Last updated: September 21, 2016
Infiltrating the Water Cycle
- Grade Level:
- Upper Elementary: Third Grade through Fifth Grade
- State Standards:
- ESS2.A ESS2.C PS1.A
Materials: Intro to water cycle: Inflatable globe (optional), 1 liter container, 100ml graduated cylinder, eye dropper, 10ml graduated cylinder, salt
Infiltration: 6 graduated 250ml beakers, several 2 or 3 liter soda bottles (same size), sand, gravel, clay, glue, small scraps of fabric, tray, food coloring.
Key Vocabulary: aquifer, infiltration, permeable/impermeable
Background: When rain water falls on the earth it has three ways to go. It can evaporate, become runoff, or infiltrate the ground. How much of the water becomes groundwater depends on a few factors.
- Precipitation: The greatest factor controlling infiltration is the amount and characteristics (intensity, duration, etc.) of precipitation that falls as rain or snow. Precipitation that infiltrates into the ground often seeps into streambeds over an extended period of time, thus a stream will often continue to flow when it hasn't rained for a long time and where there is no direct runoff from recent precipitation.
- Soil characteristics: Some soils, such as clays, absorb less water at a slower rate than sandy soils. Soils absorbing less water result in more runoff overland into streams.
- Soil saturation: Like a wet sponge, soil already saturated from previous rainfall can't absorb much more ... thus more rainfall will become surface runoff.
- Land cover: Some land covers have a great impact on infiltration and rainfall runoff. Vegetation can slow the movement of runoff, allowing more time for it to seep into the ground. Impervious surfaces, such as parking lots, roads, and developments, act as a "fast lane" for rainfall - right into storm drains that drain directly into streams. Agriculture and the tillage of land also change the infiltration patterns of a landscape. Water that, in natural conditions, infiltrated directly into soil now runs off into streams.
- Slope of the land: Water falling on steeply-sloped land runs off more quickly and infiltrates less than water falling on flat land.
- Evapotranspiration: Some infiltration stays near the land surface, which is where plants put down their roots. Plants need this shallow groundwater to grow, and, by the process of evapotranspiration, water is moved back into the atmosphere.
Sand and gravel store and transmit water the easiest. Though clay can store some water, water does not transmit through it easily. So sand and gravel are more permeable than clay. Permeable rock layers include limestone and poorly-packed sandstone. Impermeable rock layers include marble, granite, slate, and well-packed sandstone.
Pollutants can build up on impermeable surfaces such as parking lots, roads, and building and during a rainstorm be washed into the ground water in concentrated areas. Areas underneath impermeable surfaces are also deprived of moisture.
Wind Cave National Park's visitor center and parking lot are located directly above the cave. A drainage and filtration system was added to skim off the oil and gas before the water is released.
Wind Cave has three streams that enter the park: Highland Creek, Beaver Creek, and Cold Spring Creek. All of these streams lose all or (during wet seasons) part of their flow to infiltration and absorption. The three included photos show where the remains of Highland Creek completely disappear into the ground. The three creeks can lose a combined 2.5 million gallons per day.
Introduction to the Water Cycle
- Have students stand at their desks. Toss inflatable globe around the room and record if the student’s right index finger lands on land or water. Have students sit down after they have caught the ball. Repeat if necessary. Discuss how most of the globe is covered with water. But how much can we drink? Have students hypothesize.
- Bring out a liter of water. Pour 25 ml into the 100ml graduated cylinder. And salt to the remaining water. Discuss how the 25ml represents all the fresh water in the world and where it is located.
- When glaciers are mentioned add 7ml to the small graduated cylinder and state that the remaining 18ml represents all the glaciers and ice caps.
- The 7ml is the liquid freshwater. Basically all of that is underground. While many people get their water from underground, much of it is unavailable…either buried in bedrock or soil moisture. In order to demonstrate how much is in lakes and rivers, use an eye dropper to remove some water and place a single drop in a student’s hand. (or all students if you wish.) This represents all non-polluted, surface water.
- Ask what happens to a rain drop after in lands on the ground. Show poster/slide/handout of the water cycle. Start in a cloud and lead kids on an imaginary journey of a raindrop. Ask if there are other paths a raindrop could take. Explain that the class will be focus on infiltration.
- Pre-Class: Cut the bottom off three soda bottles. Glue a small piece of cloth inside of the neck to keep materials from falling out. Place sand in one, gravel in the second, and clay followed by some sand in the third.
SEE ATTACHED DIAGRAM FOR BOTTLE SETUP
- Introduce aquifers. (Diagram C) Discuss how water seeps into the ground until it hits an impermeable layer. Then it begins saturating the surrounding ground until an aquifer forms, an area of completely saturated soil. Discuss how some materials transmit and store water easier than others.
- Bring out the bottles and have students hypothesize which materials will transmit water faster.
- Have the bottles between desks or have students hold them. Place 250ml beakers underneath and drop 250 ml of water into the open ends of the bottles. Have students time how long until the first water exits at the bottom. Also record how much water eventually exits.
- Discuss how aquifers recharge. Ask students to come up with factors that influence how much water infiltrates into the ground. See background information for examples.
- Discuss and show students pictures of Highland Creek disappearing in Wind Cave National Park. Discuss where the water goes.
Extension: Have students make a pie chart of where water is located on the earth. (salt, glaciers, ground, surface)