Bed load sediment transport in ephemeral and perennial gravel bed streams

Abstract

Perennial gravel streams are usually dominated by a bed material stratified in terms of grain size, with a coarse surface layer overlying a finer subsurface (Figure 1a). However, field observations from some ephemeral gravel streams in the Middle East and other locations exhibit the opposite stratification (Figure 1b).Recent studies have found that under the same range of flow strengths, such an ephemeral stream has a much higher transport efficiency of bed load sediment (the movement of particles by rolling and sliding on the bed, or by making short hops of a few grain diameters in distance), which suggests a completely different behavior from perennial streams [e.g., Laronne and Reid, 1993; Reid and Laronne, 1995].