The trap efficiency of a shallow reservoir depends on the characteristics of the inflowing sediments and the retention time of the water in the reservoir, which in turn are controlled by the reservoir geometry. With the purpose of controlling the trapped and flushed sediments in shallow reservoirs, the effects of the geometry on sediment deposition and removal were investigated with systematic physical experiments. The geometry shape factor is an important factor to predict the flow and sediment deposition in the reservoir. The evolution of trap efficiency has an increasing or decreasing effect according to the geometry shape factor and flow patterns. The channel formed during flushing attracts the jet and stabilizes the flow structures over the entire reservoir. Empirical formulas to describe the relationship between the geometry shape factor and sediment trap efficiency as well as flushing efficiency were developed.