Including...
Occurrence and movement of groundwater
Review Water Cycle
Evaporation to precipitation (hard rain video - Pooh & Blustery Day?)
Produces fractured and broken rock, and a soil horizon
In a natural setting soil soaks up precipitation
Results in a groundwater system
Which in places leaks onto the surface
General description of groundwater
Floodplain water vs. bedrock aquifers
Groundwater has always held a special and mystical place in human development
Groundwater and wells have been the basis of life forever
Wells have always been important to the development of an area
Source of unpolluted water
Walled cities needed a good INTERNAL source of water to withstand sieges
Water availability represents the ultimate demographic control
Rome - did lead poisoning from water pipes cause the Empire to fall?
Wells - some were quite deep
Orvieto, Italy - 200' deep and had 2 spiral ramps used by donkeys to bring water to the surface
Some Chinese wells were >4900' deep! - How did they dig these?
Technology has allowed humans to seriously impact the water balance
Increased agriculture and urbanization in fundamentally arid lands
The ability to economically retrieve deep groundwater
As opposed to near-surface "floodplain" water
The ability to move it long distances
This is a poor practice in the long term
Will probably result in severe social, economical and political unrest in the N-T-D-Future
Groundwater and surface water are part of the same system
Lots of factors can force the water to leak onto the surface
Climates where there is too much precipitation for the ground to hold
Tropics vs. arid lands
Climates where the weathering & erosion processes are incomplete
Lack of fractures and/or soil
Places where there is some sort of blockage which forces the water out
Springs - places where water flows or seeps onto the surface
Occur where the water table intersects the surface
Can be caused by many different sub-surface conditions
Effluent stream - Gets its water from the water table
Common to temperate climates
Actually, effluent streams are just springs with a lot of water!
Associated with relatively stable water tables (in a natural setting)
Directly reflects the water table
Deer Creek bridge example
Influent stream - Adds water to the groundwater supply
Common in arid regions
The water is usually from more humid areas upstream which are destined to flow down into a desert
EXAMPLE: the Colorado River
Nearly all comes from surface precipitation which soaks into the ground
Estimates of the water budget in the U.S. indicates that:
Precipitation averages 30" per year
Evapotranspiration returns 21" to the atmosphere
Runoff returns 9" to the sea
So, where does groundwater come from?
Obviously, major groundwater systems develop very slowly
And, they are in a very delicate balance relative to use vs. recharge
DEFINE: Recharge area - where water is added to the aquifer
In many areas, groundwater can be considered a non-renewable resource
This is especially true of deep aquifers and arid environments
Water Table - the upper surface of the groundwater
All openings in the rock below are saturated with water
Not necessarily completely level - Roughly parallels the ground surface
Rises with the hills & sinks with the valleys
Intersects the surface in springs, streams and lakes
Vadose Zone - above the water table
Completely dry to partially wet (but not saturated!)
Water moves downward through this zone to the water table
The water table doesn't extend down into the ground forever
Increased heat and pressure creates a lower limit
Sub-surface storage reservoirs:
Aquiclude - can't hold or transmit water
Aquifer: a sub-surface layer of rock which can hold and transmit water
Two basic types of aquifers
Unconfined aquifer
Water level stands at the water table
The water level will drop as a result of pumping
A "Cone of Depression" will form around the well
Over-pumping can cause adjacent cones to intersect
Can result in a regional lowering of the water table
Confined aquifer
A permeable horizon between two impermeable rock layers
Can result in artesian wells
The percentage of the total volume of rock occupied by void space
Factors which determine porosity
Igneous and metamorphic rocks
Generally very dense crystalline rocks
Porosity usually controlled by fractures and faults
Sedimentary rocks
Degree of sorting - probably most important
Amount of cement already filling up the void spaces
Grain size: the effect is confusing
Some shales can actually have up to 90% open space!
However, these extremely fine-grain rocks usually make poor aquifers due to surface tension which holds the water in the rock, leading us to...
The measure of a rocks capability to transmit liquid through it's pore spaces
Generally a very slow process (one reason why the ground leaks!)
Size of the pore spaces can be more important than the amount of space!
As I said above, extremely fine-grain rocks usually make poor aquifers
Porosity alone is useless as far as aquifers is concerned
Without interconnected pore spaces, the water won't flow
Fill beakers with different types of sediments and weigh
Pour in water to fill - measure amount of water in milliliters (1 ml = 1 cm^3)
Weigh again (1 gram = 1 cm3 = 1 ml)
Cover with cheesecloth and pour out water
Record time to completely drain
Weigh again
Note difference - represents the water held due to surface tension
Drilled or dug to tap water from aquifers
Over-pumping can be a real problem in areas of slow recharge
Almost like mining - non-renewable resource in most areas
Southwest - relate the problems in Tucson (Dave Christopherson)
Southern California - relate some of the water haggles
Mono Lake a good example
Now they want to divert water from up here
Open for class discussion?
I say give them the water, even if it means some additional dams
That's better than them all moving up here
Remember-water is the ultimate demographic control, and population centers will adjust to reflect availability
Problems related to water wells
Coastal areas - encroachment of sea water
EXAMPLE: Fountain Valley, California
Land subsidence due to over-pumping
Due to compaction of the sediments after the water is removed
Also results from over-production of oil and/or gas
EXAMPLE: Gulf Coast island
Aquifers can become contaminated easily and in many ways
Axiom: the closer to the surface, the easier to contaminate
Many in developed areas have already been polluted beyond rational use
There are lots of ways an aquifer can become contaminated
Unfortunately, many aquifers were contaminated in the past without an understanding of, or regard for, the long-term consequences
Direct pumping of pollutants underground
"Out of sight, out of mind"
Sanitary landfills in recharge areas
Percolation of water through the dump and into an aquifer
Not-so-sanitary landfills
Hazardous waste dumps
Poor underground mining practices
Relate the problems in the Tri-State lead/zinc district
Nuclear waste disposal
Possibly the most significant long-term problem
Relate the current findings at Hanford
The radioactive waste is reaching the Columbia much sooner than expected
The Columbia River basalt is more permeable than they thought!
Search on for a "permanent" storage facility
Yucca Mountain, Nevada
In areas of poor recharge, restricted permeability, etc., contaminants can persist far longer than we have!
Important to the formation of many sedimentary rocks
As a cementing agent
Transports natural cementing agents into unconsolidated sediments
Geysers and hot springs
Percolating groundwater is heated by a near-surface magma
Mineral deposits commonly surround them
These are leached from subsurface rocks which the super-heated water passes through
2 kinds of hot-water deposits occur
Siliceous sinter - composed of silica
Travertine - composed of calcium carbonate
Geothermal energy
Often these areas can be tapped as a source of geothermal energy
Limestone and Karst topography
Most rain is slightly acidic
Carbonic acid (H2O + CO2 = H2CO3)
Dissolves limestone
Results in underground caverns
Stalactites, Stalagmites, Columns
Karst topography - surface features common to areas underlain by limestone
Distinctive features include:
A lack of surface drainages
Water sinks into underground caverns and waterways
Re-appears farther away, often as a river emerging from a giant spring
Large surface depressions
Can be kilometers across
Probably caused by subsurface solution cavities
Sinkholes
Smaller depressions
Definitely the result of solution of the underlying limestone
Some extend down into caverns
Can act as natural wells if they intersect the water table