Franks Tract Restoration Feasibility Study
The 2016 Delta Smelt Resiliency Strategy (PDF) identified a number of actions to be implemented to improve conditions in the Delta for the declining state listed endangered and federally listed species. As a result of the extended drought between 2013 and 2015 Delta Smelt abundance had declined to historic lows. The Strategy identified thirteen management actions including development of the Franks Tract Restoration Feasibility Study. The Department of Fish and Wildlife is the lead for preparing the study.
The objective of the Study was to assess the feasibility of restoring components of the historic tidal marsh form and function to create habitat suitable for Delta Smelt. Key restoration objectives include reducing the extent of aquatic weeds, decrease predation on Delta Smelt and other native fishes by lowering habitat suitability for non-native species, and improve food webs.
Franks Tract & Little Franks Tract facing westward - CDFW Photo
Franks Tract and Little Franks Tract are flooded islands in the Central Delta located in northeastern Contra Costa County adjacent to the community of Bethel Island. The 3,532 acre area, flooded by levee breaches in 1937 and 1982, is currently shallow open water habitat and remnant levees managed as part of the Franks Tract State Recreation Area.
Franks Tract is one of the most popular and heavily used areas of the Delta. Neighboring Bethel Island hosts numerous bass fishing tournaments, including some of national importance.These tournaments and associated recreational boating directly affects the sustainability of the local communities.
Franks Tract Futures?, the final study report, summarizes the restoration concepts developed to date, early stakeholder feedback, and results of initial hydrodynamic modeling and engineering studies including preliminary cost estimates. Findings conclude that it is feasible to restore portions of Franks Tract to improve habitat conditions for Delta Smelt and other native and pelagic fish species. Restoration has the potential to enhance water quality in the central and south Delta, reduce the extent of aquatic weeds, and limit the entrainment of fish from the west Delta into the south Delta.
Invasive species control has been identified as a high priority component of a Central Delta Corridor vision, and as an important near-term action within this corridor. Improving habitat for endangered Delta smelt populations is another primary focus of the vision, as has been outlined in the Delta Smelt Resiliency Strategy.
Existing Delta salinity intrusion video
The restoration design eliminates tidal pumping from False River, an important mechanism of salinity intrusion into the mid-Delta. Two video animations, one of the existing Delta salinity intrusion (YouTube)
in the summer, where saline water from San Francisco Bay is entering and exiting the central Delta with the tides, and a simulation with a restored Franks Tract (YouTube)
also in summer. The video animations provide conceptual illustrations of how tidal pumping of saline water works with and without a restored Franks Tract. On flood tide, a jet of higher salinity (red) water is seen entering Franks Tract from False River through an aperture sometimes referred to as a nozzle. Water quality in this jet is heavily influenced by that of the San Joaquin River at Jersey Point which is saltier than most of the Delta and Franks Tract. The return flow from Franks Tract is fresher— the salty jet of water will have mixed out somewhat and the ebb flow is drawn radially from a broader area so it includes more of the ambient water in Franks Tract.
Restored Franks Tract video
Even if the volume of flow is the same in both directions, the asymmetry between a salty flood and fresher ebb adds up and causes a net transport of salt into the Delta — like a bus that travels both north and south, but carries many more passengers in the southern direction. The CDFW Franks Tract restoration approach reduces False River flows and isolates the tidal pumping region from the Old River fresh water corridor. Regions upstream of the restoration site are shielded from ocean saltwater intrusion and the central Delta becomes fresher.
Stakeholders have many concerns about restoration adversely affecting economically important navigation access, fishing, recreational boating and hunting. The report makes recommendations for next steps in planning following the Delta Conservation Framework. While local boaters, hunters, and fishers value the open waters of the Tract, the ecological and water quality problems of the area are starting to impinge on the greater Delta and California water uses. Franks Tract/Little Franks Tract restoration is part of a larger vision that the Central Delta Corridor Partnership is exploring further in a regional planning process in 2018.
The restoration feasibility study was conducted in 2017-18 to inform a feasible and locally accepted restoration design. The following versions of the report are available for download here:
For fast viewing
For high-resolution on-screen viewing and printing
Reports of the following study components are available below
- Appendix A: Hydrodynamic Modeling in Support of Franks Tract Restoration Feasibility Study, Delta Resiliency Strategy (PDF)
- Appendix B: Franks Tract Engineering Feasibility Assessment (PDF)
- Appendix C: Franks Tract & Little Franks Tract User Survey (PDF)
- Appendix D: Franks Tract ROM Cost Estimate - Locally Proposed Conceptual Design (PDF)