Predicting river channel pattern based on stream power, bed material and bank strength

Abstract

Rivers exhibit a wide variety of channel patterns, and predicting changes in channel pattern is important in order to foresee river responses to climate change and river restoration. Many discriminators have been developed to define approximate boundary conditions for different channel patterns, based on channel-pattern-controlling parameters such as discharge and valley gradient. However, presently available discriminators have two main shortcomings. First, they perform poorly for rivers with cohesive, relatively erosion-resistant banks. For this subset, discriminators tend to indicate an actively meandering channel pattern, whereas the river morphology and dynamics show that many of these rivers should be classified as laterally stable. Second, channel pattern discriminators are often used to predict channel patterns, which is only valid when parameters are used that are independent of actual channel pattern. This condition is often not met, as many discriminators use the channel slope or width–depth ratio of the channel as input. To resolve both shortcomings, we first propose an additional class of rivers with scroll bars and tortuous channel patterns, which have an inhibited mobility due to their self-formed cohesive deposits. Second, we compare frequently used empirical and mechanistic channel pattern discriminators, taking into account the success in predicting channel pattern and the independence of causal factors used. Thirdly, we present a novel channel pattern discriminator and predictor that includes the effect of a cohesive floodplain, using the average silt-plus-clay fraction of the river banks as proxy. We show that this new predictor outperforms previously used empirical and mechanistic approaches, and successfully predicts channel pattern for 87% of the rivers from a dataset of 70. This new predictor is widely applicable, as it is relatively simple and based on easily obtainable, and mostly independent, parameters.

The fluvial architecture of buried floodplain sediments of the Weiße Elster River (Germany) revealed by a novel method combination of drill cores with two‐dimensional and spatially resolved geophysical measurements

“…Accordingly, in a diagram showing different fluvial channel types with respect to potential specific stream power and median grain sizes of the stream bed, Meilitz and Trebnitz plot between meandering and moderately braided, and Salsitz with currently two channels in the range of meandering with scroll bars (Kleinhans & van den Berg, 2011) (Figure 14a). This classification also holds true for a clay and silt content of the overbank deposits of 75% (Candel et al, 2020) (Figure 14b). Therefore, even moderate changes of the controlling parameters could have caused a shift towards more intensive meandering or braiding.…”

“…(a) Potential specific stream power and median grain size ( D 50 ) of the bed load of the studied sites plotted on the diagram of Kleinhans and van den Berg (2011) showing several formerly studied rivers (M = Meilitz, S [2CH] = Salsitz with currently two channels, T = Trebnitz). (b) Repeat of (a) but with channel patterns adapted for a medium silt + clay content of 75% (Candel et al, 2020): I = highly braided; II = moderately braided and meandering, scroll and chute bars; III = meandering with scroll bars; IV = tortuous, scroll bars; V = laterally immobile, no bars. Notes: (i) Potential specific stream power was calculated according to Kleinhans and van den Berg (2011) and MHQ was taken as channel forming discharge.…”

Rivers Try Harder. Reversed “Differential Erosion” as Geological Control of Flood in the Large Fluvial Systems in Poland

“…The pattern of geological setting, which we reveal in Figures 2-7 and idealized on the scheme in Figure 8, can be adopted as an environmental framework by hydrotechnical engineers who aim to develop instream river training [73,74]. Such a design practice faces a problem of too high stream power [39,[75][76][77][78][79][80][81][82][83][84][85] in the channel which leads to erosion. There are few concepts of energy dissipation of the stream.…”

Geomorphic responses of fluvial systems to climate change: A habitat perspective

“…At a given location within a fluvial system, a variety of geomorphic responses is possible depending on the magnitude of global warming and the associated hydrologic changes as influenced by the various basin and site‐specific physical characteristics (Figure 1). Possible geomorphic responses include changes in channel dimensions (e.g., enlargement or shrinkage), channel pattern, gradient, short‐term erosion and deposition, long‐term aggradation and degradation, bank erosion rates, channel migration rates, and channel stability (Ashmore & Church, 2001; Blum, 2007; Candel, Kleinhans, Makaske, & Wallinga, 2021).…”