资源环境科技发展态势分析平台

Recent studies reveal that low‐slope bedrock reaches (bedrock surface slope milder than ~ 5 m/km) are more common than previously thought and can be found in engineered rivers and densely populated deltas. Here we present a novel formulation of alluvial morphodynamics of low‐slope bedrock rivers transporting non‐uniform bed material that accounts for the non‐uniformity of the sediment size and the presence of small scale bedforms such as dunes, and can thus be of aid to solve management/restoration problems in low‐slope bedrock rivers. The formulation is implemented in a one‐dimensional morphodynamic model. Numerical results are compared with laboratory experiments on equilibrium bedrock reaches downstream of stable alluvial‐bedrock transitions. The differences between experimental and numerical results are comparable with those obtained in the alluvial case. Model applications simulate 1) bedrock reaches with a stable bedrock‐alluvial transitions, 2) an alluvial‐bedrock transition subject to sea level rise and 3) steep bedrock reaches. Upstream of a stable bedrock‐alluvial transition the flow decelerates in the streamwise direction with the formation of a stable pattern of downstream coarsening of bed surface sediment. In response to sea level rise, alluvial‐bedrock transitions migrate downstream and bedrock‐alluvial transitions migrate upstream. Opposite migration directions are expected in the case of sea level fall. When applied to steep channels the model predicts gradual alluviation, but it fails to reproduce runaway alluviation.