River relocation, or avulsion, is a fundamental process that fi lls alluvial basins. However, it is diffi cult to predict avulsion patterns because the landscape conditions associated with different avulsion styles are currently unknown. Two end-member avulsion styles have been documented in modern rivers: progradational avulsions, during which signifi cant fl oodplain deposition occurs as a new channel is built, and incisional avulsions, during which fl oodplain erosion captures fl ow from a parent channel. Here we propose that avulsion style is related to the tendency for overbank fl ows to erode or deposit sediment (i.e., fl oodplain morphodynamics). We present a scaling comparison of fl oodplain erosion and deposition rates, test it with morphodynamic modeling, and show fi eld data from ancient deposits that are consistent with modeling results. These results demonstrate that fl oodplain morphodynamics may determine how rivers relocate and that assessing the relative infl uence of fl oodplain erosion and deposition may be useful for predicting sedimentation patterns in avulsive systems.
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