The Groundwater Reservoir
Atmosphere
Evaporation
Eva
Evaporation
iratio
n
( ) = Storage
potr
Liquid
Flow
ansp
Vapor
Precipitation
(water vapor)
The Hydrologic Cycle
surface
Land
Streams
Lakes
etc.
Surface
Oceans
Infiltration
Overland flow =
Direct Runoff
(Surface water)
(Seawater)
Volcanic outgassing
Interflow
Vadose Zone
(Soil moisture)
Runoff = Streamflow
Infiltration
Groundwater flow
and Baseflow
(Ground water)
Subduction
Subsea outflow
Water Table
Seafloor
vents
Gravity
drainage
Hydrologic
Cycle
(Ice, snow,
depression
storage)
Water Table
•Follows the slope of the land
•Meets the surface at wetlands
Stream
Water Table
Groundwater Flow
•Flow from high to low water table
•Flow exits the subsurface at streams = discharge
•Baseflow = groundwater flow feeding streams
•Gaining / perennial stream = fed by groundwater
Gaining Stream
Groundwater Flow
Recharge Area
• Streams
• Swamps
• Lakes
• Springs
• Seeps
Discharge Area
Drought
•Water no longer infiltrates from the surface
•Flow continues underground
•Water table drops
Gaining Stream
Drought
•Water no longer infiltrates from the surface
•Flow continues underground
•Water table drops
Gaining Stream
Drought
•Water no longer infiltrates from the surface
•Flow continues underground
•Water table drops
Gaining Stream
Drought
•Water no longer infiltrates from the surface
•Flow continues underground
•Water table drops
Gaining Stream
Drought
•Water no longer infiltrates from the surface
•Flow continues underground
•Water table drops
Gaining Stream
Drought
•Water no longer infiltrates from the surface
•Flow stops underground
•Water table flattens
Drought
•Water no longer infiltrates from the surface
•Flow reverses underground
•Stream becomes a losing or ephemeral stream.
Losing Stream
Losing Stream
Subsea outflow
• discharge of freshwater along shoreline
Discharge Area
saltwater
Low Tide
freshwater
outflow face
Cape Ann, Mass.
My charming wife.
Aquifer - geologic unit that can store and transmit water in
amounts and at rates high enough to supply usable
wells.
Aquifuge - absolutely impermeable layer.
Aquiclude - low permeability unit that forms upper or
lower boundary.
Aquitard - low permeability unit that can store and slowly
transmit water.
Confining Units - leaky / impermeable
Porosity
• percentage of open spaces in rock and sediment that
can hold water.
• Grain size does not affect porosity.
primary
secondary
Permeability
• The ease with which water flows through porosity.
• Most important variable is grain / pore size.
Pendular water
Porosity Permeability
Gravel
20%
Very high
Aquifer
Sand
20%
High
Aquifer
Clay
50%
Very low
Confining unit
Three types of Aquifers
• Unconfined (water table aquifer open to recharge from the surface)
• Confined (artesian aquifer - capped
by a confining layer)
• Perched (small aquifer above main
water table)
Perched Water Table
Unconfined aquifer (water table aquifer)
• open to recharge directly from the surface
• water table - upper limit of saturation
•recharges directly from precipitation
recharge
water tab
le
unconfined
Well in
unconfined
aquifer
Confining
layer (clay)
Confined aquifer (artesian aquifer)
• NOT open to the surface - topped by a confining layer
• no water table - aquifer is fully saturated
• recharges slowly by leakage across the confining layer
recharge
unconfined
confined
Confining
layer (clay)