Mitigating the effects of high-head dams on the Columbia River, USA: experience from the trenches

Abstract

Worldwide, humans have tremendously altered freshwater ecosystems and arguably, construction of dams has had the greatest effect. Maintaining natural ecological processes and developing mitigation strategies that will maintain species while retaining dam benefits is challenging. In the Columbia River, USA, over the last 30 years more than US$7 billion has been spent on efforts to save historically large runs of salmon. These efforts have included improving passage conditions at dams through construction of efficient fish ladders for adult salmon, effective fish passage facilities for downstream migrating juvenile salmon, voluntarily spilling water to decrease the number of downstream migrants that pass through turbines, modifying dam operations to provide more constant flow and providing additional flow from storage reservoirs to create more natural flow through areas inundated by dams. Construction of hatcheries to offset losses in habitat for wild fish has also occurred. Further, for salmon from the Snake River, the largest tributary to the Columbia River, a large percent of juvenile salmon smolts are collected at upstream dams and transported in barges to the lower river to avoid passage through dams, turbines, and reservoirs. Experiences in the Columbia River suggest that the sum of all of these actions may keep salmon stocks from going extinct, but the technological fixes will not likely provide complete mitigation for altered freshwater ecosystems.

Tracking Fish Movements and Survival on the Northeast Pacific Shelf

“…The listing had major economic consequences for the fi shing industry and for the operators of the dams, who have spilled water to accommodate salmon migration, resulting in lost potential revenue ever since. Over the past several decades, improvements in fi sh passage at the dams and the implementation of a fi sh transportation program to bypass the impounded section of the river basin have improved the survival of seaward migrating juveniles (smolts) (Muir et al 2001 ), but adult return rates have not substantially improved (Williams 2008 ;Schaller et al 2007 ).…”

Match-mismatch dynamics and the relationship between ocean-entry timing and relative ocean recoveries of Central Valley fall run Chinook salmon

“…Such influences might include altered migration timing due to slowed passage around dams (e.g. Raymond 1979Raymond , 1988, altered river flows and temperatures from water management (Zabel & Williams 2002, Williams 2008, Petrosky & Schaller 2010, or changes to hatchery release strategies (Rechisky et al 2012). Another management activity that directly affects salmon ocean arrival timing is barging (e.g.…”

Perspective: Towards environmentally acceptable criteria for downstream fish passage through mini hydro and irrigation infrastructure in the Lower Mekong River Basin

“…Increased development of tributary streams, however, could have an equally substantial ecological impact if fish are not considered during design, construction and operation of new infrastructure projects. 25 …”

“…25 However, the North American perspective also illustrates how difficult and costly it can be to mitigate fish passage impacts once infrastructure is built. In the Columbia river alone, more than US$7 billion has been spent (since 1950) on efforts to save iconic salmonid species 25 by constructing fishways, stock enhancement, screening irrigation diversions, habitat rehabilitation, and providing downstream passage. Whilst this has helped save salmonids from extinction, there still is a strong reliance on hatchery production throughout the entire catchment.…”

“…Whilst this has helped save salmonids from extinction, there still is a strong reliance on hatchery production throughout the entire catchment. 25 Therefore, there is an urgent need to better understand the potential risks faced by migrating fish at existing and proposed infrastructures. In some instances, the installation of certain mini-hydropower units on existing irrigation structures may have the potential to provide renewable power to regional areas, while actually improving the downstream passage of fish.…”