The role of vegetation on bankfull river morphodynamics

Abstract:

The exploration and definition of the dynamic equilibrium (typically characterized by the bankfull state) geometry of rivers are of great importance. The main use of it is to predict what variations are expected in a given section of the river. For example, how the slope, the bed content, or the width of the river section change, and how the formation of riverbeds can be predicted. In order to estimate the dynamic equilibrium state, it is essential to take into account morphodynamic phenomena, as well as the parameters characterizing the sedimentation, bed geometry, bed resistance, and water flow. In the literature, we can see the evolution of more and more precise procedures to do this. These procedures are often applicable for relatively vegetation-free settings, e.g. even for Martian. In the last decades, many field- and laboratory measurement- based investigations have shown that vegetation plays an essential role in maintining the dynamic equilibrium state. That is, further refinement of the procedures for estimating equilibrium-state parameters has become justified and has recently become an important research topic. However, due to complex processes, exploring the different impacts, including the vegetation, is a significant challenge. In this research, we attempt to reveal the effect of vegetation on the equilibrium geometry of rivers, in particular as it depends on surface-cover density. We are investigating questions as to whether denser vegetation can cause an increase in bed width. Does the effect of trees and grass differ in the case of bank stability? For example, we ask whether a floodplain covered in woody vegetation likely to be wider or narrower than that covered in grass. Our study is based on the examination of more than 150 river sections. The ultimate goal of the study is to establish relationships between vegetation features (e.g., surface-cover density) and equilibrium state parameters governing channel geometry. Then, with the support of these relationships, we attempt to improve methods for the estimation of equilibrium channel parameters that take vegetation into account.