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Virtual Waters
Virtual Waters

We live in a world made possible by water. Our way of life depends on it. So, to meet our water needs, we’ve built dams, reservoirs, and aqueducts. We’ve diverted rivers, siphoned springs, and tapped aquifers. We’ve created regulations and enacted policies that govern everything from who has priority rights over water supplies to removing dams to restore fish and wildlife habitat. And along the way scientists, engineers, and water district managers have come to understand that these activities affect water quality in ways that can harm the environment, disrupt supplies, and lead to conflicts between competing demands on limited resources.

“When it comes to water quality the stakes are high, for society and for the environment,” said Dr. Scott Wells. “Minor changes in temperature, flow, or chemical composition can have outsized effects, resulting in eutrophication, algal blooms, oxygen depletion, die-offs, and other potentially harmful phenomena.”

Dr. Wells is a professor in Portland State University’s Department of Civil and Environmental Engineering. His research and expertise in hydrodynamic modeling provides resource managers, scientists, and other engineers information critical to the development and optimization of surface water management strategies that seek to strike a balance between human use and the environment. Dr. Wells leads the Water Quality Research Group at PSU, a team of faculty, graduate students, and staff focused on using hydrological modeling software developed by the U.S. Army Corps of Engineers and PSU, called CE-QUAL-W2 (W2), to construct virtual models of actual rivers, lakes, and estuaries and simulate hydrodynamic processes that affect water quality.

For years, Dr. Wells and the Water Quality Research Group have partnered with local, state, and federal agencies tasked with managing surface water systems and maintaining water quality. And in another example of how researchers from PSU have extended the reach of the university’s mission to “let knowledge serve” beyond our national borders, Dr. Wells has partnered with foreign governments and international agencies assisting with the evaluation of surface water systems and helping address critical water quality challenges involving concerns including ecosystem health, wildlife habitat, and greenhouse gas emissions.

(Image: A shrinking lake. At the beginning of the 20th century, the Dead Sea had a surface area of 950 km2, and was -390 m below sea level. By the beginning of the 21st century, the surface area of the Dead Sea had decreased to 650 km2 and the waters had receded to -415 m below sea level.)

In Israel, for example, where the diversion of water from the Jordan River has nearly cut the Dead Sea off from its primary source of inflow, and local industries continue to draw from the sea’s dwindling waters, Dr. Wells participated in the Dead Sea–Red Sea Water Conveyance Study sponsored by the governments of Israel and Jordan as well as the Palestinian National Authority and the World Bank. That project explored the idea of building a pipeline or canal connecting the two seas that would provide potable water to local residents, generate electricity, and stabilize water levels in the Dead Sea.

“The Dead Sea is dying,” Dr. Wells said. “It’s already lost about a third of its surface area and water levels are dropping by nearly a meter a year. And now people are seriously asking what they can do about it.”
According to Dr. Wells, the idea was to move water from the Gulf of Aqaba on the Red Sea up the Araba Valley to the Dead Sea. The question is, however: how might the project impact the region? What could be expected as a consequence of mixing the characteristically distinct waters of the Red and Dead Seas?

Dr. Wells was invited to join the team of scientists, engineers, and policymakers evaluating potential outcomes that could result from mixing the waters of the two seas. Using the W2 software, he and his team explored possible answers to questions such as how the dynamics of stratification in the Dead Sea might change given the introduction of Red Sea water. They asked how the chemistry of Dead Sea water might change and what could happen as a result. Is there a potential for harmful algal blooms? Would surface evaporation rates differ? They even examined how Red Sea water might affect the buoyancy of visitors that come from around the world to float in the Dead Sea’s famously saline waters.

Data and results from simulations Dr. Wells generated using a specialized version of the W2 software were included in the World Bank’s “Environmental and Social Assessment” portion of the final report on the impacts of Red Sea–Dead Sea water conveyance. According to Dr. Wells, the data didn’t necessarily bode well. The introduction of Red Sea water posed potentially major threats to ecosystems supported by the Dead Sea. As the final report states, not only would those threats be socially unacceptable, but the introduction of Red Sea water to the Dead Sea would likely result in “changes to the appearance of the water quality such that its value as a heritage site of international importance [would] be damaged.” Despite concerns highlighted in the final report, the Jordanian government is moving forward with the project unilaterally with construction scheduled to begin in 2018.

