Q.In what way do natural levees differ from point bars?

Natural levees and point bars are both depositional features of rivers, but they form in different parts of the channel and under different flow conditions.

A natural levee is a low, ridge-like deposit of coarse silt and sand that builds up along the banks of a river. It forms when the river overflows its banks during floods; as the water spreads over the floodplain, its velocity drops sharply, and the heaviest sediment settles immediately beside the channel. Over repeated floods, these ridges grow higher and higher, so they stand slightly above the surrounding floodplain.

A point bar, in contrast, is a deposit of sand and gravel that accumulates on the inside of a meander bend. As the river flows around a curve, the fastest water is thrown toward the outer bank, where erosion occurs. On the inner bank, the water slows down, and the sediment it carries is dropped, building a gently sloping, crescent-shaped bar that extends into the channel. …

A river is not a passive pipe carrying water from hills to sea. It is a restless sculptor, forever picking up sediment, carrying it, and setting it down somewhere else. Where the water slows, it drops its load; where it speeds up, it digs. Two of the most common features born from this endless give-and-take are natural levees and point bars. Both are depositional — both are made of material the river has abandoned — but they form in completely different places, under different conditions, and leave behind very different shapes.

Natural levees are the river’s own embankments. Picture a river in flood: water spills over the banks and spreads across the flat floodplain. The moment it leaves the main channel, the water loses speed sharply. The heaviest sediment — coarse sand and silt — settles out right along the bank, building a low, elongated ridge that runs parallel to the channel. Over many floods, these ridges grow higher and wider, until they stand noticeably above the surrounding floodplain. That is the levee: a raised strip of coarser material hugging the river’s edge, sloping gently away from the channel on the landward side.

Point bars are a different creature entirely. They belong to meanders — those looping bends a river carves as it matures. On the outside of a bend, the current runs fast and deep, eroding the bank. On the inside of the same bend, the water slows down. That sluggish water drops its sediment — sand, gravel, and silt — and builds a crescent-shaped deposit that curves with the bend. As the meander migrates, the point bar grows outward, and over time it may become a flat, fertile stretch of land on the inside of the loop.

The differences run deeper than location. Levees are built by floodwaters, in a sudden, episodic burst of deposition; point bars are built by the everyday current, steadily, during normal flow. Levees are long and linear, following the channel like a pair of raised lips; point bars are curved and lobate, mirroring the bend they grow inside. Levees are made of relatively coarse material — sand and silt dropped fast when the flood first breaks over the bank; point bars are often coarser still, with gravel and sand, because they form where the current is still strong enough to carry heavier grains, just not strong enough to keep them moving. …