Comment on “Wave climate, sediment supply and the depth of the sand-mud transition: A global survey” by D.A. George and P.S. Hill [Marine Geology 254 (2008) 121-128]

An extensive dataset of sediment grain size and wave conditions in the Ebro Delta (NW Mediterranean) is used to verify the local scale applicability of the work of George and Hill (George, D.A., Hill, P.S., 2008. Wave climate, sediment supply and the depth of the sand-mud transition: a global survey. Mar. Geol., 254, 121-128) on the definition of the sand-mud transition (SMT). The proposal of using either a mean grain size of 63 μm or a mud content of 25% to define the presence of the sand-mud transition was locally verified (96% well-classified of a total of 382 samples). However, determining the depth of the sand-mud transition (hSMT) based only on the wave height shows several practical and conceptual inconsistencies that could be partially solved by including the wave period into the equation. On the Ebro Delta shelf, the use of the across-shelf distribution of skin friction accurately predicts the hSMT.