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1 - Introduction to Groundwater

Read this page and complete these activities before the class. Look at this page http://techalive.mtu.edu/meec/module01/Thehydrologiccycle.htm

Q. What has to happen to make groundwater?

Water in three states: liquid, solid (ice), and water vapor in the air. Clouds are water droplets, condensed from vapor-saturated air.

Water changes from one state to another. So water can be solid, liquid or gas.

Water also moves.

We call this the Water Cycle. Another name is the hydrologic cycle.

http://ga.water.usgs.gov/edu/watercyclekoreanhi.html

cycle – 주기

circulation – move around something like a circle.

http://ga.water.usgs.gov/edu/watercycleprint.html

Complete this quiz about the Hydrologic Cycle http://techalive.mtu.edu/meec/module01/HydrologicQuiz.html

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Classroom test

1, Match the letters with the name.

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Here is an animation about Evapotranspiration. http://techalive.mtu.edu/meec/module01/Transpiration2.html

Q. In evapotranspiration, plants lose water through the leaves. How do plants get water? If there is high transpiration, what will happen to water in the soil? Discuss this with another student and answer the questions in socrative.com _______________________________________________________________________________

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Introduction to Groundwater When water is on the ground some of it goes into the ground. This is infiltration of the water into the ground. The water in the ground is called groundwater. We can’t see the ground-water environment. Often we think that the ground is solid. But there are many openings that exist between the grains of sand and silt, between particles of clay, or along the cracks in rock such as granite.

Rocks/Soil and Water

Granite Limestone

Draw a picture of infiltration.

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Porosity The ratio of openings (voids) to the total volume of a soil or rock is named its porosity. Porosity is expressed either as a decimal fraction or as a percentage.

𝑛 =𝑉𝑡−𝑉𝑠

𝑉𝑡 =

𝑉𝑣

𝑉𝑡

n is porosity as a decimal fraction, Vt is the total volume of a soil or rock sample, Vs is the volume of solids in the sample, Vv is the volume of openings (voids).

Soils are very porous natural materials

soil particles can form loose clumps and because of the root holes and animal burrows.

Porosity of unconsolidated deposits depends on

the range in grain size (sorting) and the shape of the rock particles but not on their size.

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Infiltration Look at an animation of infiltration http://techalive.mtu.edu/meec/module01/Infiltration2.html Infiltration rates depend on land use, the type and moisture content of the soil, and the amount of precipitation. Look at this animation of infiltration rates http://techalive.mtu.edu/meec/module01/ImperviousSurface.html What happens as the percentage of impervious surface increases?

In this picture you can see that here the groundwater is higher Infiltration replaces soil moisture, and then moves slowly to the saturated zone.

Water Flow What happens to the water which has risen highest? Water will move down a slope. This moving is called flow.

The groundwater will move from high areas to low areas such as valleys or the sea. The direction of flow is shown by the slope of the groundwater which is called the hydraulic gradient. Or the flow is in the direction from high pressure to low pressure. Generally, water will flow from high to low. Here is a diagram showing that we can make a map of how high the groundwater is. It is a contour map.

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Groundwater Zones

Unsaturated Zone = Vadose Zone = Soil-water Zone = Zone of Aeration. It has rock/soil, water and air. The upper part of the unsaturated zone is the soil-water zone. Soil water is used by plants, but it also can evaporate into the atmosphere.

Saturated Zone. It has rock/soil and water, but no air. All the spaces are filled with water.

Water in the saturated zone is called ground water.

Voids = spaces = pores

The Water Table is the top of the saturated zone.

The depth to the water table: zero, when it is at land surface, to hundreds or even thousands of meters.

Surface waters are exposed water table. We can see surface water as lakes , rivers or the sea. Surface waters are directly connected to groundwater.

Capillary Fringe is above the water table. It is where water rises because of capillary forces in the porous medium.

Some parts of the subsurface do not let water in. These are confining layers, or confining beds, or impervious layers.

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Infiltration and Recharge

Ground water moves along flow paths. Groundwater is transmitted from areas of recharge to areas of discharge. Usually, the depth to the water table is small near surface water such as streams, lakes, and wetlands. The water table can change by season and year because groundwater recharge is related to the quantity (how much), distribution (where), and timing (when) of precipitation.

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Water can dissolve many things. Water - 2 atoms of hydrogen and 1 atom of oxygen, - a chemical formula of H2O. Water can dissolve at least small amounts of almost all substances that it contacts. Ground water usually has the large amounts of dissolved solids. What substances dissolved in ground water depend on

- chemicals in the precipitation, - biologic and chemical reactions on the land surface and in the soil, - what substances are in the aquifers and confining beds through which the water moves.

Quality of Groundwater.

The concentrations of substances dissolved in water are in units of weight per volume. In the International System (SI), the most commonly used units are milligrams per liter.

A milligram equals 1/1,000 (0.001) of a gram, and a liter equals 1/1,000 of a cubic meter, so 1 mg/L equals 1 gram m -3.

The concentration of most substances dissolved in water is small. The weight per weight unit commonly used is parts per million (ppm).

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Groundwater is an important source of freshwater.

Water is used for agriculture 농업

56% is used by animals and plants

20% is lost when the water is moved

24% flows back into the stream or ground.

Water is used for making electricity. This is

87% of all industrial water use.

Questions 1. Draw a diagram showing the different zones of groundwater. 2. Draw a diagram showing infiltration. 3. What is a capillary fringe? 4. What is infiltration? 5. What is recharge? 6. How does infiltration affect recharge? 7. What is porosity? 8. Why is porosity important for groundwater?

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