Sandy-Salmon Floodplain Reconnection
The confluence of the Sandy and Salmon Rivers represents one of the largest and most productive restoration opportunities in the Sandy basin. An initial opportunity analysis and conceptual design process in 2011 identified the confluence floodplain as the highest potential restoration opportunity in a 13-mile reach between the former Marmot dam site and the Zigzag River.
The floodplain extends nearly a mile, encompassing approximately 418 acres, and is owned primarily by the Bureau of Land Management and Clackamas County. Like much of the Sandy, the floodplain is isolated behind levees built after the record 1964 flood. Because of this, several historic side channels and backwater ponds are disconnected from the Sandy, except in extreme high flows.
2/25/2019 project site tour, walking on the levee that separates the Sandy River (left) from historic side channel (right).
Plans for this project include partial removal of the levee and in stream installations of large wood structures that mimic natural log jams. Project actions will reconnect the river with its floodplain and historic side-channels, which helps to slow the rivers energy across the floodplain, increasing resiliency of surrounding community infrastructure, and providing migratory and rearing habitat for native salmon and steelhead.
Project construction begins in summer 2019. SRWC looks forward to working with the Bureau of Land Management, Clackamas County, Clackamas Soil and Water Conservation District, Portland Water Bureau, National Fish and Wildlife Foundation, and local residents to reconnect the Sandy-Salmon floodplain and extend the Sandy’s corridor of healthy wild fish habitat.
The 2011 study indicated that the Sandy is working its way through the upper levee, as evidenced by sand deposits on the high surface behind the levee. Portions of the levee on its upstream end have continued to deteriorate. This potentially risks a passive breach through naturally erosive intrusions into the 1964 levee. The structure is not a registered flood control structure nor maintained by the Army Corps of Engineers.