Sediment transport rates of major floods in glacial and non-glacial rivers in Norway in the present and future climate

This paper considers possible sediment transport impacts in both glacial and non-glacial rivers in Norway from climate scenarios predicted by the RegClim (2005) project. The significance of high magnitude, low-frequency events as sediment transport agents is discussed on the basis of sediment transport measurements during major floods in various types of rivers. It was found that suspended sediment concentrations and volumes were dependant on the availability of sediments, the type and character of the erosion processes, and the temporal development of the flood. Measurements in a glacier outlet river during a flood of 100-year recurrence interval gave a high sediment load, but of the same order of magnitude as the mean. The reason for this is attributed to a limited availability of sediment for erosion in the subglacial channels. In reaches downstream from the glaciers and in non-glacial rivers, measurements during floods of 100- to 200-year recurrence indicate transport rates of about 30-40 times the mean of the preceding years. Due to the predicted increase in precipitation high-lying glaciers may advance in the first part of the 21st century. As a result of the continued increase in temperatures a general recession will occur and most glaciers will have disappeared by 2100. This will probably increase the formation of glacier dammed lakes that may generate lake outbursts. Large magnitude floods are found to be an important controlling factor of ravine development in the clay areas. It is thus anticipated that the equilibrium of the ravines will be altered by climate change because of the increase in flood frequency and magnitude. As a result, an increase in vulnerability to clay slides may take place.