Drainage Basin Systems Overview

Drainage Basin Systems

• Drainage basins are areas of land that drain water into a common outlet, like a river.
• A watershed is another term for a drainage basin.
• Inputs to a drainage basin include precipitation (rain, snow, etc.), and in some cases, water from streams outside the basin.
• Outputs from a drainage basin include channel flow, evaporation, transpiration, and water entering other basins.
• Stored volumes of water in a drainage basin include; surface storage, groundwater, interception storage, and soil moisture.

Elements of Drainage Basin Systems

• Precipitation: Water falling from the atmosphere.
• Evaporation: Water changing from a liquid to a gaseous state, often from open water surfaces.
• Transpiration: Water released from plants into the atmosphere.
• Potential evapotranspiration: The maximum amount of water that could be lost to evaporation and transpiration under given climatic conditions.
• Actual evapotranspiration: The amount of water actually lost to evaporation and transpiration, which is usually lower than potential evapotranspiration due to factors like soil moisture availability.
• Interception: Precipitation that is caught by vegetation.
• Interception storage: Water stored on vegetation.
• Throughflow: Water moving horizontally through the soil.
• Stemflow: Water flowing down the stems of plants.
• Secondary interception: Interception by already wet vegetation.
• Surface storage: Water stored on the ground surface.
• Surface runoff/overland flow: Water flowing over the land surface.
• Infiltration: Water soaking into the soil.
• Percolation: Water moving vertically down through the soil.
• Channel flow: Water flowing within the channels of a river or stream.
• Drainage patterns: The arrangement of streams and rivers in a drainage basin.

Drainage Patterns

• Parallel: Streams flowing roughly parallel to each other.
• Dendritic: Streams branching like the roots of a tree. Often found in areas with uniform geology
• Radial: Streams flowing outward from a central high point.
• Trellis or rectangular: Streams following the lines of weakness in the landscape, such as faults or folds.

Law of Stream Order

• A system used to describe the hierarchical organisation of streams and rivers.

Hydrographs

• A graph showing the discharge of a river over time.
• Hydrographs are influenced by various factors in a drainage basin, including rainfall patterns, soil type, and land use.

Controls in Drainage Basins and Hydrographs

• Factors affecting the characteristics of drainage basins and the shape of hydrographs include; rainfall characteristics (duration, intensity, distribution), topography (elevation, slope, aspect), geology (porosity, permeability), soil characteristics (permeability, water holding capacity), vegetation cover, and land use (farming, urbanisation).

Open, Closed, Isolated Systems

• Open systems: Exchange matter and energy with surroundings.
• Closed systems: Exchange energy but not matter with surroundings.
• Isolated systems: Exchange neither matter nor energy with surroundings.

Dynamic Open Systems

• An open system always undergoes change.

Slope and Systems

• Slopes play a role in influencing water movement in a drainage basin.
• Slopes of land influence the speed of water and the rate of runoff in drainage basin.
• Systems such as drainage basins are always dynamic or always changing.

Example Drainage Basin Figure Identification Questions (for students)

1. Identify inputs to a drainage basin, processes involved, and outputs.
2. What are the different types of storage in a drainage basin?
3. Explain how precipitation impacts overland flow.
4. Describe the processes that lead to the formation of various drainage patterns, and relate them to the geology.

This quiz explores the key components and functions of drainage basin systems, including their input and output processes. It covers concepts like precipitation, evaporation, transpiration, and storage within the basin. Test your understanding of how these systems interact with the environment.