the island because any loss of freshwater resources would cause significant impact to the emotional and economic
well-being of island residents. Coastal communities that are threatened by saltwater
intrusion usually resort to finding new freshwater sources (e.g., exploiting other
aquifers or surface water bodies, piping water from other areas) or desalinizing
saltwater to make it potable. All of these options are very costly and take significant
amounts of time and resources to develop.
Our project on Bogue Banks was of interest because saltwater intrusion was
occurring on the western part of the island where intrusion was least expected.
Logic suggests that intrusion should occur closest to the source of salty water (the
A. K. Manda
wedge-like feature in the subsurface, owing to density differences between freshwater and seawater at the coast (seawater is denser than freshwater). The interface
between freshwater and saltwater is neither sharp nor static. It is a diffuse zone
(known as the freshwater-saltwater transition zone) where mixing between freshwater and saltwater occurs.
The location of the transition zone in the subsurface depends on drivers such as
sea-level, subsidence, and groundwater withdrawals. Some of these processes occur
on short and intermediate timescales (days to weeks) whereas other processes occur
on long timescales (months to years). An increase in sea level, and/or or land subsidence would move the transition zone further inland thereby causing saltwater intrusion. Groundwater withdrawals would reduce the flow of freshwater that
counterbalances saltwater and as a result would cause saltwater to migrate further
inland. The extent and magnitude of saltwater intrusion in coastal aquifers may
therefore be caused by natural and/or anthropogenic drivers.
Surface water bodies are also threatened by saltwater intrusion. Sea-level rise
and wind-tides are examples of drivers that may push saltwater into fresh surface
water bodies. The saltwater in these bodies may then infiltrate into adjacent aquifers
thereby making groundwater more saline. Studying and mitigating the effects of
saltwater intrusion therefore depends on the causal mechanism (e.g., sea-level rise
vs. groundwater withdrawals) as well as the type of water body affected by intrusion
(i.e., groundwater vs. surface water). My research interests focus on investigating
saltwater intrusion drivers in both surface water and groundwater in coastal North
Carolina.
Tale 1: Saltwater Intrusion into Groundwater on a North
Carolina Barrier Island
A recent project that my research team and I undertook involved using groundwater
modeling techniques to understand how groundwater withdrawals were causing
saltwater intrusion in a limestone aquifer beneath Bogue Banks, NC (Fig. 8.1). The
Castle Hayne aquifer is the source of domestic water supply for thousands of permanent residents on the island and tens of thousands of holiday makers that frequent
Bogue Banks during the summer. The threat from saltwater contamination is therefore taken very seriously by water managers on the island because any loss of freshwater resources would cause significant impact to the emotional and economic
well-being of island residents. Coastal communities that are threatened by saltwater
intrusion usually resort to finding new freshwater sources (e.g., exploiting other
aquifers or surface water bodies, piping water from other areas) or desalinizing
saltwater to make it potable. All of these options are very costly and take significant
amounts of time and resources to develop.
Our project on Bogue Banks was of interest because saltwater intrusion was
occurring on the western part of the island where intrusion was least expected.
Logic suggests that intrusion should occur closest to the source of salty water (the
A. K. Manda