Not all laterally accreting facies are point bar in origin. On confined meandering rivers where concave benches are commonly associated with rapid channel migration, appreciable amounts of fine sand and mud can be deposited by within-channel lateral accretion of concave benches. Concave benches develop against the upstream limb of the concave bank of abruptly curving meander bends, and are formed of mainly fine suspended load deposited within the channel below the riffle in the upstream end of the pool. Erosion of the upstream limb of the convex bank widens the channel, producing a zone of expanded flow which facilitates flow separation near the upstream limb of the opposite concave bank. A platform of sand in the form of a longitudinal-shaped bar is deposited in this zone, followed by further aggradation with fine sand, mud and organic matter. Even when fully formed, at high flow the concave bench remains isolated from the rest of the floodplain by a secondary channel around the margin of the original concave bank of the main channel. With the continued downvalley migration of the meander bend, another concave bench is formed, and this process continues until eventually a new floodplain is locally created by the lateral accretion of these benches.