Feeding the hungry river: Fluvial morphodynamics and the entrainment of artificially inserted sediment at the dammed river Isar, Eastern Alps, Germany

We use a multi-method approach on a range of spatial and temporal scales. First, we analysed historical maps and aerial photos to analyse river planform and landcover changes within the river corridor of the whole study area on a temporal scale of over 100 years. Results show that major changes occurred before the construction of the Sylvenstein reservoir, suggesting that present morphodynamics represent the reaction to different disturbances on different time scales. Second, changes in mean bed elevation of cross profiles regularly surveyed by the water authorities are analysed in light of artificial sediment insertion and floods; they are also used to estimate the sediment budget of river reaches between consecutive cross profiles. Results suggest stability and a slight tendency towards incision, especially near the Sylvenstein reservoir; further downstream, the sediment balance was positive. Third, we acquired multitemporal aerial photos using an unmanned aerial vehicle and generated high-resolution digital elevation models to show how sediment artificially inserted in the river corridor is entrained. Depending on the position of the artificial deposits in relation to the channel, the deposits are entrained during floods of different return periods.