Don’t Blame the Rain

Here in the Northwest, we often complain that the skies are grey and the rain never stops. In the CUB office it’s no different; we would rather be out biking or playing catch on all those rainy afternoons, too.  In an exceptionally rainy year, while we gripe about the rain’s impact on our plans, we also consider the rain’s impact on the region’s rivers and streams.

The Columbia River has the second largest drainage in the United States; only the Missouri-Mississippi River system is larger. At the John Day Dam, the annual average runoff is 165 billion cubic meters, the equivalent of the amount of water in two Olympic-size swimming pools passing through one point on the river every second of every day! Although swimming pools are a good illustration of flow, in reality the amount of water pouring down the river is not constant. Normally, 60% of the natural runoff occurs during May, June, and July. This runoff in the spring and early summer is due to the melting of snowpack in the Cascades and Rockies, in addition to the regular rainfall at that time of year.

Another unique aspect of the Columbia River is its exceptionally wide range of flows, with the highest flows 35 times larger than the lowest. Compare that with the mighty Mississippi, whose high flows are only 5 times larger than its lowest, and you can see that the Columbia River has an significant level of variation in water flow between days, months, and years. Since 2000, the Columbia River’s flows have been lower than average, and 2010 was another low-water year in a low-water decade.

In the Northwest we are fortunate to receive a lot of rain. However, this rain does not flow to the ocean unobstructed. The Northwest has developed a string of dams and reservoirs that capture this flow and use it to create electricity. The federal government uses these dams to produce low cost power, and, as a result, residential electricity customers in Oregon pay some of the lowest electricity rates in the nation. Dams, in addition to providing electricity, also manage flood control, allow for irrigation, and provide recreational lakes. In order to manage sporadic flows, reservoirs collect water in the spring and then gradually release it over the rest of the year. The combined storage in the reservoirs behind dams on the Columbia River system is 67.8 billion cubic meters. Surprisingly, this storage capacity represents only about 30 percent of an average year’s runoff at The Dalles. By comparison, dams on the Missouri River hold two to three times its annual runoff.

Despite its comparatively small storage capacity, the power production and flood control system have a significant impact on the river’s fish populations. Accordingly, dams across the Northwest are managed to protect the region’s iconic salmon in addition to providing power, irrigation, and flood control. In low water years, dams are required to keep their flow at a minimum level that allows fish to continue their run. Last year, in Klamath Falls, this created a problem for farmers who received less than half of the water they expected to use for irrigation. In the face of a drought during a low-flow year, dam operators prioritized the survival of the river’s salmon population over unlimited crop production, and farmers were left with reduced irrigation.

Farther north, the Columbia River also experienced low flow in 2010, but the first two weeks of June 2010 brought a storm system with torrential rains that produced a much higher flow than the system was expecting. The system struggled to handle much more water than it planned for. The system’s reservoirs, which had not been completely drained in expectation of a low flow year, filled up to their maximum levels quickly. The storm also brought strong winds, which resulted in high wind power production at the same time the reservoirs needed to be emptied. This high wind production prevented the dams from producing their maximum power output, and instead the dams’ operators spilled water without creating power to ensure that the reservoirs did not overflow. This spill produced high levels of total dissolved gases in the river, which almost reached Washington State’s legal limit for protecting the river’s salmon. While some salmon advocates question the biological basis of Washington State’s total dissolved gases limit, it is undisputed that both low-water and high-flow conditions can threaten salmon runs if the region’s dams are not managed carefully.

Currently, we are heading into the Spring and Summer with great hydro conditions. Our major hydro storage is at 118% to 120% of normal. This should mean good hydro run-off through July and into August, and the cost of meeting summer peak load should be relatively low. So, the next time you are ready to complain about how the rains are mucking up your weekend plans and how seasonal affective disorder has you down, take some time to be thankful for the rain’s work keeping your electricity bills low and the salmon runs strong.

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