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Abstract The effects of rigid ditch bank weeds/ vegetation on the flow parameters and the bed morphology were investigated. One hundred sixty-eight tests were conducted to study the impacts of different vegetation densities. Tests were run for three vegetation densities (1600, 400, and 178 stems/m2) along a fixed 4.00 m reach, against four different discharges, each with three different depths. The measured water levels, velocities and scour depths along the vegetated reach were analyzed. It was found that the existence of bank vegetation increased the water depth upstream of the vegetated reach and lowered it within the vegetated reach, when compared to the unvegetated case. The water’s velocity profile as a ratio to the unvegetated case (V/u) is sigmoid, i.e., the maximum velocity (V/u) max occurs in the lower half of the water column, increasing shear stress near the bed, and, in turn, the likelihood of bed erosion along the vegetated channel’s centerline. V/u increased with increasing vegetation density and Fro. Also, it is remarkable that the presence of bank vegetation increases scour around the center of the vegetated reach and reduces it near the vegetated bank. The change in both water level, velocity and scour depth is a function of vegetation density and channel geometry (Fr). Finally, a multiple regression analysis was done to assess the impact of ditch bank vegetation density on flow parameters and the canal’s bed morphology. Fourteen empirical equations were deduced to estimate the change in flow parameters and bed level due to ditch bank vegetation. |