Abstract: Most energy dissipation formula are applicable to rectangular wing wall sections. In view of this, the most unfavorable condition of energy dissipation for diffusing trapezoidal wing of sluice wall was investigated according the hydraulics theory, the mathematical function theory and the dimensionless principle. Analytical formulas of the relative contracted water depth and the relative water depth after jump were deduced.By using Matlab software for numerical analysis and mathematical derivation, simple formulas were given to calculate the extremes of pool depth and water jump length of the stilling basin of coastal tidal drainage sluice influenced by tide level. Through engineering example calculation, the analytic formulas are proved to be convenient with high precision and reliability.

Key words: engineering hydraulics, sluice, the most unfavorable conditions of energy dissipation, diffusion trapezoidal wing wall, depth of stilling pool, water jump length