Rainfall and Accumulation:
1. Rainfall and Watershed: Rivers begin with precipitation in the form of rain or snow. This precipitation accumulates in low-lying areas called watersheds or drainage basins.
Erosion and Sediment Transport:
2. Surface Runoff: As water accumulates on the land, it starts to flow downhill due to gravity. This is called surface runoff.
3. Erosion: As the water flows, it picks up loose soil, sand, and other sediments through erosion. The force of moving water dislodges particles from the ground, leading to the formation of small channels.
4. Rills and Gullies: As water continues to flow and accumulate, the small channels grow larger and become known as rills. Several rills merging together form larger channels called gullies.
Formation of River Channels:
5. Stream Development: As gullies become larger and deeper, they start to exhibit characteristics of a river. They become wider and more defined, and the flow of water becomes more constant.
6. Bank Erosion and Sediment Deposition: As water flows through the river channel, it continues to erode the banks, causing the river to widen. Sediment is deposited along the river's course, forming floodplains and deltas.
7. Meandering: Over time, rivers may develop bends and curves known as meanders. This happens due to the erosion of the outer bank and deposition on the inner bank as water flows around obstacles or changes in the landscape.
River System:
8. Tributaries and Watersheds: Rivers do not exist in isolation. They are often joined by smaller streams or rivers called tributaries, forming a river system. The entire area from which a river and its tributaries collect water is known as a watershed or drainage basin.
9. River Discharge: The amount of water flowing through a river is referred to as its discharge. This can vary significantly over time, influenced by factors like precipitation, snowmelt, and groundwater recharge.
10. River Mouth and Estuaries: As a river approaches its end point, it usually empties into a larger body of water such as a lake, sea, or ocean. The area where a river meets the larger water body is called its mouth. In some cases, rivers form estuaries, which are coastal wetlands where freshwater from the river mixes with saltwater from the sea.
11. River Dynamics: Rivers are dynamic systems that continuously reshape the landscape through erosion, deposition, and sediment transport. Over millions of years, they can alter the topography and create landforms such as canyons, valleys, and deltas.
