ABSTRACT
River flow occupies a special place in a family of environmental and industrial flows. It indeed exhibits a set of properties that make this flow unique and exciting, i.e.: (1) flow boundaries (sedimentary bed and free surface) are ‘deformable’ and dynamic, i.e.,constantly changing in response to varying flow; (2) river biota is a significant factor directly and indirectly influencing flow and its boundaries; (3) channel boundaries have a complex hierarchical structurecovering scales spanning 7-10 orders of magnitude; (4) flow submergence(i.e., ratio of the flow depth to the height of prevailing roughnesselements such as sediment particles, their clusters, or bedforms) is typically low, i.e., less than 10-15; and (5) flow-sedimentsbiota-channel interactions occur at many distinct scales, such as grain scale, ripple scale, dune scale,scales, such as grain scale, ripple scale, dune scale, bar scale, and meander or braid scale. These conditions differentiate river turbulence from all other types of turbulent flows makingit both attractive and difficult to study.
