This work involves the experimental investigation of flow patterns, preferential regions of deposition and trapping efficiency in rectangular shallow reservoirs. The main flow patterns that can be encountered in rectangular shallow reservoirs are described: symmetrical flows without any reattachment point (S0), asymmetrical flows with one reattachment point (A1) and asymmetrical flows with two reattachment points (A2). The influence of geometrical and hydraulic parameters on reattachment lengths is intensively investigated. A shape parameter is introduced to classify symmetrical and asymmetrical flows. For each flow pattern, the preferential regions of deposition are studied. To conclude, a number of practical recommendations are given. Reservoirs with a shape parameter lower than 6.2 limit sediment deposition. Reservoirs with a shape parameter greater than 6.8 are favourable for sediment deposition. Finally, perspectives for maximizing and minimizing deposition are given, respectively by exploiting the great trapping potential of the flow pattern A1 and the poor trapping potential of the flow pattern S0.