In this research an effort is made to better understand the scour caused by submerged square jets in a cohesionless bed. The variables of interest are the densimetric Froude number, the tailwater depth and sediment grain size. Experiments were carried out at three different values of densimetric Froude numbers (= 3.9, 6.6 and 10.0), a range of tailwater conditions varying from low to very high submergence, and two different sand bed grain sizes. Velocity measurements were conducted using a laser Doppler anemometer.; At a given densimetric Froude number, progressing from the start of the test towards asymptotic conditions, the geometric parameters used to describe scour are found to be sensitive to tailwater conditions and the ratio of the nozzle size-to-grain size. The present results indicate that the effect of nozzle size-to-grain size can be important and needs to be incorporated in the interpretation of scour. This effect is reduced as asymptotic conditions are reached. Turbulent bursts have been noted to have an important role in the scour process, and are more distinguishable with the finer bed material. At low values of the relative tailwater depth, the flow and the corresponding scour patterns tends to be non-symmetrical. Moreover, at low values of tailwater depth and higher densimetric Froude number, the scour pattern is quite different from the other test conditions. Empirical equations to describe the scour geometry are proposed for the asymptotic state. These relations are found to be valid for a wide range of test conditions.
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