US Army Corps of Engineers
Walla Walla District Website

Divers perform inspection of Ice Harbor’s Removable Spillway Weir

Walla Walla District Corps of Engineers
Published Feb. 9, 2021

For the Corps of Engineers, the onset of colder weather signals the beginning of dive season.

While perhaps not an official season, most dive work is scheduled between November and March, when salmon runs are at their lowest. On November 17, a team of divers suited up at Ice Harbor Dam to perform the required 3-year inspection of the Removable Spillway Weir.

A Removable Spillway Weir, or RSW, is essentially a chute that fish use to travel through the spillway of a dam. An RSW raises the entrance to the spillway to make it easy for fish to find. As indicated by the name, an RSW can be removed in case increased spill is needed, i.e. during a flood event.

For the inspection, Associated Underwater Services (AUS), a commercial dive company and contractor for the U.S. Army Corps of Engineers, brought their dive team to check the mechanics of the weir.

Before they could dive, the dive team verified the completion of the lockout tagout procedure, to ensure the area was safe.

Differential pressure, or suction, can pose a danger to divers. Before a dive, nearby intake gates are closed to stop water from flowing through the nearby turbines. Otherwise, the flow of water could pull a diver in, leading to serious injuries. Corps personnel place locks and/or tags on equipment and switches to make it clear why certain turbines or controls are turned off and to prevent equipment from accidentally being turned back on while divers are in the water.

After the lockout tagout procedure, AUS loaded their team and equipment onto a boat and drew up along the upriver side of the dam, right near the RSW. Divers took turns suiting up to perform the inspection, diving down as far as 85 feet. While one team member was underwater, others monitored the dive using the camera built into the diver’s helmet. There was also always one member to manage the diver’s cable, making sure to provide enough slack for easy movement, but not so much as to risk entanglement.

A diver’s cable, called an “umbilical,” is very important as it provides air, power for a light and a direct communication link between the diver and the surface. In an emergency, an umbilical can also be used to pull a diver out of the water. However, dive teams must be very careful not to allow the umbilical to get snagged or tangled on anything.

The dive investigation will be used to decide on potential repairs that will need to be made to the RSW to make sure it is in good working condition before juvenile salmon start travelling downriver in the spring.