GEOMORPHOLOGY OF RIVERS DAMS, WEIRS, AND SEDIMENT TRANSPORT When a dam or weir is built across a river, the natural flow of water and sediment is disrupted. Sediments that would normally travel downstream get trapped behind the structure, forming reservoirs with silt and sand buildup. Downstream, the river becomes “sediment-starved,” often leading to increased erosion of riverbeds and banks, changes in channel shape, and impacts on ecosystems. Over time, this alters floodplain dynamics and can r