Fish-friendly future

Gemma Newman talks to Peggy Brookshier of the US Department of Energy about the latest research and developments in advanced hydro turbine technology

What research is currently being performed to understand and reduce the effects of turbine-induced injury to fish?

Brookshier: Research into turbine passage fish injury falls into three general categories: laboratory studies, field studies and advanced computational studies. Laboratory studies are devoted to establishing the responses of fish to particular turbine passage stresses (eg, shear stress or pressure), so that safe levels can be determined. Field studies quantify the injuries and mortality due to different turbine designs and operating conditions at actual power plants. Other field studies are aimed at developing advanced instrumentation so that the levels of fish injury mechanisms in all parts of the turbine system can be measured. Finally, advanced computational analyses serve a variety of purposes, including estimating physical conditions within unmeasured areas of the turbine, clarifying the causes for observed fish injuries in the laboratory and field, and predicting the effects of turbine design changes on fish survival.

The Advanced Hydro Turbine System programme is part of the Department of Energy’s (DOE) Hydropower Programme which is funded by Congress and supports the above activities. A fuller description of the activities can be found in these papers:

• Cada, GF and BN Rinehart. 2000. Hydropower R&D: Recent Advances in Turbine Passage Technology. This report can be downloaded from the DOE Hydropower Programme website: http://hydropower.id.doe.gov/turbine/TurbineR&D.pdf

• Cada GF, Sommers GL and Sale MJ. 2001. What’s Going On in There? Efforts to Describe the Experiences of Turbine-Passed Fish. Available in the proceedings of Waterpower XII.

What injury mechanisms exist?

Brookshier: Turbine passage injuries to fish are caused by rapid and extreme pressure changes, cavitation, shear stress, turbulence, colliding with a turbine structure (strike) and getting caught in the gaps between fixed and moving parts of the turbine (grinding). In some cases these mechanisms may be severe enough to kill a fish directly. In other cases, they may temporarily stun a fish so that it is more susceptible to predators.

How does advanced turbine technology minimise fish injury and changes in water quality?

Brookshier: Advanced turbine designs seek to minimise all of these injury mechanisms. A variation of the Kaplan turbine (the minimum gap runner or MGR) reduces the size of the gaps that can cause grinding injuries. Operational changes can eliminate cavitation and reduce the pressure changes to non-injurious levels.

Although less well understood, we believe that damaging shear stresses and turbulence can also be reduced in advanced turbine designs. The Alden/Concepts NREC runner, which is being tested with the support of the DOE Hydropower Programme, is expected to have low values for all of these injury mechanisms. It should be remembered that there will be some unavoidable injury and mortality due to strike or shear stress, but these can be significantly reduced compared to older turbine designs.

Other advanced turbine designs can add dissolved oxygen to the discharged water through passive mechanisms (the so-called self-aerating or auto-venting turbine).

Are the turbine modifications aimed at a particular species of fish, such as trout and salmon, or do they help all species?

Brookshier: It is expected that these modifications will improve the turbine passage survival of all fish species. Most of the studies have focused on species of commercial or recreational interest, especially migratory fish like salmon, trout and eels. But all fish are similar in their response to these injury mechanisms, and reducing the levels should help non-game fish as well. It is unlikely that improving turbine passage conditions for one fish species will make things worse for another species.

How efficient are the modified turbines compared with standard Kaplan turbines?

Brookshier: A turbine performance comparison of the minimum gap runner (MGR) and state-of-the-art Kaplan designs indicates the following:

• At the best efficiency point, the MGR is about 1.5% more efficient than the conventional Kaplan.

• At an average range of operating conditions (both head and flow), the MGR efficiency remains slightly higher or equal to the conventional unit.

• At the greater range of operating conditions (both head and flow), the efficiency of the conventional unit exceeds the MGR.

What future research is being planned?

Brookshier: Future research into the effects of turbulence on fish is planned for this year. The will give us more information on the injury mechanisms which may occur in various sections of the turbine system.

Planning is under way to continue with environmental mitigation reports, with the next report focusing on instream flow requirements. DOE completed the fish passage report several years ago and will now look at the effectiveness of fish passage. This will prove to be valuable to developers and regulators by providing factual information.