Advances in the study of bedload sediment transport in gravel-bed rivers
Event details
| Date | 27.04.2010 |
| Hour | 12:15 |
| Speaker | Prof. André G. Roy, Chaire de recherche du Canada en dynamique fluviale, Département de géographie, Université de Montréal |
| Location |
CO 124
|
| Category | Conferences - Seminars |
Estimating bedload sediment transport is critical for the maintenance of river bed morphology and channel stability. In spite of its importance, bedload sediment transport is very difficult to measure and evaluate in situ. Several techniques provide measures at limited spatial and temporal scales, thus limiting their usefulness for estimating sediment transport rates and sedimentary budgets. This presentation has two objectives. Firstly, we will briefly review a set of techniques to measure bedload transport in rivers and will examine their potential and efficiency as a function of the objectives and spatiotemporal scales of the study. Several innovations offer new avenues in particular for monitoring the displacement of individual clasts. For example, passive transponders (PIT tags) and accelerometres are now used for an efficient tracking of pebbles in gravel-bed rivers and they are informative on the modes of transport. Secondly, we will present the results from two studies illustrating the usefulness of combining techniques and approaches to gain insights on the role of turbulence in the movement of particles as bedload and on the dynamics of a small gravel-bed river. In the first study, we have used video images taken simultaneously with measures of the flow velocity fluctuations with the objective of linking turbulent flow properties and the motion of particles. Results show that fluid acceleration and deceleration are critical variables to explain sediment transport events. The figure below shows that transport events of individual particles are generally associated with combinations of streamwise and vertical velocity acceleration values that are larger than those observed during periods without transport. In a second study, we have gathered observations in a 6 meter wide gravel-bed river from sediment traps, tagged particles, topographic measures of the river bed, erosion chains et bed markers assessing the active area of the bed during sediment transport events. Data show an intense and complex activity of bedload transport while the bed remained relatively stable. Our hypothesis to explain these dynamics is related to the dilatation and contraction of the sediments composing the river bed during floods.
Practical information
- General public
- Free
Contact
- Jean-Denis Bourquin