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How water travels through the ground

About this lesson

Students learn about porosity and permeability by conducting their own experiments


Year level: 6

Theme: Water conservation


Learning objectives

Students can:
  • undertake an experiment to investigate porosity and permeability
  • suggest improvements to their experiment
  • be able to define porosity and permeability.

Curriculum links

Science

  • The growth and survival of living things are affected by the physical conditions of their environment ACSSU094
  • Scientific knowledge is used to solve problems and inform personal and community decisions ACSHE100
  • Suggest improvements to the methods used to investigate a question or solve a problem ACSIS108

Things you will need

Materials needed per group:

  • 5 plastic flower pots
  • 5 plastic cups
  • Overflow trays (if working inside)
  • 2 magnifying glasses
  • Water
  • A timer
  • 5 different types of soil e.g. clay, beach sand, pea gravel, potting mix, crushed limestone, garden soil etc.

Lesson description

Activity 

Part 1 – quiz

  • Break students into groups. Advise students they are to watch a video that explains the terms porosity, permeability and aquifers. Following the clip there will be a quiz with a reward for the winning group .
  • Watch the What is groundwater? video (10:30)

Quiz questions:

  1. Where is freshwater found? (Answer: Rivers, lakes, streams, manmade reservoirs e.g. dams.  Fifty times more fresh water is found underground).
  2. What is groundwater? (Answer: Groundwater is water stored within pores in rock or soil underground).
  3. What does porosity mean? (Answer: The ability to store water in the pores between individual grains and particles. Think of a sponge).
  4. What is permeability? (Answer: The capacity to transmit water underground between pores. Pores between sand grains are large and very permeable. Different soils have different rates of permeability).
  5. Does clay have low or high permeability? (Answer: The grains in clay swell up and the space between particles close up blocking the passage of ground water, it therefore has low permeability).
  6. What is the best material to accumulate groundwater? (Answer: Material that is both porous and permeable such as sandstone or limestone).
  7. Materials that transmit and accumulate groundwater are known as? (Answer: Aquifers).

Part 2 – investigating porosity and permeability

Divide students into groups of 5. Students use the activity sheet to examine different materials to discover their porosity and permeability.

Reflect & summarise

  • What did you discover?  Review and discuss the questions listed on the activity sheet.
  • Discuss ways each group decided to run the experiment. What improvements could have been made?
  • Ask students to define porosity and permeability.

Extension activities

  • Compare plant growth in low porosity soil and high porosity soil. Explore how porosity and permeability could be changed to increase plant growth.

Teacher background information

What is porosity?

Porosity or pore space is the amount of air space or void space between soil particles. Porosity depends on both soil texture and structure. For example, a fine soil has smaller but more numerous pores than a coarse soil. A coarse soil has bigger particles than a fine soil, but it has less porosity or overall pore space.

Water can be held tighter in small pores than in large ones, so fine soils like clay can hold more water than coarse soils, such as sand. The shape, arrangement and packing of soil particles also help determine porosity. Particles exist in many shapes and these shapes pack in a variety of ways that may increase or decrease porosity. Generally, a mixture of grain sizes and shapes, results in lower porosity.

What is permeability?

Permeability refers to the movement of air and water through the soil, which is important because it affects the supply of root-zone air, moisture, and nutrients available for plant uptake.

Soil is a valuable resource that supports plant life, and water is an essential component of this system. As the foundation for any garden, soil provides nutrients and water for plants and anchors them to the ground. Soil is made up of a variable mix of minerals, organic matter, water, air and a whole range of living organisms.

The size of pore space and interconnectivity of the spaces help determine permeability, so shape and arrangement of grains play a role. Water can permeate between granular void or pore spaces, and fractures between rocks. The larger the pore space, the more permeable the material. However, the more poorly sorted a sample (mixed grain sizes), the lower the permeability because the smaller grains fill the openings created by the larger grains.

The most rapid water and air movement is in sands and strongly aggregated soils, whose aggregates act like sand grains and pack to form many large pores. Some of these particles fit closely together and some do not and this creates spaces of many different sizes in the soil. Such soils are more stable and less susceptible to erosion.

Clay has low permeability due to small grain sizes with large surface areas which results in increased friction and these pore spaces are not well connected. Clay often creates confining layers in the subsurface.

Resources

Did you know?

We should take every opportunity to improve soils, for example, by adding compost and other organic material.

Key vocabulary

  • Aquifer: Porous soil or rock that holds groundwater and is sufficiently permeable to yield significant volumes of water
  • Groundwater: Water located beneath the ground surface in soil pore spaces and in the fractures of rock formations
  • Permeability: The ability of a fluid to move through soil or limestone rock
  • Porosity: The amount of space in a rock or soil that is able to store water
  • Soil aggregates: Clumps of soil particles held together by moist clay, organic matter and organic compounds