Dam Planning and Regulation
For dams that have not yet been built there are many steps that can be taken to minimize the impacts. First, efforts should be made to increase energy and water efficiency as much as possible; in the past, increases in technological efficiency, recycling, enforcement of environmental legislation, and reduction of industrial water use allowed water consumption to grow much slower than population (WCD). However, if a dam is definitely needed, research should be conducted to determine its environmental impacts. The World Commission on Dams reports that many of the negative impacts are not foreseen; it predicts that use of environmental impact assessments could significantly reduce these effects (WCD). Furthermore, proper placement of dams (such as on tributaries rather than on a main branch) and the use of minimal numbers of dams on a given river (because multiple dams can have cumulative effects) should be required by governments as such restrictions can minimize the large-scale negative impacts of large dams (WCD). Once these data are collected, the dam planning may begin; in this way, the dam design can take into account such features as gates that allow managed flood releases on a scale that can mitigate effects to the ecosystem; the permit for dam construction can require these provisions. The use of such managed floods in Kenya has been economically favorable by maintaining sectors of the economy that relied upon flows that would have been blocked entirely by damming (WCD). These floods help to release nutrients and sediments and help lessen the impact of the dam overall (WCD). These managed floods should be tailored to a specific river, as flood cycles are highly unique. It is important, however, that all such planning occurs before dam construction, as post-construction mitigation techniques have not been shown to be effective; the WCD reports rates of 20% effectiveness. It is possible that the IFIM (Instream Flow Incremental Methodology), as described here, could be used to help predict the effects of a dam and the effects of controlled flooding.
Fish passes around, through, or over dams currently have a very low success rate. In Norway, fish passes report a 26% rate of "good efficiency" and 32% of no success at all (WCD). In many parts of the world, fish passes are not used at all. Also, even with fish passes, fish often suffer from a lack of environmental cues (like currents) that help them find their spawning site (WCD). However, properly designed fish passes (specific to each dam and species of intended use) do hold promise; in Pennsylvania, fish passes were ineffective until tailored to the American shad, at which point they became very helpful in shad restoration (Richardson). Fish hatcheries and stocking may also be required to augment populations until the spawning routine is reestablished with the dam in place; successful restoration of American shad and striped bass required such measures (Richardson), and these methods are likewise advocated by the WCD. The creation of artificial wetlands around shallow dams can also help mitigate dam impact by providing new habitat (WCD). Our recommendation is for governments to require dams to have appropriate fish passes or to pay a yearly fee to the government which can be used for restoration and study of the species affected by the dam.
For developed countries with large budgets and effective environmental legislation (such as France and the United States) decommissioning dams is a way to aid fish such as salmon (WCD, 2000). While short-term effects of dam removal include large-scale sediment flushing, over relatively short time scales fish will return and spawn in those areas. However, dam removal is costly and must be studied beforehand; in many cases, toxins and chemicals can build up behind dams and the effects of these toxins washing downstream can be severe (Francisco).
Ways to address the negative fishery impacts of existing dams include controlled floods, installation of wetlands, and introduction of nutrients downstream of the dam (Wuest). The viability of these measures may be limited by factors ranging from budgetary concerns to the design of the dam itself.
Appropriate consideration of environmental impacts should be mandatory at every step of the dam planning process.