Author(s): Jinzhao Li; Meilan Qi; Yakun Jin
Linked Author(s):
Keywords: Post-damaged riverbed; Evolution; Steep slope; Two-dimensional model; Shear stress
Abstract: Riverbed is likely to be damaged in the natural conditions or due to human activities, which results in river morphology changed, and even the presence of extreme cases, such as crack or geological fault due to earthquake. Thus, riverbed evolution is different from natural evolution owing to flow structure around the damaged zone has changed. In order to facilitate research in this paper, the postdamaged riverbed is simplified as a triangular pit which has a steep slope appeared on the riverbed. This paper presents the investigation on riverbed evolution behavior in the vicinity of the pit in different flow conditions by experiments and numerical simulations. This study mainly focuses on explaining the mechanism of pit migration by measuring the shapes of the pit in different time during its development and numerical simulating the flow field in corresponding moment. Two kinds of flow conditions are included in experiments, clear-water and live-bed conditions. The experimental result under the former condition shows that the migration of pit is not obvious; the phenomenon in the latter condition shows that the upstream side slope of the pit moves forward and the downstream side slope is eroded, and the retrogressive erosion to upstream is not found. A vertical Two-dimensional standard k-ε turbulent model is used and its validation is achieved against experimental results of velocity field measured by an acoustic Doppler velocimeter (ADV). The results of the numerical simulation show that the longitudinal vortex in the pit hole develops to the bottom with migration of the pit and the velocity is small (<0. 1m/s) in the pit hole. The maximum value of bed-shear stress amplification τα appears at the upstream and downstream ends of the pit. This paper only analyzes one post-damaged riverbed form, for other riverbed forms in different flow and sediment conditions, this problem needs further studying.
Year: 2013