The Sustainability of the Columbia Basin’s Irrigation System

June 2, 2014
By Andrew McGuire

Although now teenagers, while in Ephrata’s elementary school my three daughters learned about hydropower generation, electricity and the dams owned and operated by the Grant County Public Utility District. This is good. I believe that people should know where the basics of life come from, so I would tell them at the dinner table that I was glad they were getting a good dam education. Eyes rolled. But earlier this year, when a crack appeared in Wanapum dam necessitating a 26′ drop in water level behind the dam, my girls knew what was at stake; the future of a unique and productive irrigation system.

Wanapum Dam at normal operation (photo: Dept of Ecology)

Wanapum Dam at normal operation (photo: Dept of Ecology)

My own dam education was less direct. I moved from Nebraska to Ephrata in 1999, ready to take on my new job with WSU as an Agricultural Systems Educator, “responsible for the promotion of sustainable irrigated agricultural systems.” As I contemplated how to do this, I also wondered about the sustainability of the Columbia Basin irrigation system itself; was I trying to improve an agriculture which itself was not going to last?

Feeling the need to feel good about my work, or face the truth that I could not feel good about it, I looked for information. A new book, Pillar of Sand; Can the Irrigation Miracle Last? by Sandra Postel of the Worldwatch Institute, had just come out, so I read it.

In her book, Postel points out the various reasons that irrigation systems have failed throughout history: salinity buildup, siltation from soil erosion, water scarcity due to droughts and other causes, and failure to protect and maintain irrigation infrastructure. Could one of these, I asked myself, be the downfall of our irrigated agriculture?

Salinity is a problem in many irrigated regions. When water containing mineral salts evaporates, it leaves the salts in the soil. Over time, salt levels increase to the point that they reduce crop yields. The problem is aggravated by irrigating with high-salt water and by poor drainage which allows more water to evaporate leaving more salt.

Although relatively young, the Columbia Basin’s irrigation system does not have significant salinity problems; the combination of low-salt Columbia River water (rated Class A, Excellent by WA State) and well drained fields may prevent future problems. In those fields that did not have good drainage (~18% of the irrigated project acres), project developers had the foresight to install artificial drainage to prevent any buildup of salts. So, salinity is not a critical issue, as long as drainage systems are maintained.

Siltation of reservoirs, canals and ditches can destroy the ability of irrigation systems to deliver water to fields. Postel tells stories of deforestation of watersheds providing irrigation water leading to increased erosion and buildup of sediments. Again, the Columbia Basin is in good shape; the water from the Columbia River, pumped out behind Grant Coulee Dam, has relatively low amounts of sediment. The watershed behind Grand Coulee Dam is mainly Canadian forest and high mountain glaciers where erosion is not a large problem. Any sediment making it to the river is deposited at the top of 150 mile long Lake Roosevelt, far from the pumps at Grand Coulee Dam.

Right now in the Central U.S., water scarcity due to over pumping and a prolonged drought is threatening the viability of the irrigation system over the Ogallala aquifer. However, water scarcity for irrigation in the Columbia Basin is unlikely, if climate change forecasts hold up. The Columbia Basin Irrigation Project pumps out about 3% of the Columbia River’s flow at Grant Coulee Dam so only a drastic reduction in the Columbia’s flow would cause water scarcity to become a problem. A joint study by WSU-CSANR, WA Departments of Ecology, and of Fish and Wildlife, estimate that although the timing of peak water flow will shift earlier in the year due to climate change, the flow could actually increase slightly. Although there are many factors to consider here, in contrast to the bleak forecasts for many irrigation projects around the world, the future for the water supply in the Columbia Basin is encouraging.

For these reasons, the Columbia Basin irrigation project receives scant attention in Postel’s book, but the recent crack in Wanapum dam, and last year’s fire in the pumping station at Grand Coulee Dam reminds us of the key requirement for the future of Columbia Basin irrigation: maintenance of the irrigation infrastructure, both hydraulic and power.

Water uniformity test being conducted on a center pivot sprinkler system in the Columbia Basin.

Water uniformity test being conducted on a center pivot sprinkler system in the Columbia Basin.

Irrigation in the Columbia Basin requires a well maintained water conveyance system: pumps, reservoirs, canals, siphons, and ditches. It also requires power, both at the beginning and at the end. At the beginning, turbines in Grand Coulee Dam power pumps that lift irrigation water to Banks Lake, the high point of the system. At the end, water delivered to fields is spread on fields using center-pivot and drip irrigation systems. While these systems are much more efficient than the surface systems that they replaced, they require power, power generated at Grand Coulee and other dams, like Wanapum, along the Columbia. This infrastructure must be maintained.

It turns out that, after 50 years of producing power for Grant County PUD, the crack at Wanapum dam was due to a math error during its design. First, thank engineers for factors of safety. Second, the $61 million in repair costs, ultimately covered by PUD ratepayers like me, is key to sustaining the productivity of the Columbia Basin’s unique irrigation system. It is an investment in a remarkable irrigation system that will help sustain it for another 50 years of food production, production that will become even more important as our global population increases and other irrigation systems fail.

Postel, S. 1999. Pillar of Sand: Can the Irrigation Miracle Last? New York: W. W. Norton & Company.

World Commission of Dams, 2000 report on Grand Coulee Dam.

WA Department of Ecology, 2011 report on Columbia River Basin Long Term Water Supply and Demand Forecast

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