Whidbey Island Dam-burst Mudflow
May 1, 2009
This is one of the more odd landslides to occur this year in Washington State. On April 3rd, at about 2:30am, in the small community of Glendale on south Whidbey Island, residences were evacuated by the fire department. A beaver dam had clogged the Glendale Road culvert, created a pond about 20 acres in size and the torrential rainstorm was continuing to add water behind the dam. Road crews tried to pump out the creek to relieve stress on the road. By 7am, the road gave way, washing out a 100-150ft section of the road and sending a torrent of mud, woody debris, and water 6-10 feet high into the community below. Up to twelve homes were damaged by the dam burst mudflow.
The community of Glendale is located at the mouth of Glendale Creek. The area is probably prone to periodic flooding from the creek.
There is a nice deep-seated landslide just south of the community which is clear in the LiDAR image. The dam-burst traveled about 4,700 feet downstream with an elevation drop of about 210 feet, or a slope at about 4%. That is a fairly low slope to move at, so this event must have had a good deal of force behind it. Most of the debris that came into the town appears to be fine grained or large woody debris. Woody debris, though bulky, is fairly light in weight. Any coarser material was probably deposited upstream.
Who ever would suspect something so cute and cuddly.
A bit of beaver dam information from Wikipedia:
“Beaver dams are created as a protection against predators, such as coyotes, wolves and bears, and to provide easy access to food during winter. Beavers always work at night and are prolific builders, carrying mud and stones with their fore-paws and timber between their teeth. Because of this, destroying a beaver dam without removing the beavers is difficult, especially if the dam is downstream of an active lodge. Beavers can rebuild such primary dams overnight, though they may not defend secondary dams as vigorously. (Beavers may create a series of dams along a river.)”
Maybe someone should see if the beavers rebuilt after this disaster.