![]() The velocity reversal hypothesis emerged as an attempt to explain this behavior ( Keller, after Seddon and Gilbert ). During high-discharge episodes, however, this situation is inverted, and pool erosion takes place while riffles aggrade. Observations of the mechanisms responsible for the self-maintenance of pools and riffles have shown that during low and medium discharges, aggradation occurs in pools while riffles are eroded. One of the main complexities of pool-riffle dynamics is that spatial patterns of erosion and aggradation vary with flow conditions. Restoration efforts that seek to reestablish natural pool-riffle sequences have revealed the lack of a practical and comprehensive theory of pool-riffle morphodynamics applicable to real-life flow and sediment conditions. Human impact on streams has often modified pool-riffle structure either by physically removing them (e.g., through channelization) or by altering pristine flow and sediment conditions in the catchment. More recently, the topic has received increasing attention because of a growing awareness of its crucial importance in establishing habitat diversity in streams. An issue that has puzzled geomorphologists for a long time is the ubiquity and persistence of pool-riffle sequences in rivers with different slopes and substrate conditions. The morphodynamic analysis bridges the gap between observations and current theories based mainly on hydrodynamic information. These findings provide the support for a physically based, integral description of pool-riffle morphodynamics and highlight the importance of flow and sediment variability on pool-riffle self-maintenance. The results show that self-maintenance occurs more frequently than previously thought as a result of grain sorting and that erosion or deposition of contiguous riffles also constitutes a self-maintenance mechanism. Two effects that have been only marginally explored in the past, i.e., bed sediment sorting and downstream riffle control, are explained and quantified with the help of the model's outputs. After showing the model's ability to describe the general reach hydrodynamics and morphological evolution over 1 year, the detailed sediment and flow information is used to investigate pool-riffle dynamics in terms of self-maintenance mechanisms. The model is first applied to a pool-riffle sequence on a 1.1 km reach of the lower Bear Creek, Arkansas, United States. This paper uses an unsteady 1-D flow-morphology and bed-sorting model to analyze pool-riffle dynamics. A lot less attention, however, has been paid to the coupled dynamics of flow and sediment, which is essential to fully understand these complex geomorphic systems. ![]() In the last few decades, significant advances have been made in characterizing and modeling the hydrodynamics of pool-riffle sequences, and this information has been extensively used as the basis of conceptual models to describe or infer pool-riffle morphodynamics. Pool-riffle dynamics is governed by complex time and spatial interactions between water and sediment flows.
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