The extraction of water by aquifers implies:
- Reduction of groundwater storage
- Groundwater outflow reduction
- Reduction of surface runoff
Safe Yield: The annual amount of water that can be pumped without adverse effects on the aquifer
Overpumping: Any quantity other than safe yield
Zero risk approach: Safe Yield < Annual Recharge
This principle is conservative since in general the exploitation of groundwater, to some extent redistributes, the components of the water balance e.g. increase of pumping à decrease of Groundwater Flow (Qt) the decrease of surface runoff (basic water flow) and losses to the sea.
Each aquifer is evaluated as unique case. For example a coastal aquifer with escapes to the sea is totally different to a karstic aquifer on a mountain.
Undesirable effect of over-pumping that should be avoided.
- Soil settleing (π.χ. Mexico city)
- Ταπείνωση στάθμης φρεατίων οριζόντων
– Aύξηση του κόστους άντλησης
– Καταστροφή πιο αβαθών γεωτρήσεων (νομικά κ.α. θέματα) - Reduction of river runoff (effects on ecosystems, restriction of surface flows)
- Reduction of surface water supply of lakes (effects on ecosystems, surface extraction restrictions)
- Over-pumping in coastal areas -> seawater infiltration -> gradual salinization of groundwater
Estimating safe yield
- From water balance
- Pumping Test
