Abstract
Abstract. Landslides of contaminated soil into surface water represent an overlooked exposure pathway that has not been addressed properly in existing risk analysis for landslide hazard, contaminated land, or river basin management. A landslide of contaminated soil into surface water implies an instantaneous exposure of the water to the soil, dramatically changing the prerequisites for the mobilisation and transport of pollutants. In this study, an analytical approach is taken to simulate the transport of suspended matter released in connection with landslides into rivers. Different analytical solutions to the advection-dispersion equation (ADE) were tested against the measured data from the shallow rotational, retrogressive landslide in clayey sediments that took place in 1993 on the Göta River, SW Sweden. The landslide encompassed three distinct events, namely an initial submerged slide, followed by a main slide, and a retrogressive slide. These slides generated three distinct and non-Gaussian peaks in the online turbidity recordings at the freshwater intake downstream the slide area. To our knowledge, this registration of the impact on a river of the sediment release from a landslide is one of few of its kind in the world and unique for Sweden. Considering the low frequency of such events, the data from this landslide are highly useful for evaluating how appropriate the ADE is to describe the effects of landslides into surface water. The results yielded realistic predictions of the measured variation in suspended particle matter (SPM) concentration, after proper calibration. For the three individual slides it was estimated that a total of about 0.6% of the total landslide mass went into suspension and was transported downstream. This release corresponds to about 1 to 2% of the annual suspended sediment transport for that river stretch. The studied landslide partly involved an industrial area, and by applying the analytical solution to estimate the transport of metals in the sediments, it was found that landslides may release a significant amount of pollutants if large contaminated areas are involved. However, further studies are needed to develop more detailed descriptions of the transport processes. There is also a need to increase the knowledge on possible environmental consequences in the near and far field, in a short- and long-time perspective. In summary, the release of pollutants should not be neglected in landslide risk assessments.
Highlights
1.1 Mass movementMass movement of contaminated soil into surface water encompasses both physical and chemical processes and is an interdisciplinary research area
Data on turbidity collected in connection with a minor landslide into Gota River, SW Sweden, showed that the suspended sediment concentration downstream the release point exhibited a non-Gaussian variation with time, being strongly skewed
Most parameter values in the advection-dispersion equation (ADE) are straightforward to obtain through measurements at the site of interest, but some parameters may require detailed investigations, for example, the dispersion coefficient and the amount of sediment that is likely to go into suspension during a landslide
Summary
Mass movement of contaminated soil into surface water encompasses both physical and chemical processes and is an interdisciplinary research area. The stability of a slope (e.g. hillside or riverbank) is governed by the balance between resisting and driving forces. When the driving forces exceed the resisting forces by cohesion and friction between soil particles, the soil starts to move (Lambe and Whitman, 1979). As the contact between particles diminishes, and as the moving soil mass becomes liquefied (a slurry), particles come into suspension and are no longer attached to each other. The effective stresses between particles are reduced and the forces act through the fluid instead (TerStepanian, 2000). As the soil mass moves into a surface water (a river, lake, or coastal area), it causes instantaneous hydraulic changes and generates surface gravity waves through
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