Please enable JavaScript.
Coggle requires JavaScript to display documents.
Hydrogeology II (Aquifers (Properties (Porosity: fraction of void space in…
Hydrogeology II
Aquifers
Definition : A geological system, an underground layer of water-bearing permeable rock, rock fractures, or unconsolidated materials (sand, gravel) from which groundwater can be extracted using a water well.
Properties
Water table: the upper groundwater surface in an unconfined aquifer. its depth varies according to topography, tidal effects, and quantities of water pumped.
Saltwater Intrusion: Movement of saline water into freshwater aquifers which can lead to contamination of drinking water sources. it can occur naturally to some degree in most coastal aquifers.
Process: Because saline water has a higher mineral content than freshwater, it is denser and has a higher water pressure, salt water can push inland beneath the freshwater.
Groundwater pumping can lead to marine intrusion.
Why do we pump from coastal aquifers?: in small islands, the lack of surface water and long periods of absence of precipitation make groundwater the only conventional and cheaper water resource availability. To avoid this, there are two types of solutions:
-
Horizontal drilling: most suitable solution, but the costs are much higher compared to other techniques.
Capillary fringe: subsurface layer in which groundwater seeps up from a water table by capillary action to fill the pores.
The layer depth ranges from a couple of inches to a few feet, and it depends on the pore size of the material.
Capillary action : the ability of a liquid to flow in narrow spaces without the assistance or even in opposition to external forces like gravity.
-
Catchment area: Hydrological unit where each drop of precipitation that falls eventually ends up in the same river going to the sea if it doesn't evaporate, however, it can take a very long time. catchment areas are seperated by watersheds
-
Acid mine drainage: outflow of acidic water from metal or coal mines. the liquid that drains from the mine is highly acidic and treated as acid rock drainage.
This liquid often contains toxic metals like Copper or Iron, theses, combined with reduced pH, have a detrimental impact on streams aquatic environments.
Radioactive waste repository: A stable geological setting in which a facility for waste is needed, to ensure harmful no quantities of radioactivity ever reach the surface (salt mines).
Types
Unconfined (free): Groundwater is in direct contact with the atmosphere through the open pore spaces of the overlying soil or rock. Usually, recharge by rain or streamwater infiltrating directly through the soil.
Confined: Bodies of water that accumulate in the permeable rock and are enclosed between two impermeable layers.
water pressure is greater than the atmosphere, it takes up all pores and voids of the geological formation completely saturating it.
Recharged by rain or stream water infiltrating the rock at some considerable distance from the confined aquifer.
Perched Aquifer: A special case of an unconfined aquifer. it occurs when an impervious layer of limited area in the form of a lens is located in the water-bearing unconfined aquifer. the top layer is called a perched water table.
Pumping tests
Range of Influence: while doing a pumping test, it is important to know the range of influence, to avoid affecting other wells that are going to be used during the test in the nearby area.
-
-
-