Grunnvatn

Grunnvatn is subsurface freshwater held in soil pores and rock fractures. It is a major component of the world’s freshwater and a key source for drinking water, irrigation, and industry. Grunnvatn is replenished mainly by infiltration of precipitation and surface water and discharges to streams, springs, or wells. Movement through the subsurface is generally slow and controlled by geology.

Groundwater occurs in aquifers, permeable rock or sediment that store and transmit water. An unconfined aquifer has its upper boundary at the water table and is recharged directly from above. A confined aquifer is trapped between impermeable layers and may be under pressure, with groundwater rising to the surface as springs or being pumped.

Groundwater flow follows hydraulic gradients and is described by Darcy's law. It is influenced by porosity and hydraulic conductivity. Residence times vary from months to centuries, depending on depth and permeability. Quality is controlled by geology and interactions with surrounding soil and rock.

Quality concerns include contamination from farming, industry, and road salt, as well as naturally occurring minerals such as iron or arsenic. Slow groundwater movement can prolong polluted plumes. Protection of recharge areas and monitoring are common management measures.

Management seeks sustainable yield and protection of water bases for surface systems. Approaches include mapping, regulated pumping, and artificial recharge where appropriate. Climate change and sea-level rise can alter recharge and cause saltwater intrusion in coastal aquifers.