Centennial Channel Response to Climate Change in an Engineered River

Abstract

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.

Semicentennial Response of a Bifurcation Region in an Engineered River to Peak Flows and Human Interventions

“…In the future, the impact of SLR on the bifurcation region will increase through backwater effects and associated upstream-migrating bed level adjustment. However, we expect that the increased probability of extreme precipitation and flow events associated with climate change (Klein Tank et al, 2014;Sperna Weiland et al, 2015) will affect the bifurcation region more strongly than SLR (Ylla Arbós et al, 2023). In addition, the sediment supply from the Niederrhein may coarsen further.…”

Large‐Scale Channel Response to Erosion‐Control Measures

“…The reduction of the upstream backwater effects given by a lower elevation of the fixed bed surface results in less sediment trapping upstream of the fixed bed, which implies less erosion mitigation over the upstream reach or, depending on the specific conditions, even channel‐bed incision. Operations to reduce the fixed‐bed surface elevation may need to be repeated over time, if the large‐scale channel‐bed incision that leads to fixed bed protrusion is expected to continue over the next decades (e.g., Ylla Arbós, Blom, Sloff, & Schielen, 2023; Ylla Arbós, Blom, White, & Schielen, 2023).…”

“…The latter consists of a gravel mixture of 6 and 15 mm in proportions of 30% and 70% in the substrate, respectively. This composition is loosely based on the characteristics of the gravel reach of the lower Rhine River (Ylla Arbós, Blom, Sloff, & Schielen, 2023; Ylla Arbós, Blom, White, & Schielen, 2023). The model bed surface composition has adjusted due to the narrowing (i.e., it has become slightly finer), though it remains coarser than the substrate sediment.…”

“…For simplicity, we use the same discharge in the constant discharge-mixed-size sediment case, as the definition of the dominant discharge for a mixed-size sediment case is less straightforward (Blom, Arkesteijn, et al, 2017). In the variable discharge cases, we use a 20-year cycled hydrograph (i.e., a repeated hydrograph of a 20-year duration with a daily frequency which is equal to measured data at Köln (river km 640) over the period [1967][1968][1969][1970][1971][1972][1973][1974][1975][1976][1977][1978][1979][1980][1981][1982][1983][1984][1985][1986], and is statistically representative of the long-term discharge conditions of the lower Rhine River (Ylla Arbós, Blom, Sloff, & Schielen, 2023;Ylla Arbós, Blom, White, & Schielen, 2023).…”

System‐Wide Effects of Local Bed Disturbance on the Morphological Evolution of a Bifurcating Channel Network

“…In single‐thread fluvial channels, their morphological evolution under disturbances has received extensive attention (Best, 2019; Wohl et al., 2015). With fixed channel width, the evolution of longitudinal profile of river channel under human interventions or natural changes has become the main focus (Blom, Arkesteijn, et al., 2017; Gao, Nienhuis, et al., 2020; Wang et al., 2008; Ylla Arbós et al., 2023; Zheng et al., 2022). This is basically built upon the in‐depth understanding of the equilibrium longitudinal profiles of river channels thus far (Blom et al., 2016; Chang, 1986; Ferrer‐Boix et al., 2016; Gao, Li, et al., 2020).…”