2) Using the Smithsonian Institute's Global Volcanism Program Website (

Geol 4110 5/1/08

Class 13 - Water Resources

In Class

·  Intro to the Hydrologic Cycle

·  Water Quiz http://water.usgs.gov/education.html

·  In Class exercise – Porosity and Permeability

In Class Exercise - Porosity and Permeability

Objective - To understand the difference between these two parameters and how they affect the way water moves through earth materials.

Groupings - Work in pairs

Materials - 2 styrofoam cups

Plastic Fork

Graduated water vessels

Large bowl to collect water

4 groups of sediment that differ in grain size and sorting; fine sand, one mixed sediment (clay to coarse sand), coarse sand and fine gravel.

Watch with second hand

Part 1: Porosity - the percentage of open space volume in a given volume of material

1)  Measure the volume of your styrofoam cup which will hold the sediment by filling it to the top with measured volumes of water. Record the volume in column A in the table below

2)  Fill the cup with one type of sediment. Determine what volume of water you can pour into the sediment before it becomes saturated (water crests to the top of the sediment). This volume is the amount of pore space in the sediment. Record this volume in column B in the table below.

3)  Calculate the percent porosity by dividing column B by A and multiplying by 100.

Part 2: Permeability - the rate at which water flows through material

1)  Take the other styrofoam cup and punch a grid of 16 holes into the base with a plastic fork.

2)  Fill the cup half full with the sediment from the porosity measurement

3)  Holding the cup in the palm of your hand, pour enough water into the cup to just saturate the sediment; then pour an additional 40ml into the cup

4)  Positioning the cup over the collection bowl, take your hand away and immediately begin timing how long it takes the water to drop below the top of the sediment. Take general note if the drain rate changes over the observation period.

5)  Record the time in column C in the Table below.

6)  Divide 40ml by the time and record in Column D, this is a measure of the permeability (or flow rate) in ml/sec

7)  Repeat steps 3 to 7 twice more; report your average permeability to the class

Plot the porosity and permeability of your sediment type and those measurements of your classmates on the graph below.

Follow-up Questions

1)  Do porosity and permeability show a linear correlation?

2)  If not, why not?

3)  If so, do you think this will always be the case?

4)  Did the flow rate changed during the draining period? If so, how and why do you think this occurred?

Water Quiz

True False (1) Water contracts (gets smaller) when it freezes.

True False (2) Water has a high surface tension.

True False (3) Condensation is water coming out of the air.

True False (4) More things can be dissolved in sulfuric acid than in water.

True False (5) Rainwater is the purest form of water.

True False (6) It takes more energy to heat water at room temperature to 212o F than it does to change 212o F water to steam.

True False (7) If you evaporate an 8-inch glass full of water from the Great Salt Lake (with a salinity of about 20% by weight), you will end up
with about 1 inch of salt.

True False (8) Sea water is slightly more basic (the pH value is higher) than most natural fresh water.

True False (9) Raindrops are tear-shaped.

True False (10) Water boils quicker at Denver, Co. than at the beach.

Proportion of Freshwater to Saltwater

A) 1.5 : 98.5

B) 2.8 : 97.2

C) 5.4 : 94.6

D) 10.1 : 89.9

E) 21.3 : 78.7

Freshwater Sources

Surface Water 0.2%

Ground Water 14.3%

Ice Cap / Glaciers 85.5%

Vapor 0.04%

(1) Like most liquids, water contracts (gets smaller) when it freezes. --False Actually, water expands (gets less dense) when it freezes, which is unusual for liquids. Think of ice -- it is one of the few items that floats as a solid. If it didn't, then lakes would freeze from the bottom up (that would mean we'd have to wear wet suits when ice skating!), and some lakes way up north would be permanent blocks of ice.

(2) Water has a high surface tension. True Water has the highest surface tension among common liquids (mercury is higher). Surface tension is the ability of a substance to stick to itself (cohere). That is why water forms drops, and also why when you look at a glass of water, the water "rises" where it touches the glass (the "meniscus"). Plants are happy that water has a high surface tension because they use capillary action to draw water from the ground up through their roots and stems.

(3) Condensation is water coming out of the air. This is actually true -- water that forms on the outside of a cold glass or on the inside of a window in winter is liquid water condensing from water vapor in the air. Air contains water vapor (humidity). In cold air, water vapor condenses faster than it evaporates. So, when the warm air touches the outside of your cold glass, the air next to the glass gets chilled, and some of the water in that air turns from water vapor to tiny liquid water droplets. Clouds in the sky and the "cloud" you see when you exhale on a cold day are condensed water-vapor particles.

(4) More things can be dissolved in sulfuric acid than in water. False Sulfuric acid might be able to dissolve a car, but water isn't known as the "Universal Solvent" for nothing! It can dissolve more substances than any other liquid. This is lucky for us... what if all the sugar in your soft drink ended up as a pile at the bottom of the glass? The water you see in rivers, lakes, and the ocean may look clear, but it actually contains many dissolved elements and minerals, and because these elements are dissolved, they can easily move with water over the surface of the earth.

