Today’s Delta region faces numerous threats that are projected to worsen. Absent intervention, California’s water supply system and the Delta ecosystem are at risk of collapse and are projected to worsen due to a variety of natural and man-made stressors.
There are several faults running through the San Francisco Bay Area region that could affect the Delta. According to the U.S. Geological Survey, there is a 66 percent chance of a magnitude 6.5 earthquake hitting the Bay-Delta region by 2032. Such an earthquake could cause the levees that surround the Delta islands to collapse, flooding up to 30 Delta islands. Salt water from San Francisco Bay could migrate eastward, rendering the Delta as an undrinkable source of water supply for up to three years until extensive repairs are completed. The statewide economic costs of such an event could exceed $40 billion.
The official state guidelines call for planning efforts in the Delta to assume a 16-inch rise in sea level by 2050 and 55 inches by 2100. Rising sea levels will not only put greater pressure on the Delta’s dirt levees, but will cause seawater to intrude further inland impacting water quality.
When levee construction beginning in the 1850s transformed the Delta from marshland to farmland, it exposed the peat soils, which began to oxidize, compact and blow away. This process of subsidence continues. What were once islands are now more like bowls, constantly depending on levees. The total volume of soil lost, or the void currently below sea level, is in excess of 3.5 million acre-feet or almost 8,000 Rose Bowl stadiums. As the subsidence continues, the water pressure on the levees becomes greater.
While numerous scientific panels have attributed the decline in the Delta’s health to numerous causes, enforcement efforts to date have focused almost exclusively on curtailing public water supplies from Delta facilities. Export agencies experienced cutbacks to pumping dating back to 1991 due to Endangered Species Act requirements. During the last two decades export pumping to the State Water Project and Central Valley Project has been reduced by more than 2 million acre feet.
More than 95 percent of the biomass in the Delta is non-native. Striped bass, Black bass, Asian clams and many other invaders, large and small, are either eating the native populations or the foods on which they rely.
In this highly-altered environment, the introduced species are over-running the native species and are a key factor in reducing populations of some endangered species.
Public water agencies like Metropolitan are promoting a more comprehensive approach to restoring the Delta as a way to restoring reliable water supplies long-term.