What geographical feature develops as each flood builds up a new layer of sediment?

The correct answer is a river delta. A river delta forms when a river carries sediment and deposits it at its mouth as it enters a body of water, such as an ocean or a lake. Each time the river floods, it deposits additional layers of sediment, leading to the gradual buildup of land at the mouth of the river. Over time, this process creates a delta, which is typically characterized by a fan-like shape and a network of channels.

In the context of floodplains, while these are areas adjacent to rivers that are covered by water during flooding, they do not accumulate sediment in the same distinctive way as deltas. Floodplains are more about the expansive flatlands surrounding a river where floodwaters naturally spread out, rather than the specific development of landforms from sediment deposition at the river's mouth.

Meanders are bends in a river that develop as water erodes the bank, while ox-bow lakes are formed when a meander is cut off from the main river, leading to stagnant water that can also change sediment deposits. However, neither of these processes reflects the continuous sediment accumulation characteristic of a delta.