The Drainage Basin: A Component of the Water Cycle

The Drainage Basin

• A drainage basin is an area of land where water from rain or snowmelt drains downhill into a body of water, such as a river, lake, reservoir, estuary, wetland, sea or ocean.
• It's often referred to as a catchment area.
• The boundary separating different drainage basins is known as a watershed.

Basic Structure of Drainage Basin

• It mainly consists of three parts: The Source, where a river begins, often high in hills or mountains; The Course, the path that the river follows to its mouth; The Mouth, where the river ends by flowing into a larger body of water.
• Other structures include tributaries (smaller rivers or streams flowing into a larger river), the confluence (the point where the main river and its tributaries meet) and the river channel (the course through which the river flows).

Processes in the Drainage Basin

• Infiltration: The process where water on the ground surface enters the soil.
• Percolation: The downward movement of water within the rock under soil surface.
• Throughflow: The movement of water down-slope through the soil layer.
• Surface runoff: The flow of water that occurs when excess rainwater, meltwater, or other sources flows over the Earth's surface.

Components of the Hydrological Cycle in Drainage Basin

• Key processes of the water cycle in a drainage basin include precipitation (rain, snow, etc. falling from the sky), interception (water being prevented from reaching the surface by trees or grass), evapotranspiration (the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere), transpiration (the process where plants absorb water through the roots and then give off water vapor through pores in their leaves), and runoff (water that flows over land surface).

Importance of a Drainage Basin

• A drainage basin is a crucial component of the Earth's water cycle.
• It plays a crucial role in water supply (supports human life and agriculture), filtration of water, and habitat for wildlife.
• They help in flood prevention by absorbing excess water during heavy rainfalls.

Human Impact on Drainage Basins

• Human activities like deforestation, urbanisation and agriculture can significantly impact the functioning of drainage basins.
• These activities can change the natural processes taking place in a drainage basin, often leading to increased surface runoff, soil erosion, and decreased water quality.
• The creation of dams and reservoirs can also alter the natural flow of water within a drainage basin.