Umm from what I've learnt, concentration cells are a type of galvanic cell due to the generation of electricity from the reaction alone. In the case of a concentration cell,there is a differing level of electrolyte concentrations in two regions. The cathodic region occurs where the concentration of the electrolyte is greatest and the anodic region occurs where the concentration of the electrolyte is least. As a result, the anodic region will undergo oxidation and the cathodic region will undergo reduction. For example, differential aeration is an environmental condition which will favour the formation of concentration cell corrosion whereby varying oxygen levels will make the regions of a metal anodic and cathodic (and often involves water).