Journal of Geophysical Research: Earth Surface
© 2014 American Geophysical Union
Impact Factor: 3.44
ISI Journal Citation Reports © Ranking: 2013: 24/173 (Geosciences Multidisciplinary)
Online ISSN: 2169-9011
Associated Title(s): Journal of Geophysical Research
River bed transport measurements show bed dilation and contraction
A new study of bed load transport-the movement of the gravel or other grains on a stream bed-has turned up a previously undetected effect. Marquis and Roy (2012) used several different methods to monitor bed load activity in a gravel bed river, Beard Creek, in Quebec, Canada. They examined stream flow, bed load, and bed morphology before, during, and after 20 flood events. They found that two of the methods-measuring changes in bed topography between successive floods and surveying bed activity-gave inconsistent results. Changes in elevation of the bed did not always correspond to movement of bed load. The authors believe that this can be explained by dilation or contraction of sections of the bed following a flood, as gravel grains can become more or less tightly packed, with the grain-grain interactions playing a key role. The dilation or contraction results from complex interactions between flow intensity, flood history, sediment supply, and the initial conditions of the gravel bed before flooding. The study is, the authors believe, the first reported observation of gravel bed dilation and contraction and highlights the need for future studies considering interactions between grains in the gravel bed when investigating bed load dynamics. It also shows that it is important to use multiple observational methods to get a complete picture of the bed load dynamics of a gravel-bed river.