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Conjuctive Use

Yolo County is blessed with an abundant supply of ground water, and through foresight, has secured the rights to significant surface water supplies. The use of both groundwater and surface water supplies is known as conjunctive use. Conjunctive use management involves making sure that each of these resources is used to the optimum benefit with the least amount of negative environmental and economic effects.

Surface water is made available in Yolo County through storage in Clear Lake and Indian Valley reservoir. Lakes and reservoirs have the advantage of being able to store large amounts of water in a short period of time, providing flood control. Supplies of surface water also have the possibility of renewable or green power generation.

The aquifers that supply the cities of Woodland, Davis and Winters and thousands of acres of farmland have the ability to store large amounts of water indefinitely, without concerns of evaporation or sediment dislocation. Groundwater has the advantage of being available throughout the region simply by drilling a well and its' use is completely unregulated.

Surface water and groundwater have been traditionally treated as two separate entities, but like all natural systems, they are connected. Ignoring the relationship between surface water and groundwater can have disastrous consequences. Virtually all of the surface water used in Yolo County is used for agriculture, but in dry years this supply is limited or not available. This results in farmers pumping more and more groundwater. Aquifers can store water for an indefinite period of time, but the amount of water stored is finite; it needs to be refilled by surface water supplies. Overdraft of groundwater can lead to wells drying up, significant reduction in water quality, and subsidence. More importantly, once an aquifer experiences compaction, it is impossible to reverse, and the storage capacity is lost forever.

Throughout the normal growing season, the earth-lined canals of YCFCWCD irrigation system supply an average of 25,000 acre feet of natural recharge to our aquifer. During the winter in rainy years, many acre feet of water travel through Yolo County via the sloughs, irrigation canal system and Cache Creek unused. This excess winter water can be used to recover lost groundwater storage in the aquifer by either pumping water back into the aquifer or providing additional area for the water to permeate down into the aquifer.

Active management of water resources requires solid information on which to base decisions. The District is collecting data through the Flow Monitoring Network, the Groundwater Monitoring Program and the Groundwater Surface Water Modeling Program. This information will facilitate policy development and management practices, helping to ensure the reliable water supply essential to the economic viability and quality of life in Yolo County. By conjunctively managing our surface water and groundwater supplies, we can protect and enhance the use of one of our most important resources.

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