Experimental Evaluation of the Discharge Capacity of Flow Constrictions by Check Dams in Mountain Rivers

Sebastian Schwindt, Mário J Franca, Anton J Schleiss

Wednesday 1 july 2015

11:45 - 12:00h at Oceania (level 0)

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

Parallel session: 9B. Sediment - River

Open (slit) check dams are a sub-category of check dams and may have filtering, sieving as well as dosing effects on sediment transport. The combination of an upstream reservoir in front of an open check dam is designated as bed load trap. These structures are crucial elements for flood protection in mountainous regions as the sediment transport capacity of mountain streams is tremendous, highly volatile and therefore an imminent danger for dwellers. The contemporary design criteria for openings of slit check dams originate from theoretical approaches, laboratory experiments or empirical experiences. A multitude of different opening types and shapes were studied and built, mostly based on design parameters which are related to grading curves of the river bed. However, in the light of experience, it is more convenient to relate the design to the hydraulic framework conditions of rivers, as the grain size may change for every event, depending on the source of the sediment. Starting with the basic geometry of a natural cross-section of a mountain torrent, in order to optimize the shape of the slit check dam openings, systematic laboratory experiments were run to evaluate the influence of this artificial flow constriction on the river equilibrium. The influence is then evaluated by a parameter _ which relates the undisturbed bed shear stress in a non-modified stream to the stress observed at a reference position in the bed load trap. Since _ exceeds a threshold value, depending on the river discharge, the check dam clogs. This article discusses preliminary the influence of the opening width and height on the parameter _.