Mass transport of contaminated soil released into surface water by landslides (Göta River, SW Sweden)

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.

Landslide-Induced Mass Transport of Radionuclides along Transboundary Mailuu-Suu River Networks in Central Asia

“…The transport simulation was based on the ADE model in HEC-RAS, which describes the mass conservation of substances transported in the direction of the flow [39]. The dispersion of suspended matter is mathematically described by Fick's law, where the dispersion coefficient includes the combined effects of molecular diffusion, turbulent mixing, and mixing due to transverse and vertical shear associated with cross-stream velocity differences [12,52].…”

“…The translational landslide mass moves along a roughly planar surface with little rotation or backward tilting, and the seismically triggered translational landslides are likely to cause secondary losses associated with earthquakes, with effects sometimes exceeding those of direct shaking [10,11]. In case of a landslide that occurs in the areas of tailings ponds and dumps, the sudden release of radioactively contaminated sediments into the local surface waters encompasses both physical and chemical processes and may cause instantaneous hydraulic changes, redistribution of sediments, and an increase in suspended particulate matter (SPM) [12][13][14]. Due to the significant societal, economic, and environmental impacts related to landslide-induced mass movements, quantifying the mass underlying the subsequence of landslides has become key to prevent radioactive pollution through surface waters, particularly through river networks [13,15,16].…”

“…Numerical hydrological models are one of the tools for the impact assessment and the regulatory decision-making process, such as assisting in the simulation of the transport of landslide-induced contamination, quantification of the maximum contaminant concentration in the water, or evaluation of different feasible remediation strategies [33]. As stated by numerous studies, numerical simulation is a useful and advantageous tool in both the prediction and retrospective evaluation of mass transport of pollutants in surface waters [12,[34][35][36]. Transport models provide the possibility to simulate the concentration changes along river networks and to evaluate the effects of different geological and hydrological scenarios on water quality problems [34].…”

“…Transport models provide the possibility to simulate the concentration changes along river networks and to evaluate the effects of different geological and hydrological scenarios on water quality problems [34]. Furthermore, knowledge of dispersion processes in flowing waters may also be useful for river modification, outlet design, or river confluence design to mitigate potential negative influences on aquatic biological communities [12].…”

“…Spatially, the concentration of suspended matter follows a normal distribution, which propagates downstream with the water velocity. Therefore, the concentration varies only along dendritic river networks [12,39].…”