UT Arlington GEOL 1301 - Groundwater (3 pages)

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Lecture number:
Lecture Note
University of Texas at Arlington
Geol 1301 - Earth Systems
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GEOL 1301 Fall 2014 Lecture 22 Outline of Last Lecture I Hydrologic Water system cont Outline of Current Lecture II Groundwater Groundwater is the water located beneath the earth s surface in soil pore spaces and in the fractures of rock formations A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table Groundwater is recharged from and eventually flows to the surface naturally natural discharge often occurs at These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute springs and seeps and can form oases or wetlands Groundwater is also often withdrawn for agricultural municipal and industrial use by constructing and operating extraction wells The study of the distribution and movement of groundwater is hydrogeology also called groundwater hydrology Typically groundwater is thought of as liquid water flowing through shallow aquifers but in the technical sense it can also include soil moisture permafrost frozen soil immobile water in very low permeability bedrock and deep geothermal or oil formation water Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults It is likely that much of the Earth s subsurface contains some water which may be mixed with other fluids in some instances Groundwater may not be confined only to the Earth The formation of some of the landforms observed on Mars may have been influenced by groundwater There is also evidence that liquid water may also exist in the subsurface of Jupiter s moon Europa 1 Groundwater makes up about twenty percent of the world s fresh water supply which is about 0 61 of the entire world s water including oceans and permanent ice Global groundwater storage is roughly equal to the total amount of freshwater stored in the snow and ice pack including the north and south poles This makes it an important resource that can act as a natural storage that can buffer against shortages of surface water as in during times of drought 3 Groundwater is naturally replenished by surface water from precipitation streams and rivers when this recharge reaches the water table 4 Groundwater can be a long term reservoir of the natural water cycle with residence times from days to millennia as opposed to short term water reservoirs like the atmosphere and fresh surface water which have residence times from minutes to years The figure 5 shows how deep groundwater which is quite distant from the surface recharge can take a very long time to complete its natural cycle The Great Artesian Basin in central and eastern Australia is one of the largest confined aquifer systems in the world extending for almost 2 million km2 By analysing the trace elements in water sourced from deep underground hydrogeologists have been able to determine that water extracted from these aquifers can be more than 1 million years old By comparing the age of groundwater obtained from different parts of the Great Artesian Basin hydrogeologists have found it increases in age across the basin Where water recharges the aquifers along the Eastern Divide ages are young As groundwater flows westward across the continent it increases in age with the oldest groundwater occurring in the western parts This means that in order to have travelled almost 1000 km from the source of recharge in 1 million years the groundwater flowing through the Great Artesian Basin travels at an average rate of about 1 metre per year Reflective carpet trapping soil vapor Recent research has demonstrated that evaporation of groundwater can play a significant role in the local water cycle especially in arid regions 6 Scientists in Saudi Arabia have proposed plans to recapture and recycle this evaporative moisture for crop irrigation In the opposite photo a 50 centimeter square reflective carpet made of small adjacent plastic cones was placed in a plant free dry desert area for five months without rain or irrigation It managed to capture and condense enough ground vapor to bring to life naturally buried seeds underneath it with a green area of about 10 of the carpet area It is expected that if seeds were put down before placing this carpet a much wider area would become green

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