Soil is main material through which “throughflow” occurs and is an important method of transport of water through the hydrological cycle. Where soil acts as both a filter, removing compounds/physical particles from the soil but also may add to it.
Measuring the rate of infiltration allows us to estimate the amount of water that a soil is able to absorb during rain events, this allows for further assumptions to be made about the rate of surface runoff that a soil will be subject to and potential erosion or flooding risks.
Specific learning outcomes
- Understand the practical nature of infiltration through soil
- Witness and apply measurement to infiltration rates within soils
- Contract and compare various soils infiltration rates
Equipment for a group of 5
- Piece of drainage pipe cut to 30cm (note diameter for calculation)
- Piece of net cloth
- 10litres+ of water
- Measuring cylinder
- Wood block
- Electrical tape
- Spirit level
Estimated time 30 minutes.
- Chop drainage pipe to size and place electrical tape around the outside to mark 10cm from base.
- Introduction 5 mins
- Select location and cut turf – 5 mins
- Insert ‘infiltrometer’ (pipe) 10 mins
- Prepare ground 5 mins
- Add measured water and timing 5-20 mins (dependent on soil)
- Calculating hydraulic conductivity 5 mins
Total timing 35-50 minutes.
Background learning needs
- Understanding of basic soil horizons (eg. O, A, B and C)
- Understanding of hydrological cycle
- Select location for recording hydraulic conductivity and place tube on the ground and use this a block to cut around with the knife- this allows for the vegetation or binding within the soil to be broken apart and makes driving the ‘infiltrometer’ in easier.
- Use the block of wood to knock the pipe into the cut that has been made using the hammer/mallet. Knock the ‘infiltrometer’ into the ground until the level of 10cm, which is marked by the tape.
- Check that the top of the ‘infiltrometer’ is level using the spirit level, at ~3 points across the diameter, and alter with the block and hammer where it is not.
- Place the net fabric in the base and pour water both within the ‘infiltrometer’ and outside to ensure that the ground is wet.
- Measure out 1litre of water into the measuring cylinder.
- Remove the cloth from the ‘infiltrometer’.
- Set the stopwatch to 0 and begin it as the water is poured into the ‘infiltrometer’. This method uses the constant-head method so keep the water topped up to the rim of the ‘infiltrometer’ until all the litre is within the tube.
- Stop the stopwatch at the point when all the water has been absorbed by the ground.
- Calculate hydraulic conductivity by: ?