Tropical rivers challenge our understanding of rivers. In this thesis we investigated the Mahakam River, East Kalimantan, Indonesia. Many meander bends in this river are sharp and reach depth of sixty meters, more than four times the average depth. This sharp bends and deep scours are associated with a non-conventional meandering behavior. While usually river bends erode on the outer side and aggrade on the inner side, these bends show the opposite behavior. This non-conventional behavior has large implications for our ability to predict the development of such rivers. In the past year these scours might have been the cause of a collapsing bridge, causing several casualties and the collapsing of a coal mine harbour, with large economic damage. New methods have been developed to analyse the flow in the deep scours of the Mahakam.