The term Delta was coined by Herodotus (484-425 BC) after the Greek letter delta. The letter was found befitting the deltoid-shape at the mouth of the Nile. As per geomorphologic inferences, a delta may be formed when a river deposits material, primarily sand and clay, faster than the sea can remove it. Below is a short treatise of various delta types and their typical surface formations.
Nile Delta / Photo Courtesy : NASA
Nile: Formed in Northern part of Egypt where the Nile spreads out and drains into the Mediterranean, this is one the world’s largest river deltas.The delta is classified as an arcuate river delta which features many active, short distributaries that carry sediment to the oceanic mouths. As the sediment exits through many mouths, the waves push it back, making the coastline very smooth. The coastline extends from Alexandria in the west to Port Said in the east and covers 240 kilometers of the Mediterranean coastline. A very rich agricultural region, from north to south the delta is approximately 160 kilometers in length.
Sundarban: Measuring about 40,000 sq km our very own Sundarban forms the largest river delta in the world, and is formed by the coalescing of two very large rivers – the Ganga and the Brahmaputra.This is an also arcuate river delta which features many active, short distributaries pushing heavy sediments to their mouths.There is a cluster of low-lying islands in the Bay of Bengal, spread across India and Bangladesh, famous for its unique mangrove forests and thriving wildlife.
Mississippi: The river forms a bird-foot delta as it empties into the Gulf of Mexico. As the name suggest this delta is in the shape of a bird’s foot and tend to have one or a very few major distributaries near their mouths. The receiving basin has currents that carry the sediment away as it exits the distributaries mouth. There is a broad, shallow shelf that deepens abruptly, so the trend is to grow long and thin like a bird’s toe. The Mississippi delta is the seventh largest delta on earth and is an important coastal region for the United States, containing more than 2.7 million acres of coastal wetlands.
Tiber: This Italian river forms cuspate delta before emptying into the Tyrrhenian Sea of the Mediterranean. This type of river delta, usually have one distributary emptying into a flat coastline with wave action hitting it head-on. This tends to push the sediment back on both sides of the mouth, with a ‘tooth’ growing out onto the shelf. Hence it is named cuspate. The Tiber Delta stretches over some 25 km and includes a delta plain region and a submerged fan. This Delta plain, located some 25 km west of Rome, is an area of great interest that enables the study of the relationships between natural environmental changes and human activity.
Narmada: The west flowing river of India, Narmada passes through a rift valley. The River contains a small amount of silt and due to its sustained speed throughout its course, forms an estuary. The river empties into a long, narrow estuary that eventually becomes filled with sediment (inside the coastline). Estuaries form a transition zone between river environments and ocean environments and are subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of fresh water and sediment. The inflow of both seawater and freshwater provide high levels of nutrients in both the water column and sediment, making estuaries among the most productive natural habitats in the world.
Seine: This river is the third-longest river in France, which emerges from the earth in a remote spot called Source-Seine, in the Burgundy wine region of northeastern France and forms a stark estuarine river delta that drains into the English Channel.
Endnote : River deltas are found almost everywhere in the world, wherever a sediment rich river empties its water into the sea. These river deltas not only supports a rich biodiversity but also adds up to the beauty of our earth.