Wenatchee River-Monitor Side Channel Construction

The Monitor Side Channel project site is a 27.5-acre site located on the left bank of the Wenatchee River at RM 5.3. The site is characterized by a large island within the floodplain of the Wenatchee River and a 2,200-foot-long side channel that prior to 2013 was used to supply water to an irrigation canal (Gunn Ditch/Canal) via the Pioneer Diversion located approximately 600 feet downstream from the side channel inlet. The majority of the mid-channel island is approximately 4 feet higher in elevation than the OHWM of the Wenatchee River and is infrequently flooded with initial flow across preferential flow paths occurring at approximately a 10-year event. Bedrock outcrop abuts the channel on river-left and naturally constricts the channel migration zone and potential meandering of the existing side channel. Across the island to river right, the existing channel is confined by the Burlington Northern Railroad and riprap bank protection on private parcels.
Prior to project implementation, the side channel was 60 - 90 feet in width with a shallow plane bed consisting of slightly armored river cobble. Riparian vegetation along the channel margins was sparse with some willow establishment but little channel shading. Prior to project implementation, there was very little hydraulic or habitat diversity, and no large wood or pools. The channel maintained inlet flows from the Wenatchee River nearly year-round until very low flows during late summer. During late summer hyporheic flows within the side channel maintain a wetted connection with the outlet at the Wenatchee River. Prior to the removal of the Pioneer Diversion in 2013, the side channel inlet was dredged annually to remove gravels to maintain flows into the side channel and towards the diversion structure. The inlet has subsequently maintained the pre-dam removal geometry and continues to provide perennial flow into the side channel. Shallow water depths, and lack of riparian habitat contributed to the existing high summer temperatures on the lower Wenatchee River. With the removal of the Pioneer Diversion in 2013, the side channel provided an excellent opportunity on the lower Wenatchee River to reduce the width-to-depth ratio, and provide cover and pool habitat. Once the outcomes of this project are fully realized, this side channel will maintain hyporheic flows in late summer and will become a cool-water input to the main channel.
The lower Wenatchee River is currently the fifth ranked assessment unit within the Wenatchee sub-basin in terms of prioritization for restoration potential (UCRTT 2017). The highest priority ecological concerns on the lower Wenatchee River in descending order are (UCRTT 2017):
- Peripheral and transitional habitat (side channel and wetland connections)
- Riparian condition
- Water quantity
- Water quality
- Channel structure and form
Specific restoration goals were developed based on addressing the priority ecological concerns from the Biological Strategy (UCRTT 2017) and guidance from the Upper Columbia Tributary Fund Committee. For each goal, objectives were identified and design elements were developed to achieve the desired outcome. Below, each project element that was implemented through this project is listed with the corresponding goal. Target species: Spring Chinook overwintering juvenile salmonids. Improvements to side channel habitats will also benefit juvenile summer Chinook, steelhead, and bull trout.
Goal 1: Increased structural and hydraulic complexity of side channel
- Objectives met to achieve goal: Installed nine large wood structures to increase number of pools, initiate thalweg formation, and increase woody cover engaged with channel.
- Objectives met to achieve goal: Installed six boulder clusters to increase local hydraulic diversity and provide refuge for juvenile salmonids.
- Objectives met to achieve goal: Minimized hydraulic effects to the existing inlet and outlet areas as the side cha

To improve instream habitat complexity by adding large wood and boulder structures, and planting riparian vegetation, thus benefitting all life stages of ESA-listed Chinook and steelhead.