The River delta

Herodotus used for the first time the Greek letter “delta” to indicate the area with a particular triangular shape were the different branches of the Nile river deposits its load in the Mediterranean Sea.

The extension of a delta may reach a surface of some hundred kilometers and a delta can be defined as the amount of sediments, partly exposed and partly submerged, carried downstream near the mouth of the river. When the river reaches the sea, the rate of flow decreases and the sediments can accumulate, in a way that the river bed becomes higher compared to the neighbouring area. In this area, the river breaks its banks much easily during floods period and it can find new ways toward the sea. Two or more channels are created, forming a river delta over a long period of time. Sediments can also accumulate beyond the mouth of a river and extend channels of a delta further into the sea or other body of water. The rate of flow, the type of sediment and the action of tides can all affect the formation of a delta. As regards its morphology, a delta may be distinguished between Triangular delta in shape (Nile River) and Bird’s foot delta (Mississippi River).

Below a series of different false-color deltas images, captured by Proba-V. Proba-V 100-m images provide very useful information for coastal application.

Nile – Egypt

The Nile Delta in Egypt extends across an area from 8,000 to 10,000 square miles of land according to different sources. There are two main channels that now flow from the Nile to the Mediterranean Sea: Rosetta near to Alessandria and Damietta.

Mississippi – US

This image shows here the Mississippi delta. Red indicates plant cover, which contrasts with the shades of white and blue representing the water. The Mississippi Delta is the largest river delta in North America, covering an estimated area from 10,000 to 13,000 square miles of land according to various sources. About half of this area includes wetlands formed within the delta.

Ganges – India and Bangladesh

The world´s largest river delta is the Ganges Delta, particularly present in the country of Bangladesh. One third of the delta lies in India, and all waters flow into the Bay of Bengal. Sources differ for land coverage of the Ganges Delta, ranging from 23,000 to over 40,000 square miles of land.

Lena – Russia

The Lena River delta is the largest delta of the Arctic Ocean. The Lena River consists mainly of organ mineral sediments, commonly called peat that contain a huge organic carbon reservoir.

Betsiboka – Madagascar

PROBA-V captured the Betsiboka River Delta in Madagascar. Betsiboka River is known as the Red River because of the large amounts of reddish-orange silt carried out to sea. These river sediments show the problem of large-scale soil erosion that is occurring in the northwestern part of the island in the past 50 years.

Fitzroy – Australia

The Fitzroy delta runs in Australia. This delta is characterized by massive systems of mangroves and wetlands. The presence of this kind of environment is vital for the health of the Reef. The Delta indeed filters vast volumes of water that flow into the Reef, and provides an area with plentiful food, in which the juveniles reef fishes undergo growth and development.

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