Comparing the Cohesive Effects of Mud and Vegetation on Delta Evolution

Abstract

Cohesive sediment exerts a significant influence on delta evolution, increasing shoreline rugosity and decreasing channel mobility. Vegetation has been assumed to play a similar role in delta evolution, but its cohesive effects have not been explicitly studied. We use the model DeltaRCM to directly explore two effects of vegetation: decreasing lateral transport of sediment and increasing flow resistance. We find that vegetation and cohesive sediment do alter delta morphology and channel dynamics in similar ways (e.g., more rugose shorelines and deeper, narrower, less mobile channels) but that vegetation may have additional implications for deltaic sediment retention and stratigraphy, by confining flow and sand in channels. Our results suggest that sediment composition is a first-order control on delta morphology, but vegetation has a stronger influence on channel mobility time scales. To fully understand the cohesive influences acting on a delta, vegetation influence should be considered in addition to fine sediment.