Alluvial accumulation in the mouth, the first in a series of underwater start Shoal, heart or beach sand spit, the water flow in bifurcation, while the tilt to the formation of the underwater delta.

• 钱塘江挟沙少，河口海岸下降，潮差大，不仅使河流携带的泥沙不能在河口堆积，而且引起强烈的冲刷，使河口加深与展宽，逐渐形成三角港。