VELOCITY-REVERSAL HYPOTHESIS - A MODEL APPROACH

Hydraulic modelling of a riffle-pool-riffle sequence in a straight rea ch of Dry Creek near Winters, California, indicates that while at low flow the mean (section average) velocity at riffles exceeds that of an adjacent pool, during high flow the mean velocity of the pool exceeds that of adjacent riffles. This supports the velocity-reversal hypothe sis which is based on limited field measurements of near-bed flow velo city. A velocity reversal does not occur at the same discharge in both riffle-pool sequences modelled, and a more detailed explanation is ne cessary to account for complex aspects of channel form and process in riffle-pool sequences. Nevertheless, the velocity-reversal hypothesis helps to explain many of the observations and processes that operate i n the riffle-pool environment.