High Water In Area Ponds A 'Window' On Groundwater

By: Tim Wood

Although it's retreated somewhat, the water level at Schoolhouse Pond is still high and leaves dry sand for beachgoers. TIM WOOD PHOTO

 

CHATHAM – Thanks to a wet winter and spring, groundwater levels earlier this summer were at record levels. Although water levels have dropped some during the course of the summer, groundwater remains as high or higher than seen in many years.

While groundwater levels are measured by monitoring wells scattered throughout the Cape, anyone can see how high the aquifer is just by visiting a freshwater pond.

“Ponds are what I refer to as a window on our aquifer,” said Tom Cambareri, technical services director of the Cape Cod Commission's water resources department. The Cape relies on a sole-source aquifer, meaning all drinking water comes from a single groundwater source.

Schoolhouse Pond proved a perfect example. Earlier this summer, water levels were so high that the beach had nearly disappeared. Water covered several inches of a bench that used to sit several yards from the water's edge, and it was almost possible to jump into the pond from the lifeguard chair.

“That's about as high as I've seen the water in all the years I've been here,” said Park and Recreation Director Dan Tobin.

The high level of the pond prompted one summer resident to question whether something unusual had triggered the situation.

“I have a feeling this isn't normal,” Nelson Saks said at last week's summer town meeting. He said he's been going to Schoolhouse Pond for 20 years and has never seen water levels like this.

“They're not abnormal,” responded Director of Natural Resources Robert Duncanson. “It's part of a natural cycle.” Just a few years ago, he added, drought conditions resulted in a much wider beach at the pond. He said he measures the pond's water level by gauging how much of the sand bar that separates Schoolhouse from the smaller adjacent Ryder's Pond is exposed. A few years ago there was 300 to 400 feet of dry sand between the two ponds; today they're basically one water body, with the former sand bridge covered by two to three feet of water.

Cambareri, who serves on the state water resources commission, said recent hydrological reports confirmed that no parts of the state are now in drought. “Everything is normal, but we're way, way above normal,” he said.

In the spring the water table as measured in more than 40 observation wells around the Cape was two to three feet higher than readings in January, putting many of them at record levels. The readings are reported to the U.S. Geological Survey, which keeps water table records going back more than 60 years; some wells were at the highest levels ever seen, he said.

Testing in July showed the majority of wells within the 75 to 90th percentile higher than is usual for this time of year, Cambareri said.

An observation well in South Chatham showed the groundwater level at 22.8 feet below the surface on July 11, according to the USGS National Water Information System website. In October 2016, the water level was nearly three feet lower, at 25.6 feet – deeper water levels mean lower groundwater – among the lowest of the data on the site, which goes back to 1962. There were several years – 2005, 1998, 1987, for instance – where water levels were in the 21-foot range, slightly higher than current levels. The lowest levels during that five-decade period are in the 25-foot range and also appear periodically.

Usually water levels decline in the summer due to transportation, he explained. But last summer was cool and wet, and water levels in the fall, when they are historically at their lowest, did not recede as much as usual. Winter is when the water table typically recharges, but it was already higher than normal when the Cape was hit by a series of nor'easters; in February alone, the region received double the usual precipitation, some 7.3 inches, according to a Cape Cod Commission press release. That water builds up the aquifer, since there is little transportation or evaporation in the winter and spring.

High groundwater has other ramifications besides increasing water levels in ponds, Cambareri said. It can impact septic systems and increase the chance of flooding, especially in shorefront areas that get inundated during coastal storms. Chatham's Little Beach is an example of that; during the winter's coastal storms, flooding from Chatham Harbor created huge pools of water just inland that was slow to percolate into the ground.

While water supply concerns recede with the high groundwater levels, it's still important for people to be aware of water use and pay attention to voluntary restrictions such as those imposed in Chatham this summer, Cambareri said. During the recent drought, Chatham well pumping exceeded the town's state water withdrawal permit – the limit on how much drinking water the town's wells can extract – and wells were pumping longer than advisable to keep up with demand.

“We have to remain ever vigilant about the water supply situation on the Cape, Cambareri said, emphasizing education and awareness, especially during boom economic periods like the present when demand increases steadily.

Meanwhile, the high water level in Schoolhouse and other area ponds is “just Mother Nature doing what Mother Nature does,” said Tobin. At Schoolhouse, the lifeguard chair can't be moved since it's just a few feet away from the parking lot. An attempt to dump sand at the edge of the parking lot to fill in a dropoff backfired when it eliminated some parking spaces and caused a bit of a backlash.

“It's just a limited location, where there's just so much space,” said Tobin, who is a fly fisherman and said the high pond levels have made the shoreline of many Cape ponds inaccessible. “There's nothing we can do about the water level.”