Growth-decay model of vegetation based on hydrodynamics and simulation on vegetation evolution in the channel

Abstract

Hydrodynamic conditions are important controlling factors in the evolution of vegetation and ecosystems, especially aquatic ecosystems. This study established a conceptual vegetation evolution model to explore the succession law of vegetation patches in the effective area of a channel, including the evolution of vegetation coverage (Ce) and the corresponding longitudinal dispersion coefficient (Ke). 2D shallow-water equations were implemented to calculate flow variables, and the equivalent Manning coefficient was used to reflect the effects caused by vegetation patches. New vegetation emerged in regions where the bed shear stress is lower than the critical bed shear stress, whereas the original vegetation was removed in regions where the bed shear stress is higher than the critical value. Two typical cross-sections and two initial Ce were considered to better understand the succession trend of vegetation patches under different external conditions. The findings showed that Ce and Ke increased to a constant value with increasing simulation duration, whereas a higher critical bed shear stress, defined by the threshold value (TV), was linked to a higher final vegetation coverage (Cf) and final longitudinal dispersion coefficient (Kf). Furthermore, different initial vegetation distributions, including coverage and position, caused little effect on the Cf in the rectangular channel, but the Cf in the parabolic channel was linearly affected by the averaged bed shear stress at the initial patches. The maximum Kf in both channels occurred with regularly distributed initial patches on one side of the bank. The vegetation patches in all scenarios evolved from block-shaped to strip-shaped and finally formed a stable vegetated landscape. This conceptual vegetation evolution model will improve our understanding of the influence of hydrodynamic conditions on the vegetation evolution in aquatic ecosystems.