EPSC 201 Lecture Notes - Lecture 19: Hydraulic Head, Subsidence, Aquifer

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!OpenNended%pipe%%%
!Installed%below%the%water%table%%
!Water%level%is%the%hydraulic%head%
!!Flow%paths%are%not%straight%lines.%%
!Flow%follows%a%curved,%concaveNup%path.%%
!Water%can%flow%upward%as%it%moves%to%a%lower%hydraulic%head.%
!!Groundwater%flow%occurs%on%a%variety%of%scales.%%%
!Local—shallow%flow%over%short%times%and%distances%%
!Intermediate—flow%of%moderate%depth,%time,%and%distance%%%
!Regional—deep,%longNdistance,%longNduration%flow%
!!Groundwater%infiltrates%through%recharge%areas.%%
!Flow%is%directed%downward.%%
!Commonly%found%in%topographic%uplands.%%
!!Groundwater%exits%the%subsurface%at%discharge%areas.%%
!Flow%is%directed%upward.%%
!Usually%observed%in%topographic%lows%
o!Permeability%mainly%controls%groundwater%flows%
!!Permeability%is%the%ease%of%water%flow%due%to%pore%interconnectedness.%%%
!!Highly%permeable%material%allows%water%to%flow%readily.%
o!Aquifer%
!!It%is%a%hydrogeological%unit%that%is%saturated%and%sufficiently%permeable%to%
transmit%economic%quantities%of%water%to%wells%and%springs%
!!Five%main%qualities:%
!Groundwater%
!Permeable%Material%
!Good%porosity%
!Drinkable%water%
!Economic%quantities%
!!Wells%are%holes%drilled%or%dug%into%the%saturated%zone.%%
!Water%is%recovered%by%lifting%or%pumping.%%
!Water%flows%from%the%aquifer%into%the%well.%
!!With%drawdown,%the%water%table%near%the%well%drops.%%
!!WaterNtable%decline%forms%a%cone%of%depression:%%
!A%downwardNpointed%conicalNshaped%surface%%
!Steepest%near%the%well;%flattens%with%distance%%
!The%cone%may%expand%outward%with%continued%pumping.%
o!What%are%groundwater%problems?%
!!Saline%Intrusions:%
!Saltwater%intrusion%renders%the%water%unpotable.%%
o!Beneath%coastal%land,%freshwater%“floats”%on%saltwater.%%
o!Pumping%causes%the%fresh/salt%boundary%to%rise.%%
o!Eventually,%saltwater%may%enter%the%pumping%well.%
!!Pore%Collapse%and%Land%Subsidence%
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