In alpine environments, open check dams are constructed for retaining sediments which cannot be transported in critical downstream river sections in case of floods. Critical sections are settlement areas where the river has undergone torrential corrections works. For maximizing the sediment storage volume of open check dams, upstream retention basins are essential elements. Based on a case study on a physical model, it turns out the retention basins which are not directly connected with the check dam do not only still fulfil their basic purpose, but also optimize the clogging process of the open check dam.