Hydrodynamics of Flow Through Vegetation in Open Channels: A Review

The effect of vegetation is often an important consideration in hydraulic engineering. The design flowrate for hydraulic structures reflects the amount of overland flow and storage, both of which are affected by vegetal resistance. In open channels, the energy loss from the flow through and above vegetation affects the water surface profile, which could result in flooding. The velocity distribution, pressure distribution, and boundary shear stress distribution are also affected by the hydraulic resistance of the vegetation. Knowledge of these flow parameters is typically needed for the design of hydraulic structures. The density, extent, and type of vegetation present affect the capacity of water supply and flood diversion canals. Canals designed with earth linings can be susceptible to weed infestation, which can increase flow depth and lead to overbank flow or increased seepage, or which can create flow concentrations leading to increased erosion. The Research Institute for Weed Control and Channel Maintenance in Cairo, Egypt estimated that 10% of the earth-lined canal length in Egypt is infested with emergent weeds, and 50% is infested with submerged weeds (Balay, Gates and Khattab, 1992). Grass lining is frequently used in irrigation canals, spillways, terraces. and roadside ditches. The condition and type of the grass directly influence channel capacity and stability. As with earth-lined channels, weed maintenance plays a significant role in channel performance (Temple, Robinson, Ahring, and Davis, 1987).