Notes: Ch 14 Groundwater

Precipitation that infiltrates the ground is stored as GROUNDWATER

Water that fills the open spaces in rocks, sediments, and soil beneath the surface.

Rock layers that carry groundwater in enough quantity to supply wells are called AQUIFERS.

Groundwater moves underground from areas HIGH elevation to LOW elevation (just like rivers).

Water movement is SLOW. Imagine water flowing through a sponge. It might move anywhere from less than a millimeter up to a mile in a day.

Ground water that meets the land surface also helps keep rivers, streams, lakes and wetlands FILLED WITH WATER.

GROUNDWATER ZONES

HOW DOES THE AMOUNT OF PRECIPITATION AFFECT THE WATER TABLE?

The water table rises and falls with seasonal changes in PRECIPIATION Precipitation is also known as RECHARGE The area where permeable soil allows water to seep into the ground is known as the RECHARGE AREA

WHAT PROPERTIES OF ROCKS, SOIL AND SEDIMENTS AFFECT HOW MUCH WATER THEY CAN HOLD?

POROSITY:

The percent of a material’s volume that is pore space (How much water a material can hold) Depends on the amount of PORE SPACE or the space between the mineral or sand grains.

PERMEABILITY:

How easily water can travel through a material

FACTORS THAT AFFECT POROSITY

ZONE OF AERATION

ZONE OF SATURATION WATER TABLE

Zone of Aeration: area where the pore spaces in the rock/soil are EMPTY / FILLED WITH AIR

Water Table: boundary between zone of saturation & zone of aeration

Zone of Saturation: area where the pore spaces in the rock/soil are FILLED WITH WATER

FACTORS THAT AFFECT PERMEABILITY

Permeability is affected by PACKING and PARTICLE SIZE

HIGH permeability = loose packing and large particles. Ex. Conglomerate, Sandstone

LOW permeability = tight packing and small particles. Ex. Siltstone, Shale

GROUNDWATER CHARACTERISITICS

Groundwater is a replica of the land surface. Groundwater will move downslope. Rivers & lakes are intersections of the water table and the land surface. Most groundwater empties or discharges into rivers, lakes, ocean Where the water table meets the land surface, groundwater can seep from the ground forming a

SPRING

WELLSGroundwater is good for drinking, watering crops, bathing and much more. How do we get it to the surface? Make a WELL. Wells must be dug BELOW THE WATER TABLE to reach water. In Virginia, most of our drinking water is from RIVERS & GROUNDWATER.

TYPES OF WELLS

1. PUMPING Well

A hole is drilled or dug down below the water table into the zone of saturation.

When water is pumped out it creates a CONE OF DEPRESSION.

Over pumping can lower the water table and is a major problem in some areas.

2. ARTESIAN Well

Water in the well flows to the surface without being pumped because it pressurized (under the force of gravity).

Forms when the aquifer is confined on top and bottom by impermeable rock layers known as an ARTESIAN FORMATION.

Notes: Ch 14 Karst Topography & Caves

1. PARTICLE SIZE - rounded particles have greater porosity than angular particles

2. PACKING - the more closely packed the particles the lower the porosity

3. SORTING - well sorted particles will have a higher porosity than poorly sorted ones

Karst Topography

They are regions characterized by CAVES, SINKHOLES, lost rivers or sinking streams, and underground drainage.

Forms in areas with carbonate bedrock (made of the mineral calcite – CaCO3) like LIMESTONE or dolomite. Development of Caves

1. LIMESTONE is a common carbonate bedrock that dissolves more easily than some types of rock.

2. The carbonic acid found in groundwater dissolves the CALCITE found in limestone.

3. Over time as more and more water flows through cracks in the limestone bedrock, the carbonic acid DISSOLVES the limestone and carries it away in solution.

4. After thousands of years, these cracks become larger eventually forming a network of TUNNELS

5. These CAVERNS, or caves can be many miles long and hundreds of feet deep.

Development of a Sinkhole by Erosion

Step 1: ACIDIC GROUNDWATER DISSOLVES LIMESTON. Then the water table drops, leaving empty caves.

Step 2: Ground above the caves is eroded away.

Step 3: Thin rock above the cave collapses, CREATING A SINKHOLE

Other Causes of Sinkhole Formation: GROUNDWATER WITHDRAWL, SUFACE LOADING

Lost Rivers and Sinking Streams

Because rainwater drains through sinkholes, there

are FEW SURFACE RIVERS in Karst regions.

LOST or SINKING RIVERS/STREAMS form when the

surface stream disappears underground and flows

out of a cave many miles away.

Cave Formations

3.2.1.

When water drips from the roof of a cave, calcite is deposited.

Slender deposits called STALACTITES hang like icicles from the roof.

On the cave floor beneath them, a rounded mass called STALAGMITES form.

When they meet, a COLUMN is formed.

GEOTHERMAL – heat from within Earth

Geothermal Energy heats groundwater forming HOT SPRINGS & GEYSERS