UC Davis

Research regarding self-maintenance of pool-riffle river morphology has focused on hydraulics within individual pool-riffle couplets. Here, we make a scientific leap from one site on river to 702 pool-riffle couplets across northern California to understand the frequency of the foundational velocity-reversal hypothesis. A geometrical, mass and energy conservation-based velocity reversal criterion was used to predict the occurrence of a velocity reversal. Only 18% of all couplets met the established criteria indicating a velocity reversal. At locations with riffle-to-pool bankfull width ratios greater than 1.2, more than 50% of couplets met velocity-reversal conditions. Velocity reversal pools were almost always (89%) associated with channel constrictions while riffles were typically (71%) associated with channel expansions, albeit less often. Therefore, across landscapes, it appears channel constrictions propagate velocity reversal maintenance. Phasing between width and depth variability is central to fluvial morphodynamics and ecology and must be considered in sustainable river eco-engineering.