Chapter 9 Water Underground

The World’s Water Approx. 97% of the Earth’s water is salt water.Approx. 97% of the Earth’s water is salt water. Approx. 3% is fresh water. –Of this 3%, most is frozen in the ice caps and in glaciers. –This leaves only about ½% of all Earth’s water as usable fresh water. Most of this usable fresh water is found underground. hydrosphereAll of the Earth’s water is part of the hydrosphere

Water Cycle water cycleMovement of water from one part of the hydrosphere to another is called the water cycle. The energy to start the water cycle comes from the sun (causes evaporation to begin).The energy to start the water cycle comes from the sun (causes evaporation to begin). Water enters the air as vapor from evaporation and transpiration (water given off by plants). The vapor cools and condenses into clouds, precipitation occurs, and the water flows back into the ground or runs off over the ground into other bodies of water. This is a continuous cycle.

Water in the Ground: Characteristics

The percentage of pore space in the soil is called POROSITYThe percentage of pore space in the soil is called POROSITY. The amount of water that the ground can hold depends on the amount of open space (pore space) between the soil particles.

The Porosity of the soil depends upon 3 things:

The porosity of the soil depends on: #1) Particle shape - –Rounded particles do not fit together well, so they will have more space between them. –Angular particles fit together (like a puzzle), and therefore will have less space between them. Rounded fragments Angular Fragments Which one has higher porosity? Rounded or Angular?

The porosity of the soil depends on: #2) Sorting Well-sorted particles (all the same size), don’t fit together well and have the greatest pore space. Unsorted particles have small particles which fit between large particles, decreasing the amount of open space.

The porosity of the soil depends on: #3) Packing or arrangement Tightly-packed particles are compressed together densely. The amount of space between the particles is reduced, therefore decreasing the pore space. Loosely-packed particles are not compressed together. The amount of air space between the particles is higher, therefore increasing the pore space.

**Particle size does not affect the porosity** Large particles have large spaces, but few of them. Small particles have small spaces, but many of them. The porosities will be equal!! 9 spaces x 2.0 cm 3 = 18 cm 3 30 spaces x 0.6 cm 3 = 18 cm 3

Porosity Percentage Example Before: Beakers filled with 1000 ml of sand (left) and 500 ml of water (right). The water is poured into the sand. After: Sand-filled beaker now contains an additional 350 ml of water. The water filled original pore spaces. The water level in the second beaker had declined from 500 ml to 150 ml. The difference was in the sand-filled beaker. The 350 ml of water filled the pore spaces between sand grains. Therefore, 350 ml of the original 1000 ml sand volume was made up of air-filled pore spaces (porosity = (350  1000) x 100 = 35%).

Permeability Def. - the ability of a liquid to pass through a material’s pore space

Usually, permeability will increase as the size of the particles increases.Usually, permeability will increase as the size of the particles increases. The larger the particles, the larger the pore spaces.The larger the particles, the larger the pore spaces. Liquids (water) move easier through larger openings.Liquids (water) move easier through larger openings. –(water moves easier through a fire hose than through a garden hose)

gravel sandclay

Impermeability If a liquid cannot pass through a material, then it is considered to be impermeable.If a liquid cannot pass through a material, then it is considered to be impermeable. If a material is porous but the pores are not connected, then the material will be impermeable.If a material is porous but the pores are not connected, then the material will be impermeable.

Soil Water Movement

When water infiltrates (soaks) into soil, it gets pulled through the pores by gravity.When water infiltrates (soaks) into soil, it gets pulled through the pores by gravity. The water continues to flow downward until it reaches an impermeable layer.The water continues to flow downward until it reaches an impermeable layer. The water then begins to fill in the pore spaces above the impermeable layerThe water then begins to fill in the pore spaces above the impermeable layer –(like filling a glass with soda – the soda hits the bottom of the glass and then begins to fill the glass).

The layer of soil where all of the pore spaces are filled is called the zone of saturation.The layer of soil where all of the pore spaces are filled is called the zone of saturation. The top of this layer is called the water table.The top of this layer is called the water table. The layer of soil above the water table is called the zone of aeration (air fills the pore spaces).The layer of soil above the water table is called the zone of aeration (air fills the pore spaces). There is a part of the zone of aeration that is just above the water table called the capillary fringe.There is a part of the zone of aeration that is just above the water table called the capillary fringe. –This is where tiny droplets of water move upward by attaching to small particles of soil.

The Water Table

The depth of the water table varies, depending upon the amount of rainfall, seasons, climate, soil thickness, etc.The depth of the water table varies, depending upon the amount of rainfall, seasons, climate, soil thickness, etc. Where the water table does not reach the surface, a pipe may be drilled into the ground down to the water table.Where the water table does not reach the surface, a pipe may be drilled into the ground down to the water table. Water may then be pumped out (similar to using a straw to drink with) through the pipe.Water may then be pumped out (similar to using a straw to drink with) through the pipe. –This is called an ordinary well. –If the water flows out of the pipe without being pumped, because of the pressure in the ground, it is called an artesian well.

Groundwater below a layer of solid rock or clay is in a confined aquifer. The rock or clay is called a confining layer. A well that goes through a confining layer is known as an artesian well.

Groundwater usually remains cool all year. Because of its depth, groundwater is not affected by the weather changes at the surfaceGroundwater usually remains cool all year. Because of its depth, groundwater is not affected by the weather changes at the surface Below 20 meters deep, water may become heated by the Earth’s interior. If it becomes heated to boiling, hot springs may rise to the surface. They may also erupt as gushing springs of boiling water and steam called geysersBelow 20 meters deep, water may become heated by the Earth’s interior. If it becomes heated to boiling, hot springs may rise to the surface. They may also erupt as gushing springs of boiling water and steam called geysers –(Yellowstone National Park in Wyoming is famous for its hot springs and geysers)

And the question on everyone’s mind…what does all this have to do with erosion? Groundwater causes erosion by the following means….

Groundwater can dissolve limestone underground.Groundwater can dissolve limestone underground. Carbonic acid naturally found in groundwater dissolves the calcite in limestone.Carbonic acid naturally found in groundwater dissolves the calcite in limestone. Eventually, large portions of the limestone are dissolved and a cavern (cave) may form.Eventually, large portions of the limestone are dissolved and a cavern (cave) may form. –Howe Caverns in upstate New York is an example of a limestone cavern.

Sinkholes

Devil’s Sinkhole, Rocksprings, Texas (we HAVE to keep the tradition going!)

Groundwater Contamination Groundwater may become polluted by many different means