A new machine learning model is shedding light on the often devastating impacts of new dams on water temperature, and may help policy-makers and engineers mitigate the harm to river ecosystems of the more than 3,700 structures lining up for construction worldwide.
“The ubiquitous dams around the world are built to guard against extreme flooding, meet steadily increasing water demands, and provide hydroelectric power,” reports the Washington Post. But the dams “also alter river ecosystems—such as by changing temperatures downstream—and can substantially change nearby fish populations.”
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The study authors also created a public tool for their first-of-its-kind model that allows users to determine a future dam’s impacts on downstream temperatures by inputting its dimensions. They hope the tool can be used to avoid the past century’s dam installation mistakes.
“Maybe we can look at what the temperature changes might be, bring the community together, and explore other alternatives in a cost-effective way, and then thereby minimize the negative impacts on Mother Nature,” study co-author Faisal Hossain, a professor of civil and environmental engineering at the University of Washington, told the Post.
Large bodies of water are thermally stratified, with cooler temperatures along the bottom rising to warmer temperatures at shallower depths, the Post explains. When a dam is installed, it pulls water from the lower layers, leading to cooler summer and warmer winter temperatures downstream.
Several factors determine the extent of warming or cooling, including the size and depth of a dam’s reservoir and whether the dam is located in a region that is warm and arid or humid and snowy, writes the Post. But those factors can change typical temperatures by as much as 6°C, which is significant for plants and animals living within carefully balanced river ecosystems.
Yet there are plans to build 3,700 new dams worldwide, the majority of them concentrated in South America, Africa, and South and East Asia, where hundreds of millions of people rely daily on plants and animals that are adapted to current river conditions. A dearth of data regarding dam impacts—especially in developing countries—means the impacts of these dams was not quantified prior to the study. Of the 216 planned dams that were analyzed using the tool, about 73% would reduce downstream summer water temperatures by 6.6°C, while roughly 25% would increase downstream winter temperatures by 4.7°C.
With the monitoring tool informing decision-making, communities can avoid the worst impacts of new dams by drawing less water from lower layers, replacing dam power using smaller turbines or, in some locations, not installing a dam at all, the Post writes.