Fig. 1: Temporal evolution of bedforms towards a locked end state.

a Bedform troughs were continuously tracked both before (blue) and after clay additions (red). After the addition of clay, bedforms slow and eventually lock in place. Red horizontal lines indicate immobile bedforms (i.e., celerity = 0). b Red and blue points represent bedform celerities calculated for the trough locations shown in a, while the solid black line represents the accumulation of clay within the bed. As the clay accumulates, the bed temporally locks (celerities approach zero near 250 h) and then bed movement restarts due to upstream turbulent fluctuations. The bed relocks after sufficient clay accumulates in the bed (near 410 h). c From top to bottom, images showing clean bed mobile bedforms (50 h), post clay addition partially mobile bedforms (300 h), and locked bedforms (450 h), respectively. Images have been color matched to aid in visualization of the clay layer. Under conditions of high bed sediment transport rates, ongoing sand transport leads to a segregated end state with mobile bedforms propagating over a layer of deposited clay. However, in cases dominated by stabilization, extensive clay deposition within bedforms produces a locked end state.