In fluvial geomorphology, a debouch is a place where runoff from a small, confined space emerges into a larger, broader space. Common examples are when a stream runs into a river or when a river runs into an ocean. 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. ==Geography==