It is commonly thought that in a spiral membrane the fouling is high at the module inlet and progressively decreases toward the outlet. Thanks to an experimental mapping of the irreversible fouling existing in a spiral membrane of 6.5 m(2) area, this paper shows that it is not systematically true and that the fouling distribution can be much more complex. This paper shows also in what extent the mapping of the irreversible fouling existing in a spiral membrane is a powerful approach to deal with the role of the velocity/turbulences gradient that can be experimentally studied independently of the transmembrane pressure gradient in appropriate filtering conditions. The fouling distribution suggests that the velocity/turbulences are roughly constant on 50% of the membrane area located in its centre when dealing with a radial dimension, whereas part of this mean position, velocity/turbulences can increase or decrease. (C) 2014 Elsevier B.V. All rights reserved.