Tulare Lake Basin
Until the early 1900s, central California’s Tulare Lake naturally appeared every winter as the southernmost rivers flowing out of the Sierra Nevada Mountains filled the dry lakebed with rainfall and melted snow.
In the spring, the shallow lake could be larger in area than Lake Tahoe. By the end of the hot San Joaquin Valley summer, however, it could disappear.
Farmers adjacent to the lake also used the water to irrigate their lands. But the variable shoreline made growing seasons unpredictable. In response, Pine Flat Dam was built by the U.S. Army Corps of Engineers to control flows from the Kings River and keep the lakebed dry and available for crops year round. The Kings River is still used extensively for irrigation.
This irrigation also created water disposal issues.
Tulare Lake Basin and Agricultural Drainage
Because the Tulare Lake Basin’s irrigation water does not have an outlet, agricultural drainage is stored in a series of evaporation ponds in and near the lakebed, which has been converted to farm fields. By the 1980s the water drained into 28 ponds totaling 7,300 acres. Crop production improved in part due to improved drainage.
Today, drainage water from about 44,046 acres of farmland is contained and evaporated from eight basins encompassing 4,740 acres of evaporation ponds.
Some migratory birds that historically wintered at Tulare Lake now use the evaporation ponds as feeding, nesting and breeding grounds. However, studies show the selenium content in the ponds is elevated to levels that may impact birds and the environment [see also Kesterson Reservoir]. Of the eight existing drainage ponds, embryo deformities have been confirmed at four of them, according to the U.S. Fish and Wildlife Service. (There are also programs to deter birds from the reservoir.)
Meanwhile, the California Department of Fish and Wildlife, USFWS and evaporation pond operators have used the Tulare Lake Basin as a testing ground for new methods to avoid and mitigate the impacts of agricultural drainage.
Tulare Lake Basin Next Steps
Long-term solutions for the Tulare area don’t come easily. Some operators believe the best solution is to build a drain to the Pacific Ocean. But state regulators say they are not seriously considering an ocean drain as a potential solution because the economic and environmental costs would be too high.
In the meantime, the Tulare Lake Drainage District, which represents more than 60 percent of drained lands in the area, is the subject of an ongoing environmental review by the Central Valley Regional Board. The Lost Hills Water District and Rainbow Ranch, which has some of the most contaminated pond waters, is also reviewed by the CVRB.
To help mitigate the effects of agricultural drainage, both the TLDD and Lost Hills operate evaporation basins and maintain alternative wetland habitat. So far, reports by the San Joaquin Valley Drainage Implementation Program and the University of California Salinity Drainage Program have concluded that more quantitative data is needed on the effectiveness of mitigation measures and the management and use of deposited salts in evaporation ponds.
Tulare Lake Basin and Land Subsidence
Recent reports by UC Irvine and the U.S. Geological Survey found that about 60 million acre-feet of groundwater has been lost in the San Joaquin Valley since 1961. According to USGS, while the northern and western parts of the valley have seen water level recovery, “overall, the Tulare Basin part of the valley still is showing dramatic declines in groundwater levels and accompanying increased depletion of groundwater storage.”