The influence of flow acceleration on the stability of stones

Measurement of stability of stones in accelarated flow; follow up of the dataset of Dessens. An attempt is made to quantify the difference in velocity of the accelerated situation with the velocity of a uniform situation for which the same amount of stone movement would occur. With the help of the 7 stages of movement defined by Breusers (1969) a translation is made from the amount of moved stones in the experiments to the Shields number that represents this amount of movement. With this Shields (1936) parameter the critical velocity can be calculated for which this amount of movement occurs in uniform flow conditions. This velocity will be compared with the velocity measured in the experiments. A shift in velocities should occur between the average velocity of the accelerated flow and the average calculated velocity for a uniform flow.