Monday, September 14, 2009

California Water Wars

Friday night the California State Legislature ended its session for the year without taking any action in regards to the state’s water supply issues. There were a set of bills that reportedly would have both diverted water from the Sacramento San Pablo Delta and restored the habitat while potentially adding damns that would somehow add additional water along with the storage. The bills would also require a reduction of 20% in per capita urban water use and created a monitoring system for groundwater statewide. The legislation reportedly lost support of the Sierra Club, the Republicans and some other environmental groups. The fundamentals of the water supply system for California need to be addressed carefully and in a coordinated manner. The legislature has essentially chosen to continue the status quo which is unsustainable. The entire economy of California and possibly the United States will be impacted by the way in which California chooses to allocate water. Slapping another band-aid on the California water supply system is not how to address the complicated ecological, economic and human issues; nor is doing nothing. Cutbacks in surface irrigation water will results in increased pumping in the Central Valley which is nothing more than a geologic trough filled with sediments containing groundwater.

For more than a half a century the Central Valley of California has been one of the most productive agriculture regions of the world. This has been made possible by the ample supply of water used for irrigation. On less than 1% of the total farmland in the U.S. the Central Valley produces 8% of the agricultural output (as measured by value). In 2002 this translated to $17 billion in crop value. This is all made possible by a combination of surface water diversions and groundwater pumping. Approximately one sixth of the irrigated land in the United States is in the Central Valley (Bureau of Reclamation, 1994) and approximately one eighth of all groundwater pumped in the United States is pumped in the Central Valley.

According to the US Geological Survey the before the extensive development of irrigation of the Central Valley the natural recharge of groundwater from precipitation and surface water inflows equaled the outflows to evapotranspiration and surface water. After development of irrigation in the Central Valley the balance changed. Recharge to the groundwater was from irrigation return flow, precipitation and surface water inflow. Outflow was from groundwater withdrawals and increased surface water outflows. The net result was that the Central Valley, a 20,000 square mile area of California was mining groundwater at approximately 1,900 cubic feet per second from 1962 to 2003.

When you withdraw the groundwater from fine-grained compressible confining beds of sediments and do not replace it, the land subsides. The incredibly fertile Central Valley was identified by the research efforts of Joseph Poland as the location of maximum subsidence in the United States. Though the tremendous amount of subsidence was famously documented in 1977, it was not until 2003 that the water balance changed to slow the subsidence. In 2007 the USGS estimated the rate of groundwater mining to be 300 cubic feet per second. This change is due to the surface water agricultural deliveries of 13,000 cubic feet per second while groundwater irrigation deliveries are now (or at least were) at 5,900 cubic feet per second. When I was consulting, I saw vineyards and orchards in the Central Valley with groundwater irrigation wells. These vineyards were mortgaged. If the surface water allocation is reduced, how much groundwater are they going to pump? It is their livelihood, it is their investment, it is their way of life. Even if the surface water allocation to irrigation is not reduced the Central Valley is still mining groundwater that is not being recharged. The problems in the Delta estuary maybe more visible, but the long term viability of groundwater is our future.

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