Editor”s note: Dac Collins wrote To Spill or Not to Spill on the dispute over the increased amount of water being spilled over the eight federal dams on the Lower Snake and Columbia Rivers. In this issue Fisheries Scientist Emeritus, Alec Maule, gives background on scientific studies on the spill. He expands on efforts to help juvenile anadromous salmon and steelhead reach the ocean–via a river system modified for hydropower, irrigation and freight transportation.
By Alec Maule, June 14, 2018. Before the dams, the Snake and Columbia Rivers were cold, fast moving, and generally narrow waterbodies. Salmon smolts swam hundreds of miles on a down-river current and reached the Pacific Ocean in a few days. The completion of Bonneville Dam in 1937 began an era of harnessing the Columbia Basin rivers. The basin extends from the Pacific Ocean to Wyoming’s Teton Mountains and from the Oregon-Washington border far into Canada. It encompasses an area about the size of France. Today there are several hundred dams on the basin’s rivers and streams.
Ice Harbor Dam on the Snake River. Rivers back up behind dams creating broad lakes rather than narrow rivers.
Dams changed the rivers into a series of slow moving lakes. Now the smolts’ journey can take up to several weeks, leaving them vulnerable to predation by birds and other fish. Slow moving water gives more time for the sun to heat the water raising water temperatures too high for these cold water fish. Getting through the dams exposes them to the turbines in the hydropower dams.
The challenge for fisheries scientists is how to increase the survival of salmon smolts in today’s environment. The scientists have studied a variety of scenarios: spill (increasing the amount of water the dams release over spillways to benefit fish), breaching some dams, or transporting fish around dams. They used biological models to ask: What would happen to the fish in each case?
Spill and Transport
For most dams most of the time, the amount of water passed over a dam is equal to the amount flowing in. These are known as run-of-the-river dams as opposed to storage dams. Grand Coulee and the Canadian dams on the upper Columbia are storage dams, but all the others throughout the Snake and Columbia are run-of-the-river. So, the question is: Will the water be passed through the turbines or over the spillways? When there is more water flowing in than can be used to generate power, dam operators have to spill the excess (involuntary spill). When there is less water than can drive all the turbines but water is spilled over the spillways, this is called ‘voluntary spill.’
Spillway at The Dalles Dam
Hydropower dams in the Columbia Basin pose a number of problems for juvenile anadromous salmon and steelhead emigrating from their natal streams to the ocean. The first concern is the mortality caused by passing through the dams’ turbines. In 1960s the National Marine Fisheries Service working with the US Army Corps of Engineers estimated that 10% to 15% of juvenile salmon would be killed at each dam. But fish have to pass through eight Snake and Columbia river dams, which meant a minimum 55% fish mortality.
Beginning in the 1970s, dams were fitted with fish passage systems to divert fish around the turbines and/or collect them in barges and transport them below Bonneville Dam. Primarily, transporting juvenile salmon started at two dams: the Lower Granite Dam, the first dam encountered by salmon from the upper Snake River; and at McNary Dam, the first dam below the confluence of the Snake and Columbia Rivers. Transporting reduced the mortality of migrating juvenile salmon to about 2%. Despite this improvement, adult salmon returns remained very low.
Led primarily by the states and Tribes, a movement began in the late 1990s to have the dams voluntarily spill water over the spillways to provide a way to pass fish without going through turbines or fish-collection systems. But that also came with problems. Spilling water can lead to gas supersaturation (also known as Total Dissolved Gas, TDG), which can cause gas bubble disease in fish. Historically the EPA and the states mandated that voluntary spills could not create TDG greater than 110% saturation–a level that has little effect on fish.
After a great deal of research (a significant amount of this research was conducted at USGS Columbia River Research Laboratory at Cook, WA.) the EPA, states and court judged that voluntary spills could continue until maximums of 115% TDG were reached in the forebays of dams and 120% in the tailraces.
About the same time voluntary spill was started, a group started research called the Comparative Survival Study (CSS). The study’s goal was to determine if juvenile salmon and steelhead survived to adulthood better via transport or spill or if there was any difference. The group included a broad group of stakeholders: the States of Oregon, Washington, Idaho, the U.S. Fish and Wildlife Service, and Columbia River Inter-Tribal Fish Commission.
The CSS found that increased spill for juvenile passage correlated with increased survival to adult. They also found that in many, but not all years, juvenile fish that passed all dams via spill survived to adulthood better than fish that were transported.
