Aquifer in a tank: porosity, permeability and a pumped well

The idea

Groundwater fills the pore space between grains; how much a layer holds is its porosity and how fast water moves through it is its permeability, and pumping a well lowers the water table around it.

Safety card

What you need

• Part A (porosity): 3 × 500 mL clear plastic cups each filled to the 500 mL line with dry gravel (5–10 mm), coarse sand (0.5–1 mm) and pottery clay crumbs; 1 × 250 mL measuring cylinder
• Part B (permeability): 3 funnels of at least 150 mm rim diameter (about 800 mL brimful, so a 100 mL pour stands above the material instead of overflowing), each lined with a piece of fine stocking held by an elastic band and filled two-thirds with one dry material, 3 collecting cylinders, stopwatch
• Part C (aquifer): clear tank 40 cm × 20 cm × 25 cm; 3 cm of pottery clay pressed flat over the whole floor, then 10 cm of coarse sand; three clear 12 mm tubes pushed down to the clay, one as the pumping well and two as observation wells 10 cm and 20 cm from it, each with stocking over its lower end; a 60 mL syringe with thin tubing that fits inside the well tube as the pump; blue food colouring; 2 L jug
• Ruler taped to the tank face and to each tube

How to do it

1. Part A: slowly add water from the cylinder to each cup until it just reaches the top of the material; the volume added is the pore volume. Porosity = volume added ÷ 500 mL. Repeat with a fresh dry sample.
2. Part B: pour 100 mL of water into each funnel at once, checking as it goes in that it stands above the material without spilling; time until water first comes out of the funnel, and record the volume collected at 30 s, 60 s, 5 minutes and at the end of the lesson. The clay funnel may still be dripping then: record the volume collected and that it had not finished, not a completion time.
3. Part C: press the clay flat over the tank floor, add the sand and push in the three tubes. Pour 1.5 L of water slowly onto the sand at one end and read the water level in each tube every minute until the three levels agree: that level is the water table.
4. Pump 60 mL of water from the well and measure what comes out: draw the plunger slowly, and as soon as air enters, stop, lift the syringe clear, expel the air and empty the water into a 100 mL measuring cylinder. Keep drawing and emptying, letting the bore refill from the sand between draws, until the cylinder holds 60 mL of water; record the number of draws and the time taken. The bore itself holds only about 6 mL at a 5.4 cm water table (a 12 mm bore holds π × 0.6² × 5.4 = 6.1 cm³), so nearly all of the 60 mL comes out of the sand, and a syringe that draws a mixture of water and air does not report the water removed, which is why each draw is decanted and measured. Read the level in the well and in the two observation tubes after the 60 mL is out; then wait until the three levels agree again and record the new level. Repeat for three lots of 60 mL.
5. Add 5 drops of colouring onto the sand at the far end ("a leaking tank") and pour 500 mL of water there; pump slowly and steadily from the well, recording the volume drawn each minute, and time how long until the pumped water shows colour.
6. Report porosity for the three materials, the drainage times, the drop at each tube per 60 mL pumped, and the fall of the level water table compared with the calculator's value.

What you should see

Part A: each material gives a porosity the learner computes from its own volumes (for example 200 mL added to a 500 mL bulk gives 0.40); clay crumbs take up water slowly, so the class records how long it waited. Part B: gravel is expected to drain fastest and clay slowest, and the clay funnel may still be dripping at the end of the lesson, which is recorded as not finished rather than as a time; which shows that holding water (porosity) and passing it on (permeability) are different properties. Part C: the three tube levels settle to one water table; the 1.5 L poured gives a saturated layer at most 1500 ÷ (0.35 × 800) = 5.4 cm thick for n = 0.35 over the 800 cm² floor, less where water is held above the table or taken up by the clay. Each 60 mL of water pumped out and measured lowers the level most in the well and less in the observation tubes, a cone of depression; once the levels even out, the table sits lower than before. The calculator's fall (2.1 mm per 60 mL for n = 0.35 over 800 cm²) is the smallest possible fall for that porosity, because not all pore water drains out of sand. The time for dye to reach the well is the class's own measurement.

What changes

What you change

material (gravel, sand, clay)

What you measure

porosity (ratio) and drainage time (s)

What you keep the same

• bulk volume 500 mL for porosity
• funnel two-thirds full for drainage
• water added at the same rate
• dry starting material

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

• Groundwater flows in underground rivers and lakes.
• Clay holds no water because it does not drain.
• Pumping a bore lowers the water table evenly across the whole aquifer at once.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

• Geography K–10 Syllabus (2015), NESA; current and taught in 2026, replaced from 2027. The outcome codes are not printed on the NESA landing page for this syllabus, which only links the document, so the url given is the syllabus document itself (geography-k-10-syllabus-2015.docx); the code and its outcome text were read in that document on 23 September 2026.GE4-1GE4-2GE4-7
• Geography 7–10 Syllabus (2024), NESA; implementation from 2027, not yet taught; code read on this page on 22 September 2026GE4-DFC-01GE4-PRI-01
• Australian Curriculum v9AC9HG7K01AC9HG7S02

Sources

The pages the author read to write this activity.

1. www.ga.gov.au/education/classroom-resources/how-do-rocks-store-groundwater
2. www.ga.gov.au/education/classroom-resources/groundwater-mini-unit
3. www.ga.gov.au/education/classroom-resources
4. curriculum.nsw.edu.au/learning-areas/hsie/geography-7-10-2024/outcomes