Flume experiments on wood entrainment in rivers

A flume experiment on entrainment of woody debris is carried out. Woody debris is modeled using smooth, cylindrical dowels, in touch with the flume bed. The water depth and velocity are evaluated that initiate the motion of the partially submerged dowels. On the basis of the experimental finding, a theoretical model of log entrainment is developed, providing in dimensionless form the equilibrium equation for incipient motion. The experiment shows that the equilibrium equation must keep into account the modification of the local water profile, affecting the force balance at incipient motion. This issue has been apparently neglected in the wood entrainment models so far developed. The entrainment model is less sensitive to the choice of the apparent drag coefficient. The capability of the model in predicting the critical log diameter for initiation of motion is discussed and compared with that from the recent entrainment model from Braudrick and Grant, 2000. The comparison shows interesting results and provide evidence of the needs for further studies on wood entrainment in rivers.