Side channel construction is a common intervention to increase both flood safety and the ecological value of the river. Three side channels of Gameren in the river Waal (The Netherlands) show amounts of large aggradation. We use bed level measurements and grain size samples to characterize the development of the side channels. We relate the bed level changes and the deposited sediment in the side channels to the results of hydrodynamic computations. Two of the three side channels filled mainly with suspended bed-material load. In one of these channels, the bed level increased enough that vegetation has grown and fine suspended load has settled. In the third side channel, the bed shear stresses are much smaller and, in addition to the suspended bed-material load, fine sediment settles. Based on the side channel system at Gameren, we identify two types of side channels: one type fills predominantly with suspended bed-material load from the main channel and a second type fills predominantly with fine suspended load. This gives an indication of the main mechanisms that lead to the aggradation in artificial side channel systems.