Abstract: For a stilling basin in combined use with flaring gate piers, the flow velocity near its bottom much depends on its geometrical shape. This paper presents a study of hydraulic model tests to optimize the shape of the Ludila stilling basin, considering several commonly-used existing shapes. Our model tests show that if such a stilling basin is modified with an embedded notch in combination of double arcs and a compound tail sill, the double arcs are able to guide the flow near the bottom so as to reduce the bottom velocity, hence improving the energy dissipation rate. In the stilling basin with the optimized shape, its bottom velocity can be reduced by 15% - 30% on average, and bottom pressure fluctuations also reduced even in the most unfavorable flow conditions.