Question

Why is a delta formed at the meeting point of sea water and river water

Answer 1

sea water contains lot of electrolytes. river water colloids of sand and clay. when they meet electrolytes neutralise a charge on coloidal particles and result in the prepration of sand , clay etc
thus result in a delta formation

Answer 2

The river contains colloidal particles of sand and clay which carry negative charge. The sea water contains a number of ions such as Na+, Mg+, Ca2+ ion etc. When the river comes in contact with sea water, the negative charge present on colloidal sand and clay particles get neutralised by positively charged ions and they get coagulated. The coagulated sand and clay particles settle down and take the shape of Delta in due course of time.