Integrated Water Management Plan Evaluation: A review of the Salton Sea Authority’s preferred project concept for rehabilitating the Salton Sea

The USGS Salton Sea Science Office convened an experts workshop, from November 15-17 in Riverside, California, to evaluate a Salton Sea rehabilitation proposal known as the Integrated Water Management Plan (IWMP) (also known as the ‘North Lake Plan’). Salton Sea Restoration: Preferred Project Report (Salton Sea Authority 2004) describes the IWMP and provided the basis for this evaluation. As described further in the following, the IWMP would build a causeway across the middle of the current Salton Sea, creating a smaller north lake that discharges into a proposed 20,000 acres of shallow-water wetlands in the southern portion of the Sea, and a terminal brine pool, as well as various treatment wetlands.

A recently implemented water conservation and transfer agreement, along with several unrelated actions, will significantly decrease the volume of water flowing into southeastern California’s Salton Sea in the next 20 years, shrinking the Sea and increasing salinity beyond the tolerances of most of the species currently present. Future conditions at the Sea will be very different from current conditions, whether or not the IWMP is implemented.

The surface elevation of the Salton Sea fluctuates by more than 0.3 meter (one foot) annually, primarily in response to agricultural irrigation patterns in the Imperial Valley. On January 1, 2005, the surface elevation of the Salton Sea was ~69.8 meters (228.86 feet) below mean sea level. The Sea is a terminal lake; the only outlet for its waters is via evaporation. The Sea is an officially-designated sump for the water draining from fields in the adjacent Coachella and Imperial Valleys; the Sea also receives agricultural and municipal drainage from the Mexicali Valley, in Baja California. The Sea is currently 33% saltier than the ocean and getting saltier each year. The Sea is also eutrophic, with extremely high levels of biological productivity, fed by fertilizers draining off of the fields in the basin. This productivity has attracted more than 400 species of birds to the area, including large numbers of breeding birds and special status species.

The objective of the experts workshop evaluation process was to develop a credible description of the future physical and biological conditions created by implementation of the IWMP. The objective of the evaluation process was not to support or reject the proposal. This was a scientific review process. Economic and recreational impacts generated by implementation of the proposal, although important, were beyond the scope of this evaluation process and were not addressed. The evaluation did not concern itself with regulatory, policy, political or agency positions. Based on the scientific expertise of the participants, the evaluation sought to identify any critical flaws in the proposal, as well as major beneficial outcomes, major questions to be resolved, and considerations of importance in judging the effectiveness of the proposal. The views and opinions reflected in this report are those of the participants and do not necessarily represent the views or opinions of their agencies or affiliations, nor do they necessarily represent the views of the U.S. Bureau of Reclamation or U.S. Geological Survey.