Yakima River Basin (USA)

Basin Overview

Located in south central Washington State, the Yakima River has eight major rivers and numerous smaller tributaries. The basin extends from the wetter, higher elevation portion of the basin to a significantly drier, lower elevation.  Most of the precipitation in the basin falls during the winter months as snow in the mountains. The mean annual precipitation over the entire basin is 70cm.

The Yakima is widely known for its agricultural productivity.  There is nearly 2,600 km2 of agricultural land in the Yakima Basin, including irrigated pastures, apple, pear, and cherry orchards, grapes, hops, and field crops.  Over the last 20 years, vineyards and viticulture have grown rapidly in this basin, generating nearly $2 billion dollars in agricultural goods each year.

 

Facts and Figures

Country:  United States
State: Washington
Major Population Centers (people in 2017): Yakima (93,667), Richland (56,243), Ellensburg (20,326), Sunnyside (16,407)

River Length: 344 km
Watershed Area: 15,900 km2
Köppen Climate Classification: dry-summer subtropical

Source: Keechelus Lake
Mean annual precipitation: 305 cm/yr

Mouth: Columbia River
Mean annual precipitation: 15 cm/yr
Mean annual discharge at mouth: 1,680 m3/s

People and Land Use

Major landowners in the valley include federal and state agencies and the Yakama Indian Nation. Private ownership accounts for 5,045.69 km2. The United States Forest Service manages 3,611.86 km2, and the indigenous Yakama Nation owns 3,600.84 km2 within the basin. Forested areas (5,700 km2) are used for recreation, wildlife habitat, timber harvest, grazing, and tribal cultural activities. Range lands comprise about 7,500 km2 and are used for military training, grazing, wildlife habitat, and tribal cultural activities.

Major Issues

The Yakima River and its tributaries have been heavily modified to support irrigated agriculture. Modifications include three dams and hundreds of kilometers of irrigation canals and runoff drains. Intensive irrigation in the basin can lead to periods of both severe river dewatering and elevated flows, compared to the historical streamflow regime. As a result, discharge statistics for the Yakima River are heavily affected by the irrigation system (https://nativefishsociety.org/watersheds/yakima).

More frequent and more intense droughts can negatively impact junior water rights holders in these agricultural areas.  When streamflow is low, junior water rights are curtailed and some farmers lose crops because water for irrigation is not available.