Wave ripples can provide valuable information on their formative hydrodynamic conditions in past subaqueous environments by inverting dimension predictors. However, these inversions do not usually take the mixed non-cohesive and cohesive nature of sediment beds into account. Recent experiments involving sand–kaolinite mixtures have demonstrated that wave-ripple dimensions and the threshold of motion are affected by bed clay content. Here, a clean-sand method to determine wave climate based on orbital ripple wavelength has been adapted to include the effect of clay and a consistent shear-stress threshold parameterisation. Based on present-day examples with known wave conditions, the results show that the largest clay effect occurs for coarse sand with median grain diameters over 0.45 mm. For a 7.4% volumetric clay concentration, the range of possible water-surface wavelengths and water depths can be reduced significantly, by a factor of three and four, respectively, compared to clean sand.

Meander chute cutoffs are a common and geomorphically important feature of meandering rivers. They exhibit complex dynamics and distinctive morphologic features. To date, however, the geomorphic processes governing the evolution and formation of these features are poorly understood due to limited knowledge of cutoff hydrodynamics. This paper investigates three-dimensional mean flow structure, turbulent flow structure, and bed shear stress distribution from high-resolution flow velocity data in a sediment-free physical model. The results show that 1) the chute channel conveys around 1.4 times the unit-width flow discharge as the cutoff bend; 2) mean flow structure is highly three-dimensional, with strong convective acceleration throughout the bends and pronounced flow separation zones in both the chute channel and the cutoff bend; 3) turbulent kinetic energy is intense at shear layers bounding the flow separation zones at several locations in the channel; and 4) bed shear stress is elevated due to strong turbulence in the chute channel and is low in the cutoff bend. The unique hydrodynamics of meander chute cutoffs explain their distinctive morphologic behaviors, including the rapid widening and deepening of chute channels and locations of bars and pools. Moreover, this paper quantitatively compares the secondary flow structure before and after the cutoff, showing that cross-sectional redistribution of streamwise momentum by secondary flow decreases due to more vertically uniform flow in the presence of the chute cutoff, suggesting lesser correction on the 2D depth-averaged hydrodynamics compared with the pre-cutoff single-channeled meander in numerical modeling.