ABSTRACT
The morphodynamics of a highly urbanized gravel-bed watercourse have been investigated to evaluate the influence of land-use change (hydromodification) on channel bed morphology. In-situ inter-event-based particle tracking, utilizing radio frequency identification tags, combined with event-based pressure-difference bedload sampling has revealed bed material pulsing and capture behind keystones on an increased annual frequency. Observations have also noted limited longitudinal movement of the coarsest size fractions yet there is an increased frequency and decreased spacing interval of intermediate pools formed between keystone clusters resulting from bed contraction. Results further show that the path lengths of the coarser particles are not sensitive to discharge magnitude. The evolving channel morphology in this historically riffle-pool dominated channel is emulating a step-pool morphology at a lower gradient. The observed channel bed evolution is interpreted as an additional mechanism of energy dissipation resulting from more frequent competent discharge events observed through these systems. The results may be applicable to other hydromodified watersheds that exhibit similar hydrologic characteristics, such as reaches downstream of hydroelectric facilities where hydropeaking practices are undertaken.
