چکيده
The increasing need for water resources and the improvement of water quality and quantity require us to research various river engineering issues. Riverbed shapes are an effective factor in creating turbulence, changing flow patterns, predicting stability, the dynamics of sediment particle movement, and resistance to their movement. Bed shape, or in other words, the various forms of roughness that are created in the riverbed due to sediment transport, which has a direct impact on calculating velocity, shear rate, and consequently resistance to flow. [3] Bed shape in the form of a series of pits and gullies is one of the important characteristics of sandy rivers. Gullies are formed in shallow parts of the flow by the accumulation of materials such as coarser sand, while pits are formed in deeper parts of the flow with finer-grained materials and less turbulence. Pits are prone to erosion, and gullies are suitable for the accumulation of transported particles.
Vegetation cover, by creating roughness in the walls of channels and floodplains of rivers, affects the geometric shape, hydraulics, and flow resistance in them, and consequently has a great impact on sediment transport. In rivers, vegetation cover is mentioned as a source of flow resistance and has been periodically removed to reduce the risk of flooding in high flows. This is while vegetation cover is an essential component of river ecosystems by providing valuable ecological services. [1] Therefore, understanding the interaction of bed shape with vegetation cover of walls in calculating flow characteristics and predicting sediment transport parameters plays a significant role in river engineering projects.
Bed shape geometry, including surge, plays an important role in calculating river engineering parameters, including friction coefficient, sediment transport, and Shields parameter. The surge geometry depends on the entry and exit angles of the bed shape, bed crest characteristics, sediment particle size, and interaction with vegetation formed on the bed or on the river wall. Accordingly, it is necessary to investigate the interaction of the geometry of the weir and the vegetation cover of the wall on the characteristics of the turbulent flow, including the velocity distribution and the distribution of the stress tensor components.
