Rivers are natural watercourses that flow towards an ocean, sea, lake, or another river. They are an essential part of the Earth's hydrological cycle and play a crucial role in shaping the landscape, providing habitats for various species, and supporting human activities such as agriculture, transportation, and recreation.
The course of a river can be divided into three main sections: upper, middle, and lower.
1. Upper course: The upper course of a river is typically located in the highlands or mountains where the river originates. In this section, the river is characterized by steep gradients, fast-flowing water, and narrow valleys. The upper course is often marked by the presence of rapids, waterfalls, and cascades as the river erodes the landscape and cuts through the rocky terrain. The upper course is also where the river's source is located, usually a spring or glacier.
2. Middle course: The middle course of a river is where the river begins to meander and flow through wider valleys and plains. In this section, the river's gradient is less steep, and the water flow is slower compared to the upper course. The middle course is characterized by the deposition of sediment carried by the river, forming meanders, oxbow lakes, and floodplains. This section of the river is often where human settlements and agriculture are located due to the fertile soil deposited by the river.
3. Lower course: The lower course of a river is where the river flows towards its mouth, usually an ocean or sea. In this section, the river's gradient is very gentle, and the water flow is slow and steady. The lower course is characterized by the widening of the river channel, the formation of deltas, and the mixing of freshwater with saltwater. The lower course is also where the river's discharge is the highest, as it collects water from its tributaries and drains into the sea. This section of the river is often heavily influenced by human activities such as urbanization, industrialization, and pollution.