Roughness of successively developed armor layers in a large laboratory flume is analyzed considering gravel surfaces as two-dimensional random fields of bed elevations. Statistically derived roughness parameters are evaluated from precise digital elevation models (DEMs) of bed surfaces and are discussed with respect to successive development of stable armor layers. The key results relate to evolution of the probability distribution of bed elevations and its moments and structure functions of various orders with respect to armoring discharge. Our results suggest that statistical analysis of bed elevations is a helpful tool for defining roughness parameters, quantifying armoring effects, and identifying particle orientation, flow direction, and surface-forming processes.