Channel Avulsion Dynamics in Meandering Rivers

Abstract

Meanders and avulsions are common in many rivers. The associated channel migration involves progressive changes of channel position over time (meandering) as well as abrupt and rapid changes (avulsions). Abrupt changes tend to be unexpected and unpredictable.Both situations involve dynamic processes. During meandering there may be a dynamic equilibrium among the factors driving the meandering process, with continual adjustments taking place. Avulsions cause rapid sequential changes that create disequilibrium of channel conditions and unbalanced channel dynamics. Avulsions form new channels and alter or abandon former channels within a short time. Thus, avulsions have major consequences in meandering rivers.The dynamic processes of meanders and avulsions are discussed, with particular attention to factors that may trigger avulsions. A preliminary evaluation scheme is presented for meanders with avulsions. It is based on three phases of avulsion: (1) avulsion set-up phase, (2) triggering phase for avulsion to occur, and (3) post-triggering adjustment phase. Major factors include river sediment load and rate, channel type, river gradient, channel sinuosity, meandering evolution, floodplain connectivity, presence and density of former channels, bank stability, channel incision, channel hard points, and flow deflection ability.

Temporal and spatial adjustments of channel migration and planform geometry: responses to ENSO driven climate anomalies on the tropical freely‐meandering Aguapeí River, São Paulo, Brazil

“…In meandering rivers, neck cutoffs, chute cutoffs and avulsions are often a response to a large flood event (Slingerland and Smith, ; Camporeale et al ., ; Coles and Klingemann, ). Regardless of their cause, the abandonment of channels here has reduced sinuosity by straightening the river and increasing the meander wavelength (Tables I and II).…”