WESTBROOK — A large landslide completely blocked the Presumpscot River in Westbrook on Wednesday afternoon, threatening nearby water and gas mains and triggering a flash-flood watch and an emergency order from the city.
The landslide was reported Wednesday morning after people saw trees moving on the river’s forested bank. The landslide, located directly behind Les Wilson & Sons at 161 Warren Ave., also took a large area of soil and pile of excavation fill.
The landslide was so large it initially blocked the river just downstream from the Sappi Mill, Westbrook Fire Chief Andrew Turcotte said Wednesday afternoon.
The National Weather Service issued a flash flood watch that was in effect until 11 p.m.
“River levels behind the slide are rapidly rising. Expect water levels upstream of the landslide to continue to rise. Downstream of the slide, sudden changes in river level are possible if the slide breaks,” the weather service said.
A landslide has occurred blocking the Presumpscot River downstream of Westbrook, ME. River levels are rising rapidly. A Flash Flood may occur downstream of the landslide if it gives out. A Flash Flood Watch has been issued and persons near the river should monitor.#MEwx #NHwx pic.twitter.com/NUZKe8F1Uj
— NWS Gray (@NWSGray) September 16, 2020
The river appeared to be at least partially flowing through the area by 2:30 p.m. although it was unclear how much the level had risen behind the landslide. It also wasn’t immediately clear if responders had moved some of the obstruction to restore flow.
Mayor Michael Foley declared a state of emergency in the city following the landslide. He said the city is working with the Maine Department of Environmental Protection, the U.S. Army Corps of Engineers, Sappi and other agencies to address the situation. An emergency operations center has been established, he said.
Foley asked people not to attempt to go to the area to view the damage.
Turcotte said crews were on the scene Wednesday afternoon assessing the potential flood impact. They also were assessing the possible impact to a nearby 60-inch water main and a 16-inch gas main.
“We’re still trying to assess everything,” Turcotte said early Wednesday afternoon. There were no reported injuries and there are no impacts to roads in the area, Turcotte said.
The cause of the landslide wasn’t immediately clear. The area is known to have a layer of soft clay deep underground that was linked to a historic landslide nearby.
Chris Wilson, owner of Les Wilson and Sons, an excavating contractor, said the slide began around 9 or 9:30 a.m. and consumed piles of aggregate he was keeping on his lot.
Wilson said his property extends back toward the river from Warren Avenue, but the property line stops before the river. Sappi and the Portland Water District own the land closest to the river, he said.
“After their land failed, my land and the neighbor’s land followed,” Wilson said. “A lot of money went over the edge,” he said, referring to the wasted material.
The sliding earth eventually consumed one pile of dirt and half of a second pile, and dragged a metal building and some equipment with it. Cracks in the earth were visible in Wilson’s equipment yard near the edge of the slide.
Mike Maples, who rents a garage nearby and went to the site of the slide Wednesday afternoon, said that decades ago the area that is occupied by Les Wilson and Sons used to be a large ravine that led to the river. But over the years, Maples said, Wilson dumped fill into the ravine, reclaiming more space.
“That used to be a big ditch and they filled it in,” Maples said.
Another witness, Jeremy Tardif, who was working on a job site finishing a concrete foundation that overlooks the area, said a bucket loader on the Wilson property was dumping buckets of earth on top of a large pile before the slide.
“The next thing you know, you see everything moving and it kept going,” Tardif said. “The bank kept moving and moving.”
Wilson dismissed the idea that his company’s piles of fill and aggregate and daily operations with heavy equipment might have contributed to the unstable soil conditions.
Wilson said the piles of road-building material and clean fill have been there on and off for years, growing and shrinking with the various construction projects that require it.
Wilson also pointed out that his property is about 200 feet from the river’s edge, and that nothing has changed recently in how they do business. The gully that existed near his property was filled in at least a decade earlier, he said.
“Nothing’s changed with our operations or footprint or anything,” Wilson said.
Wilson also pointed out that Wednesday’s slide is across the river from the site of the state’s largest landslide, which occurred in 1868, when about 20 acres of land shifted, eventually covering about 38 acres with displaced soil, according to materials published by the Maine Geological Survey.
A geologic investigation of the area in 1990 found that a layer of soft clay lies beneath the area and extends deep underground. The softness of the clay means that the material behaves like a viscous fluid that can “flow” rather than break into discrete pieces.
This layer is referred to as the Presumpscot Formation, and a later 2008 geological survey found that the formation surrounds the river outside of its immediate banks.
This story will be updated.