There has been abundant research into the effect of tree roots on stabilizing river banks, and also on the effect of trees on bed-scour after they have fallen into the stream, but there is little research into the effect of instream logs on bank erosion. Here we develop the hydraulic theory that predicts local and reach scale bank erosion associated with instream logs with various configurations and distributions and conclude that individual log can increase local bank erosion, but multiple logs can reduce overall reach erosion. Where there is consistent bank strength, the local erosion varies in a non-linear way with the angle, size and position of the log. The reach scale effect of multiple logs depends on the distribution of logs and the proportion of the reach occupied by logs. Erosion effects of instream logs are difficult to measure. We are testing the above theory of erosion associated with instream logs in a series of anabranches of different sizes that experience consistent irrigation flows each year (on the Murray River in SE Australia). These channels have high erosion rates, abundant logs, and are like a giant flume that allows us to measure erosion processes, as well as hydraulics, in a controlled setting
