WATER SUPPLY ISSUES OF THE SAN JOAQUIN VALLEY IN CALIFORNIA

The San Joaquin Valley of California is undoubtedly one of the most productive agricultural regions of the United States, and of the world. The valley was a Miocene epicontinental sea bounded by the Sierra Nevada igneous arc in the east and the Coast Range accretionary terrane in the west. It is now filled with thick layers of Neogene and Quaternary sediments derived from rocks with marine origin in the west and continental origin in the east. The valley encompasses 4 million hectares of rich farmland and has an annual production exceeding US$25 billion of fruits, nuts, vegetables, and livestock products, comprising approximately 20% of the U.S. agricultural production. However, the climate is semi-arid with average annual precipitations ranging from only 5 inches in the south to 13 inches in the north. Due to the warm dry climate and high evapotranspiration rates, irrigation is essential for all crops. On the east side of the valley, irrigation water is mostly derived from the Sierra snow melt. On the west side, water used for irrigation is imported from the more humid region in the northern part of the state through a network of canals and aqueducts built by both Federal and State government water projects. Ground water is also used for both east and west sides of the valley to supplement surface water sources. After years of intense irrigation, a number of water supply and water quality issues emerged. They include groundwater overdraft, land subsidence, water contamination by agricultural drainage laden with selenium, salinity buildup in soil and water, water contamination by nutrients from fertilizers and livestock production, competition for water supply with California’s megalopolis, and also with environmental use and restoration. All these problems are intensified by the effect of climate change that has already taken place and other geological hazards, such as earthquakes that can bring the water supply system to a complete halt. To find practical and achievable solutions for these complex problems, scientists must employ a holistic approach. Towards this end, we cannot just rely on scientific research and technology development alone; we must also take into consideration of the social and economic contexts, and work with governments, stakeholders, and the community.