Physical model of scour at the toe of rock armoured structures

Toe structures are a common feature in coastal rock armoured structures, both safeguarding the structure against scour at the toe and providing support to the armour layer. The toe structure itself is often comprised of rocks as well. Hence, generally some form of scour protection, such as a filter layer or a geotextile, is applied underneath the toe structure. Currently, there is a lack of available methods to judge the necessity of these kinds of costly scour protection measures underneath the toe structure. In this paper, a unique data set from physical model tests of scour at the toe of rock armoured structures is presented. The bed level change is measured by a laser scanner across the entirety of the sand bed, including underneath the structure. Additionally, the temporal development of the scour at the glass wall of the flume is measured using an innovative combination of video imagery and a deep learning algorithm. The sand diameter is not varied in the physical model tests. In all tests, scour was observed both in front of the structure and underneath the structure. Two expressions have been derived that give estimates for both kinds of scour, and thus can give insight into the necessity of scour protection underneath the toe structure.