Mass movements as contamination carriers in surface water systems : Swedish experiences and risks
Abstract: Recent studies indicate a widespread but largely overlooked hazard of contaminant mobilisation and transport in connection to mass movement activity into surface water systems in Sweden. Concerns are exacerbated by predicted effects of climate change, which suggest national increases in rates of precipitation, pore water pressures, run -off, erosion and mass movement occurrence. In this study, the national scope, character and potential of the proposed hazard and associated risks are assessed based on a review of approximately 400 mass movement events. Hazard analyses of three risk areas along rivers Viskan, Klarälven and Ångermanälven are also presented. It is concluded that parts of most major Swedish river systems, as well the lakes and coastal areas into which these debouch, are already likely to be at risk of the proposed hazard. Within the three studied risk areas, 102 environmentally hazardous facilities and/or sites of established or suspected soil contamination were found to lie within areas at risk of slope failure. The variation in character of historical mass movement activity on the one hand, and types of environmentally hazardous facilities/soil contamination on the other, indicate that the scope and nature of the hazard in between as well as within any given risk area varies with time and location according to concurrent geologic, climatic and biologic conditions, and, according to extent and type of human activity. It is shown that materials set into suspension upon slope failure into running waters may stay in suspension for months, being carried upstream for several kilometres, and downstream for several tens of kilometres. Displaced materials are further demonstrated to be able to cause enhanced mobilisation of materials through surging, and, through upstream inundation and long-term/permanent alterations of downstream flow- and erosion patterns brought about by damming. Mass movements into surface water systems hence appear as an efficient potential means of widespread, short- and long-term contaminant transport throughout much of Sweden. For the future, hazard awareness raising and clarification of responsibilities amongst involved actors are considered the main and most important tasks. The need for more interdisciplinary collaboration, research and exchange of experiences - nationally and internationally - is also stressed.
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