Recently Parker and Wilcock, and M. Hassan of the University of British Columbia, obtained a fascinating result from numerical experiments.  This result indicates that gravel-bed rivers subject to repeated hydrographs tend to develop armor layers that are essentially invariant over the hydrograph.  That is, the armor layer seen at low flow may be very similar to that during floods.  This numerical research builds on earlier experimental research by Wilcock and others.  The result is of value for stream restoration because it suggests that surface gravel samples at low flow can be used to characterize surface grain size distributions at flows where gravel transport is active.  The same formulation that indicates invariance of the surface layer also indicates that cyclic aggradation/degradation associated with the hydrograph should be restricted to a zone near the gravel feed point.  M. Wong and G. Parker have demonstrated this related result via both experiments and theory.  The results have been presented in two papers in refereed journals, as well as a long invited paper to appear in the proceedings of the Gravel-bed Rivers VI conference in Lienz, Austria, 2005.

Major accomplishments:

Papers

Parker, G., et al. (in press), Adjustment of the bed surface size distribution of gravel-bed rivers in response to cycled hydrographs, paper presented at Proceedings of the Gravel-bed Rivers VI Conference, Lienz, Austria, September 5-9, 2005 conference.

Wong, M., and G. Parker (2006), One-dimensional modeling of bed evolution of a gravel bed river subject to a cycled hydrograph, Journal of Geophysical Research Earth Surface, 111, doi:10.1029/2006JF000478.

Wilcock, P.R., and B. T. De Temple (2005), Persistence of armor layers in gravel-bed streams, Geophysical Research Letters, 32, L08402, doi:10.1029/2004GL021772.