The Challenge of Sediment Management

Moinak Hydro Power Plant.
Moinak Hydro Power Plant, on the Sharyn River in Kazakhstan. (Photo: Wikipedia Commons)

A new research study entitled “Ecosystem impacts of Alpine water intakes for hydropower: the challenge of sediment management” explores the effects of different hydropower capture techniques on human and ecosystem water needs. Rivers fed by glacial melt and snowmelt in Alpine regions serve as a critical resource for hydroelectric power production. However, the management systems used in hydroelectric systems heavily impact both river and sediment flow. This disruption, in turn, heavily, and often negatively, impacts downstream communities and ecosystems, which face consequences of habitat change, degradation, and temperature increases. The authors note that few policy solutions are currently available to reduce and manage these impacts, and call for fresh ideas to address them.

The cover image of the Wiley' January/February 2016 issue.
Researchers taking measurements at a stream gauge (Photo: Jim Constanz)

The study, published in the latest January/February issue of Wiley Interdisciplinary Reviews: Water, reviews the three main types of water management techniques used in hydropower systems. Dams impound water behind barrages in a valley, while abstraction removes water from a ground source. Once abstracted, water is moved laterally (shifted nearby) or downstream (to a lower part of a river) in order to reach the hydroelectric plant.

The article systematically examines how these different methods impact water and sediment flow of the river. Though previous work has studied the impact of different types of water management techniques on river flow, this study is the first of its kind to closely investigate the impact of water abstraction and transfer systems on sediment displacement, which, the study argues, “can significantly influence habitat, which in turn impacts ecosystems.”

The disruption and transfer of sediments have important impacts on human and natural ecosystems because they interfere with what the researchers call the “the natural sediment ‘conveyor belt’” — the process of sediment transfer that is usually determined by natural processes such as erosion, abrasion, sorting, and deposition. Though rivers primarily transport water, they are also vital vessels of sediment transfer. Fine sediment particles enter the river as the water erodes the banks, or tiny fragments break off from rocks in the water. The river carries these particles downstream, allowing the larger ones to drop out—or be deposited—in places where currents slow down.

Disruption of water and sediment flow puts Alpine ecosystems, whose flow regimes are a “key driver” of their physical habitat, at risk. Alpine habitats face risk of physical habitat change, degradation, temperature increases, and major changes to riparian vegetation. Previously inundated rivers may become dry. Such rapid changes in stream flow may leave Alpine fish not able to adapt quickly enough to sustain these alterations. Water abstraction may also “induce lower or higher nutrient levels, depending on the geology; increase electrical conductivity depending on the solute-richness; and/or increase pH.”

Chilime Hydropower Dam
The Chilime Hydropower Dam in Nepal. Image credit: Wikipedia (Photo:Wikipedia Commons)

In order to guarantee both human and ecosystem water needs and minimally disrupt natural sediment transfer processes, hydroelectric systems and water management systems must replicate as close to a natural flow regime as possible. However, attempts to mimic variables of water magnitude, frequency, duration, timing, and rate of charge of each river are unlikely to be met due to simple “constraints of hydroelectric production,” the researchers note. Natural river and sediment flows fluctuate seasonally, making them difficult to mimic because hydropower systems are designed to operate with steady, slow flows. These flows, in turn, rarely provide enough speed to carry larger particles, but also never slow enough to allow smaller particles to settle.

The researchers offer several suggestions to reduce the impacts of sediment transfer on downstream ecological and human communities. They seem some promise in sediment management processes, such as reducing sediment flushing during flows, creating artificial sediment sinks, and finding ways to permanently accumulate remaining sediment into floodplain systems. Such management processes, the researchers noted, are “rarely considered in legislation designed to create more environmentally sustainable river flows.” As such, their suggestions create important policy implications for alpine and glacial river communities near hydropower facilities.

Reinforsen power plant, norway
The Reinforsen power plant in Mo i Rana, Norway. (Photo: Flickr/Statkraft)

However, researchers noted that it is still difficult to determine best practice procedures for sedimentation management which could improve river ecology. They comment that “[t]his is a particular problem for water intake systems where there are almost no experiments, and hence scientific bases, that might be used to define the kinds of instream flow needs necessary.”

Though hydropower poses promise for clean, alternative energy, the study introduces underlying environmental tensions between clean energy solutions and the negative impacts of such alternative energy sources on surrounding communities and ecosystems. In this way, it alerts policy-makers and the public at large to challenges in bringing about a successful transition to low-carbon energy systems. economies and societies.

 

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