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.
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 due to the high cost of the work. And when measures are implemented, they typically involve conventional technical approaches such as gabions, stone settlements, concrete, soil cement, and geotextiles.
With the above in mind, the authors say the search for environmentally friendly, economically viable, and sustainable technical solutions has gained importance in recent years, with soil and water bioengineering techniques offering a viable alternative. Taking into account both technical and environmental factors, these techniques mostly use living materials (seeds, plants, plant parts, etc.) that can be combined with inert materials.
In their study, the authors investigated four different types of soil and water bioengineering measures to stabilise and control erosion processes on the banks of hydroelectric reservoirs. The study area focused on the reservoir of the Ita hydroelectric power plant on the Uruguay River in southern Brazil.
The proposed nature-based solutions aim to cover and protect the banks with native rheophyte plant species that were naturally present on the banks of the Uruguay River before the power plant was built. Techniques designed for the upper slope included coconut bioretention, wooden bank pile wall and enveloped soil – all of which proved effective in stabilising and protecting the base of reservoir’s water level. While techniques designed for the lower slope included live siltation, square planting, wooden palisades and coconut bioretention. These acted as living physical barriers against the action of waves, dissipating their kinetic energy.
Even after a short time of data collection, and the focus of what has been called a very empirical approach, the authors say their results show that such natural engineering techniques offer innovative and technically feasible solutions for rehabilitation projects in the vicinity of hydroelectric dams, and can be used independently or in addition to conventional engineering techniques. They go on to add their use offers additional ecological, economic, environmental and aesthetic benefits in addition to the intended technical effects.
Admitting that these effects will change over time due to the evolution of plants, the authors conclude it is essential to have a longer period of data, of vegetation, erosion and load, to have more secured results and develop numerical models to optimise such bioengineering efforts against these specific erosion processes.
Indonesian experience of erosion
Studies into erosion and sedimentation have also been carried out at Indonesia’s Batujai Dam and are being used to not only help determine the magnitude of the problem, but provide future reference for controlling and maintaining the reservoir.
Batujai Dam is the largest dam in Central Lombok. At the beginning of its construction in the late 1970s, the reservoir had a depth of 18m. By 2019 it decreased to 12m, with more than 35% of the surface covered by water hyacinths, causing reservoir capacity to fall from 25Mm3 to 18.4Mm3.
Land degradation due to erosion in the watershed area upstream of the reservoir is believed to have contributed significantly to such high sedimentation rates, compounded by the presence of the water hyacinths. And although the government has carried out sediment dredging to increase reservoir capacity, it hasn’t yielded good results.
A study carried out by Utari et al in the Asian Journal of Engineering, Social and Health estimated the magnitude of erosion at this Indonesian reservoir. They used the Universal Soil Loss Equation (USLE) which is a parametric model used to predict erosion from a land area, and the Modified Universal Soil Loss Equation (MUSLE) – an extension of the former model which replaces the rainfall erosivity factor with the surface runoff factor.
After successfully identifying the level of erosion and sedimentation in the Batujai reservoir, the researchers determined that factors such as rainfall erosivity, soil type, slope length and slope, and land use and soil vegetation directly influence the increase in erosion rates. Erosion also tends to be low in areas with gentle slopes and dense vegetation cover.
It was also suggested that for any future research, existing erosion values can be used and grouped into erosion hazard classes, so that subsequent conservation actions can also be determined based on areas with high erosion.
Morocco
Another study conducted in the Chichaoua watershed in the High Atlas Mountains of Morocco, aimed to quantify soil loss, investigate its causes, and evaluate its effects on the construction of the new Boulaouane dam.
Situated southwest of Marrakech city, the Chichaoua basin covers an area of 2696km2 and is drained by the Oued Chichaoua, along with its tributaries, the Oued Imintanout and the Oued Seksaoua.
In their research, Baiddah et al were able to quantify potential soil losses and show they exceeded tolerance thresholds. With results indicating that the watershed substantially contributes to downstream sediment loads, the authors say this could impact the hydrological performance and lifespan of the Boulaouane dam.
Highlighting the critical need for implementing erosion control measures, especially in upstream areas, this study in Ecological Engineering and Environmental Technology, suggests intense erosion impacting the Chichaoua watershed will present substantial challenges for the sustainable management of the region’s soil and water resources. It underscores the pressing necessity of implementing targeted erosion control strategies, particularly around key infrastructures like the Boulaouane dam.
The authors believe the results of their study could serve as valuable tools for basin managers to design effective soil and water conservation policies. Their significance would be further enhanced if combined with methods based on field measurements, ensuring the sustainability of future reservoirs.
Maintaining vegetation
Properly maintained vegetation can not only help prevent the erosion of embankment dams, in the US it can also aid in the control of troublesome groundhogs and muskrats.
As the Association of State Dam Officials (ASDSO) explains, although grass vegetation is an effective and inexpensive way to prevent erosion of embankment surfaces, uncontrolled growth of vegetation can damage embankments, making them more difficult to inspect.
Embankment slopes are normally designed and constructed so that surface runoff will be spread out in a thin layer as “sheet flow” over the grass cover. However, if the grass is in poor condition or flow is concentrated at one or more locations, the resulting erosion will leave rills and gullies in the embankment slope. This can cause loss of material and make maintenance of the embankment difficult. Prompt repair is required to prevent more serious damage.
