In this paper, the effect of clay content on the local scouring downstream of a rigid apron due to a submerged horizontal jet has been studied experimentally. Seven different mixtures of cohesive sediments with clay content equal to 0, 10, 15, 20, 25, 30 and 40 % were used. Results showed that the clay content has an important effect in the scouring process. It shows that with clay content equal to 40%, the maximum depth of scour may be reduced up to 80% of the non-cohesive materials. Using dimensional analysis, a new non-dimensional parameter is introduced which includes the effect of both the grain densimetric Froude number and clay content. It was also found that there is a critical value for the mentioned dimensionless parameter, where no erosion occurs below that value. Also, dimensionless equations and graphs are presented to determine the characteristic lengths of the scour hole including the maximum scour depth, the maximum longitudinal extension of the hole and the sand wave height.