Evolution of a sediment wave in an experimental channel

Abstract

Abstract. The routing of bed material through channels is poorly understood. We approach the problem by observing and modeling the fate of a low-amplitude sediment wave of poorly sorted sand that we introduced into an experimental channel transporting sediment identical to that of the introduced wave. The wave essentially dispersed upstream and downstream without translation, although there was inconclusive evidence of translation late in the experiment when the wave was only 10-20 grain diameters high. Alternate bars migrated through zones of differing bed load transport rate without varying systematically in volume, celerity, or transport rate. Sediment that overpassed migrating bars was apparently responsible for dispersion of the wave. The evolution of the wave was well predicted by a one-dimensional model that contains no adjusted empirical constants. Numerical experiments demonstrate, however, that the theory does not predict sediment waves that migrate long distances downstream. Such waves can only be explained by the following processes not represented by the theory: selective bed load transport, spatial variations in bar and other form roughness, the mechanics of mobile armor, and perhaps other mechanisms.

The dominance of dispersion in the evolution of bed material waves in gravel‐bed rivers

“…We used this model to predict evolution of bed material waves in our experiments and field studies. All three models predict strong dominance of dispersion over translation of waves in flows of high F, which are characteristic of gravel-bed channels (see Figure 8 in Lisle et al, 1997), and further impedance of wave translation when the amplitude is high enough (roughly at the scale of the flow depth or greater) to create significant backwater effects.…”

“…Numerical models using these equations have been derived for aggradational profiles downstream of an increase in sediment supply, and similar approaches are borrowed for bed material waves, which include the upstream limb of an aggradational profile. These models are described fully elsewhere (Lisle et al, 1997;Cui and Parker, in preparation;Dodd, 1998). We can identify factors that influence dispersion and translation from an equation that can be derived from Equations 1-5 and applied to sediment-wave evolution, even without an analytical solution.…”

“…Lisle et al (1997) introduced a bed material wave into an experimental channel (average F D 0Ð90) carrying a relatively high sediment load. The wave dispersed symmetrically, although a delta such as depicted in Figure 1B was not observed, probably A well-documented field example is provided by a bed material wave that originated from a landslide that entered the Navarro River in northern California in 1995 Sutherland et al, 1998) (Figure 2).…”

“…Equation 13 in Pizzuto's model (Lisle et al, 1997), which is equivalent to Equation 6 in this paper, is solved using step-backwater methods to determine the velocity and depth for steady, gradually varied flow. Dodd (1998) uses the McCormack finite-element approximation (Chaudry, 1987), which is a coupled solu tion assuming the existence of unsteady flow.…”

Simulating Transient Sediment Waves in Aggraded Alluvial Channels by Double-Decomposition Method

“…Soni (1975) conducted aggradation experiments in a laboratory flume subjected to a wide range of sediment loading at the upstream end of the flume and recorded bed elevation changes. Many laboratory flume flow and sediment transport experiments are summarized in Lisle et al (1997). Field studies of sediment transport have also been conducted by Langbein and Leopold (1968), Wathen and Hoey (1998), and Lisle et al (2001), among others.…”