Partial transport in a natural gravel bed channel

Abstract

Partial transport is documented in the gravel bed channel of Carnation Creek using magnetically tagged stones. For four flood peaks the active proportion of surface grains was used to map streambed areas into distinct units of three different levels of grain entrainment. In partially mobile regions of the bed, the active proportion of surface grains declines with grain size. As flow increases, areas of partial transport grow at the expense of inactive areas and fully active areas replace areas with partial mobility. Approximately 25–50% of the bed remained in a state of partial mobility during a flood with a 2‐year return period, indicating that inactive regions of the bed surface typically persist from year to year. During a flood with a 7‐year return period, surface grain entrainment was nearly complete, indicating that full mobilization of surface grains is not a frequent event.