Ann Miracle and Thomas Carlson from the Pacific Northwest Laboratory in the US have been researching spillway induced injury in fish


The successful migration of juvenile salmonids downriver in the Columbia and Snake rivers to the Pacific Ocean in the US Pacific Northwest has been challenged due to the multiple hydropower facilities located on these rivers. There are currently 13 listed salmon and steelhead evolutionary significant units (ESUs) that are impacted by the Federal Columbia river power system (FCRPS). The most recent Biological Opinion issued in 2008 by the National Ocean and Atmosphere Administration (NOAA) aimed to specifically evaluate FCRPS operations with consideration towards juvenile migrant survival strategies.

Risk of injury

Physical injury resulting from impacts with turbine and other hydropower structures and the hydraulic forces associated with spill and sudden depth changes are the main hazards associated with hydropower-related passage. The US Army Corps of Engineers (USACE) is modifying FCRPS dam structures and operations in response to the Biological Opinion. Major changes in the configuration of FCRPS dams have included the addition or modification of bypass systems to divert juvenile fish from turbine intakes, internal turbine components, and a variety of modifications to dam spillways and sluiceways.

Spillway and sluiceway modifications have been designed to increase the amount of water that can be safely released through these structures while protecting water quality from unacceptably high levels of total dissolved gas. In addition, these modifications in many cases provide a surface oriented flow that decreases the time juvenile migrants spend locating dam passage routes.

Screens have been installed at most of the turbine intakes at FCRPS dams , diverting juvenile fish entrained in turbine flow into bypass systems that redirect fish around the dam. Turbine modifications include installation of new redesigned turbine runner assemblies, the moving parts of hydro turbines, intended to reduce fish injury during turbine passage from contact with or strike by turbine parts, as well as exposure to rapid changes in pressure.

The original design of FCRPS dams provided passage of water in excess of the hydraulic capacity of their powerhouses through spillways and the passage of debris and ice through sluiceways. When non-turbine passage routes for juvenile fish past dams were sought these structures were evaluated and eventually structurally modified and their operation optimised to improve fish passage safety. The result is a variety of non-turbine fish passage alternatives that range from the simple addition of spillway chute flow deflectors to extensive modifications that route sluiceway flow into conduits that transport fish a considerable distance downstream from the dam. Spillway modifications that draw water from the surface of a dam’s forebay have been shown to pass fish safely and capitalise on the nearer surface migratory behavior of juvenile salmonids.

Surface oriented bypass routes pass more fish per unit of water than other non-turbine routes thereby optimising fish passage while permitting more available river flow to pass through turbines and generate power. Modifications to spillways that provide surface bypass routes are all weirs but differ in structural details, cost, and operational complexity. The most complex are spillway weirs, large metal structures that straddle the crest of a spillway and are designed to be removed in the event of high river flow, to return the spillbay to its original function. Less complex are weirs placed in bulkhead openings that were originally designed to close off a spillway in the event of failure of a control gate or for servicing of a control gate. Redesign of dam structures and allocation of water to non-turbine passage routes considers the need to efficiently generate power at FCRPS dams while achieving Biological Opinion requirements to effect changes to FCRPS dams that provide the opportunity for recovery of stocks. However, an assessment of the redesign for compliance with the Biological Opinion is needed to ascertain effectiveness of structural changes.

The injury biomarker

Laboratory studies of the effect of exposure to severe hydraulic events on juvenile salmonids have found a variety of adverse effects caused by strike, shear, pressure gradients and disorientation. Recent studies have also found that fish exposed to high shear and turbulence are subject to direct injury and are more susceptible to predation than migrating fish which have nonturbulent passage [1].

Standard efforts to assess these and strike-related injuries are performed using a direct injury and mortality approach by gross observation up to 48 hours post passage treatment. Subacute injuries are not routinely measured as there is no available metric to determine non-visible injuries short of assessments for disorientation following laboratory treatment, and this type of observation is not used in field studies for testing hydropower structure configurations. Injury-based biomarkers were assessed as quantitative indicator of injury severity. Because head injury is a likely result from physical trauma, such as impacting a physical structure or extreme high velocities, the development of a biomarker assay to quickly assess subacute physical injury and recovery is essential to determine the impact of hydropower structures on fish health.

In 2009, Miracle et al [2] described the first laboratory and field study to test the use of a molecular protein marker to assess and compare head injury occurrence in migrating juvenile Chinook salmon. The basis for testing this approach came from recent advances in human biomedical research with the development of a specific mammalian biomarker to rapidly assess traumatic brain injury [3-7]. Molecular biomarkers used in human health applications are often applicable to other mammals; specifically for veterinary medicine [8,9]. However, application for risk management of non-mammalian wildlife has been limited or difficult due to the lack of specific biomarkers for exposure and effect to environmental, chemical, or physical stressors [10,11]. Specifically, the biomarker assay examines the concentration of breakdown products of the protein alpha II spectrin; an important cellular structure protein.

The application of the biomarker assay correlated with observations of visible head injury rates in two separate field studies with different spillway passage configurations [12, 13] and could be used as a potential biomarker for subacute brain damage induced by migration passage. Both studies used a fraction of the total number of fish required for standard gross mortality observations (30 to 40 compared with 300-400 fish), and provided similar information in assessing which particular spillbay and structures were the least injurious to migrating juvenile salmonids. These results had increased significance when examined with measures of physical and hydrological forces, which found the biomarker was more prevalent in live fish that experienced increased collisions and high water pressure.

What’s next?

More recently, the examination of the biomarker assay in blood plasma samples is being used to determine relative internal injury to the fish; not just specifically to brain trauma (Miracle et al, in prep). This unique application is of greater significance in that lethal sampling is not required, and the biomarker can be used to determine systemic injury response to a condition, or set of conditions to be monitored for hydropower operations. Current studies are also underway to correlate the biomarker assay results with fish physiology and behavioural information to establish mortality rates with levels of biomarker expression.

While this is especially critical to FCRPS operations in assessing relative risk of delayed mortality and showing compliance with fish survival and effective hydropower operational modifications, the application of the biomarker assay would also be important for other hydropower facilities in mitigating impacts to local fisheries.

Ann L. Miracle and Thomas J. Carlson are Staff Scientists at the Pacific Northwest National Laboratory in the US. Email: