Exceptional river gorge formation from unexceptional floods

An understanding of rates and mechanisms of incision and knickpoint retreat in bedrock rivers is fundamental to perceptions of landscape response to external drivers, yet only sparse field data are available. Here we present eye witness accounts and quantitative surveys of rapid, amphitheatre-headed gorge formation in unweathered granite from the overtopping of a rock-cut dam spillway by small-moderate floods (~100–1,500 m3 s−1). The amount of erosion demonstrates no relationship with flood magnitude or bedload availability. Instead, structural pattern of the bedrock through faults and joints appears to be the primary control on landscape change. These discontinuities facilitate rapid erosion (>270 m headward retreat; ~100 m incision; and ~160 m widening over 6 years) principally through fluvial plucking and block topple. The example demonstrates the potential for extremely rapid transient bedrock erosion even when rocks are mechanically strong and flood discharges are moderate. These observations are relevant to perceived models of gorge formation and knickpoint retreat

Sediment Yield in Mountain Basins, Analysis, and Management: The SMART-SED Project

Sediment yield from mountain basins and solid transport in rivers are widely studied and still represent a major issue when dealing with hydrogeological hazard. The correct determination of flooding scenarios involving huge amounts of debris also has implications for cities and human infrastructure safety. However, studies focused on catchment scale modeling tend to decouple the hydraulic processes from the sediment yield processes. Indeed, a large amount of hydraulics research literature has focused on hydro-morphological river models in which the sediment yield must be provided only as a boundary condition. This approach has clear limits, and decoupling such processes could lead to a weak understanding of the complexity of interactions within the watershed. To overcome such limitations, a new approach is proposed. The project we present aims to develop a complete model able to simulate sediment yield: from slope erosion down to in flow transport. The use of innovative mathematical approaches seeks to improve accuracy and performance over classical models and to find a right balance between computational cost and detailed description of physical processes. The model relies mainly on preexisting geographic databases to retrieve data. A set of test synthetic cases are also presented in the final part of the work