AUGUSTA, Maine – A recently completed joint study between the Maine Geological Survey and the U.S. Geological Survey shows not only that the Freeport watershed has an adequate water supply for local use, but it also has resulted in a new, three-dimensional computer model that will help future water studies, according to state officials.
The two-year Freeport study, published in 2012, is the most exacting analysis of water withdrawal from this watershed done to date, and the study approach already is being applied to another site, said Dr. Robert Marvinney, Maine state geologist and project manager.
“This is the most rigorous analysis of the impact of water withdrawals in this watershed, and it now provides watershed managers with a robust tool to consider future water-use scenarios under varying climatic conditions,” Marvinney said. “This effort married the respective strengths of the Maine Geological Survey (MGS) and the U.S. Geological Survey (USGS) in a well-coordinated and useful study.”
The newly developed computer model is “a detailed model of the aquifer system that explicitly shows how the groundwater system and streams interact in the study area,” said Martha Nielsen, USGS hydrologist and study author. “The purpose was to understand how climate and aquifer management affect overall water availability and changes in stream flow.”
The extensive study was directed by the Water Resources Planning Committee, a statewide advisory group composed of water professionals, such as water district officials, state and federal officials, commercial water users, environmental groups and geologists. Marvinney, the committee’s chairman, said the group meets several times a year to discuss water issues in Maine and to recommend where state agencies should focus resources and research.
A watershed is defined as a geographic area in which all precipitation flows to a common point such as a river or lake. In 2006, MGS did a study of smaller watersheds in Maine that had the potential for “too much water use for what was available,” Marvinney said. Out of 973 watersheds examined – each about 35 square miles in size – about a dozen sites, including Freeport, were shown to have relatively high water use compared to supply.
That earlier study “was used as a guidance tool for where we should focus additional work,” the state geologist said.
The Freeport watershed was chosen collectively for the detailed study, begun in 2009, because it is a relatively small watershed, at 19 square miles, with a use of 100 million gallons a year; it has a major water user, the Freeport Water District utility; and there is a well-defined aquifer, or underground water source, Marvinney said.
For Freeport, “the overall goal was to look at how ground water and surface water [flowing streams, ponds and rivers] are tied together and how withdrawals from ground water would affect surface-water flows,” the state geologist explained. Environmental water need for aquatic habitats also was taken into consideration along with human use, he said.
In building the computer model, the purpose was to look at different climate and demographic risks and pumping scenarios, he continued. “What happens if there’s a drought? What happens if the population grows? So managers can begin to use the model as a planning tool,” Marvinney said.
As part of the project, Dan Locke, MGS hydrogeologist and study author, made numerous stream-flow measurements during 2009 and 2010 at five sites along Harvey and Merrill brooks in the Freeport-Pownal area. The measurements were made under different flow conditions and through the changing seasons. He also compiled information on groundwater levels and oversaw the drilling of two new observational wells. In addition, the Freeport aquifer also was studied in detail to understand its dimensions and thickness of sand, gravel, mud and clay layers, Marvinney noted.
Compiling data into the computer model resulted in “the most detailed analysis we’ve done on a small watershed in Maine,” Nielsen said. As a result, “what we have now is a tool that can help water resources managers look at future impacts on water resources, as in drought conditions and population increases. It gives us a framework that we can use for other watersheds.”
For Freeport, the computer model indicates there is an adequate water supply to meet direct demand, both human and environmental, the state geologist said. “With current usage, there is not an issue of annual supply,” he said.
The same modeling approach now is being used in an investigation of the Branch Brook watershed in York County where data collection is under way, Marvinney said.
The state geologist pointed out that the USGS is initiating a water census for the entire nation, and the analytical approach, designed for small watersheds, “undoubtedly” could be used in the Northeast and the type of geology found there.
“Our work can be part of this national effort,” Marvinney said.
To view the Freeport report, go to: http://pubs.usgs.gov/sir/2011/5227
For a summary of the study, go to: http://www.maine.gov/doc/nrimc/mgs/explore/water/sites/may10.htm
For more information about the Maine Geological Survey, go to: http://www.maine.gov/doc/nrimc/mgs/explore/water/sites/may10.htm
May 11, 2012