how a river changes its characteristics when it reaches the lowland
Upland and lowland Upland habitats are cold, clear, rocky, fast-flowing rivers in mountainous areas; lowland habitats are warm, slow-flowing rivers found in relatively flat lowland areas, with water that is frequently coloured by sediment and organic matter.
Tigris–Euphrates river system The ecoregion is characterized by two large rivers, the Tigris and Euphrates. The rivers have several small tributaries which feed into the system from shallow freshwater lakes, swamps, and marshes, all surrounded by desert. The hydrology of these vast marshes is extremely important to the ecology of the entire upper Persian Gulf. Historically, the area is known as Mesopotamia. As part of the larger Fertile Crescent, it saw the earliest emergence of literate urban civilization in the Uruk period, for which reason it is often described as a "Cradle of Civilization".