For small face heights production of plain suction dredgers can be calculated with the so-called wall theory or retrogressive erosion theory. For vertical movements of the suction tube all material from the face will flow directly to the suction tube and spillage will only occur when the suction tube is moved to another place before the slope has come to its equilibrium. However, when the suction mouth is moved with a constant horizontal speed, some of the material flowing from the face will not reach the suction mouth due to its movement, but will settle behind the suction mouth. Depending on the horizontal speed of the suction tube and the permeability of the material to dredge, the spillage can easily reach values of 15% or more. So a better knowledge of this phenomenon is essential when dredging with plain suction dredgers. Therefore a theory is set up to determine this type of spillages. To verify the theory, model test has been carried out in the Dredging Laboratory of the Delft University of Technology in the Netherlands. This paper describes the theory set up to calculate the spillage and discusses the results of the model tests.
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