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Watersheds

Yamhill Watershed

Who can swim in the summer, hunt crayfish, fish, row a boat, or even skate in winter on a polluted, smelly stream? Who in this generation knows what the Willamette ever looked like when it was a free running turbulent river, glistening in color, and abounding in game? This is now true also of the Yamhill River and its tributaries. If the people in the county were aware of the expected increase in the population that has been published by the different surveys they could rearrange their thinking. But authority is needed to be able to state some hard-to-accept facts.
     -- Yamhill County Economic Development Committee, 1963

The landscape of the Yamhill River Watershed is rich in diversity. Agricultural fields dominate the lower south and eastern portion, but share the landscape with floodplains, riparian areas and wetlands. The western portion of the watershed is dominated by steep forestland.

Geologically, after a millennia as part of the sea floor, the land was lifted through subduction, sedimentation and volcanism. The Missoula floods caused by the bursting of an ice dam in Montana about 12,000 years ago spilled south down the Willamette River channel and filled the valley with deep deposits of rich sedimentary soil. Elevation ranges from 60 feet at the Willamette River to 3,423 feet at Trask Mountain. The watershed is bordered by the Coast Range, Eola hills, and Red Hills of Dundee.

The watershed covers almost 781 square miles and has a population of 65,000 people (2002 census). There are 440,724 acres of private land and 52,927 acres of federal land in the watershed.

Major tributaries include the North Yamhill River, Willamina Creek, South Yamhill River, Deer Creek, Salt Creek, and Mill Creek.

The watershed experiences two very different rainfall regimes due to variations in elevation. The western section, in the Coast Range Mountains, receives 80 to 100 inches of precipitation annually. Reports on Trask Mountain show it receiving over 135 inches annually. The low elevations on the eastern side of the watershed receive 40 to 60 inches annually.

The Che-ahm-ill, the indigenous people of the "Yam Hills" area and a sub-group of the Kalapuyan culture, occupied the Yamhill River Basin at the time of Euro-American contact.

Fire suppression has created a watershed with a greater acreage of Douglas-fir and much less oak savanna and prairie than before settlement. Also, present day rural residential developments may face catastrophic fires. The lack of fire breaks surrounding private residential properties, limited water availability during periods of low precipitation, and the absence of fire over the last 100 or more years contribute to a fire hazard in the forested area of the watershed.

During the years following the settlement of the watershed, agriculture meant cattle grazing and subsistence farming. During the first 20 years, "the valleys were settled rapidly, the range cattle were pushed back into the hills, and the growing of wheat on the level lands became the dominant industry". A census by the United States in 1880 reported wheat, oats, and hay accounted for 99 percent of the agricultural production in the area. During the 1930s, the federal government started to encourage the planting of cover crops during the winter to hold soil. Grass seed crops became important between 1935 and 1939, and the acreage for lawn grass seed continued to increase to its present day levels. Today, the rich soil supports a variety of commodities ranging from grass seed, grain, row crops, grapes, berries and nurseries.

Splash damming and the associated impacts occurred throughout the mainstem of the North Yamhill up to RM 30 and on Haskins Creek and Fairchild Creek. Log drives and splash damming operations of the 1883-1910 exposed channels to extreme "flood" events on an annual basis. These events would be equivalent to a "dam break flood" or "debris torrent" where streambed material and wood would be mixed in a fluid mass scouring the channel and stream banks. The magnitude of the equivalent peak flow associated with these events is estimated to have a 50 to 100 year return period. The Fairchild Creek splash dam impounded 5 million cubic feet of water. In some years this occurred twice a year as logs were distributed along the channel during the summer and transported to the mill during the winter high flow. During the drives of 1906, logs were "splashed" daily during the winter period.

The priority natural resource issues for this watershed are soil erosion affecting surface water quality, surface and ground water quality, wildlife habitat and increasing urbanization. The challenge is for producers to achieve profitable, sustainable agricultural production while maintaining and improving watershed health amid the growing pressure of urbanization.

Sources

Yamhill Basin Council

Confederated Tribes of the Grande Ronde

NRCS Yamhill site

Compiled by John Ame, Science Writer (2007)