On May 14, 2022, Ahtna Construction & Primary Products Company’s (AC&PPC) Baseline Crew responded to flooding on Moose Creek near the Trans Alaska Pipeline in Glennallen. Moose Creek is typically a tame creek, but this year’s heavy snowmelt caused the water levels to rage, eroding a high bank next to the pipeline at Pipeline Milepost 686.5. Crews immediately began hauling riprap to stop the erosion that was less than 50 feet from the mainline pipe. The creek running over its banks also blocked roads and flooded the nearby Glennallen Library parking lot, Legislative Information Office, and old DOT buildings.
The next day, Moose Creek avulsed (abandoned its original channel) and a new channel formed upstream, creating a shortcut to the confluence with the Tazlina River. This avulsion from the main channel diverted the water from the eroding high bank close to the pipeline. However, the avulsion shifted the erosion location downstream and still needed to be mitigated. The downstream erosion site had lower bank heights and additional buffer to the pipeline, making it easier to mitigate.
Days following the initial event, the crews continued monitoring the water levels. A plan was put in place for the erosion repairs to protect the pipeline. Over 800 cubic yards of Class 3 and Class 5 riprap were hauled in, and work was done to install a buried rock sill and rock apron to the creek bank. Repairs of the original erosion to the high cut bank are scheduled to be performed later in the fall.
Additionally, while all of this was taking place, an oil spill contingency response plan had to be developed in the event the erosion caused a slope failure leading the pipeline to buckle or crack, thus releasing oil.
The AC&PPC crew at the Glennallen Response Base works every day to maintain the pipeline right of way, support projects and maintain readiness in the event of an oil spill response.