WEBINARS

A setback dike is built away from the riparian edge of a river, allowing the river room to flood. This creates naturalized channels in the floodplain that increases the storage capacity of the waterway to hold more water and improves side channel habitat for salmon and other fish, protecting them from being washed downstream with flood waters. Where appropriate, setback dikes can protect the built environment by setting roads and building back from the river’s floodplain. The land in front of the dikes can be used as wetland habitat and walking trails outside of high water events.

Self-regulating gates are a modified version of a top or side mounted gate. They have a counter-balance mechanism, such as a float and a more buoyant gate flap that results in the gate being open more often, and for longer periods of time. The only time the gate closes is when the water levels on the river gets high enough to push the float up, which closes the gate. This means the default position of the gate is open, making it the most friendly gate design for salmon. Designs vary widely, using remote sensors, floats, or cables sensitive to resistance to activate gate closure and opening. Examples include Nehalem Marine, Golden Harvest, and Juel Tide gates.

An impeller pump is essentially a fan blade that forces water through a pipe from the creek side out into the mainstem river. As one might imagine, this is not fish-friendly at all! Fish mortality with these types of pumps can be quite high, as fish get chopped up and killed, or injured severely, making them prone to predation and disease. There can also be drastic pressure changes inside the pump that can pop the swim bladders of fish. Not shown in this animation but typical to most stations, the pump is paired with a floodgate, but the gate closes when the water levels in the river or ocean get too high. Once the gate closes, there is only one way water and fish can get out from the stream and that is through the pumps. Though fish-unfriendly designs are much more common, there are fish-friendlier versions of impeller pumps that have larger spaces between the blades, rotate at slower speeds, and are housed in cages to prevent fish getting caught between the blades and the sides of the pump station.