Downstream fish passage improvements at Hiram M. Chittenden Lock and Dam, Seattle, WA: a new Approach for an old dam

The Salish Sea is ringed with human development and infrastructure of multiple generations, some of which strongly influenced patterns of early development and continue to this day to maintain significant elements of the human environment. These developments are not going away, we will not “preserve” our way out of the environmental challenges they pose. Thus, it remains the role of the scientists, engineers, and owners to collaboratively guide their modification and maintenance to make their operation and presence more benign to the fish and the environment. One such development is the US Army Corps of Engineers owned and operated Hiram M Chittenden Dam and Locks in Seattle, Washington. This facility just celebrated its 100th year this past summer, in part with improvements to downstream fish passage and monitoring facilities and equipment. Aging downstream fish passage infrastructure, consisting of wedge wire flow dissipation screens and pipe flumes that dropped downstream migrants 20 to 30 feet to the water on low tides, were replaced by a large rectangular fiberglass smolt flume with updated passive integrated transponder (PIT) tag antennas. The profile of the flume mirrored the profile of the dam ogee and is segmented for removal for storage during the winter months. Safety of smolt passage through the flume was evaluated using Normandeau’s HI-Z Turb\u27N Tag, a proprietary balloon tag technology and found to safely pass smolts with no harm or visible physical damage. Tagged coho smolts were held for 48 hours for observation of delayed effects. All fish were found healthy and vigorous at the end of the holding period. Two more flumes are presently under construction to be ready for installation in the spring of 2018, completing the change to the new downstream fish passage approach