Explain the formation of delta.

When a river meets the sea, extensive deposits of sand and clay are formed at the mouth of the river in the sea. Such deposits are called delta.

River water is a colloidal solution of clay (negative charges). Sea water contains a number of electrolytes ( which contains ions carrying positive charge like Mg2+, Ca2+ etc.). When river water meets the sea water, the electrolytes (positive charges) present in sea water coagulate with the colloidal solution of clay (negative charges) resulting in its deposition with the formation of delta.