The potential of technological innovations to cope with threats to biodiversity

Background/Question/Methods

Hydroelectric power projects can act as a barrier to movements of aquatic organisms. The dam comprises an obvious block to upstream (and often downstream) passage. In addition, inadequate environmental flow releases or degraded water quality discharged from the dam can diminish the movements or habitats of biota below the project. These effects are most immediate for migratory species (e.g., diadromous and potamodromous fish), but they may affect the longer term viability and gene flow of resident populations as well. In order to enjoy the benefits of hydropower, it is important to mitigate these possible impacts to biotic communities and the human populations that rely on them.

Results/Conclusions

A wide variety of engineering measures have been developed to enhance water quality and fish passage at hydropower projects. Water temperatures can be improved by multi-level intakes, and dissolved oxygen concentrations have been increased by reservoir aeration, turbine aeration, and tailwater weirs. Fish passage around the dam is a more problematic issue. Upstream passage may be accomplished by fish ladders, fish elevators, and nature-like fishways, but many of these measures are species- and size-selective. There is little assurance that technical fishways, which are often designed to transport commercially or recreationally important fish species, provide the same passage opportunities for all aquatic organisms as did the unimpounded river. Downstream passage through the reservoir and dam has proven even more difficult to accomplish. Efforts to ensure safe downstream passage around the dam have often involved passing fish over the spillway or through the turbines. If turbine passage mortality is too high, the deployment of fish screens leading to bypass conduits is usually considered. The limited experience with new, fish-friendly turbine designs suggests that high levels of turbine passage survival might be achieved concomitant with increased electrical power production. There have been few studies aimed at enhancing reservoir passage, but the loss of downstream-moving migratory fish in the relatively static waters of large storage reservoirs may be a serious problem.