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Lesson Plans: Rainfall and Water Table

Objective

The objective is to show how an increase of rainfall under climate change can affect the water table and soil salinity underground.

Materials

Each student or group of students will need the following:

Important Points to Understand

Due to climate change processes, it is predicted, that there may be a higher rainfall in some areas and a lower rainfall in others. It is easier to illustrate the effects of lacking rainfall (recent drought in the Papua New Guinea area could be an example).

If rainfall increases, water flow in rivers will increase and so too will erosion by those rivers. Rivers that erode more carry more silt. When the river runs into the nearby sea that silt is deposited. Among many processes, an increase in rainfall may raise the water table nearer to the surface. A similar process can occur when deep-rooted trees are removed and the region is suddenly denied the water take-up and evapotranspiration which the trees provided. Salt may then come to the surface as the water evaporates.

Preparation

Students often have misconceptions about wind and where it comes from. Before the lesson begins, discuss wind with your class. The main point of the discussion is to reveal students' ideas of wind and its origins. Be sure that all materials are either centrally located or already distributed to the student groups.

Procedure

  1. Punch a few small holes in one of the trays, these will drain away water in a similar way to tree roots taking up water.
  2. Place a layer of salt evenly over both trays and a thick layer of sandy loam on the salt (about 5 cm).
  3. Sprinkle the same amount of water evenly over the soil in each tray until it is wet.
  4. Place both trays in the sun to dry. Once dry, repeat the watering and drying.

Questions

  1. In nature, where does the salt come from?
  2. What happens to the salt in each tray?
  3. What can you infer from what you have seen?
  4. Can you discuss the advantages and disadvantages of the increase of rainfall in general?
  5. Release of salt and silt into coastal ocean will have an effect: What is it?