Yet, it is what percentage of the total liquid freshwater?

-94.05 %

Why can streams flow even when it is not raining?

-Much of the water that flows in rivers is not direct runoff from rain and snowmelt.  Rather, a large percentage of precipitation soaks in and then moves slowly underground to stream channels.

-Groundwater is thus a form of storage that sustains streams during periods when rain does not fall.

-Therefore, when we see water flowing in a river during a dry period, it is rain that fell at some earlier time and was stored underground.

How many gallons of freshwater are used daily in the US?

345 billion gallons

zones of groundwater

(1)    Zone of Soil Moisture

(2)    Unsaturated Zone –

 (3)  Capillary Fring

     (4)  Water Table –

                  (5)  Zone of Saturation –

(1)    Zone of Soil Moisture – 

-This near-surface zone is called the zone of soil moisture.

-It is criss-crossed by roots, voids left by decayed roots, and animal and worm burrows that enhance the infiltration of rainwater into the soil.  

(1)    Unsaturated Zone – 

-the areas above the water table that includes the capillary fringe and the zone of soil moisture is called the unsaturated zone.

-the pore spaces in this zone contain both air and water. 

                  (3)  Capillary Fringe –

                  -extending upward from the water table is the capillary fringe.

                                    -here groundwater is held by surface tension in tine passages between grains of soil or sediment.

                  (4)  Water Table – 

                                    -the upper limit of the zone of saturation 

                  (5)  Zone of Saturation –

-water that is not held as soil moisture percolates downward until it reaches a zone where all of the open spaces in sediment and rock are completely filled with water.

What influences the storage and movement of groundwater?

1. Porosity

2. Permeability

                  3. Aquitards and Aquifers

Porosity

the percentage of the total volume of rock or sediment that consists of pore spaces.

-water soaks into the ground because bedrock, sediment, and soil contain countless voids or openings. These openings are similar to those of a sponge and are often called pore spaces. 

Permeability

(1)    material’s ability to transmit a fluid.

-rock or sediment may be very porous yet still not allow water to move through it. The pores must be connected to allow water flow, and they must be large enough to allow flow.

permeability

material’s ability to transmit a fluid.

                  What is a good example of a material composing aquitards?

-Impermeable layers that hinder or prevent water movement are termed aquitard

-Clay 

                  What makes for a good aquifer?

                  -permeable rock strata or sediment that transmit groundwater freely are called aquifers.

-Sands and gravels are common examples.

  What is the most common method of extracting groundwater?

- Well- a hole drilled into the saturated zone.

-While pumping a well, the water table may fluctuate.

                  -mostly due to seasonal changes.

                  How far must a well be drilled in order to be productive?

-the water-table level may fluctuate; therefore, to ensure a continuous supply of water, a well must penetrate below the water table. 

What happens if you pump too much water from a well?

-a conical depression in the water table known as a cone of depression.

 What is an artesian well?

-free-flowing wells that are abundant in Artois regions of France.

                  What are the two conditions needed for artesian wells to exist?

(1) Water must be confined to an aquifer that is inclined

                  (2) Aquitards, both above and below the aquifer must be present to prevent water from escaping.

-Artesian wells are products of confined aquifers.

                  -when such an aquifer is tapped, the pressure created by the weight of the water upslope will force the water to rise.

10.  What are some common groundwater contaminants?  (Don’t have to list them all, just a few!)

-pollution is a serious matter where aquifers provide water to a large population.

-common sources of groundwater contamination:

-highway salt (North)

-fertilizers

            -pesticides

                  -etc.

 How can groundwater be purified (naturally!)?

-contaminated groundwater can be purified simply by migrating through the subsurface

                  -a few dozen meters usually purifies the groundwater

-possible when pore spaces are large enough to permit water migration

                  -yet, the migration needs to be slow enough to allow time for its purification,

                  About how fast does groundwater move?

~1/3 foot per day…..SLOWWWWWWW

-high permeability aquifers allow contaminated groundwater to freely travel without being purified.

-permeable aquifers allow contaminated groundwater to be cleansed given enough time.

