Statistical roughness properties of the gravel bed surfaces in a meandering channel

•Laboratory experiments were conducted to investigate the statistical roughness properties of the gravel bed surfaces in a meandering channel.•The elevation probability distributions of the detrended water-worked bed surfaces in the meandering channel are positively skewed and leptokurtic.•The armor layer in the meandering channel can resist the increasing flow strength to a certain extent, but its protective ability is very limited.•The bed surface roughness and the averaged influence scale of the constituent grains are large in the main stream path and small in the main stream separating areas.•For any local zone, the roughness and the averaged influence scale in the longitudinal direction are obviously greater than the corresponding values in the lateral direction.