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Geography K–10 · Years 7–8

Longshore drift in a wave tray, with and without a groyne

Landscapes and landforms (ACARA Year 8 sub-strand); NSW Stage 4 focus area Landscapes and Landforms (2015 syllabus) and Landscapes and landforms (2024 syllabus)

Practical, model not builtLow risk

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The idea

Waves that arrive at an angle carry sand along the beach in the direction they travel, and a wall built across the beach traps sand on the side the sand comes from and starves the other side.

Safety card

Low riskAn adult supervises

Hazards

  • water spill
  • asbestos in bought coloured sand

Controls

  • tray on a tarp; wipe spills
  • tracer made in class from the tray's own play sand; no bought coloured or decorative sand

Note

No heat is used. On 12 November 2025 the ACCC warned that children's coloured sand products (Kadink Sand, Educational Colours Rainbow Sand and Creatistics Coloured Sand) had been recalled after tremolite asbestos was found in them, so the tracer is made in class and bought coloured sand is not used. The only added material is non-toxic acrylic paint of the kind used in art lessons: check it against the NSW Department of Education Chemical Safety in Schools package and record the practical in RiskAssess (riskassess.com.au).

What you need

  • Clear tray 60 cm × 40 cm × 10 cm; about 3.5 L of damp play sand shaped into a straight beach along one long side, rising about 6 cm over about 18 cm (a slope of about 1 in 3), so the beach stands clear of the water with open water in front for the paddle
  • Water to 3 cm depth in front of the beach
  • A wave paddle: a 20 cm × 8 cm plastic board pushed by hand
  • 50 g of the tray's own play sand made into tracer grains: stirred with 1 teaspoon (5 mL) of non-toxic acrylic paint and dried overnight on newspaper, so the tracer has the same grain size as the beach and a known source (no bought coloured or decorative sand; see the safety note)
  • A groyne: a 10 cm × 6 cm plastic card pushed into the beach at right angles to the shore, halfway along
  • Ruler, metronome app at 60 beats per minute, camera

How to do it

  1. Sprinkle the tracer sand in a 5 cm strip on the beach face at one end. Photograph.
  2. Push the paddle once per beat for 2 minutes with its face at about 30 degrees to the shoreline, from the tracer end towards the far end, with strokes of the same length.
  3. Photograph and measure how far the centre of the tracer strip has moved along the beach (cm).
  4. Rebuild the beach and tracer, insert the groyne, and repeat the 2 minutes of waves at the same angle.
  5. Measure the tracer movement and the difference in beach width on the two sides of the groyne (cm).
  6. Repeat both runs with the paddle square to the shore (0 degrees) as a control.

What you should see

With angled waves the tracer moves along the beach in the wave direction by a measurable distance in 2 minutes; the tracer grains follow a zig-zag path, up the beach at an angle with the swash and straight back down with the backwash. With the groyne, sand piles against its updrift face (the beach is wider there by a measurable amount) and the downdrift side is narrower and scoured. Square-on waves move the tracer up and down the beach but little along it. The learner reports three tracer displacements and the two beach widths in cm.

What changes

What you change
wave angle (30 degrees, 0 degrees) and groyne present or absent
What you measure
tracer displacement along the beach (cm); beach width each side of the groyne (cm)
What you keep the same
  • stroke rate and length
  • water depth
  • beach shape
  • run time

Common misconceptions

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

  • Waves only move sand up and down the beach, not along it.
  • Waves reach the beach at the same angle they had out at sea.
  • A sea wall or groyne protects the whole beach.

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.GE4-2GE4-5GE4-7GE4-8
  • Geography 7–10 Syllabus (2024), NESA; implementation from 2027, not yet taught; code read on this page on 22 September 2026GE4-PRI-01GE4-MAN-01GE4-TAP-01
  • Australian Curriculum v9AC9HG8K01AC9HG8K04AC9HG8S02AC9HG8S03

Sources

The pages the author read to write this activity.

  1. www.ga.gov.au/education/classroom-resources/australian-coast-teacher-notes-and-student-activities
  2. www.ga.gov.au/education/natural-hazards/coastal-erosion
  3. www.ga.gov.au/scientific-topics/dea/dea-data-and-products/dea-coastlines
  4. www.coastalwiki.org/wiki/Shallow-water_wave_theory
  5. curriculum.nsw.edu.au/learning-areas/hsie/geography-7-10-2024/outcomes
  6. www.accc.gov.au/media-release/customers-warned-of-recalled-children%E2%80%99s-sand-due-to-asbestos-risks

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