(5) Rainwater is the purest form of water. False Actually, distilled water is "purer." Rainwater contains small amounts of dissolved minerals that have been blown into the air by winds. Rainwater contains tiny particles of dust and dissolved gasses, such as carbon dioxide and sulfur dioxide (yep, acid rain). That doesn't mean rainwater isn't very clean -- normally only about 1/100,000th of the weight of rain comes from these substances. In a way, the distillation process is responsible for rainwater. Distilled water comes from water vapor condensing in a closed container (such as a glass jar). Rain is produced by water vapor evaporating from the earth and condensing in the sky. Both the closed jar and the earth (via its atmosphere) are "closed systems," where water is neither added or lost.

(6) It takes more energy to heat cold water to 212o F than it does to change 212o F water to steam. False First, water at boiling temperature (212o F at sea level) is not really the same as boiling water. When water first reaches boiling it has not begun to turn to steam yet. More energy is needed to begin turning the boiling liquid water into gaseous water vapor. The bonds holding water molecules as a liquid are not easily broken. If I remember correctly, it takes about seven times as much energy to turn boiling water into steam as it does to heat water at room temperature to the boiling point.

(7) If you filled a glass full of water from the Great Salt Lake, when it evaporated there would be 1 inch of salt left. True They don't call it the Great SALT Lake for nothing. Water in the Great Salt Lake varies in salinity both by location and in time. In this example, we are assuming about a 20-percent salt concentration. In other words, about one-fifth of the weight of the water comes from salt. And how much saltier is Great Salt Lake water than seawater? Quite a bit. Seawater has a salt concentration of about 3 ½%. (8) Sea water is slightly more basic (the pH value is higher) than most natural fresh water. True Neutral water (such as distilled water) has a pH of 7, which is in the middle of being acidic and alkaline. Seawater happens to be slightly alkaline (basic), with a pH of about 8. Most natural water has a pH of between 6-8, although acid rain can have a pH as low as 4.

(9) Raindrops are tear-shaped. False When you think of a drop of falling water you probably think it looks like . When a drop of water comes out of a faucet, yes, it does have a tear shape. That is because the back end of the water drop sticks to the water still in the faucet until it can't hold on any more. But, using high-speed cameras, scientists have found that falling raindrops look more like a small hamburger bun! Gravity and surface tension come into play here. As rain falls, the air below the drop pushes up from the bottom, causing the drop to flatten out somewhat. The strong surface tension of water holds the drop together, resulting in a bun shape (minus the sesame seeds).

(10) Water boils quicker at Denver, Co. than at the beach. True The boiling point of water gets lower as you go up in altitude. At beach level, water boils at 212o Fahrenheit. But at 5,000 feet, about where Denver is located, water boils at 202.9o F, and up at 10,000 feet it boils at 193.7o F. This is because as the altitude gets higher, the air pressure (the weight of all that air above you) becomes less. Since there is less pressure pushing on a pot of water at a higher altitude, it is easier for the water molecules to break their bonds and attraction to each other and, thus, it boils more easily.

Ground Water Quiz

True False (1) The water table is the altitude (below ground) where the water level in a well will rise to when the well taps a confined aquifer.

True False (2) If you ate canned corn last night, there is a good chance that it was irrigated with ground water.

True False (3) Land subsidence occurs in areas underlain by highly-fractured granite, which is readily dissolved by moving ground water, especially when the water is slightly acidic.

True False (4) Water can flow in streams even during periods of drought due to ground water seeping into the streambanks.

True False (5) Artificial recharge to an aquifer can occur when people inject water down into a well to force it back into an aquifer so they can withdraw it later.

True False (6) Big cities drill deep wells to tap naturally heated water because the heat kills bacteria and the water needs less treatment.

True False (7) Bottled water often is advertised as "artesian well water." Artesian water is ground water that is naturally filtered by an aquifer composed of fine, porous material—this artesian water can be put directly into bottles.

True False (8) The heaviest users of ground water for drinking water and other public uses are the Southwest desert States, where surface water is scarce.

True False (9) The porosity and permeability of an aquifer define its ability to yield water to wells in productive amounts.

True False (10) For some wells along the coastline that are drilled into porous aquifers, pumps are turned off twice a day (during periods of high tides), since tides temporarily raise saline ground-water levels, causing saltwater intrusion into freshwater aquifers.

True False (11) Cities prefer to use ground water for drinking-water supplies because surface water is in constant contact with streambeds and, thus, contains a higher concentration of dissolved minerals and other substances that must be removed.

True False (12) Excessive pumping of a well can reverse the natural flow of ground water into a river, causing the water level in the river to fall.

True False (13) Most wells are shallow because a significant amount of water cannot be obtained from wells deeper than about 1,000 feet. This is because it is difficult for pumps to overcome the force of gravity and push water up to the land surface.

True False (14) The most productive wells tap large open areas in subsurface rocks, including horizontal fissures, caverns, and lava tubes, which have connections to the land surface, thus allowing the aquifer to be quickly recharged by precipitation.

True False (15) A cone of depression occurs when you drop your scoop of ice cream (made with ground water) on the ground on a hot summer day.

(1) The water table is the altitude (below ground) where the water level in a well will rise to when the well taps a confined aquifer FALSE

Maybe it is not fair to start off with a trick question, but the correct answer is false. The only thing that makes it false is referring to "confined aquifer," instead of an "unconfined aquifer." A confined aquifer is an aquifer with layers of generally impermeable rock above and below the aquifer (aquifers tend to run in horizontal layers below ground). As water flows into this aquifer it gets "squeezed" between the rock layers, thus causing pressure to build up in the aquifer.