Erosion causes landslide at Public Works in Petersburg

PETERSBURG - Water from this month's heavy rainfall ripped at deformities in a culvert that runs underneath the Public Works yard, opening up a portion of the pipe and causing a landslide near Hammer Slough.

The culvert diverts water from a creek that runs parallel to Kiseno St. to Hammer Slough. When 6.63 inches of rain fell over the town on Nov. 30 and Dec. 1, water in the creek became backed up as the culvert struggled under the volume of water, said Public Works Director Chris Cotta. The gushing water grabbed at defects in the culvert. One of those defects opened up and water started gushing up into the earth.

"It was such a massive amount of water that came down that one night," said Cotta. "That covert filled up, so if there's an edge hanging down, it's going to grab that edge."

Erosion in the earth eventually led to a landslide. Crews set to work moving the dirt and cutting away about 40 feet of damaged culvert that had been exposed. Cotta said the damage extends further into the culvert, though on the opposite end of the culvert where the creek feeds into it is in good condition.

The whole culvert needs to be excavated and replaced, said Cotta. Although his staff can excavate the pipe themselves, Cotta said the borough will likely contract someone to excavate the culvert due to the sheer volume of dirt that has to be moved.

Mixed in with the dirt from the landslide were pieces of metallic debris and car parts. Cotta said when the abatement was made about 40 to 50 years ago, city staff must have used garbage to help fill up space. Public Works staff have been regularly patrolling the slough for any garbage that may have originated from the landslide. No oil had been found in the debris from the landslide.

Cotta said he doesn't anticipate another landslide occurring before the culvert can be replaced later this spring. The culvert had always managed storms common to Southeast Alaska without any problems.

"As long as we don't get another rain event like we had, I think we'll be fine until the spring," said Cotta.