Numerical Modeling of Plant Root Controls on Gravel Bed River Morphodynamics

Abstract

The role of vegetation in shaping the geomorphology of rivers and deltas, along with tidal and estuarine environments, is widely recognized. While mutual interactions between flow, plant canopy, and morphodynamics have been extensively investigated, similar studies considering plant roots are limited. Here we present results from a numerical model that quantify the feedbacks of both the aboveground and belowground vegetation on gravel bed river morphodynamics. Plant root biogeomorphic feedbacks, that is, uprooting and root‐enhanced riverbed cohesion, are quantified through the description of the vertical root distribution. By investigating the evolution of the riverbed of a straight gravel channel with a vegetated patch, we show that uprooting is the primary plant root biogeomorphic feedback determining the evolution of the riverbed and the competing influence of the potential flow erosion versus uprooting depth mediates the plant root controls on morphodynamics. These findings broaden our understanding on the role played by plant roots on gravel bed river morphodynamics.

Morphodynamics of alternate bars in the presence of riparian vegetation

“…Moreover, the parametrization of vegetation mortality through uprooting may be too strict in this model (Bywater‐Reyes et al. ; Caponi and Siviglia, ; Edmaier et al. ; Perona and Crouzy, ).…”

“…The local influence of vegetation (stem scale) on the hydrodynamic and sediment transport is beyond the scope of the study's objectives. Furthermore, the effect of plant roots on soil cohesion and sediment entrainment conditions is not considered here as it affects marginally bed morphodynamics on non‐cohesive substrates (Caponi and Siviglia, ). The presence of vegetation, its characteristics and its evolution in different areas of the model domain are determined by a set of rules representing the main ecological processes regulating the life cycle of one type of vegetation representative of salicaceous species, i.e.…”

“…), which occurs when erosion exceeds root depth; see, for example, Bywater‐Reyes et al. (); Caponi and Siviglia (); Edmaier et al. () Perona and Crouzy () Erosion and deposition are recorded over 1 year from September 1st to August 31st, allowing vegetation to recover from partial burial or partial root exposure at the end of each growing season.…”

“…Conversely, in sparse vegetation, plants develop turbulent flow, which increases sediment transport (Yager and Schmeeckle, ). Riparian vegetation also has a stabilizing effect on river channels due to their root systems, which enhance sediment cohesion and prevent soil erosion (Caponi and Siviglia, ; Pasquale and Perona, ; Simon and Collison, ; Thorne, ). These mechanisms can have a profound impact on channel dynamics, such as triggering a shift from braiding to meandering planforms (Tal and Paola, ).…”

Management of vegetation encroachment by natural and induced channel avulsions: A physical model

“…In addition, numerical modelling may provide a suitable tool to evaluate the optimal location of artificial avulsions, test the effect of different amounts and positions of moved sediments, and identify the best anabranch to block and/or reopen. The ability of numerical models to include the effects of vegetation on sediment transport and morphological evolution is increasing rapidly (Caponi & Siviglia, ; Solari et al, ). Coupling vegetation dynamics with accurate bank erosion and channel avulsion is still a challenging task that requires state‐of‐the‐art modelling and thorough calibration.…”