Physical modeling of sandbar dynamics to correlate wave-induced pore pressure gradient, sediment concentration, and bed-level erosion

In coastal areas, it is important to understand the surf zone sandbar dynamics. This involves the interactions between waves and sediment during wave breaking. In this study, pore pressure gradients, sediment concentration, and erosion patterns were explored using a scaled-down artificial sandbar. Ten experimental sandbar formation cases with D50 = 0.33 mm were tested, comprising two different compaction conditions and five different wave steepness. The results showed a consistent horizontal pore pressure variation for each experimental case. However, as sediment depth (z′ ≥ 3.5 cm) increased, there was a distinct pore pressure amplitude attenuation with a simultaneous rise in the phase lag. Loosely compacted sandbar formations exhibited an average 1.3 times higher maximum vertical pressure gradient than medium-dense formations. The phase-averaged sediment concentration beneath the wave crest was significantly higher than the trough. The erosion volume of the sandbar under loosely compacted conditions exhibited a strong correlation (R2=0.84) with the average sediment concentration. A strong dynamic correlation (R2=0.89) was established between the maximum phase-averaged vertical pressure gradient and sediment concentration under the same conditions. These significant inter-correlations contribute to enhancing the current understanding of erosion prediction in surf zone sandbars.