The hydraulic condition analysis and optimal cross-section design of the “rectangle -v” shaped drainage canal of debris flow

The drainage canal is one of the most widely-used engineering measures in preventing debris flow. The cross- section shape and size are important parameters for designing the drainage canal of debris flow. While how to choose the optimal shape and size to make the drainage canal of debris flow have the best discharging ability is a problem few people have researched. The "Rectangle-V" shape is one of the widely-used cross-section shapes of debris flow drainage canal. This paper chooses it as a researching object, analyzes its optimal hydraulic condition, and discusses its optimal cross-section design. The cross-section configuration parameter (M) of "Rectangle-V" shaped debris flow drainage canal is defined as the ratio of wetted perimeter (P) to hydraulic radius(R). Based on the definition, the calculation formula of M is deduced under the optimal hydraulic condition. The formula indicates that M only relates with the bottom transverse slope coefficient under the optimal hydraulic condition. Assuming the discharge of debris flow (Q), the longitudinal gradient of debris flow drainage canal (I) and the gradation of debris flow grain size as known, we deduce the combinatorial calculating formulas of the cross- section size of "Rectangle-V" shaped debris flow drainage canal by using the simultaneous numerical solution method. On the basis of the analysis of the optimal hydraulic condition of "Rectangle-V" shaped debris flow drainage canal, this paper takes the Huoba Gully as an example for the optimal cross- section design of debris flow drainage canal.