Groundwater
Groundwater
•
Groundwater ---> water stored in open spaces
within underground rocks and sediments.
•
More than 65% of the groundwater used in the
U.S. is attributable to agricultural needs.
•
in many places.
>
New sources must be found;
>
Existing resources must be protected.
>
A non-renewable resource in most places
•
Capable of shaping the landscape (
>
erosion and deposition of silt, clay, and dissolved materials
>
forms
caves, sinkholes, and speleothems
•
Groundwater ---> water stored in open spaces
within underground rocks and sediments.
•
More than 65% of the groundwater used in the
U.S. is attributable to agricultural needs.
•
Demand has depleted the supply of groundwater
in many places.
>
New sources must be found;
>
Existing resources must be protected.
>
A non-renewable resource in most places
•
Capable of shaping the landscape (
Karst
)
>
erosion and deposition of silt, clay, and dissolved materials
>
forms
caves, sinkholes, and speleothems
Porosity & Permeability
Porosity & Permeability
•
Porosity
>
that portion of the material's volume which is
pore spaces.
>
i.e.
•
Permeability
>
the ability of a material to transmit fluids.
>
i.e.
the degree of interconnectedness of
the empty space
•
Porosity
>
that portion of the material's volume which is
pore spaces.
>
i.e.
the amount of empty space in rock
or sediments
•
Permeability
>
the ability of a material to transmit fluids.
>
i.e.
the degree of interconnectedness of
the empty space
Porosity affected by
particle size, particle shape, sorting of particles, amount of material cementing the grains together, fractures in materials, and internal arrangement of particles
Typical Porosity values
Permeability
Permeability
•
Materials must have both
&
Permeability
to allow water to move
through it!
•
Materials must have both
Porosity
Permeability
to allow water to move
through it!
•
Styrofoam has high porosity
>
this makes it a good insulator
-
keeps things hot or cold
•
Styrofoam has low permeability
>
allows you to keep liquids in it.
>
clay has high porosity, but low
permeability-> little water movement
through clay
•
Styrofoam has high porosity
>
this makes it a good insulator
-
keeps things hot or cold
•
Styrofoam has low permeability
>
allows you to keep liquids in it.
>
clay has high porosity, but low
permeability-> little water movement
through clay
Materials with high porosity AND high permeability
Unlithified (sediment)
Sand
Gravel
Lithified (rock)
Sandstone
fractured limestone
fractured granites
Aquifers and Aquicludes
Aquifers and Aquicludes
•
Aquifer
>
a
porous
&
permeable
layer capable of
transmitting groundwater.
-
well rounded, well sorted, sand & gravel.
•
Aquiclude
(or
Aquitard
)
>
an
impermeable
layer preventing
movement of groundwater.
-
Shales, unfractured Ign & Mm Rxs.
•
Aquifer
>
a
porous
&
permeable
layer capable of
transmitting groundwater.
-
well rounded, well sorted, sand & gravel.
•
Aquiclude
(or
Aquitard
)
>
an
impermeable
layer preventing
movement of groundwater.
-
Shales, unfractured Ign & Mm rock, crystalline
limestone.
Water Table
the boundary between saturated (filled) vs unsaturated (unfilled) pore spaces
In unconfined aquifer systems only
Confined systems
Groundwater is confined between impermeable
layers (
Aquicludes
or
Aquitards
) and builds up
hydrostatic pressure.
Water rises to that pressure surface once a well is
drilled.
Groundwater is confined between impermeable
layers (
Aquicludes
or
Aquitards
) and builds up
hydrostatic pressure.
Water rises to that pressure surface once a well is
drilled.
Many rural communities utilize this principle with
water towers as the municipal water supply.
Many rural communities utilize this principle with
water towers as the municipal water supply.
Modifications & Effects on
Groundwater
Modifications & Effects on
Groundwater
•
•
Modifications will....
>
1) lower the water table;
>
2) decrease hydrostatic pressure;
>
3) allow saltwater encroachment;
>
4) cause subsidence;
>
5) allow contamination of the groundwater.
•
Currently ~20-30% of the water used in the U.S. is
groundwater. Much higher in some places
•
Modifications will....
>
1) lower the water table;
>
2) decrease hydrostatic pressure;
>
3) allow saltwater encroachment;
>
4) cause subsidence;
>
5) allow contamination of the groundwater.
Salt Water Intrusion
Ground water related subsidence
ground levels have decreased in elevation due to water withdrawal from aquifers
Contamination issues-1: Septic tanks
Contamination issues-2: landfills
Wetlands and groundwater
Many wetland areas are tied to water by location
e.g., riverine, downslope, lake/sea margins, etc.
Most wetlands are fed in part by groundwater and surface water
e.g., fens, marshes, swamps
Thus groundwater serves to stabilize water levels over longer term, feeding water to the system over extended dry periods, and providing mineralogical nutrients to the biological and geological systems.
Bogs are a unique case, as they are not typically influenced by groundwater outside the perimeter of the wetland area, yet still have groundwater within them.
Types of Wetlands
Marshes – areas of land that are frequently to constantly inundated and are characterized by soft stemmed emergent vegetation
Swamps -areas of land that are frequently to constantly inundated and are characterized by woody emergent vegetation
Bogs – a wetland fed almost exclusively by precipitation characterized by excessive peat deposits, acidic conditions, are somewhat nutrient poor, and have a sphagnum moss surface carpet.
Fens – Peat forming wetlands fed by many sources of water/nutrients. Nutrient rich, less acidic, and generally more diverse than Bogs
Swamp
Marsh
Bog
Bog- note the boardwalk
Fen
Hot groundwater-geysers and hot springs
Karst landscapes
Created by groundwater and streams dissolving limestone
pseudokarst involves dissolving non-carbonate rock
Enlarges fractures and pore spaces as rock dissolves
Increases flow of water through the system
Triggers more dissolution of limestone.