A convenient designation for the optimal hydraulic cross-section of "Rectangle-V" shaped drainage canal of viscous debris flow

The "Rectangle-V" shaped drainage canal is one of the most-widely used engineering measures in debris flow prevention in the west mountain area in China. The cross-section shape and size of the "Rectangle-V" shaped drainage canal are important parameters in the design. How to choose the shape and size to let the drainage canal have the optimal drainage capacity is rarely revolved before. This paper discusses the design of the optimal hydraulic cross-section. First, the parameter of cross-section size (F) and characteristic parameter of cross-section (S) are defined. Then, the calculation formulas of F and S are deduced. It indicates that F and S are only related to the transverse slope coefficient(I C ) under the optimal hydraulic condition. At last, the calculation formulas of the optimal hydraulic depth and width of the drainage canal are deduced. Taking Xinqiao gully, a first-order distributaries in the upper Min River after "5.12" earthquake as an example, this paper designs the optimal cross-section of the drainage canal of viscous debris flow. Compared to the other design methods, the method can confirm the shape and the sizes of "Rectangle-V" shaped drainage canal of viscous debris flow. And the calculated result is the only confirmed value, while the calculating method is convenient and efficient and can be adapted to the actual engineering.