An endorheic basin is a closed drainage that retains water and does not allow for overflow to other external bodies such as the rivers and or oceans. The endorheic basin may form either permanent or seasonal lakes or swamps that equilibrate only through evaporation. The basin is also commonly referred to as internal drainage system or a closed basin. However, under normal circumstances, the water that accumulates in the drainage basin flows out through rivers or streams or by underground diffusion through permeable rocks and finally ends up in the ocean. This scenario is not common in the endorheic Basin since water that flows into the basin cannot flow out and may only leave the drainage through evaporation or seep into the ground.
The word endorheic is an Ancient Greek word which translates to “to flow within.” An Endorheic Basin can either be small or massive depending on the effect of climate and the rate of water removal. Endorheic Basin does not have enough inflow and depends mainly on rainfall. It also has no overflow. Thus any loss of water either by evaporation or seeping leads to immediate shrinking of the lake. Most of the Endorheic lakes such as Lake Chad and Lake Urmia have been reduced to smaller remnants of their former sizes while other lakes such as Tulare and Fucine are completely gone. The basins which have disappeared have left behind salt pans and remnant saline lakes.
Endorheic lakes do not flow into an ocean or a sea like most of the lakes whose waters find their ways to the ocean or sea through a network of rivers or streams. Endorheic lakes are located in a watershed where the topography does not allow their drainage into the oceans. These watersheds are often referred to as terminal lakes or sink lakes. Endorheic lakes are located in the interior of the land mass far from oceans or seas and also in areas that experience low rainfall. When the waters from Endorheic lakes evaporate a large concentration of minerals and other inflow erosion products are left behind. The mineral deposits and erosion material left behind may cause the lake to become saline over time. Because of lack of an outlet, Endorheic lakes are more sensitive to environmental pollutants than lakes which have access to the oceans or sea. Endorheic lakes can either be permanent or seasonal and can form in endorheic basin.
Occurrence Of Endorheic Basin
Endorheic basins can occur in any climate but are most common in deserts with low rainfall or stream flow. In areas of high rainfall, erosion is likely to curve the drainage channel or cause water in the terminal basin to rise thereby finding an outlet into the sea or ocean. Endorheic regions are far inland places whose boundaries are defined by mountains and other geographical features which block their access to other water bodies. Australia has the highest concentration of endorheic regions followed by North America at 21% and 5% concentration respectively. About 18% of the earth drains into Endorheic lakes. Some of the notable Endorheic basins and lakes include Lake Vanda, Lake Bonney, the Caspian Sea, Lake Urmia, Lop Lake, and Sistan Basin in Asia, Lake Eyre Basin, and Lake George in Australia, and Chad Basin, Lake Turkana, Lake Chilwa, and Lake Rukwa in Africa.