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Effects of Wells, Droughts, and Land Cover

Pumping from wells causes changes that limit the availability of groundwater for human use. Changes in recharge caused by droughts, climate change, and land-cover changes also affect groundwater availability.

Effects of Wells


Most municipal wells on Saipan withdraw groundwater from the thin freshwater lens in the limestone aquifers. Withdrawing groundwater from these wells causes the lens to shrink—the water table declines and the underlying saltwater and transition zone rise and migrate inland. 

Withdrawals also cause a reduction of natural groundwater discharge to the ocean. Wells drilled too deep (for example, into the transition zone) can pump salty water. Wells can also become salty over time, depending on how deep the wells are, the spacing between wells, and how hard they are pumped. The risk of pumping saltwater can be reduced by distributing withdrawal among many small-capacity wells rather than a few large-capacity wells.

 

Media
Cross section of the island hydrology for pre-pumping and while pumping groundwater.

 

Effects of Droughts and Changes in Land Cover


Because the ultimate source of groundwater is rain, droughts can cause reductions in groundwater recharge, which in turn can cause thinning of the freshwater lens and greater potential for saltwater intrusion into wells. Also, because vegetation and other types of land covers can affect how much of the rainwater becomes groundwater recharge, changes in land cover can affect groundwater resources.
 

 


 

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