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Coupled Morphodynamic-Physical Habitat Modelling: MORPHED

Introduction to Morphodynamic Modelling:

Morphodynamic models and Landscape Evolution Models (LEMs) simulate the geomorphic response (typically of a catchment or a channel reach) to certain drivers (usually a minimum of climate and topography). The landscape (inclusive of a river channel) is represented with a topographic model, and at every time step a new topographic model is produced representing the products of erosion, deposition and storage.

Such models come in a variety of forms (see here for links to models), which are normally dictated by the model developer's research interests and coding experience. The distinction between morphodynamic models and LEMs is vague, but has largely to do with the temporal and spatial scope of the modelling. The term LEM implies modelling geomorphic evolution over longer time scales (e.g. 100's to 1000's of years) and does not necessarily include a hydraulic solution; whereas morphodynamic models often focus on the dynamics produced by individual hydrologic events over time-scales of hours to tens of years.

Belief in Importance of Geomorphic Dynamics to Fish:

There is a wide spread belief that the quality of physical habitat (for both flora and fauna) in riverine environments is a direct product of geomorphic dynamics and natural variability of flows. Morphodynamic models fully coupled to simple vegetation regeneration and growth models have been in circulation for at least a decade. The quality of physical habitat for fish in response to hydraulic and hydrologic variability has been studied and modeled extensively (ecohydraulics). However, we know of no examples of a fully coupled morphodynamic model to an ecohydraulic fish habitat model (please email me if you know otherwise). Such a model could give significant insight into the implications of geomorphic dynamics on physical habitat quality. Among the key physical requirements of such a model are:
  • Capability to assess fish habitat suitability changes through time in response to both hydrodynamics and morphodynamics
  • Produce a hydraulic solution (velocity and depth on a cell-by-cell basis) good enough to drive sediment entrainment, sediment transport, sediment deposition and an ecohydraulic fish habitat model
  • Produce a morphodynamic solution (i.e. mobile and changing bed) with emergent properties of morphological unit preservation, persistence and reproduction after destruction (i.e. dynamics of pool, riffle and bar morphology appears geomorphicaly reasonable)
Initially, I attempted to modify the CAESAR LEM (with the ooCAESAR project) to meet the above requirements. Owing primarily to unrealistic preservation and production of morphological units at a scale relevant to fish (third bullet above), the simple modification of CAESAR proved unfit for this purpose. As such, we have gone back to the drawing board and are in the process of developing a model specifically geared to meet the above requirements. Tentatively, I call it 'MORPHED' - Model Of Riverine Physical Habitat & Ecohydromorphic Dynamics. As the model is fundamentally concerned with capturing changes (Δ) and habitat dynamics defined by morphology, and the project itself morphed out of the ooCAESAR effort, MORPHED is a dually appropriate name. Details of the model will be forthcoming from this website.

Collaborators and Researchers on this Project:

Dr. James Brasington (Aberystwyth) is my primary collaborator on this project. Other collaborators include my PhD supervisors Professor David Sear (Southampton) and Dr. Steve Darby (Southampton), and Dr. Mike Bithell (Cambridge).

Relevant References:

  • Cox C, Brasington J, Richards K, Wheaton JM and Williams R. (Submitted). A Comparison of Cellular Automata Flow Routing Models. Earth Surface Processes and Landforms.