Irrigation in the Pacific Northwest

Washington Irrigation

Washington's designation as "The Evergreen State" really only applies to half of the state. The Cascade Mountain Range effectively drains most of the moisture from the atmosphere onto the west side of the mountains leaving the east side with plenty of sunshine, but very little rainfall.

In Washington, irrigation is necessary for the profitable production of most crops east of the Cascade Mountains. Supplemental irrigation is also important in some parts of Western Washington during the hot summer months of June, July, and August. The primary water sources for Eastern Washington are the Columbia, Yakima, and Snake River watersheds. All three of these rivers converge in the Tri-Cities area and flow out to the ocean in the Columbia River. Irrigation is responsible for the large majority of consumptive use of water from these rivers. Water shortages are causing significant concern for the spawning and lifecycles of certain salmon species in these rivers and their tributaries.

Efficient and effective irrigation water management cannot only improve the profitability of agricultural producers, but can result in a decreased need of water and therefore greater in-stream flows for aquatic habitat. Better designed irrigation systems, and more informed and vigilant irrigators can help to accomplish both of these positive outcomes.

Washington Irrigation Facts

  • 1.8 million irrigated acres
  • 80% sprinkler irrigated
  • 15% surface (gravity) irrigated
  • 5% drip irrigated.
  • 75% from surface water sources
  • 25% from groundwater sources
  • 80% of Washington water withdrawals is for agriculture
  • Only 4% of the renewable water supply in the Columbia River Basin is consumptively used.  This is compared to 103% for the entire Colorado River Basin, 35% for California and Nevada, 30% for Montana-Wyoming-Nebraska area, and 9% for the entire Mississippi River Basin. (USGS 1995)
  • In Prosser an average of 6 to 8 inches of rain falls per year and apple orchards need about 42 inches of water per year.



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