126
For this study, we hypothesized that paleochannels (very old stream valleys that
were now filled with sediment), were the mode by which saltwater was entering the
aquifer. To test this hypothesis, we included a palaeochannel in the model. We also
inserted groundwater pumping wells in the model to simulate the effect of withdrawing water on the groundwater flow patterns around the paleochannel. These
model wells were set to withdraw water at the same schedule and rate as those in the
real world. Using this approach, we were able to determine that the saltwater intrusion observed on the western side of the island could have come from paleochannels. This information is useful for formulating strategies that may be employed to
mitigate, or adapt to, the effects of saltwater intrusion in coastal aquifers. For example, water managers could opt to abandon groundwater wells, find other sources of
freshwater (e.g., deeper groundwater or surface water), or develop reverse osmosis
plants to meet the freshwater needs of coastal communities.
The results of this study indicate that groundwater pumping in coastal regions can
drive saltwater intrusion through paleochannels that are more permeable than the surrounding sedimentary units. The saltwater can then make its way to wells that provide
potable water supplies, thereby threatening the potable water supplies for coastal
communities that rely on groundwater. A knowledge of the existence and extent of
paleochannels in coastal regions that draw water from subsurface sources could help
water managers anticipate potential impacts of pumping induced saltwater intrusion
on fresh groundwater sources.
Tale 2: Saltwater Intrusion in a Surface Water Body
of the “Inner Banks” of North Carolina
On the landward (western) side of the broad expanse of Pamlico Sound (Fig. 8.1) is
what has become known as North Carolina’s “Inner Banks”. In reality these are very
low-lying lands, usually with an elevation of less than 1 m above sea level (Fig. 8.2),
that look nothing like the famed, sandy Outer Banks on the seaward side of Pamlico
Sound (Fig. 8.3). Several years ago, we investigated saltwater intrusion in a coastal
wetland system of the “Inner Banks”. In this region, saltwater intrusion is inundating low-lying lands that are used for agriculture and conservation purposes. Since
certain types of vegetation are not tolerant to saltwater, any increase in saltwater
content may seriously impact the health of this vegetation. For example, in the
Emily and Richardson Preyer Buckridge Coastal Reserve (Fig. 8.1), various tree
stands of Atlantic White Cedar are showing signs of stress, potentially due to saltwater intrusion. According to the North Carolina Forest Service, the state of North
Carolina has the largest acreage of Atlantic White Cedar in the US. Thus, any loss
of Atlantic White Cedar will have severe consequences on the ecosystems in which
these trees are found.
In other low-lying areas, saltwater is finding its way into agricultural fields
thereby preventing the growth and maturity of certain types of crops (e.g., soybeans,
corn, etc.) that are important for the economic well-being of many coastal
A. K. Manda
For this study, we hypothesized that paleochannels (very old stream valleys that
were now filled with sediment), were the mode by which saltwater was entering the
aquifer. To test this hypothesis, we included a palaeochannel in the model. We also
inserted groundwater pumping wells in the model to simulate the effect of withdrawing water on the groundwater flow patterns around the paleochannel. These
model wells were set to withdraw water at the same schedule and rate as those in the
real world. Using this approach, we were able to determine that the saltwater intrusion observed on the western side of the island could have come from paleochannels. This information is useful for formulating strategies that may be employed to
mitigate, or adapt to, the effects of saltwater intrusion in coastal aquifers. For example, water managers could opt to abandon groundwater wells, find other sources of
freshwater (e.g., deeper groundwater or surface water), or develop reverse osmosis
plants to meet the freshwater needs of coastal communities.
The results of this study indicate that groundwater pumping in coastal regions can
drive saltwater intrusion through paleochannels that are more permeable than the surrounding sedimentary units. The saltwater can then make its way to wells that provide
potable water supplies, thereby threatening the potable water supplies for coastal
communities that rely on groundwater. A knowledge of the existence and extent of
paleochannels in coastal regions that draw water from subsurface sources could help
water managers anticipate potential impacts of pumping induced saltwater intrusion
on fresh groundwater sources.
Tale 2: Saltwater Intrusion in a Surface Water Body
of the “Inner Banks” of North Carolina
On the landward (western) side of the broad expanse of Pamlico Sound (Fig. 8.1) is
what has become known as North Carolina’s “Inner Banks”. In reality these are very
low-lying lands, usually with an elevation of less than 1 m above sea level (Fig. 8.2),
that look nothing like the famed, sandy Outer Banks on the seaward side of Pamlico
Sound (Fig. 8.3). Several years ago, we investigated saltwater intrusion in a coastal
wetland system of the “Inner Banks”. In this region, saltwater intrusion is inundating low-lying lands that are used for agriculture and conservation purposes. Since
certain types of vegetation are not tolerant to saltwater, any increase in saltwater
content may seriously impact the health of this vegetation. For example, in the
Emily and Richardson Preyer Buckridge Coastal Reserve (Fig. 8.1), various tree
stands of Atlantic White Cedar are showing signs of stress, potentially due to saltwater intrusion. According to the North Carolina Forest Service, the state of North
Carolina has the largest acreage of Atlantic White Cedar in the US. Thus, any loss
of Atlantic White Cedar will have severe consequences on the ecosystems in which
these trees are found.
In other low-lying areas, saltwater is finding its way into agricultural fields
thereby preventing the growth and maturity of certain types of crops (e.g., soybeans,
corn, etc.) that are important for the economic well-being of many coastal
A. K. Manda