Debouching can generate massive amounts of sediment transport.
When a narrow stream travels down a mountain pass into a basin, an alluvial fan will form from the mass deposit of the sediment.
The four largest rivers (the Amazon, the Ganges, the Yangtze and the Yellow) are responsible for 20% of the global discharge of sediment in to the oceans by debouches.
[2] In fluvial geography, a debouch is a place where a body of water pours forth from a narrow opening.
Some examples are: where a river or stream emerges from a narrow constraining landform, such as a defile, into open country or a wider space; a creek joins a river; or a stream flows into a lake.