Rivers erode in four ways: Abrasion or corrasion-This is when large pieces of bedload material wear away the river banks and bed. Attrition-This is when the bed load itself is eroded when sediment particles knock against the bed or each other and break, becoming more rounded and smaller. Hydraulic Action-This is when the force of water erodes softer rock. Solution or corrosion-This is when acidic water erodes rock.