While most of the world's large rivers are heavily engineered, channel response to engineering measures on decadal to century and several 100 km scales is scarcely documented. We investigate the response of the Lower Rhine River (Germany‐Netherlands) to engineering measures, in terms of channel slope and bed surface grain size. Field data show domain‐wide incision, primarily associated with extensive channel narrowing. Remarkably, the channel slope has increased in the upstream end, which is uncommon under degradational conditions. We attribute the observed response to two competing mechanisms: bedrock at the upstream boundary increases the channel slope over the upstream part of the alluvial reach to compensate for the reduction of net annual sediment mobility, and extensive channel narrowing reduces the equilibrium slope. Another striking feature is the advance and flattening of the gravel‐sand transition, suggesting its gradual fading due to an increasingly reduced slope difference between the gravel and sand reaches.
Primary controls of channel response in an alluvial river system are the flow duration curve, downstream base level, and grain size-specific sediment supply (
Human intervention makes river channels adjust their slope and bed surface grain size as they transition to a new equilibrium state in response to engineering measures. Climate change alters the river controls through hydrograph changes and sea level rise. We assess how channel response to climate change compares to channel response to human intervention over this century (2000–2100), focusing on a 300‐km reach of the Rhine River. We set up a schematized numerical model representative of the current (1990–2020), non‐graded state of the river, and subject it to scenarios for the hydrograph, sediment flux, and sea level rise. We conclude that the lower Rhine River will continue to adjust to past channelization measures in 2100 through channel bed incision. This response slows down as the river approaches its new equilibrium state. Channel response to climate change is dominated by hydrograph changes, which increasingly enhance incision, rather than sea level rise.
Tsunamis, impulse waves and dam-break waves are rare but catastrophic events, associated with casualties and damages to infrastructures. An adequate description of these waves is vital to assure human safety and generate resilient structures. Furthermore, a specific building geometry with openings, such as windows and doors, reduces wave-induced loads and increases the probability that a building withstands. However, waves often carry a large volume of debris, generating supplementary impact forces and creating "debris-dams" around buildings, thus limiting the beneficial effects of the openings. Herein, a preliminary study on the 3D effect of debris-dams on the post-peak wave-induced loads under unsteady flow conditions is presented based on laboratory experiments. Both wooden logs (forest) and shipping containers were tested, showing a different behavior. Shipping containers were associated with severe impact force peaks, whereas the interlocking nature of forest-type debris provoked a compact "debris dam" leading to higher and longer-lasting hydrodynamic forces. The arrangement of the debris This material may be downloaded for personal use only. Any other use requires prior permission of the American Society of Civil Engineers. also had an influence on the resulting structural loading. All tested scenarios were analyzed in terms of horizontal forces, cantilever arm and impulse acting on the building. This study presents a methodology to support the evaluation of post-peak debris-induced loads for the design of safer resilient buildings.
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