Please note that images are drawn for an easier understanding and the actual ground layers are a lot more complex than this simplified drawing.
Firstly, a city or an industrial estate is built above a source of aquifer.
When demand for water increases, groundwater becomes an easy source of water to extract. Water extractors are usually built above the aquifer to extract water for household and industrial usage.
When the rate of extraction surpasses the rate of groundwater natural replenishment, water level decreases. Since level of water is lower than the previous level, original supporting pressure to the above layers of earth is also reduced.
Finally when the Aquifer layer can no longer support the weight of layers above it, ground subsides. The buildings above collapse as the ground subside, causing damages to properties.
After the subsidence of land, the subsided area also becomes a pan-like shape and traps water as rain falls. This unintentional water welling can be a potential health problem as mosquitoes and other insects breed in the ponds.
Another issue with groundwater extraction is Salt Water Intrusion.
Originally, aquifer filled with groundwater provides pressure to push the salt water away from intruding into land.
As groundwater is being extracted for use, Salt Water from sea is able to infiltrate the land and contaminate the water source and soil. Problem with salt water intrusion may include water contamination, soil degradation and erosion.
very good
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