Former researches indicate that the distribution of debris flow velocity is laterally asymmetrical. Due to a lack of a theoretical basis on it

velocity and load have to be calculated on uniform state advised by current design regulations when the debris flow dam and drainage canal are designed. It is different to the practical status

which may lead to the engineering failure due to the poor partial stability. Therefore

based on deposition-erosion equilibrium

isotropic fluid hypothesis and reasonable simplification for debris flow's gully cross-section

the nonlinearity features of debris flow velocity's lateral distribution was proposed by deducting the deducing process of the velocity calculation formula at any cross-section. With the instance analysis of debris flow mitigation and control work at earthquake-stricken areas in Lixian

Sichuan province

we found that the debris flow velocity at channel line is triple the one at either side

and conducted the structural optimization design for debris dam on the premise of ensuring its function

reducing the risk of the dam break and instability of debris dam

which would rise the dam stability coefficient by 20%

and save the engineering cost by 5%.