Mengsi Dong

Alternate bars are three-dimensional large-scale river bed forms that scale with river width. They are characterized by diagonal fronts, ending with scour holes in the neighborhood of the banks alternating from the left to the right bank. In contrast to ripples and dunes, which form only under sub-critical flow conditions and typically occur in sand streams, alternate bars occur under both sub-critical and super-critical flow conditions, and are particularly prominent features in gravel and gravel-dominated streams.  Even though many hydraulic related aspects of alternate bars have been the focus of intensive research in the past, it is not until very recently that they have been recognized as a major contributor to the health of the river eco-system. They lead to sequences of pools and riffles along the streams, with the pools providing resting places for the fish as they migrate upstream and the riffles being a preferred feature for the fish to deposit their eggs; and they are a primary factor in the development of hyporheic flows (exchanges of water between the surface and groundwater flows) thus playing an important role in moderating habitat life conditions in the riverbed and determining the spatial and temporal patterns of dissolved oxygen and nutrients along rivers. Mengsi's research will aim at advancing the understanding of the formation and effects of alternate bars in rivers and streams, by focusing on aspects that remain unknown and are of particular relevance to the enhancement of river characteristics promoting habitat for fish and subsurface micro-organisms.