In the most recent CSS report, researchers reported on a biological model they developed to estimate the possible effects of increasing the maximum allowed spill to allow total dissolved gas to increase from 120% to 125%. The model showed that increasing spill to 125% TDG would likely have a positive impact on the Columbia and Snake Rivers’ salmon recovery.
Dam Breaching
This scenario is increasingly supported by environmental groups like Earthjustice and Sierra Club. It is the indirect impacts of dams that may be more threatening to juvenile salmon than the direct mortality caused by passage. These impacts caused by the slow moving water include higher water temperatures and exposure to predators. The Bonneville Power Administration spends up to $4 million per year on a bounty program to remove the native, but predatory northern pike minnow around dams. In late summer water temperatures above McNary Dam can exceed the lethal level for juvenile fall Chinook salmon emigrating at that time.
Save Our Wild Salmon banner at US Army Corps of Engineers planning session
Removing the Snake River dams would have costs associated with reduced energy generation, reduced or ended barge traffic and increased costs to irrigators. Depending on whose analysis one reads (see links below), these costs may be very high or insignificant relative to the benefits of increased salmon.
This March the NW Energy Coalition released their study aimed “to investigate the technical feasibility of replacing the Lower Snake River (LSR) Dams with an energy portfolio that meets the power needs of the region while minimizing costs and increases in greenhouse gas (GHG) emissions.” The study’s findings: 1) “A portfolio of clean energy resources, including solar, wind, energy efficiency, demand response, and energy storage, can effectively replace the most critical power attributes the four Lower Snake River Dams contribute to the Northwest region; 2) Dam replacement using clean resources is achievable from both a technical planning regional reliability/adequacy standpoint, and from a resources availability standpoint.”
A key objective of many of these studies is to get smolts safely down the Columbia and Snake, which will increase the likelihood that those small fish return as mature adults.
Bob Lessard, quantitative fisheries scientist with the Columbia River Inter-Tribal Fish Commission, was quoted on this issue in the May 7, NW Fishletter. As you spill more, he told them, “…the abundance (of returning adults) goes up by a factor of around two.” Breaching the lower four Snake River dams “everything is pushing twofold or greater. And if you combine breaching the lower four and spilling to 125 percent on the lower Columbia River dams, we’re seeing in some cases a fourfold increase in abundance, and in others, a two-and-a-half [times increase] at least.”
About the author: Alec G. Maule, Ph.D. is Scientist Emeritus, US Geological Survey, Western Fisheries Research Center. His research has been directed at explaining how deleterious and restorative alterations in habitat regulate the viability of native fish populations. Surprisingly he is not a fisherman.
For More Information:
2007 report (Revenue Stream) on dam removal by several NGOs:
BPA?s response to the Revenue Stream report:
Analysis of the Revenue Stream report by the Independent Economic Analysis Board for the NW Power & Conservation Council. This report pretty much discounts the Revenue Stream as not presenting enough information to judge its validity:
A 2018 report from NW Energy Coalition
Thanks so much. Answered many questions I had. The 40’s and 50’s and 60’s was a time of harnessing and untethered use of our raw materials. Now we are
trying to figure out what we have done and how we can back pedal damage done while trying to continue use of natural resources in a
more efficient, alternative, and careful way. Glad to see the scientific approach to resolving issues.
Adult chinook returns were around 250,000 in 1938 when Bonneville first started counting fish. Over the course of the 80 years, as the dams were completed, returning fish levels rose to as high as over a million in ‘12, ‘13, ‘14-this despite the fact that hundreds of millions of smolts were being dumped into the river. Fish returns actually rose during the years of dam building/completion. Although dams are certainly barriers, they aren’t the cause of the depletion of the salmon runs. What’s going on in the oceans, aka climate change as well as the destruction of spawning grounds have had far greater impact along with the misguided attempts to fill the river with hundreds of millions of hatchery fish which have a detrimental effect to native stocks as well as create a salmon Ethiopia on the river-not enough food for all the little fish, plus the attraction of non native species particularly birds, to feast on the little fish. He only hope to prevent salmon extinction, is the restoration of spawning grounds. An example of where this having success is the efforts being made in Yakima River Basin spearheaded by the Yakama Nation. By restoring spawning grounds and improving watersheds salmon might be saved as well as improving watershed quality which benefits humans as well as fish.