Wave climate, sediment supply and the depth of the sand–mud transition: A global survey

The influences of wave climate and sediment supply on the depths of sand–mud transitions (hSMT) are investigated. Depths of sand–mud transitions (SMT) are based on published granulometric data from surface samples gathered from 14 sites in different wave-dominated coastal environments with fluvial input, including high energy (Columbia, Eel, Russian, San Lorenzo, Copper, and Nepean rivers), moderate energy (Ebro, Nile, Santa Clara, Tseng-wen and Kao-ping rivers), and low energy (Po, Pescara and Tronto rivers) regimes. Geometric mean diameter (GMD) and mud percent are compiled from samples along shore-normal transects, and significant correlation is found between these two textural descriptors. Nominally, the SMT is defined as the transition from GMD > 63 µm to < 63 µm. The correlation between mud percent and GMD permits an alternative, complementary definition of the SMT as the transition from < 25% mud to > 25% mud. This dual definition is applied to the 14 systems, and hSMT is tabulated for each system. Correlation is found between hSMT and the depth at which wave-induced bottom shear stress equals the critical erosion shear stress of the largest mud particles and also between hSMT and significant wave height. Lack of correlation between hSMT and sediment load of nearby rivers indicates either that the influence of sediment supply on depth of the sand–mud transition is small or is not adequately represented in this study. Shelf width and slope do not correlate with residuals from a formalized linear relationship between hSMT and significant wave height. The relationship between hSMT and wave climate is useful for calibration of numerical models of erosion and deposition in wave-dominated coastal environments, for prediction of seabed properties in remote or inaccessible areas, and for reconstruction of paleodepth based on facies changes from sand to mud in ancient rocks.