Increased wave load on the Gudong seawall caused by seabed scour

Abstract

Seawalls play an important role in protecting coastal regions by resisting storm surge and waves. However, a seawall can cause seabed erosion at its foot by facilitating hydrodynamic scouring, but the effects of seabed scour on wave loads have not been sufficiently considered. This paper presents a case study of increased wave load on the Gudong seawall in the Huanghe delta, China, which has experienced serious erosion since its construction. Four commonly-used empirical formulas, which were also verified through our physical simulation experiments, were used to calculate the wave loads on the crown wall of the seawall based on observed wave conditions. The maximum allowable wave load on the seawall was also determined based on historical extreme sea conditions that caused severe damage to the seawall. Our calculations showed that, the wave load has increased at least two times since the seawall's construction due to seabed scour, and the present crown wall cannot resist large waves with a 5-year return period, much less than the 50-year return period it was designed to resist. This suggested that the reasonable design of seawalls needs to adequately consider seabed scour as well as the associated increase in of wave loads.