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Wetlands as barriers

Rivers in the Murray–Darling Basin are more than just paths for water; they provide links to floodplains and wetlands.

Demonstration: River flow into wetlands

Key points

  • Wetlands are often on higher ground than main river channels.
  • This means particular river flows are often required to reach wetlands e.g. seasonal flood waters of a certain height (see River flows diagram).
  • This demonstration will mimic a river under wet conditions flowing into a wetland. The plate represents the higher ground where wetlands are situated, the sponge is the wetland and the large flat container is the river.


  1. Place plate in the large, flat container.
  2. Place weight (cup or rock) on plate.
  3. Position farms animals and sponge on plate.
  4. Fill large flat container with water until the water almost overflows onto plate.
  5. Slowly pour more water into the large flat container until the first few drops overflow onto the plate. Tip: use less than a cup to pour the last bit of water.
  6. Observe and record what happens to the water, wetland and farm.

Use sponges of different dryness to show the differences between wetlands that have been in drought (sponges will soak up more water) and those that have retained water or received water recently.

Experiment: Wetland barriers under different conditions


  • 1 very dry sponge* (see teacher notes to speed dry sponges)
  • 1 damp sponge (rinsed and squeezed out)
  • 1 dinner plate with lip
  • 1 large, flat container to hold plate
  • Water (start with enough water to fill the plate to the lip – so the animals can ‘escape’ the floodwaters; variations included below in the teacher notes)
  • Cup or rock to weigh plate down
  • Small farm animals or light objects that could represent farm animals and wetland vegetation (opportunity for students to make or find objects to represent animals on their farm)
  • Paper towel or separate sponges for drying


Use different sponges for different conditions (see student worksheet for full method)

  1. Place the plate inside the flat container.
  2. Place farm animals on the plate, inside the lip (add a damp sponge for wet conditions or dry sponge for dry conditions).
  3. Predict what will happen when water is poured onto the plate.
  4. Pour water slowly from the cup onto the plate.
  5. Write down what you notice, about the water, farm animals, etc. Was your prediction correct? If not, what was different from what you predicted?

Worksheet teacher notes

No wetlands

  • In this scenario students will see the water spread over the plate and flood the farm.
  • Real life consequences: There is nothing to protect farms from rising floodwaters, especially where wetlands have been cleared and water still pools in an area. Animals may not have time to move to higher ground or may get trapped by the water, crops may be destroyed.

Wet conditions

  • In this scenario the sponge will immediately soak up water (water is attracted to water – this is called cohesion).
  • Real life consequences: The wetland should act as barrier and soak up at least part of the water protecting the farm. This may give the farmer/animals time to move.
    The wetland may store some water to use during dry times e.g. parts of the wetland can be fenced off and reserved for wildlife and parts can be open for farm animals to drink from.
  • In very wet conditions, like a flood, the wetland along with the farm will also be inundated with water.

Dry conditions

  • In this scenario the sponge may not soak up water immediately, but it will after some soaking.
  • It may seem to students that the dry sponge soaks up more water than the wet sponge. If the sponges are the same size, they will hold the same amount of water; the dry sponge is emptier in this case and will soak up the full volume of water it can hold.
  • Real life consequences: After a drought or dry period we expect riverbeds to soak up the water they need. This means that even after rain, rivers may not flow immediately because there is only enough water to wet them, not saturate them. Once the waterways are saturated the water will flow again.

Worksheet answers

  1. Based on how the sponges soaked up water, how do you think wetlands might be helpful for farms?

    Wetlands can act as barriers against rising floodwaters. This may give farmers time to move their animals to keep them safe or it might prevent their farms being flooded.

    In some cases, the extra water might be helpful to grow plants and animals on the farm, because wetlands can store water.

  2. What do you think happens if wetlands are cleared, by cutting down trees and removing all the plants in the wetland?

    (If asked, wetlands did not used to be valued and were often destroyed for farming and towns. Refer to the biofiltration experiment to see how wetlands are used now.)

    When we clear wetlands, by cutting down the trees, we remove the obstacles that water has to flow through i.e. we remove the barriers that slow water down. Removing plants also changes the how water is soaked up. Often less water is soaked up when trees are removed because plants with roots soak up water.

  3. What do you think happens if farmers were to use all the water in wetlands?

    When we use all the water in wetlands, they can dry up. The plants and animals that live in them might not be able to survive or they may not be able to complete their lifecycles e.g. get the right food to grow or have the right conditions to breed.

    If wetlands are too dry for a long time the plants might also die, which could cause the same problems as clearing the wetland.

Optional activity: Draw your idea of a healthy wetland working as a barrier on a farm.

Helpful tip

To prepare very dry sponges:

Very dried out sponges are required for this investigation – sponges that have been dried out to the point they feel brittle or hard are best.

New sponges straight out of a pack are sometimes treated to be moist and will need to be prepared to work for the investigation.

Method 1

  1. Take a new sponge and wet it down.
  2. Wring it out as much as possible.
  3. Leave sponge to dry out in a warm, dry place on paper towel for at least 38 hours.
    Note: old clean sponges will work

Method 2

  1. If sponge is new, rinse it and ring it out as much as possible.
  2. Place sponge on paper towel and heat in microwave for 10 seconds at a time – i.e. keep an eye on it – once squeezed the sponge won’t contain much water and overheating could damage your microwave.
  3. Caution: Sponge will be boiling hot! Use tongs to take out sponge and shake it to help it dry.
  4. Continue drying until sponge is dry and crispy.

Further information about wetlands and farms/agriculture, see Factsheet: Wetlands and agriculture (Australian Government, Department of the Agriculture, Water and the Environment).

Updated: 25 Oct 2021