Abstract
Natural levees can be observed worldwide in nearly all river systems characterized by frequent flooding in combination with the transport of suspended bed material. Several parameters and processes have been suggested to explain the formation and the highly variable geometry of natural levees. However, the effect of bedforms migrating in the main-channel has not been amongst the studied parameters and processes. To fill this gap, this study investigates the relationship between bedforms and natural levee formation by flume experiments. Experiments were conducted in a 2 m wide and 30 m long sediment recirculating flume, monitoring the bed level elevation in the main channel by ultrasonic sensors as well as recording the levee development on the floodplain by a camera. The effect of different bed configurations on the developed levees is compared, and discussed, showing that bedforms could enhance levee formation.
Highlights
Natural levees are narrow elevated sediment deposits along the floodplain edge of compound channels
Natural levees are formed by suspended sediment which is transported from the main channel onto the floodplain edges; i.e. overbank flow is a prerequisite for the formation of natural levees and these morphological structures grow gradually with every flood event overtopping the levee crests
This paper examines the relationship between bedforms and natural levee formation
Summary
Natural levees are narrow elevated sediment deposits along the floodplain edge of compound channels. For example [7] related the diversity in levee geometry to different mechanisms of lateral sediment transfer They suggested that levees generated by turbulent shear between the main channel and floodplain exhibit a narrow and steep geometry while levees resulting from advective transport, caused by differences in the water surface elevation between the main channel and floodplain, tend to be wider and less steep. [8]) revealed a strong relation between overbank sediment transfer and the water depth ratio between the main channel and the floodplain.
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