Experimental study on fluid energy reduction through a flood protection forest

Abstract

A flood protection forest is a conventional river‐management measure that can fit well into the natural environment. This study focused on single‐line tree models placed laterally across open‐channel flows. We conducted horizontal particle image velocimetry (PIV) and drag force measurements in a laboratory flume to examine the reduction efficiency of mean kinetic energy due to the tree members. The results showed that the flow structure is related closely to a wake phenomenon for sparsely arranged trees, whereas it is similar to a jet for a dense arrangement. It was found that the drag force is related to the separation zone downstream of the trees. In particular, two neighbouring high‐speed streaks can merge and become a uniform flow. The characteristic length of this process and incident velocity define the drag force. Furthermore, a semi‐theoretical formula was developed that was found reasonable in predicting energy reduction efficiency.