Channel Complexity is being defined in the Tucannon by the number and length of side channels present within the floodplain, over a wide range of flows ranging from summer low flow (~100 cfs) to spring high flow (~1,400 cfs). Side channels provide a number of benefits over a wide range of stream flows and provide benefits to both adult salmon and steelhead while supporting properly functioning conditions. Quality side channels (that are narrow and deep) provide a greater range of habitats for fish to utilize, increasing the feeding area available to fish, increasing growth and survival over a greater range of weather conditions. Properly functioning side channels spread out high flows reducing river bed scour and increase the development of gravel bars, increasing ground water recharge, leading to greater flow of cool ground water into stream during the summer. The lower right image and the left image are aerial photos of the same location within a stream reach where log jams were placed to increase channel complexity (visible in the post-project image). Both photos were taken at roughly the same stream flow. The lower right image illustrates the straight, simplified single channel that existed in 2010 prior to restoration actions in 2016, and the upper right photo is the 2017 post project. The blue arrows in both images highlight the number of flow paths and side channels available to fish, with each channel acting like a separate stream providing rearing and feeding habitat. The upper left image illustrates a digital elevation model created from a December 2017 LiDAR data set, with the winter low-flow water surface elevation highlighted blue. The black dashed polygon indicate the approximate position of both the pre- and post- project photos.
River channel complexity in the Tucannon is being measured by the numbers and length of side channels at varied flows ranging from winter flows (~130 cfs) up to a 5 yr (~2,600 cfs) flow event. The photos above show side channels examples in a number of different landscapes including private riparian lands adjacent to agricultural fields (upper three and lower left) and public forested land with connected floodplain (lower left two). These channels provide habitat for fish to escape high flood flows and provide access to diverse food resources that main channel fish do not have access to.