Estuary: Estuary is the point where a river ends and meets the sea. Estuaries have brackish water which is not so salty as the ocean water.
There are four kinds of estuaries:
♦ Coastal plain estuaries are created during heavy rain, when the sea level rises and fills a nearby river valley. Example: Hudson River in New York
♦ Tectonic estuaries are created by the movement of tectonic plates. Example: San Francisco Bay, on the West Coast of the United States.
♦ Bar-built estuaries are built when a barrier island is built by the ocean waves near a coastal area which has river streams flowing in it. Example: Nauset Barrier Beach System in Cape Cod, Massachusetts.
♦ Fjord estuaries are created by glaciers. Fjords are also found throughout Canada, Chile, Greenland, New Zealand. Examples: Glacier Bay in Alaska and the Georgia Basin region of Puget Sound in Washington State.
Deltas: Deltas are formed at the river end when the river slows down and sediments start settling down. These sediments accumulate and form a spread-out area. Some rivers deposit so much sediment that waves and tides cannot carry it all away, and a huge delta is built. The term delta is derived from a Greek letter delta (Δ), which is shaped like a triangle. When these deltas resemble an arc, they are called arc-deltas (arcuate). The Nile River forms an arcuate delta while emptying into the Mediterranean Sea. The Nile delta is a very important farming area in Egypt.
