Deltas

 

A river delta is a landform that forms at the mouth of a river where the river flows into an ocean, sea, estuary, lake, or reservoir. Deltas form by deposition as sediment if carried by a river out of its mouth. When a river reaches a lake or the sea the water slows down and loses the energy to carry sediment. The sediment is dropped at the mouth of the river over time it builds up in layers forming a delta. Some deltas are so large that people live and farm on it such as the Nile in Egypt.

A delta plain is a flat section that is above water, small channels are cut through the plain by rivers. These channels are called distributaries, new sections of delta build up at the mouths of distributaries. The rest of the delta is under water. A steeply sloping delta front faces the lake or ocean. The prodelta is furthest away from the mouth of the river and is deepest under water.

Deltas can be different shapes and sizes depending on how much sediment is deposited by the river and how much is eroded and re-deposited by waves and tides;

A river dominated delta is often named a bird’s foot delta because of its form. Leeves build up along the sides of the narrow distributary channels.  Such as the Mississippi delta in Louisiana USA.

Tide dominated deltas have long and narrow offshore bars or islands at the mouth of the river, such as in Western Papua New Guinea.

 

Wave dominated deltas look like a trodden triangles. The lines running across the delta are ridges that formed as the delta built up, such as Caravelas, Brazil.

 

 

The UK doesn’t have any delta as deltas need to run out onto vast areas of flat land, like the Nile and Mississippi deltas. We only have one area similar to a delta and that’s the Wash between Lincolnshire and Norfolk. However there are only two or three very small rivers flowing into that unlike the Nile. River Deltas require a large source of sediment to form, usually from weathering of large high mountain ranges. Those high volumes of sediment get washed out to sea by rivers coming down from the mountains. Over time the sediment at the mouth of the river builds up to form new land forming a delta. Britain doesn't have mountain ranges the size of the Himalayas, Rockies, or Andes, which provide much of the sediment source for many of the World’s great river deltas.