Lecture 17 - Chapter 17 Groundwater Importance of...

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Chapter 17 Groundwater Importance of groundwater Groundwater is water found in the pores of soil and sediment, as well as in narrow fractures and joints in bedrock Groundwater is the largest reservoir of fresh water that is readily available to humans Geological role of groundwater As an erosional agent groundwater slowly dissolves the soluble rocks such as limestones and produces Sinkholes Subterrain caverns Groundwater serves as an equalizer of streamflow – because the groundwater itself is a form of a storage that sustain streams during periods when rain does not fall. If the groundwater supply to a river will be cut of in 11 days the river will turns dry ! Distribution of groundwater ( in descending order from ground level ) Zone of aeration – uppermost layer of soil where openings in soil, sediment and rock are not saturated but filled mainly with air Zone of soil moisture – near-surface zone within the zone of aeration Some of water that soaks in does not travel far This water is held by molecular attraction and it forms a film of water around soil particles Water not held as surface film percolates downward and forms a zone of saturation Capillary fringe – a relatively narrow zone at the base of the zone of aeration Extends upward from the water table Groundwater is held by surface tension in tiny passages between grains of soil or sediment Water table The lower limit of zone of aeration and the upper limit of the zone of saturation is a water table The water table is important in predicting the productivity of wells, explaining the changes in the flow of springs and streams, and accounting for fluctuations in the levels of lakes. Zone of saturation – zone where all of the open spaces in sediment rock are completely filled with water. Zone of aeration Area above the water table Includes the capillary fringe and the belt of soil moisture Water cannot be pumped by wells out of this zone Water Table What is the depth of the water table ? Depth is highly variable from 0 to a few hundreds of meters Varies seasonably and from year to year Does water table has a shape ? Yes it does ! Shape is usually a subdued replica of the surface topography – it reaches its highest
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Lecture 17 - Chapter 17 Groundwater Importance of...

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