Effects of vegetation on gravel-bed river channel formation

• Main Author: Munir, Yasir
• Format: Other/Unknown Material
• Language: unknown
• Published: Delft : IHE Delft Institute for Water Education; 2023
• Subjects: river channel formation; river channel evolution; morphodynamic modelling; gravel-bed rivers; Delft3D; floodplain vegetation; taiga
• Online Access: https://doi.org/10.25831/ms22-hh03; http://cdm21063.contentdm.oclc.org/cdm/ref/collection/masters2/id/130055

Gravel-bed rivers are extremely dynamic systems. They are characterized by coarse bed material, relatively steep slopes, high flow velocity, and display a development of recurring bars transforming the river into a braided system. In addition to water and sediment supply, both flood plain vegetation and riparian vegetation play a role in determining the river planform due to their capacity of retaining sediment and stabilize bars and river banks. However, vegetation does not appear in most regime formulas describing the equilibrium river width and depth. This study aims to establish the effects of vegetation on the river channel formation focusing on the development process and, in particular, to determine if the final characteristics of vegetated channels retain the footprint of their initial conditions. The tool of investigation is a 2-dimensional morphodynamic model developed using the Delft3D version 4 software. This study extends the non-vegetated model developed by Paudel, et al. (2022) and adopts the Baptist (2005) approach to produce the effects of floodplain forest. Vegetation is manually added or removed to mimic colonization and eradication by the flow. Plants are represented as rigid cylinders, and the parameters such as height, diameter and spatial density are determined based on the features of pluvial and taiga forests. Twenty eight scenarios with different type of floodplain forest, initial channel width, discharge regime and sediment input rate are simulated. The relationship between vegetation characteristics and river morphology development is analysed focusing on channel width and planform evolution. One key finding of the study is that the density of floodplain vegetation has a significant impact on the final configuration of the river channel. The study found that dense pluvial floodplain vegetation significantly controls the final width and planform of initially narrow (30 m wide) channels. For the same initial width, the less dense taiga has similar effects with constant discharge but ...