LECT7 (Subsurface)

LECT7 (Subsurface) - AOM 4932 - Subsurface Water Subsurface...

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AOM 4932 - Subsurface Water Subsurface water - Water occurring below land surface. Groundwater - Water under positive pressure in the saturated zone of earth materials. - constitutes approximately 30% earth’s fresh water approximately 99% liquid fresh water Overall residence time for global groundwater reservoir is centuries to millenia because rate of groundwater movement is generally slow ( < 1 m/day). This is in contrast to 9 day residence time for atmospheric water completely different time scales. Classification of soil-rock profile: soil water p < atm θ n intermediate vadose water capillary water p < atm = n p > atm = n porosity volume voids total volume ( ) n = water content (soil moisture content) volume water total volume ( ) = soil water - Ground surface to bottom of root zone depth depends on soil type and vegetation. May become saturated during periods of rainfall otherwise unsaturated (soil pores partially filled with air). Plants extract water from this zone. Evaporation occurs from this zone. porosity volume voids total volume ( ) n = water content (soil moisture content) volume water total volume ( ) = UNSAT’D ZONE SAT’D ZONE water table p = atm groundwater
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intermediate vadose zone - Between soil water zone and capillary fringe. Unsaturated except during extreme precipitation events. Depth of zone may range from centimeters to 100s of meters. capillary zone - Above saturated zone. Water rises into this zone as a result of capillary force. Depth of this zone is a function of the soil type. Fractions of a meter for sands (mm) to meters for fine clays. All pores filled with H 2 O, p < 0. Effect seen if place bottom of dry porous media (soil or sponge) into water. Water will be drawn up into media to a height above water where soil suction and gravity forces are equal. saturated zone - All pores filled with water, p > 0. Formations in this zone with ability to transmit water are called aquifers. Unsaturated Zone
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This note was uploaded on 03/27/2012 for the course AOE 4643 taught by Professor Graham during the Fall '11 term at University of Florida.

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LECT7 (Subsurface) - AOM 4932 - Subsurface Water Subsurface...

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