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The drainage basin - Coggle Diagram
The drainage basin
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An open system
The drainage basin is a subsystem within the global hydrological cycle, its an open system with inputs and outputs. Since thosevary overtime, so does the amount of water in the drainage basin
Inputs
Main input is precipitation, which can vary in a number of different ways. All characteristics can have a significant impact on the drainage cycle
- Form: rain, snow or hail. With snow entry of water will be delayed
- Amount: This will affect the amount of water in the drainage basin and fluxes within
- Intensity: Greater intensity, greater risk of flooding
- Seasonality: likely to result in the drainage basin operating at different flow levels ant different times of the year
- Distribution: significant in large basins where tributaries start in different climates
Flows
At least seven flows that are important in transfering the precipitation that has fallen the land into the drainage network
- Interception: retention of water by plants and soils
- Infiltration: process by which water soaks or is absorbed by soil
- Percolation: similar to infiltration, but deeper transfer of water into permeable rocks
- Throughflow: lateral transfer of water downslope through the soil
- Groundwater flow: very slow transfer of percolated water through porous rocks
- Surface runoff: movement of water that is unconfined by a channel across the surface of the ground
- Channel flow: Takes over as soon as water enters a river or stream
Outputs
Three main outputs:
- Evaporation: Process by which moisture is lost directly into the atmosphere from water surfaces, soil and rock
- Transpiration: Biological process by which water is lost from plants through minute pores and transferred to the atmosphere
- Discharge: Into another larger basin, lake or sea
Impact of human factors
River management:
- Construction of storage reservoirs holds back river flows
- Abstraction of water for domestic and industrial use reduces flow
- Abstraction of groundwater for irrigation lowers water tables
Deforestation
- Clearance of trees reduces evapotranspiration, but increases infiltration and surface runoff
Amazon basin contains largest tropical rainforest. Deforestation here has disrupted drainage basin cycle in a number of ways like more evaporation, less precipitation
Changing land use - Agriculture
- Compaction of soil by livestock increases overland flow
- Ploughing increases infiltration by loosening and aerating the soil
Changing land use - Urbanization
- Urban surfaces speed surface runoff by reducing percolation and infiltration
- Drains deliver rainfall more quickly to streams and rivers, increasing chances of flooding