The flow and spreading mechanism of three-dimensional negatively buoyant surface jets discharged on a sloping bottom was experimentally investigated by flow visualization and exhaustive temperature measurement. The flow gradually varies, through its running process, from a jet-like characteristic to a buoyancy-dominating characteristic which has great lateral spreading in surface and bottom layers and apparent constriction in a middle layer. Streamwise variations of spreading widths in upper

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... lower layers were made clear as a function of initial densimetric Froude number Fo, and their features were discussed associated with the flow characteristics. In addition, a hypothesis on the flow and spreading mechanism in the buoyancy-dominating region could be presented through physical consideration.