Science and Technology K–6 · Year 5
Rain on bare soil and covered soil: measuring runoff and washed-away sediment
Science understanding: Earth and space sciences
The idea
Plant cover and mulch slow rain, so less water runs off and far less soil is carried away, which is why erosion control on farms and building sites starts with keeping the ground covered.
What you need
- 3 identical seedling trays or cut-down 2 L bottles laid on their sides, filled level with the same soil
- cover for tray B: a square of turf or a dense sowing of grass grown 3 weeks earlier; cover for tray C: 2 cm of mulch; tray A bare
- a watering can with a rose, 500 mL per tray
- 3 clear jars to collect runoff from the lower lip of each tray
- measuring cylinder, kitchen balance reading to 0.1 g, coffee filters
How to do it
- Prop all three trays at the same slope (about 10 cm rise over 40 cm) with the lip over a jar.
- Pour 500 mL onto each tray from the same height over 30 seconds.
- Wait 2 minutes, then measure the runoff volume in each jar.
- Filter each jar's runoff through a weighed coffee filter, dry the filters overnight and weigh the sediment.
- Record runoff in millilitres and sediment in grams for bare, grassed and mulched trays.
- Explain the result in terms of what the cover does to the falling drops and the flowing water, then write a one-page proposal to the principal for one measure on a bare slope at school, with a labelled diagram and the sediment table as evidence.
What you should see
The bare tray's runoff is the muddiest and carries by far the most sediment; the grassed and mulched trays give clearer water and much less sediment. Runoff volume is usually highest from bare soil, but the learner's measured volumes are the result. Water not collected as runoff soaked into the soil, which is the second half of the finding.
What changes
- What you change
- ground cover (bare, mulch, grass)
- What you measure
- runoff volume and sediment mass
- What you keep the same
- soil
- slope
- water volume
- pouring height and time
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Plants use up rain so less reaches the soil (they slow it so more soaks in).
- Erosion only happens on hills.
- Mulch is decoration.
Safety card
Hazards
- muddy water
- soil organisms
Controls
- work outdoors
- wash hands
Note
Risk assessment before the lesson using Primary RiskAssess or the school's own template.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Science and Technology K-6 Syllabus (2017), current, taught until 2026; a Stage 2 outcome, because NSW teaches gradual erosion and its control in Stage 2 ('investigate why the Earth's surface changes over time as a result of natural processes and human activity' and 'investigate how erosion can be minimised'), while the Stage 3 surface-change content under ST3-10ES-S covers sudden geological change and extreme weather events, its other content group being Earth's place in our solar system; code read from the syllabus document on 22 September 2026ST2-10ES-S
- Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; Stage 2 content under 'Forces shape Earth's surface': 'Describe and model how forces produced by moving water cause erosion'; code read from the outcomes page and the content read from the Stage 2 content page on 22 September 2026ST2-SCI-01
- Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST3-1WS-S
- Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST3-PQU-01ST3-SCI-01
- Australian Curriculum v9AC9S5U02AC9S5H02AC9S5I02AC9S5I03AC9S5I04AC9S5I06
Sources
The pages the author read to write this activity.