Critical dependence of morphodynamic models of fluvial and tidal systems on empirical downslope sediment transport

Abstract

The morphological development of fluvial and tidal systems is forecast more and more frequently by models in scientific and engineering studies for decision making regarding climate change mitigation, flood control, navigation and engineering works. However, many existing morphodynamic models predict unrealistically high channel incision, which is often dampened by increased gravity-driven sediment transport on side-slopes by up to two orders of magnitude too high. Here we show that such arbitrary calibrations dramatically bias sediment dynamics, channel patterns, and rate of morphological change. For five different models bracketing a range of scales and environments, we found that it is impossible to calibrate a model on both sediment transport magnitude and morphology. Consequently, present calibration practice may cause an order magnitude error in either morphology or morphological change. We show how model design can be optimized for different applications. We discuss the major implications for model interpretation and a critical knowledge gap.

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

“…To be successful, they require sufficient quantitative understanding of key mechanisms that result in the different channel patterns. Although there is general consensus within the scientific community on which mechanisms affect the channel pattern, we are still far from quantitively incorporating these mechanisms into a mechanistic model (Baar et al, 2019; Kleinhans, 2010; Kleinhans et al, 2018; Parker et al, 2007; Tal and Paola, 2010). Hence, empirical discriminators are used more widely (e.g.…”

Complementing scale experiments of rivers and estuaries with numerically modelled hydrodynamics

“…Firstly, the nondimensional mobility number allows for the comparison to natural systems (Kleinhans, 2010). Secondly, it provides vital insight into sediment transport fields and morphological activity, which is especially valuable for studying multi-channel systems and channel-bar margin interactions (De Vet et al, 2017;Van Dijk et al, 2018;Baar et al, 2019). For example, these data may be used to predict future locations of erosion and deposition ( Fig.…”

“…Firstly, real material is used with its inherent laws and properties, as opposed to numerical models that require many parameters and approximations of laws for water flow, sediment transport (e.g. Meyer-Peter and Müller, 1948;Van Rijn, 2007;Baar et al, 2019) and life forms (e.g. Baptist et al, 2007;Van Oorschot et al, 2016).…”

“…On the other hand, this practice differs from remodelling the morphological development of a scale experiment (e.g. Struiksma et al, 1985), which are subject to all the combined errors of sediment transport predictors (Baar et al, 2019). The extended integration of experimental data and a numerical model would not only expand the possibilities for data analyses of a series of experiment bed scans but would also open up fast methods of testing alternative experimental settings for either an experimental or idealised morphology.…”

A Universal Form of Power Law Relationships for River and Stream Channels

“…This is not surprising, since those reported exponents (dots in Figure 3c) result from far more complicated natural settings than the ideal configurations used in this study. Some of the variability in the reported exponents is possibly due to uncertainties in field observations and other factors that may affect the cross‐sectional shape, such as inhomogeneity of bed material (Leopold et al, 1964), lateral sediment transport (Baar et al, 2019), and bank strength (Eaton & Church, 2007; Eaton & Giles, 2009). The effects of these processes on the functional forms of the regime relationships deserve future studies.…”