Alluvial Systems

Coastal alluvial plains form when streams transporting sediment from mountainous areas reach low elevations and deposit a large proportion of their sediment load. This occurs due to a decrease in stream gradient, which reduces sediment transport capacity. The extent of coastal alluvial plains is controlled in large part by sea level, and alluvium deposited during previous times of low sea level (for example, during glacial epochs) may now lay tens or hundreds of meters below sea level.