Elevated floodplains and net channel incision as a result of the construction and removal of water mills

ABSTRACT An often underrated but historically long-lasting human impact on river-floodplain systems is that of the presence of water mills. The objective of this study is to determine how the construction and later removal of water mills influence the longitudinal bed profile of a river and its floodplain sedimentation. The effects of a river-mill system were analyzed using physically-based equations of backwater effects and sediment mobility in combination with field measurements of channel slope and floodplain development pre- and postdating water mills in the Wurm River (Germany) and the Geul River (Netherlands). The results show that the construction and removal of water mills likely resulted in a net incision of the riverbed into the valley bottom to a level below the original bed, with reduced floodplain inundation rates and, consequently, reduced floodplain sedimentation.