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

摘要

Landslides of contaminated soil into surface water represent an overlookedexposure pathway that has not been addressed properly in existing riskanalysis for landslide hazard, contaminated land, or river basin management.A landslide of contaminated soil into surface water implies an instantaneousexposure of the water to the soil, dramatically changing the prerequisitesfor the mobilisation and transport of pollutants. In this study, ananalytical approach is taken to simulate the transport of suspended matterreleased in connection with landslides into rivers. Different analyticalsolutions to the advection-dispersion equation (ADE) were tested against themeasured data from the shallow rotational, retrogressive landslide in clayeysediments that took place in 1993 on the G?ta River, SW Sweden. Thelandslide encompassed three distinct events, namely an initial submergedslide, followed by a main slide, and a retrogressive slide. These slidesgenerated three distinct and non-Gaussian peaks in the online turbidityrecordings at the freshwater intake downstream the slide area. To ourknowledge, this registration of the impact on a river of the sedimentrelease from a landslide is one of few of its kind in the world andunique for Sweden. Considering the low frequency of such events, the datafrom this landslide are highly useful for evaluating how appropriate the ADEis to describe the effects of landslides into surface water. The resultsyielded realistic predictions of the measured variation in suspendedparticle matter (SPM) concentration, after proper calibration. For the threeindividual slides it was estimated that a total of about 0.6% of thetotal landslide mass went into suspension and was transported downstream.This release corresponds to about 1 to 2% of the annual suspendedsediment transport for that river stretch. The studied landslide partlyinvolved an industrial area, and by applying the analytical solution toestimate the transport of metals in the sediments, it was found thatlandslides may release a significant amount of pollutants if largecontaminated areas are involved. However, further studies are needed todevelop more detailed descriptions of the transport processes. There is alsoa need to increase the knowledge on possible environmental consequences inthe 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.