Some 4,300 miles east of the Dead Sea, in China, Dr. Wells is working with collaborators from the Three Gorges University, the Hubei University of Technology, and the Institute of Water Resources and Hydropower Research to explore water management strategies that could reduce harmful algal blooms in China’s Three Gorges Reservoir on the Yangtze River in China’s Hubei province.

(Image: Three Gorges Reservoir on the Yangtze River in China's Hubei province.)

Studies conducted by Dr. Wells’s colleagues in China suggest algal blooms along the Xiangxi River, the largest tributary of the Three Gorges Reservoir, are closely associated with patterns of water level fluctuations. Reduced water levels in the reservoir, they observed, caused more water to flow out of the tributary. The outflow flushed surface nutrients necessary for algal blooms out of the tributary. It also resulted in vertical mixing of waters from various depths, which likewise contributed to reductions in blooms.

On the surface, the obvious solution to the problem of algal blooms in the Xiangxi would be to release more water from the reservoir. The issue with that solution according to Dr. Wells is that dam operators are limited to how much water they can release from the reservoir. And even if they could release enough water to affect algal blooms upstream, the loss of that volume of water would likely result in lost power generating capacity at the dam. Dr. Wells’s collaborators, however, also hypothesized that it was possible to control algal booms by raising the level of water in the reservoir. Dr. Wells helped the team test that hypothesis.

“Fluctuations in water levels, whether natural or the result of dam operations can affect water quality in lacustrine systems,” Dr. Wells said. “The question we’re assisting our colleagues in China with is: when and how do fluctuations prevent algal blooms in the Xiangxi River side arm of the Three Gorges Reservoir? And what, if anything, can the dam operators do to improve water quality in the side arms of the reservoir?”

By running simulations of the hydrodynamics and water quality in the Xiangxi tributary, Dr. Wells hoped to identify management strategies that officials at the reservoir can use to incorporate environmental decision-making into the everyday operational practices of the dam and reservoir and reduce some of the trade-offs between improving water quality and reducing environmental degradation upstream and generating power, controlling for floods, and providing for irrigation at the dam.

Hydrodynamic and water quality simulations produced by Dr. Wells and the Water Quality Research Group corresponded to field observations recorded by the Chinese scientists and illustrated how various water management strategies at the reservoir resulted in subsurface circulation that altered the thermal and chemical stratification of the water. The results showed that raising the level of water in the tributary was indeed an effective strategy for reducing algal blooms, provided that the water flowing into the side arm of the reservoir came from the Xiangxi River and not from the reservoir. So under the right conditions in which there is inflow from the tributaries, Dr. Wells found, it is possible to operate the dam in such a way as to improve water quality without compromising utility.

“Testing field observations like those recorded by my colleagues in China is just one of the functions we’re able to use the W2 software for,” Dr. Wells said. “We’ve adapted this tool to simulate gas levels emanating from spillways on dams along the Columbia River to evaluate how dam operations affect fish in the river. We’ve used it to assess the amount of CO2 and other greenhouse gases countries in South America can expect to be released into the atmosphere from hydroelectric projects after dams have been built and forests inundated. And we’ve used it to simulate river conditions in places like California, Oregon, and Washington where water temperatures are critical to salmon and other endangered species.”

Whether in South American, China, the Middle East, or here in the Pacific Northwest, society as we know it would be impossible if we were unable to manage, store, and transport water to meet our needs. But where we have a hand in managing the water cycle, water quality issues often arise. That is why resource managers in the U.S. and abroad depend on scientists and engineers like PSU’s Dr. Scott Wells and the members of the Water Quality Research Group whose mission is to “let knowledge serve” and who are capable of monitoring and anticipating water quality issues, determining how those issues will affect society and the environment, and providing suitable solutions to maintaining water quality standards to meet the needs of all.

Note: Research highlighted in this article is supported by the Technology Cooperation Program of China (2014DEF70070), the National Basic Research Program of China (2014CB460601), the Fulbright Scholars program, and the World Bank.