Author(s): Lu Wang; Ruihua Nie; Chao Liu
Linked Author(s): Lu Wang
Keywords: Sediment-related disasters; Mountain rivers; Flash floods; Bed degradation; Grade control structures
Abstract: In the past decades, the sediment flux of many rivers around the world has varied significantly due to climate change and increasing human activities such as river damming, sediment bed mining and river training. The former generally increases the sediment supply in mountain rivers, causing bed aggradation to increase the water level and amplify flood disasters. The latter may lead to bed degradation which can cause general scour at instream structures to threaten their stability and safety. In the past 60 years, half of deadly flash flood disasters in China occurred in areas early identified as “low risk” by traditional method only considering flow process. A main reason for the inaccuracy is the limited understanding on the riverbed responses to sediment supply variation. Also, a series of recent river disasters show that strong human disturbances may cause serious bed degradation in a short period (termed as rapid bed degradation) in mountain rivers, significantly endangering the stability and safety of river embankments, instream or river-crossing infrastructures (e.g., sills, weirs, pipelines, culverts, bridge piers) and waterway. Based on field survey, flume experiments, theoretical analyses, the present study has found the prone-channels of sediment-related flash flood disasters, illuminated the corresponding key fluvial process in those channels, proposed the basic equation of riverbed morphology to sediment supply variation, and developed two early identification methods (mechanism-based and data-driven) for sediment-related flash flood disasters. Also, based on flume experiments, field survey and theoretical analysis, the present study revealed the mechanism of rapid bed degradation due to sediment supply reduction and base level fall in mountain rivers, proposed design method and recommendations for sequential grade control structures in rapidly degrading mountain rivers. The findings of the present study have improved the understanding of sediment related disasters in mountain rivers, and provided theoretical and methodological support for disaster mitigation in mountain rivers.
Year: 2024