As meanders move laterally erosion on the outer cut bank creates deposition on the inner bank. Semi circle sand or gravel deposits located on the inner banks of meanders they are formed by a spiral flow in meanders. Deposition builds up on the slip off slopes which provides sediment for the valley floor, friction between water and the land causes the velocity to decrease meaning the water deposits large amounts of its alluvium onto the floodplain. Meanders erode slowly downstream which forms floodplains. They are formed by deposition and erosion. Pools and riffles are formed when they are deep pools which are deeper and slower and then there are shallow riffles with large rocks on them, this means that the riffles are less likely to to erode as they river bed is protect by the rock. This photo, taken by an astronaut onboard the International Space Station (ISS), has been annotated to show the current state boundary (yellow line) between Arkansas and Mississippi. Delta's need ome special conditions to form: salty water to stick sediment together, calm sheltered seas, certain velocity usually slow to deposit sediment, large load. The winding Mississippi River historically has been used to define many state lines in the United States. Due to the loss of velocity as the river enters the delta it begins to deposit sediment load. Found in the lower course ( I studied the RHONE in france which joins to the mediterranean sea). Deltas are formed when a river is meeting the mouth i.e the sea.Eventually the sediment that is pushed outside seals the arms and then eventually the cut off dries up leaving a meander scar.
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