An alluvial fan.
A delta
a stream that empties into a larger river is a Tributary
A delta forms when a river empties into a larger body of water. An alluvial fan forms on land where a river emerges from a mountainous area and flows out onto a more gently sloping plain.
tributary
A river is a large stream of water that flows across the land and empties into a larger body of water. A river usually empties into a sea or ocean.
It is called a River Delta.
mouth
A river that empties into a lake is most often known as the headwaters-if it is the primary water source for body of water= or = tributary
a mouth is a place where a river empties into a larger body of water.
The Nile River delta.
A floodplain.
The flat, wide area along a river is called its flood plain. This is sometimes part of a larger area called the alluvial plain, which formed as the river shifted over time and deposited soil when it flooded.
One river is the Ganges River. Technically it is a distributary of the Ganges River, the Padma that empties into the Bay. Also there are several other rivers that flow through the Ganges Plain that enter the Bay of Bengal such as the Meghna and the Jamuna.