It’s also recommended that trees and brush are not on embankment surfaces or in vegetated earth spillways either. Extensive root systems can provide seepage paths for water, while trees that blow down or fall over can leave large holes in the embankment surface. This will weaken the embankment, possibly leading to increased erosion.
In addition, footpaths both from animals and pedestrians can pose problems for many embankments. Vehicles can also severely damage vegetation on embankments with worn areas potentially leading to erosion and more serious problems. Bare areas on an embankment are void of protective cover (eg, grass, asphalt, riprap etc), making them more susceptible to erosion which can lead to localised stability problems such as small slides and sloughs.
As the ASDSO explains, the advantages of proper maintenance of vegetal cover includes unobstructed viewing during inspection, maintenance of a non-erodible surface, aesthetics, and discouragement of burrowing animal habitation.
Indeed, rodents such as the groundhog, muskrat, and beaver are attracted to dams and reservoirs, and can be quite dangerous to the structural integrity and proper performance of the embankment and spillway. Groundhog and muskrat burrows can weaken the embankment and act as pathways for seepage.
Barriers to prevent burrowing offer the most practical protection for earthen structures. A properly constructed riprap and filter layer will discourage burrowing, and dens should be eliminated without delay because damage from just one hole can lead to failure of a dam or levee.
Recurring erosion
At the Lamtakong Dam in Thailand, recurring slope erosion is posing a threat to both the structural integrity of embankments and the operational efficiency of water storage systems. Although the Lamtakong Jolabha Vadhana power plant is one of the key hydropower projects in Thailand, erosion along its reservoir slopes has caused frequent sediment accumulation and slope collapses. These issues have necessitated the implementation of effective and sustainable erosion control measures to stabilise the surrounding terrain and mitigate further land degradation.
Vegetation can play a crucial role in reducing runoff velocity, increasing soil shear strength, and promoting water infiltration, making it a natural and effective means of stabilising slopes. The root systems of plants bind soil particles together, decreasing the likelihood of soil displacement and reinforcing slope stability.
Among various plant species, Ruzi grass has gained recognition as being a highly effective erosion control species due to its fast growth rate, extensive root system, and ability to cover slopes rapidly. It acts as a natural barrier, reducing the energy of raindrop impact and minimising soil particle detachment. Additionally, its dense network of roots helps anchor the soil in place, preventing sediment transport and reinforcing slope stability. It’s also adaptable to different soil conditions and has minimal maintenance requirements, making it an ideal candidate for large-scale slope stabilisation projects.
Despite its potential, the combined use of geocells and Ruzi grass for erosion control has not been extensively studied in field conditions. While geocells provide structural stability and soil confinement, Ruzi grass can complement this reinforcement by mitigating surface erosion and enhancing water infiltration. However, limited studies have systematically evaluated the effectiveness of this integrated approach under varying rainfall intensities and slope gradients. Addressing these knowledge gaps is said to be essential for optimising erosion control strategies that balance structural reinforcement, ecological sustainability, and cost-efficiency.
A study in Geotextiles and Geomembranes has investigated the field performance of an integrated geocell and Ruzi grass erosion control system in the Lamtakong Dam area of Thailand. Results show the combined system gives a 90% runoff reduction with geocell and Ruzi grass, with 60%–80% of geocell coverage providing substantial erosion control, and Ruzi grass alone reducing sediment by 40%. The system is also effective across slopes and rainfall intensities and proves to be cost-efficient erosion control with optimised geocell use.
The authors conclude their field study confirms the effectiveness of integrating geocell reinforcement with Ruzi grass for slope erosion control under varying rainfall intensities and slope gradients. The combined system substantially reduces surface runoff and sediment transport by providing mechanical stabilisation and promoting vegetation cover. The findings offer practical insights for implementing sustainable and cost-effective erosion control strategies, especially in steep and erosion-prone areas.
References
First results of soil and water bioengineering interventions to stabilise and control erosion processes in hydroelectric power plant reservoirs in Brazil by Rita dos Santos Sousa, Junior Joel Dewes, Hans Peter Rauch, Fabrício Jaques Sutili, Stephan Hörbinger. Ecological Engineering 211 (2025) 107458. https://doi.org/10.1016/j.ecoleng.2024.107458
Analysis of Erosion Rate and Sedimentation Rate at Batujai Dam Using USLE and MUSLE Methods by Ni Luh Putu Lavidya Amartya Utari, I Wayan Yasa, Yusron Saadi, Eko Pradjoko. Asian Journal of Engineering, Social and Health. Volume 4, No. 1 January 2025 – (218-229)
Estimating erosion, sediment yield, and dam lifetime using revised universal soil loss equation and potential erosion model in the Chichaoua watershed and Boulaouane Dam, High Atlas, Morocco by Abdeslam Baiddah , Samira Krimissa Maryem Ismaili, Sonia Hajji, Mustapha Namous, Fatima Aboutaib, Hasna Eloudi, Nasem Badreldin. Ecological Engineering & Environmental Technology, 2025, 26(3), 132–158 https://doi.org/10.12912/ 27197050/199824
Field performance of erosion control on Lamtakong dam slopes using geocell and ruzi grass cover: A case study by Nuttawut Thanasisathit, Supphanut Chuenjaidee, Panich Voottipruex, Pornkasem Jongpradist, Patara Kalayasri, Pitthaya Jamsawang. Geotextiles and Geomembranes Volume 53, Issue 6, December 2025, Pages 1610-1622 https://doi.org/10.1016/j.powtec.2025.120805
