Yakima River Mile 89.5 Side Channel Reconnection

This project has been developed as part of the Yakima Basin Integrated Plan (YBIP) collaborative. It will restore 6 miles of off-channel anadromous fish rearing and wintering habitat, and enhance hydrology to over 500 acres of riparian and wetland habitat, in the Yakima River floodplain. Restoration will be enacted by re-connecting the side channel network to fall, winter, and summer flow (out of irrigation season). This will provide extensive new rearing and migration habitat for juvenile chinook and steelhead in a reach that has lost much of its off-channel habitat quantity and complexity.



Project will deepen 2 inlet channels at the head of a 6 mile long side channel and wetland complex by excavation of former channel scars. A third inlet channel will be constructed by deepening a high flow channel and building a deflector engineered log jam at the entrance to direct and maintain flow into the inlet. In addition, selective excavation in the 6 miles of side channels will remove earth plugs that have built up over time due to insufficient flooding caused by flow regulation. Several beaver dams will be breached to ensure sufficient flow in the first years after construction. Inlet elevations will be set to connect to flow at 1,000 cubic feet per second. This flow will reconnect the side channel for the fall, winter, and spring months. During the summer, when upstream irrigation diversions reduce streamflow, the side channel will not be connected in order to leave all flow in the main channel. In addition, a 250 section of an irrigation drain berm that has eroded will be built back to original grade to protect nearby lands from back-watering during large floods. 120 acres of wetland habitat will be restored through this effort.



PCSRF funding will pay for construction oversight and project management, for construction of the third inlet channel and deflector wood structure, to excavate sediment plugs in the side channel, and to rebuild the irrigation drain berm in order to prevent backwater flooding caused by the project. Washington State Department of Ecology will pay for permitting, final design and engineering, bid support, a portion of project management costs, mobilization, a portion of inlet construction costs, and groundwater monitoring. Washington Office of Conservation and Recreation will pay for mobilization, erosion and environmental controls, site dewatering, excavation and hauling of sediment plugs removed from the side channel, riparian revegetation, a portion of inlet construction, and as-built plans.



A long-term monitoring plan has also been established. Hydrologic connectivity will be monitored using drone photography/videos at flows above design connection thresholds to verify that the project is functioning hydrologically as designed. Wetland water levels and innundation will be monitored in the same way. Fish use will be monitoring once or twice per season by snorkelling and electrofishing to collect presence/absence data. The fish data will be compared to similar data collected in prior years in the project area.

Project will increase side channel habitat by 6 miles and 40 acres of water surface, and off-channel habitat by more than 120 acres of wetlands. This habitat will provide rearing, wintering, and migratory habitat for juvenile chinook salmon, middle Columbia summer steelhead, and Pacific lamprey. The project reach is almost entirely lacking in well-connected slow-water side channel and off-channel habitat, so the increase in habitat is from a very low base-level. The reach is known to be important rearing and wintering habitat for chinook juveniles, and steelhead and lamprey juveniles are also documented in the reach.