Download Hydrologic Cycle

6th Grade – It’s Our Water
Station1: Hydrologic Cycle
- Students will be able to know and understand the water cycle
- Students will learn about groundwater and water storage locations
- Students will demonstrate how water moves through the ground
Materials
Groundwater simulation system
Hydrologic Cycle
The hydrologic (water) cycle describes the movement of water on and above the earth. Water is always
changing and moving from one place to another. The cycle is made up of a few main parts:
- Precipitation: happens when the temperature and the atmospheric pressure are right. Small
droplets of water in clouds for larger droplets and fall to earth as rain, sleet, snow or hail.
- Infiltration: Process where rain water soaks into the ground, through the soil and underlying rock
layers. Once infiltrated, the water becomes soil moisture or groundwater
- Runoff: Movement of land water to the oceans, mainly in the form of rivers, lakes and streams. It
consists of precipitation that neither evaporates, transpires nor penetrates the surface to
become groundwater.
- Transpiration: Process that happens through plants. As plants absorb water from the soil, the
water moves from the roots through the stems to the leaves. Once the water reaches the leaves,
some of it evaporates from the leaves, adding to the amount of water vapor in the air.
- Evaporation: The process where a liquid changes from its liquid state to a gaseous state. The sun
heats up water in rivers, lakes or the ocean and turns into vapor.
- Water vapor: This is water in its gaseous state and is totally invisible. It is extremely important to
the weather and climate. Without it there would be no clouds, rain or snow. All of the water
vapor that evaporates from the surface of the earth eventually returns as precipitation.
- Condensation: Formation of liquid drops from water vapor. This occurs when a parcel of air
expands and cools. This is responsible for the formation of clouds which produce precipitation.
- Collection: When water falls back to earth as precipitation it may fall back in the oceans, lakes or
rivers. It can also end up on land. When it ends up on land it will either soak into the ground to
form groundwater or run over the soil and collect in the oceans, lakes or rivers.
Groundwater
In this lesson we are going to focus on groundwater. Groundwater is the water that is contained in
saturated soil and rock materials below the earth’s surface. The source of groundwater is precipitation.
When rain falls on the surface of the ground, some of it runs off the land into lakes and streams (runoff),
and some soaks into the ground (infiltration). Groundwater moves slowly between the grains of soil or
in cracks in rock until it reaches a point where it can discharge at the surface, such as a lake, stream or
wetland, or until it is withdrawn from a well. It then becomes surface water again.
Groundwater is stored underground in the pore spaces of saturated soil and rock materials. An
underground unit of soul or rock which can yield a significant quantity or groundwater is an aquifer.
Aquifers are not always uniform because of differences in composition or in properties. Aquifers may be
separated by layers which do not transmit much water. These layers are called confining layers. If the
confining layer exists above an aquifer which is fully saturated, this aquifer is called a confined or
artesian aquifer. Aquifers without a confining layer above them are called unconfined aquifers.
Demonstration
By using the groundwater simulation system students will see how water moves through groundwater
and is discharged at the surface into rivers, lakes, streams and wetlands.
1. Charge the groundwater simulator. Do this by placing both water bottles on either end of the
model and allow the model to fill until water stops flowing into the model. Refill the water
bottles and place back on the system.
2. Inject blue die into piezometers B, F, and G. Add dye until it reaches the bottom of the
piezometer.
3. Fill the remaining piezometers with red dye.
4. With all piezometers now injected, place the tube extending from the lake/stream outlet into a
bucket. Slowly open the tube so that only a small amount of water flows out. Refill the water
bottles as needed.
As the water drains out, ask students to notice what happens to the water levels in the piezometers (if
you want to mark where the water levels started as a point of reference). Where is the water level in the
confined aquifer piezometers? How does this differ from the unconfined aquifer piezometers?
Ask students to identify where the water is moving in the ground? The dye should be moving to a
discharge area such as the lake. Once the dye starts to move you can close the lake outlet and to show
the students that the water has changed color. Ask them to identify the color and where the water came
from, the confined aquifer or unconfined aquifer. Students should answer unconfined aquifer. Ask them
why it came from the unconfined versus the confined aquifer?
To get all of the dye out of the simulator open the bottom outlet and close the lake/stream outlet. Inject
clean water carefully into the piezometers to remove all dye from them.