Natural & Human Factors Affecting The Water (Hydrological Cycle) on a Drainage Basin Scale
Table of Contents
Different factors, natural or man-made can affect inputs, flows, storages and outputs within a drainage basin. While some factors positively affects a drainage basin, some factors hinders and negatively affects the processes going on in it.
Climate covers different perspectives of weather from temperature to precipitation. High rainfalls imply more input into the drainage basin; thus, more flows and storages within the basin.
However, precipitation deficits also mean water deficit in the basin. Light to no rainfalls imply that water will not reach the ground, and if intercepted by plants or buildings, the little water quickly evaporates.
In arid regions drainage basins are dry most of the year except few days of heavy rainfall. Some of the rain does not infiltrate or get stored as groundwater because of the nature of surface (impermeable) which encourages high runoff.
The same can occur in glacial areas where frozen surfaces impede (reduces) infiltration. High temperatures favour more evaporation from the drainage basin resulting in water deficits.
Rocky or ice surfaces in arid and glacial regions impede infiltration; therefore, less water will be stored underground. These surfaces encourage large amounts of runoff.
However, porous surfaces such as limestone and sand encourages more infiltration which feeds groundwater.
Vegetation stores and impedes water from reaching the surface.This happens given that rainfall is less. However, vegetation can absorb and store water which turn can be transpired contributing to condensation and therefore rain which is supplied to the basin again. In addition, vegetation roots encourages water to infiltrate.
Rock Type/Soil Type
Impermeable rocks such as granite does not store water. Conversely porous rocks such as limestone are easily filled with water thus encourage groundwater storages. Soils such as sand have large pore spaces an can store water compared to cohesive clays.
Bioturbation (Animal Action)
Small animals burrow and leave tiny voids which water can infiltrate in feeding groundwater in the process.
Human Impact on the Hydrological cycle
Deforestation and Afforestation
Cutting down trees have positive and negative influences on the hydrological cycle. One positive influence is that water readily reaches the surface and is not intercepted by any vegetation. However, deforestation has many drawbacks to the basin.
Lack of trees implies that there is less transpiration and therefore less condensation and rainfall. Tree roots absorb water and favour infiltration and percolation to the groundwater.
In addition, vegetation reduces excess runoff which eventually leaves the drainage basin rather than being stored within the basin.
Buildings can intercept and store considerable amounts of rain water and lessen water reaching the drainage basin.
Dams provide more storage; thus, evaporation then condensation and eventually rainfall. However, dams impede flows within a drainage basin. Floodgate controls can reduce water downstream.
In addition, wells and boreholes drain more groundwater which can hinder groundwater flow or baseflow.
Smoke from industrial gases can provide condensation nuclei and therefore more rainfall entering a drainage basin. However, gas emissions can greatly reduce rainfall altogether. See Greenhouse & Global Warming
More people mean more road and pavement construction; therefore, less infiltration and high runoff which reduces groundwater and hinder flows respectively. Rivers can be dried out or diverted in order to introduce new settling areas.
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