Channels in the Making – An Appraisal of Channel Evolution Models

Abstract

Over the past 30 years, fluvial geomorphologists have sought to understand the historical trajectory of channel adjustments after disturbance by developing channel evolution models (CEMs). These models use a combination of quantitative data and qualitative indicators to describe the spatial progression of channel evolution. This article surveys the historical development of CEMs, how they function, and what types of CEMs are best suited for different geomorphic settings. It describes the logic underlying classic CEMs, and their subsequent application to predict channel response following dam removal. After this, it recounts the emergence of multi-pathway CEMs, which have been used to capture the evolutionary trajectories in complex fluvial systems (e.g., anastomosing rivers). Lastly, it argues that a state-and-transition framework offers an appropriate modeling template to document channel evolution in a wide variety of fluvial systems, including those originally modeled using classic CEMs. A state-and-transition approach sees rivers as composed of interrelated process and form (morphological) states. They identify under what conditions a river channel would undergo a transition from one formal state to another (e.g., from a single-threaded to braided planform). They can also be used to understand the form-process dynamics underlying subtle morphological transitions that produce changes in a river's biogeomorphological structure without triggering wholesale river metamorphosis.

Principles of geomorphic disturbance and recovery in response to storms

“…However, later CEMs recognized that channels may adjust to disturbances in more variable and complex ways, depending on antecedent conditions and flux boundary conditions (e.g. Makaske et al, 2002;Hawley et al, 2012;Van Dyke, 2013;Toone et al, 2014, Brierley and. Cyclical models are also linear sequential, as they depend on environmental change or disturbance to return the system to its initial stage.…”

Complexity of Earth Surface System Evolutionary Pathways

“…This is best illustrated by the supplementation of linear stream channel evolution models with constructs allowing for multiple pathways (Phillips 2013b;Van Dyke 2013, 2016.…”

“…Similar outcomes with respect to evolutionary network complexity occur as linear or cyclical sequence models are expanded and elaborated to more strongly connected state-and-transition type models. Compare, for example, the linear fluvial biogeomorphic succession model of Corenblit et al (2009) with the state transitions identified by Rountree et al (2000), or the classic linear channel evolution models compared to more recent multi-path CEMs (Van Dyke 2013, 2016.…”

Graph theory in the geosciences

“…Alternative stable states are now recognized, for instance, in global climate (e.g., Overpeck and Cole, 2006;Holmes et al, 2011), and some traditional developmental frameworks such as channel evolution models have recently been expanded to include multiple states and pathways in a state-and-transition style framework (Van Dyke, 2013). These more complex patterns of change (as well as traditional linear and cyclical patterns) are readily represented, implicitly or explicitly, in a stateand-transition model (STM) framework.…”

“…Earthquake and climate networks have emerged as distinct subfields of seismology and climatology (Abe and Suzuki, 2004;2012;Peron et al, 2014), and extension of the state-and-transition model framework to geomorphology as a guiding conceptual framework has been proposed (Phillips, 2011a;2011b;Van Dyke, 2013). Connectivity, for the quantification and analysis of which graph theory methods represent a very promising approach, is now a critical issue in hydrology, geomorphology, and ecology.…”