With drought and changing precipitation patterns on the minds of farmers and ranchers, an ongoing study of the Willamette River Basin’s dams and reservoirs is taking on a new urgency.
One of the key issues to be answered in the Willamette Basin Review is how much water agriculture really needs — or wants.
“That is indeed the question,” said Jim Johnson, land use and water planning coordinator for the Oregon Department of Agriculture.
The study is a joint project of the Oregon Water Resources Department and U.S. Army Corps of Engineers, and it could ultimately result in Congress being asked to re-allocate water stored behind 13 dams in the Willamette River drainage system.
The Corps of Engineers owns and operates the dams and reservoirs. The projects were built for flood control, irrigation, power production, navigation, wildlife and other purposes, but it’s water for agricultural use that is getting close attention.
Another federal agency, the Bureau of Reclamation, holds the water rights certificates for the entire conservation storage available in the Willamette system.
The certificates authorize 1.64 million acre-feet of stored water for irrigation annually, but less than 5 percent of it is used. That’s because the infrastructure necessary to get the water to the users — canals and pipelines — don’t exist.
Meanwhile, growing cities and industrial users can’t get at the remainder. The Willamette Basin, running roughly 120 miles south from Portland to Cottage Grove, holds about 75 percent of the state’s population and is growing rapidly.
But agriculture is big in the Willamette Valley as well, growing about 170 crops and accounting for more than 40 percent of the state’s gross farm sales, according to a 2013 Water Resources Department draft report.
Johnson and others point out that a significant amount of farmland in the valley isn’t irrigated and potentially could be used to grow higher-value crops if farmers could turn on the sprinklers. That capability should be taken into consideration when deciding future water allocations, Johnson said in an email.
“We have a great deal of acreage in the Valley that has greater potential if water could be made available,” he said.
Climate change is a big part of the discussion. In the Pacific Northwest in recent years, winter precipitation has arrived as rain rather than snow. This year, meager mountain snowpacks have already melted, according to federal hydrologists.
The WRD draft report says that may be the new normal. Scientific models indicate the Willamette Basin is headed for warmer, wetter winters and hotter, drier summers. The average temperature is projected to increase by 2 to 7 degrees Celsius over the next century, and the Cascades snowpack will decrease by 60 percent, according to the report.
Melting snow traditionally provides up to 80 percent of the Willamette River’s flow in late summer, but that flow is expected to decrease by 20 to 50 percent as the mountain snowpacks diminish, according to the report.
“The area’s reliance on high-elevation water during summer months highlights the vulnerability of the Willamette Basin to the influences of a warming climate,” the report concludes. “Water stored in the Willamette Basin Corps Reservoirs is viewed as the last remaining supply of water for meeting future needs, both in-stream and out-of-stream needs.”
The changing patterns already play havoc with reservoir operators. This year, despite near normal precipitation in some areas, water levels in the Willamette Basin reservoirs are 51 percent of normal because the peak snow melt runoff occurred before operators began refilling reservoirs.
Corps of Engineers spokesman Scott Clemans said he’s heard some people question why the Corps doesn’t begin refill operations in December or January instead of waiting until February.
The reason is that the dams were built primarily for flood control, Clemans said, and the risk from flooding must be accounted for throughout the winter months.
Clemans said there are likely to be “wilder and wider swings” in refill operations as climate change takes hold.
The Corps and state Water Resources Department are expected to finish a report to Congress in three years.