Sand movement in a sand-bed scour hole

Scours are often observed at the bottom of bridge piers in rivers and they occur around a pole standing in sand and snow. The degradation and aggradation by wind occur in the front and back of the pole, respectively. In this study, we examined the sand movement around a cylindrical structure standing on the sand bed. The relationships among the height of the structure, the depth of the scour, and the velocity were elucidated by wind tunnel experiments. There are two types of scour conditions the clear water scour and the scour with continuous sediment motion (live-bed scour) we experimented under the former condition. In our experiment, a cylindrical structure was established on the sand in a wind tunnel, and the diameter and height of the cylindrical structure and velocity were systematically changed. The depth and radius of the scour were measured by a laser rangefinder and a video camera. Flow visualization around the structure was performed using a laser sheet. The results show that the main factors influencing the scour are velocity and aspect ratio (height/diameter), with a higher aspect ratio leading to an increased scour depth. At the conclusion of the study, we proposed a formula for estimating the scour depth using aspect ratio and velocity as parameters.