Erosion | Resilient restoration
Soil erosion and its impact on dams and reservoirs is described as being a problem worldwide. Some of the latest research offers insights into how the industry is tackling the problem
EROSION AT RESERVOIRS IS described as being a worldwide problem, especially in countries with a tropical and subtropical climate, such as Brazil. Here the problem is intensified by uneven rainfall which is typically concentrated over a few months of the year, along with the presence of soils with well-developed and deep profiles. Regardless of their size, erosion can take place on the banks of reservoirs, with sedimentation accumulating on the bottom. Impacts on the banks are caused by wave action and the oscillation of operating levels, which occur over a daily to annual time scale. And as Rita dos Santos Sousa et al explain in their research published in Ecological Engineering, the impact of regular waves on reservoir embankments can result in: 1) Soil entrainment: soil material is eroded, transported and deposited at the base of the slope, creating a relatively flat area known as an abrasion and sedimentation platform, with a very steep slope or escarpment.
Below: View of the Itá dam on the Uruguay River in Brazil
2) Rapid deterioration of the protective vegetation on the slopes. The vegetation must therefore be monitored frequently and maintained if necessary.
In addition, annual oscillation means the waves affect and erode the slopes where the water level rests momentarily. As this fluctuates throughout the year, erosion processes follow this fluctuation and erode different sections of the slope located between the reservoir’s maximum and minimum operating levels. The greater the number of oscillations during the year, the greater the number of times the waves will reach different levels and the greater the erosion of the slopes will tend to be. Different rates of erosion can also occur at different levels on the slope, depending on how long the water level remains at a certain position. As the authors warn, reservoir banks, particularly
in the reservoir disturbance zone, are highly susceptible to erosion processes that result in a loss of stability. This can also lead to negative ecological consequences such as siltation, loss of native vegetation cover, reduction in biodiversity, changes in water quality and eutrophication, as well as shortening of the useful life of hydropower facilities. Nevertheless, Rita dos Santos Sousa et al claim that the control and mitigation of erosion processes at Brazilian reservoirs are not common practices, mostly
18 | November 2025 |
www.waterpowermagazine.com
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