Restoration of Reach 2B for Fisheries: Habitat and Passage: Opportunities, Challenges and Reality

Reach 2B is a low gradient, meandering  11.3 mile reach of the San Joaquin River located on the west side of the southern San Joaquin Valley in California and is geographically situated between Mendota Dam and the Chowchilla Bifurcation Structure.  This reach of the river has not received flow on a regular basis since Friant Dam began substantial water diversions in mid 1940s.  Under existing conditions the channel can accommodate about 1,700 cfs while the Settlement Agreement calls for a design capacity up to 4,500 cfs.  Prior to the interim flows, the upper four miles of Reach 2B were typically dry and supports only marginal riparian vegetation. The remainder of the reach is backwatered by Mendota Dam.  Flow management for the reach not only needs to consider upstream and downstream Chinook salmon passage under the restoration flows but also has to consider irrigation water delivery, flood management in some years and seepage that affects adjacent agricultural lands.  Water for agriculture is also delivered to the Mendota Pool into Reach 2B via the Delta-Mendota Canal. Reach 2B is one of the few locations where floodplain expansion is a goal.  The potential value of floodplain habitat is being evaluated using modeled inundation area, depth and velocity estimates compared to published information about functional floodplains.  To accommodate the variety of operational issues, Reach 2B will have flow control structures installed or modified.  The structures will be outfitted with screening devices and fish passage to provide for successful up and downstream movement for salmon and other target native species. The design of these structures is being guided by an extensive literature review of fish swimming performance and passage criteria.