The influence of shallow water on rock armour stability

The hydraulic stability of rock armour layers has been extensively discussed in the literature, with numerous formulae proposed for design purposes. However, limited attention has been given to armour stability under shallow water conditions, largely due to the scarcity of experimental data. This research aims to address this gap by providing new insights into the stability of rock armour layers with rubble mound breakwaters in shallow water. Hydraulic stability was determined for four different structure slopes and various hydrodynamic conditions, spanning from deep to extremely shallow water in presence of a 1V:30H foreshore. Newly experimental data were compared with existing stability formulae valid in shallow water, specifically those by van Gent et al. (2003, VG), Eldrup and Andersen (2019, EA), and Etemad-Shahidi et al. (2020, ES). Initially, the data were used to evaluate the accuracy of the original formulae. Following this, the formulae were recalibrated to account for the influence of shallow water, with data grouped according to water levels. Finally, modified versions of VG and ES formulae were developed to fit the experimental data, incorporating the effects of wave steepness to better capture shallow water dynamics. • Physical experiments on rock armour stability with a 1:30 foreshore from deep to extremely shallow water conditions. • Recalibration of the existing stability formulae on the new experimental data to account for the influence of shallow water. • The importance of incident wave steepness in predicting rock armour stability under very and extremely shallow water. • Modified versions of van Gent et al. (2003) and Etemad-Shahidi et al. (2020) stability formulae are presented.