Enhancement of Traditional Fish Passage Design on the Trans Alaska Pipeline System. Alyeska Pipeline Service Company

Enhancement of Traditional Fish Passage Design on the Trans Alaska Pipeline System

Jeff Streit, Anne Beesley, and Ken Wilson, Alyeska Pipeline Service Company; and Lee McKinley, ADF&G

There are hundreds of fish streams that cross the Trans Alaska Pipeline System; most go through a drainage structure called a Low Water Crossing (LWC) which is a vehicle/equipment ford that allows vehicle access and fish passage. LWCs require on-going maintenance due to vehicle use and can become widened and flattened during normal usage. They also can develop a grade break that can lead to an impedance or blockage to fish passage which can cutoff miles of important fish habitat. Traditionally, fish passage is maintained by narrowing the channel – requiring frequent maintenance and creating higher water velocity. A novel approach has shown to achieve duel goals of extending the life of the LWC between maintenance efforts while enhancing fish passage. The civil maintenance team at Alyeska’s Glennallen Base has developed a simple but effective way of backwatering the driveline with placement of large rocks at the downstream end of the crossing. With this method, small and medium sized streams are deepened without increasing the velocity, allowing for greater opportunities for fish to pass through; for larger streams, water velocity is slowed in the crossing, making it easier for juvenile fish to navigate. With placement of additional large rocks in strategic locations downstream, water velocity and turbulence is reduced or eliminated, and additional fish resting pools/eddies are created. The technique of incorporating “S” turns downstream of the LWC extends the channel through the grade break, slowing the velocity while also creating a deep water chute for fish to swim through. Jeff Streit, Anne Beesley, and Ken Wilson, Alyeska Pipeline Service Company; and Lee McKinley, ADF&G [e-mail]