New challenges in erosion and sedimentation research: a Chinese perspective

摘要

Erosion may be classified according to the erosion agent into water erosion, gravitational erosion, glacial erosion, and wind erosion (aeolian erosion). Complex erosion caused by two or more agents can occur in watersheds and river corridors, producing unique features and causing new problems. Earthquake erosion represents the mass movements caused by earthquakes. The volume of sediment mobilised by earthquake erosion may be 10-100 times greater than that for other types of erosion. Nevertheless, only a very small fraction (<0.2%) of the sediment from earthquake erosion will be transported over long distances and it may therefore have little effect on fluvial processes in large rivers. Grain erosion is a phenomenon involving the disintegration or breakdown of bare rocks under the action of insolation and temperature change, the detachment of the constituent grains by wind, the downslope flow of grains under the influence of gravity and the accumulation of the grains at the toe of the mountain forming a depositional fan. Grain erosion can result in airborne particles and cause injury to humans, and has resulted in numerous slope debris flows. More effort needs to be directed to developing control strategies. Neo-tectonic activity can trigger landslides and avalanches, which dam rivers and initiate intensive fluvial erosion. A landslide dam may develop into a knickpoint, if it is stabilized by the long-term action of the flow. Large knickpoints can totally change the fluvial processes and river morphology. Bed load motion in mountain streams is complex and the available bed load formulae are in many cases not applicable. The measured and estimated rates of bed load transport can differ by several orders of magnitude. The measured bed load transport rate in the Diaoga River can vary by as much as 1000 times under steady flow conditions, as a result of the dramatic difference in the incoming sediment load and different degrees of development of bed structures. New theories and new formulae for bed load transport in mountain streams are needed. Eco-sedimentation is a new challenge in sedimentation studies. The biodiversity of benthic invertebrates highly depends on the stability and diversity of bed sediment. Pollutants in water may be adsorbed by suspended sediment and accumulate in the bed sediment bed. Benthic invertebrates can develop high concentrations of heavy metals due to their proximity to contaminated sediment. These new challenges represent new growth points of research on erosion and sedimentation in China and worldwide.