Sediment.
The land area formed by soil carried downstream and deposited by a river at its mouth is known as a delta. Deltas are often highly fertile areas due to the rich sediment deposited by the river, making them ideal for agriculture and supporting diverse ecosystems. Examples of deltas include the Nile Delta in Egypt and the Mississippi Delta in the United States.
The fine yellow soil deposited after floods is likely to be silt. Silt is a sediment that is composed of smaller particles than sand, typically sourced from rivers and carried by water during flooding events. It is often deposited on floodplains and can contribute to the fertility of the soil.
The name given to soil deposited at the mouth of a river is "alluvium." Alluvium consists of sediments such as silt, sand, and gravel that are carried by the river's current and deposited when the flow slows down as it enters a larger body of water, such as an ocean or a lake. This process of deposition forms features like river deltas and floodplains, which are rich in nutrients and fertile for agriculture.
A floodplain is the land that is covered by water when a river overflows it's banks. When this happens, silt and clay are deposited over time and the land on either side of the river flattens out. Any depressions in the land will hold water when the river level returns to normal after flooding and therefore more clay and silt will be deposited there filling it up.
A "Delta", so-called because of the tendency of the 'channels' created by hydrologic soil deposition to frequently vary their courses due to creation of impedences to linear flow caused by precipitation of the colloidally-suspended particles of soil which fall out of suspension as the velocity of the water is reduced, raising the floor of the channels, thus forcing the flow to seek an easier [more lateral] route. "Delta" is used in a mathematical sense, meaning "variation".
sediment
Fine particles of fertile land that is deposited on the banks of a river after a flood
Land formed at the mouth of a river by deposited silt is known as a delta. It typically forms when the river's velocity decreases as it meets the ocean, causing sediment carried by the river to be deposited, building up land over time.
lake
This land deposit you speak of is called a delta.
The Delta
delta
A delta
the bank of a river
The land formed by deposited soil at the mouth of a river is called a delta (named for the Greek letter, which is similarly triangular in shape).
A delta.
The land area that includes soil carried downstream by a river and deposited at the rivers mouth is called a delta. The delta is also where the river enters the ocean or lake.