Experimental study of bed formation by groins under submerged and un-submerged conditions.

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Mohammad Reza Majdzadeh Tabatabai, Sahar Amini Sola, Mohammad Reza Kavianpour, Kamal Amini Sola, Saeedeh Amini Sola

Wednesday 1 july 2015

12:15 - 12:30h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) River morphodynamics

Parallel session: 9B. Sediment - River

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Now-a-days, with advances in science and technology and development of the river training techniques, various solutions have been developed for river protection, including installation of groins. Groins are installed at the riverbank with different angles to the bank. Since they intersect with the flow, the flow velocity increases and hence, a scour hole may establish in front of it, which may put the structure at failure risk. Therefore, the scouring pattern in front of the structure is of considerable importance. In this study, a series of groins in attractive, perpendicular and repulsive types (arrangements) were experimentally studied. Experimental study of the scour pattern in front of the groins was performed using a horizontal wide flume, 6m long, 1.6m wide and three different discharge values of Q=120lit/sec, 100lit/sec and 80lit/sec. The submerged ratio was 1.15 and the un-submerged ratios were 1 and 0.94. The bed of the Flume was filled with uniform fine aggregates (average diameter of 2.5mm) for a thickness of 20cm. The groins were arranged in three different relative distance (ratio of distance between groins S to groin length L) of S/L=1, 1.5 and 2, each with three installation angle of _=45º, 90º and 135º. Therefore, the performance of the groins was investigated under 27 experiments. Flow depth and discharge were measured in the upstream, according to the submerged ratios and the scour dimensions were continuously monitored. After 2 hours, scour dimensions (width, depth, length) reached the equilibrium condition. Bed topography measurements were made at the end of each experiment after draining water from the flume. Bed deformation was observed only between the first two groins, however, no significant changes are observed in other parts of the bed. Maximum scour hole depth was occurred just downstream of the first groin. However, by increasing the groin distance, the bed changes are also decreased so that no bed changes may be noticeable adjacent to the third groin for longer distances between the last two groins. Finally, relations were developed for stable scour dimensions (depth, length and width) with Froude number of flow, relative distance and location of the groins. Keywords: Groin, River protection, River morphology, Scour, Bed deformation