12.  What type of contamination do you have to worry about in coastal areas?

-Saltwater contamination

                  -because freshwater is less dense, it sits atop the saltwater in a large, lens-shaped body.

-saltwater can extend to considerable depth below sea level and threatens freshwater wells.

-when drilling wells in coastal areas, the Ghyben-Herzberg Relation must by calculated before drilling.

 What is the Ghyben-Herzberg Relation?

If the water table is 1 meter above sea level, the base of the freshwater body will extend to a depth of ~40 meters below sea level.

                  -the extent of freshwater below sea level is 40X greater than its elevation above sea level.

  What happens to a subsurface saltwater body during excessive pumping of a nearby freshwater well?

-Saltwater contamination

-during excessive pumping, drawdown will be reflected by a rise in the freshwater/saltwater interface.

                  -bottom of the freshwater zone will rise by 40X the amount of the drawdown.

-If groundwater withdrawal continues to exceed recharge, eventually the saltwater will be drawn into the well.

                  What type of wells are usually the first affected?

-deep wells and near shore wells are usually first to be affected.

The Geologic Work of Groundwater

-groundwater dissolves rock over time

             -soluable rock dissolves more quickly

                 Ex. Limestone

                  -resulting in caverns and sinkholes

-Why should we care?? 

-millions of km² of limestone underlie Earth’s surface.

                  -there is also a large volume of groundwater.

-Limestone is nearly insoluble in pure water

What happens when groundwater comes into contact with limestone?

-small quantities of carbonic acid  causes limestone to dissolve.

-when groundwater contacts limestone, the following reaction occurs:

                  CaCo₃ + H₂CO₃ à Ca(HCO₃)₂

   (calcite)   (carbonic    (calcium biocarbonate)

                                              acid)                  

Caverns

-spectacular result of groundwater’s effects are caverns.

-about 17,000 caves are within the US boundaries.

-most are small, but some have huge dimensions.

  What is the most extensive cave system in the world?

-Mammoth Cave, KY-

-The Big Room, Carlsbad Caverns, NM= 14 football fields

  What type of features are dripstones?

-stone formations decorating a cavern’s floor, walls, and ceilings are depositional features.

                  When can it form?- dripstones

-dripstone formation is not possible until the cavern is above the water table (not filled with water).

-as soon as air fills the cavern, dripstone can form.

  What is the technical (scientific) term for dripstones?

-Speleothems

-no two are alike

Stalactites

– icicle-like pendants hanging from ceiling

-form as water drips from the ceiling, leaving infinitesimal amounts of calcite with each drip.

-began as soda straws that were plugged with calcite, forcing water to flow on the outside of the straw.

Stalagmites

– speleothems that grow up from the floor

  -form when drops of water fall from ceiling and splatters over the surface

            -because water splatters, stalagmites appear massive

Soda Straws

– hollow tubes; “baby stalactites”

Columns

– joined stalactite and stalagmite

 What is karst topography?

-many areas of the world have landscapes that, to a large extent, have been shaped by the dissolving power of groundwater.

-named for the Krs Plateau in Slovenia located along the northeastern shore of the Adriatic Sea where topography is strikingly developed.

                  Where can you find it (karst topography) in the USA?

-In many areas that are underlain by limestone, including portions of Kentucky, Tennessee, Alabama, southern Indiana, and central and northern Florida.

-Generally, arid and semiarid areas are too dry to develop karst topography.

  What is a common feature of areas exhibiting karst topography?

-irregular terrain punctuated with many depressions called sinkholes or sinks.

          (1)        How do sinkholes form?

(1)    Some develop gradually over many years without any physical disturbance to the rock.

-in these situations the limestone immediately below the soil is dissolved by downward-sweeping rainwater that is freshly charged with carbon dioxide.  With time, the bedrock surface is lowered and the fractures into which water seeps are enlarged.

-as the fractures grow in size, soil subsides into the widening voids, from which it is removed by groundwater, flowing in the passages below. These depressions are usually shallow and have gentle slopes.

        (2)     How do sinkholes form?

   Some form abruptly without warning when the roof of a cavern collapses under its own weight.

-typically, the depressions created in this manner are steep-sided and deep. 

-when they form in populous areas, they may represent a serious geologic hazard.