How 3D Processes Drive Trench Infill and Sand Wave Regeneration After Dredging

Dynamic bedforms, such as sand waves, may pose a threat to offshore energy infrastructure. Due to their impact on seabed mobility, dredging is often required to reduce risks, for example, to avoid cable exposure. However, commonly used data‐driven methods cannot predict the evolution of partially dredged sand waves. Therefore, we apply a high‐resolution Delft3D FM model to reproduce the measured morphological evolution of a dredged cable trench through sand waves and quantify the 3D interactions between the dredged area and surrounding sand waves. Our simulations confirm that sand wave regrowth is driven by tide‐averaged vertical circulation. Remarkably, these circulation cells persist even over a flat trench bed because of the influence of adjacent nondredged sand waves. Trench infill results from gravitational modification of bed‐load transport over the trench side slopes, causing amplification, damping, and deflection of sediment transport. Because infill volume rates depend on slope steepness, sedimentation varies over time as slopes flatten and spatially with the surrounding sand‐wave bathymetry. In contrast to side‐slope steepness, trench width has little effect on infill volume rates. Temporal variations in the trench infill clearly follow the spring‐neap cycle. Although storm‐induced currents did not significantly increase trench infill rates, they cause preferential infilling on one side by altering tide‐induced transport asymmetry. The model reproduces the multiyear sediment balance over the trench well, with default model settings, showing its potential predictive capabilities. These process‐based insights help explain differences in recovery timescales between environments and trench designs.