Reach 4B of the San Joaquin River is a 32.5-mile stretch that begins at the Sand Slough Control Structure and extends to the confluence of the Eastside Bypass and San Joaquin. Reach 4B has been further divided into two subreaches; Reach 4B1 from the Sand Slough Control Structure to the Mariposa Bypass, and Reach 4B2 from the Mariposa Bypass to the confluence of the Eastside Bypass and the San Joaquin River.
Reach 4B and Eastside Bypass project consists of incorporating new floodplain and related riparian habitat to ensure conveyance of at least 4,500 cfs through Reach 4B, modifications to ensure fish passage, and modifications in the Eastside and Mariposa bypass channels to support anadromous fish migration.
The Draft Technical Summary Report was prepared by the San Joaquin River Restoration Program Team to document technical studies completed as part of the Reach 4B, Eastside Bypass, and Mariposa Bypass Channel and Structural Improvements. Studies in this area started in 2009; this Technical Summary Report documents key technical findings and summarizes the work that led to these findings. The report describes the differences between the routes for high flows through this area and compares these routes. Finally, it identifies potential near-term actions (in addition to the Eastside Bypass Improvements Project) that could provide benefits regardless of the high flow alternative selected. Appendices for this draft technical report include Timing of Flow Analysis (A); Hydraulic and Sediment Studies ( B, Parts 1, 2, 3, 4, 5); Vegetation and Wildlife (C); Soils (D); Wetland Offset (E); Groundwater Analysis (F); Fisheries (G); and, Cultural Resources (H).
In September 2019, the lower weir on the Merced National Wildlife Refuge has been removed as part of the San Joaquin River Restoration Program’s Eastside Bypass Improvements Project. The weirs, which were constructed to create seasonal pools for migratory birds on the Refuge, were a partial barrier to adult Chinook salmon and many other native fish. The upper weir will be removed in 2020 and, together, the removals will improve fish passage in the Eastside Bypass. The San Joaquin River Restoration Program has coordinated with the Refuge to provide an alternate water supply to Refuge wetlands.
Below, a time-lapse video shows removal of the lower weir.