Current- and Wave-Generated Bedforms on Mixed Sand–Clay Intertidal Flats: A New Bedform Phase Diagram and Implications for Bed Roughness and Preservation Potential

The effect of bedforms on frictional roughness felt by the overlying flow is crucial to regional modelling estuaries and coastal seas. Bedforms are also a key marker palaeoenvironments. Experiments have shown that even modest biotic abiotic cohesion in sand inhibits bedform formation, modifies size, slows development, but this has rarely been tested nature. This study used comprehensive dataset recorded over complete spring–neap cycle an intertidal flat investigate dynamics controlled wide range wave current conditions, including wave–current angle bed cohesion. A detailed picture different types their relationship flow, be they equilibrium, non-equilibrium, or relict, was captured phase diagram integrates wave-dominated, current-dominated, combined bedforms. incorporates wider conditions than previous diagrams, related near-orthogonal angles, e.g. ladderback ripples. Comparison with laboratory-derived diagrams indicates washed-out ripples, lunate interference ripples upper-stage plane beds replace subaqueous dune field, which may characteristic flats. field data provide means predicting dimensions, can transferred other areas grain sizes. We show equation for prediction equilibrium size sufficient predict roughness, though highly variable character only half time. Whilst cohesive clay limited under active spring does play role reducing dimensions quiescent neap conditions. investigated combinations waves, currents, contents zone highest potential preservation geological record. shows lowest potential, presence moderate storm waves. Hence, absence combined-flow sedimentary successions cannot taken as evidence waves were absent at time deposition.