Difference between Estuary and Delta

Key Difference: Delta is a sedimentary deposit formed at mouth of some rivers. It is usually triangular in shape. On the other hand, an estuary is a semi-enclosed body of water where fresh water meets the ocean.

Delta is basically a deposit of sediments containing sand and soil. It is normally found as a bulge of shoreline where the river enters the ocean, sea or any other standing body of water. This bulge contains sediments and therefore it is very fertile in nature. The sediments get accumulate in the condition when the river’s rate of depositing material tends to be faster than of sea.

It is found at the mouth of large rivers like the Mississippi. Deltas are classified into three main groups according to the shapes formed by them - Accurate or fan shaped, Cuspate and Bird’s foot. Most often the shape is described as triangular, and therefore it has got its name from the Greek letter which resembles a triangle. Factors like amount and type of sediment, change in volume of water discharged from river, changes in coastal level, etc., tend to influence the occurrence of deltas.

An estuary is an area where streams and rivers converge into the seawater from oceans. Bays, lagoons, harbors, inlets can be types of estuaries. Estuaries contains the mixture of salt and fresh water and results in brackish water. There are generally four types of estuaries – Coastal plain estuaries, Tectonic estuaries, Bar built estuaries and Fjord estuaries.

There are many differences between an estuary and a delta. An estuary is all about meeting of a river with an ocean or a sea typically in a single line. It has no concerned with the distributaries of a river. On the other hand, delta usually gets developed when a river meets the still water body with many distributaries. A delta is formed in coastal areas which have plains and marked by low tides. On the other hand, an estuary gets formed in a coastal area marked by high tides.

Deltas are rich in sediments, and therefore they are beneficial for agriculture, whereas the coastal areas near estuaries tend to be suitable natural harbors.

Comparison between an estuary and Delta:

	Estuary	Delta
Definition	A semi-enclosed body of water where fresh water meets the ocean	Sedimentary deposit at mouth of river due to which coastline protrudes into ocean
Types	Coastal Plains – valleys are generally shallow with gentle sloping bottoms Tectonic – Formed when sea fills the basin formed by the sinking land Bar built – these are usually shallow with reduced tidal action Fjords – valleys that have been cut deeper by moving glaciers and later got invaded by the sea.	Accurate – rounded, convex edges Cuspate - material uniformly distributed from the river Bird’s food - spread over a large area due to many distributaries of the river. Like Mississippi.
Nature	Transgressive	Regressive
Examples	Narmada and Tapi rivers form estuaries	Ganga and Brahmaputra form delta
Formed in regions	High tides and rift valleys	Low tides and coastal plants
Fertile land	It does not have fertile land	Yes
Importance	They form the wildlife habitats and even some men have also settled near to these estuaries.	Favorable for agriculture due to rich sediments. However, they are susceptible to flood.