To study water surface characteristics in strongly-curved bends in open channels, a flume was constructed at hydraulic laboratory of Ferdowsi University of Mashhad and was fully calibrated in several stages. The experiments could be carried out on 30°, 60° and 90° strongly-curved bend. Dictating conditions of strongly–curved bend, a ratio of curvature radius to channel width was chosen to be 1.5. Experiments were carried out on each bend with the given radius of curvature, considering at least 5 constant discharge values and extensive data were collected. Analyses of the data showed that in a distance equal to channel width from the bend entry and bend exit, water surface is not affected by bend. Also the ratio of super-elevation at bend entry and bend exit, to the downstream depth are not function of discharge and are almost constant for a bend with a given angle of curvature. Study of water surface at internal sections of bend revealed that in strongly-curved bends, water surface does not have a linear profile, and the transversal slope in these sections which are close to the inner bank in bend is rather much greater in comparison with outer bank. To evaluate change of water surface, a new equation is represented.

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