Geosynthetic structures created for channel erosion protection offer environmental friendly benefits and have demonstrably lower construction and lifetime costs than similar hard structures. A geotextile mattress with a sloping curtain (GMSC) offers an alternative countermeasure against channel erosion. In the present study, experiments were conducted to investigate the working mechanism and effectiveness of GMSCs which were installed on movable beds in a rectangular flume. The bathymetry of the plastic sand beds was measured before and after the tests. The results showed that the presence of the GMSC led to sediment deposition and dune formation at both upstream and downstream edges of the GMSC structure. This will prevent bottom erosion near the structure and increase its stability against flow-induced sediment scour, so that the erodible beds will be protected.