Effects of vegetation on braided stream pattern and dynamics

Investigations using a 16 m by 2 m recirculating experimental flume model of an ephemeral braided river indicate that the presence of large and erosion‐resistant plants within the channel (e.g., trees or shrubs) can have a significant impact on channel pattern and planform dynamics. Simulations show that these plants have two effects. First, they act as obstructions, in some cases forcing the flow to divide. This flow separation can allow the deposition of a small island immediately in the lee of the plant splitting the channel. The net result is a substantial increase in the number of channels and, correspondingly, the braid index. This is in direct contrast to previous studies, where increased levels of vegetation in perennial streams have decreased the braid index. Second, the plants stabilize braid bars and can form relatively stable islands in their lee, significantly reducing the longitudinal migration of islands typically associated with braided rivers.