Morphodynamics: Rivers beyond steady state

Abstract

The morphology of an alluvial river channel affects the movement of water and sediment along it, but in the longer run is shaped by those processes. This interplay has mostly been investigated empirically within the paradigm of Newtonian mechanics. In rivers, this has created an emphasis on equilibrium configurations with simple morphology and uniform steady flow. But transient adjustment, whether between equilibrium states or indefinitely, is to be expected in a world in which hydrology, sediment supply, and base level are not fixed. More fundamentally, water flows and all the phenomena that accompany them are inherently unsteady, and flows in natural channels are characteristically nonuniform. The morphodynamics of alluvial river channels is the striking consequence. In this paper, we develop the essential connection between the episodic nature of bed material transport and the production of river morphology, emphasizing the fundamental problems of sediment transport, the role of bar evolution in determining channel form, the role of riparian vegetation, and the wide range of time scales for change. As the key integrative exercise, we emphasize the importance of physics-based modeling of morphodynamics. We note consequences that can be of benefit to society if properly understood. These include the possibility to better be able to model how varying flows drive morphodynamic change, to understand the influence of the sediments themselves on morphodynamics, and to recognize the inherent necessity for rivers that transport bed material to deform laterally. We acknowledge pioneering contributions in WRR and elsewhere that have introduced some of these themes.

Large wood recruitment and transport during large floods: A review

“…In other words, each flood event (characterized by flood volume, duration, and peak discharge) derived from hydrological modelling ideally has to be translated into flow characteristics, bedload transport rates/volumes, and morphological changes by means of 1D and 2D hydraulic and morphodynamic models (the latter if actually applicable, considering the large uncertainties inherent in these models when bank erosion processes are to be captured, Church and Ferguson, 2015), as well as into LW transport rates and volumes. For example, within the integrated hydromorphological framework called 'IDRAIM', Rinaldi et al (2015) proposed a simplified, guided procedure to assess the likelihood (two classes, high or low) of LW-related obstructions forming during large events, in combination with morphological changes driven by sediment dynamics.…”

A global distributed basin morphometric dataset

“…To understand how the natural surface has grown into its current state 1–4 , what it will become 5 , and in which way it impacts the environment 6–12 , we need distributed geomorphological data at global scale. The most commonly cited geomorphological features, listed in Table 1, were defined nearly 20 years ago, while currently a number of global or regional gridded topographic datasets 13–16 are available to support newly derived geomorphological features.…”

Dramatic undercutting of piedmont rivers after the 2008 Wenchuan Ms 8.0 Earthquake

“…The resulting loose materials also induced subsequent landslides and debris flows in the mountain regions3. Observing the fluvial and geomorphological processes after such a strong earthquake is of both practical and academic importance456.…”