Large-eddy simulation is implemented for turbulent flow and gas dispersion over wavy walls across a wide range of the wave amplitude to wavelength ratio (alpha = 1.0, 1.5, and 2.0). Two tracer gases are emitted from point sources located at a single crest and trough of the wavy wall. Because the values of alpha increase under the Reynolds number based on the bulk velocity and the wavelength is 6.67 x 10(4), the flow separates behind the crest and the standard deviations of the fluctuation in streamwise and spanwise velocity components become relatively large especially at the upslope of the wavy wall. The increase are related to the vortices linked to the Corder instability mechanism. The change in the flow pattern with respect to the value of a significantly affects the gas dispersion within the valley. As the Reynolds number increases under the wavy wall with alpha = 2.0, the flow tends to follow the bottom surface of the wavy wall and the number of the vortices increases at the upslope, but the vortices do not significantly affect the gas dispersion over the wavy wall. (C) 2018 Elsevier Ltd. All rights reserved.