Rising sea poses a threat to the Island’s drinking water

The U.S. Geological Survey is investigating how climate change and sea-level rise could alter the potable groundwater on the Island.

With sea levels projected to rise between 1 and 6 feet by the year 2100 around Martha’s Vineyard, and groundwater being the only source for public drinking water, the U.S. Geological Survey New England Water Science Center is conducting a study that will directly inform Island water management.

The study will help experts understand how climate change and sea-level rise can influence the water resources and ecosystems on-Island through the 21st century. The knowledge gained from the study will inform present-day and future drinking water availability, and help experts assess where water management and conservation measures may be needed.

The USGS released a report on July 1, 2023, authored by Katrina M. Rossos, detailing the motivations and goals of the study.
“The model incorporates projected climate scenarios, such as sea-level rise and groundwater recharge fluctuations based on changing temperature and precipitation patterns, over the next 100 years,” said hydrologist Tim McCobb, lead researcher on the Island study. “These new geophysical data will be used with existing data to define the model boundaries and to develop contour maps of the bedrock surface and saltwater and freshwater surfaces across the Island.” 

Rising sea levels could directly impact public drinking water if sea water enters the Island’s shallow aquifer. As sea levels rise, so will the water table, creating a higher possibility of freshwater-saltwater interference. The study will consider the possibility of flooding to existing infrastructure like septic systems and basements. It will also examine the impact rising sea-level may have on future development, and disruptions to coastal wetland ecosystems.

The study consists of the USGS developing a groundwater-flow model for the entire Island to assess the impact of climate change on these ecological systems. The model is being developed in cooperation with the Massachusetts Department of Environmental Protection. Groundwater-flow models help experts understand the features of the land and water and their processes, including groundwater and surface-water interactions and changes in both the freshwater and saltwater flow systems, according to the USGS report. 

To create the groundwater-flow model, hydrologists with the Hydrologic Remote Sensing Branch of the USGS Water Mission Area conducted readings on the depth to bedrock by using surface geophysical techniques at 18 locations around the Island. The data collected will be used in the groundwater-flow model and add to the current understanding of the flow system and its boundaries, according to the report. Hydrologists used a passive seismic method called the horizontal-to-vertical spectral ratio technique to assess the depth to bedrock surface. 

Experts at the USGS anticipate the effects of climate change to vary across different locations on the Island and over time. The model in development is expected to be a useful tool in evaluating the impacts to the island’s water systems over the next 80 years.