The Freshwater habitats on BHI serve as the home to a wide variety of species from insects, to amphibians, reptiles, fish, birds, turtles, and alligators.
Bald Head Island’s potable water supply is produced from a sensitive and finite series of semi-confined aquifer zones completely surrounded by salt water. Over-production, contaminant impacts, salt-water intrusion, and future island development are among the largest of concerns for the health of the island’s freshwater aquifer.
Beginning in 2009, the BHI Conservancy has conducted monthly depth-to-water measurements and quarterly water quality assessments at over forty well and pond locations across the island. Analysis of this data has revealed annual trends in water quantity and quality. The primary area of concern is near the intersection of west and south beach where saltwater intrusion has been identified in the outermost wells located in close proximity to the Army Corps of Engineers maintained shipping channel.
As the island moves toward build-out, it is critical to continuously monitor water quantity and quality. The current protocol employed by the BHI Conservancy serves as an early warning system for threats to BHI’s freshwater resources. Continuing to intensively monitor the aquifer system will facilitate identification of dangerous changes in water quantity and quality throughout the year, especially during peak demand and/or in response to emerging threats (e.g. dredging, storm activity). Additionally, these data are essential to future USGS work to map the freshwater resources of BHI. Intensive mapping and modeling will provide a clear understanding of BHI freshwater resources and inform management practices into the future to minimize reliance on outside water resources. Monitoring and mapping efforts will provide the long-term data sets, trend analysis and management recommendations that inform and empower stakeholders to properly manage the freshwater resources of BHI.
The Bald Head Island Conservancy requested assistance from the USGS to provide expertise and modeling to explore the freshwater resources in the aquifer underlying Bald Head Island. Monitoring the aquifer more closely will allow decision makers to determine how much fresh water our aquifer can provide and how that supply may change in the future.
The first part of this project involves compiling historic data and collecting additional water level and water quality information. The USGS visited the island in mid-August to install a continuous water quality monitor on a well near the golf course and on the perimeter of the island. Historically, this particular well has shown increasing levels of chlorides, which indicates increasing salinity.
The equipment hooked up to the well records water level, conductance (a measure of salinity) and temperature every 15 minutes, which is then sent to a satellite. This real time data can be accessed here .
Freshwater Monitoring Program Updates
The above graph shows relative water availability in the surficial aquifer. Increases in the lines correspond to the water table being further away from the surface of the ground. These "peaks" correspond with less water availability. Water availability typically follows a seasonal pattern with the greatest draw down, or water extraction from the aquifer, occurring in later summer/early fall when there are more people on the island. Then, over winter, as there is more precipitation, the ground water is slowly recharged. From the graph above we see increased draw down in July and relatively stable levels throughout the end of the year. As more data is collected in the Spring we will add to this and interpret seasonal trends.
Perimeter monitoring wells showed similar salinity from Summer to Fall sampling. Increased salinity in these wells has been identified for several years, indicating a trend of saltwater intrusion. There are a number of reasons this could be occurring including increased sea level, increased pumping of freshwater resources, and/or changes in the underlying geology of the island. Water quality in these wells will be checked again in the next quarter.
Summer 2014 Update
Preliminary results from the freshwater monitoring program indicate minor saltwater intrusion into the perimeter monitoring wells. Increased salinity in these wells has been identified for several years, indicating a trend of saltwater intrusion. There are a number of reasons this could be occurring including increased sea level, increased pumping of freshwater resources, and/or changes in the underlying geology of the island. Aquifer water quality will be measured again in the winter and results will be presented here along with measurements conducted by USGS.