Piles of rocks and low areas are exposed around the shoreline of Cards Pond in South Kingstown after the pond breached on Saturday. The pond breaches 8 to 10 times a year.

The Providence Journal / Steve Szydlowski

SOUTH KINGSTOWN — High water, tides and heavy rain over the weekend caused Cards Pond to break through its dunes and drain into Block Island Sound, taking some of Mud Pond and Trustom Pond with it.

“It’s a natural happenstance,” said Jon Boothroyd, a professor of geosciences at the University of Rhode Island and Rhode Island’s state geologist.

“There was so much rain that it spills over and runs out,” he said. “Once it starts, it will run out really fast.”

Rushing water removed about a 70-foot section of the Moonstone Beach dunes that hold back Cards Pond. So much water was drained that the pond seemed more like a series of sandbars and channels than a body of water.

Yesterday afternoon, a new stream about 10 feet wide connected the pond with the breaking surf. Three sets of cliffs testified to the changing force and volume of the flow.

“In a few days, it will seal itself up,” Boothroyd said. Sand brought by tides and waves will move along the shore from west to east, he said, so sand from the beach in front of Trustom Pond that may have come from Watch Hill will help close the breach, and sand that washed out of Moonstone Beach will go eventually to Galilee.

“Where it washes over … and seals itself up is good piping plover habitat, because they like bare sand that’s not on the active beach,” Boothroyd said.

Laura Ricketson-Dwyer, spokeswoman for the Coastal Resources Management Council, said Trustom Pond is breached once a year and Cards Pond 8 to 10 times a year. This exposes mudflats for piping plover foraging, she said.

If Cards Pond gets full and threatens to flood Moonstone Beach Road or overrun the wells and septic systems of houses around the pond, a breach will be started under the supervision of the U.S. Fish and Wildlife Service.

Between April 1 and Sept. 15, Moonstone is closed to allow the plovers to nest. If a breach must be cut during nesting season, a biologist will inspect first for nesting pairs, said Charlie Vandemoer, Trustom Pond Wildlife Refuge manager.

Another concern is the Fowler’s toad, a protected species that is known to inhabit Mud Pond and Trustom Pond.

The Fish and Wildlife Service has a Ducks Unlimited grant of several thousand dollars to upgrade the culvert between Mud Pond and Cards Pond so the water level in Mud Pond is not tied to that of Cards.

“It’s a fairly unique and rare species, so at the culvert we’re looking to keep the water level up, as it tries to grow and reproduce there,” Vandemoer said.

The new culvert will be of marine-grade aluminum into which boards can be fitted to keep the water from rushing out when Cards Pond is low.

When a salt pond breaches, Vandemoer said, “a lot of the small fish are washed out to sea, and if the stripers or bluefish are around, it’s a real banquet for them.”

The best time for fishermen is when a breach has to be opened in the late summer or early fall.

Boothroyd said the gush of water leaving the salt pond is called an expanding jet. “Right where the expanding jet dissipates” is where the nutrients enter the sea, attracting fish, birds, fishermen and bird watchers.

dnaylor@projo.com