Geography K–10 · Years 7–8
Storm hydrograph from a stream table: bare catchment versus sponge wetland
Water in the world (ACARA Year 7 sub-strand); NSW Stage 4 focus area Water in the World (2015 syllabus) and Water in the world (2024 syllabus)
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The idea
A catchment turns a short burst of rain into a longer, lower outflow, and storage on the surface (vegetation, wetlands) lengthens the delay and lowers the peak, which is what reduces flooding downstream.
Safety card
Hazards
- water on the floor
- lifting the wet tub
Controls
- run outdoors or over a tarp; tub drained in place before lifting
Note
No chemicals or heat are used. The activity is run under the school risk-assessment procedure; RiskAssess (riskassess.com.au) holds templates for school practicals and fieldwork. The NSW Department of Education Chemical Safety in Schools package is not triggered.
What you need
- Stream table: an under-bed storage tub (about 80 cm × 40 cm) with a 20 mm outlet drilled at one end 3 cm above the base, raised 8 cm at the far end
- About 10 L of washed play sand, enough to shape a valley about 4 cm deep over the upper 65 cm of the tub with a channel running towards the outlet, leaving the lowest 15 cm around the outlet free of sand so that no sand washes through it (the stream-table sheet keeps sand at least 15.2 cm from the drain)
- 2 L jug and a watering-can rose; stopwatch
- At least 12 containers of 1 L marked every 50 mL (measuring jugs or marked ice-cream tubs), placed under the outlet in turn and swapped every 15 s
- 4 kitchen sponges for the wetland run; 3 pieces of turf for the vegetated run
How to do it
- Wet the sand and let the tub drain until the outlet stops dripping, so each run starts from the same state with the water at the low end standing at the outlet level. Place the first container under the outlet.
- Pour 2 L through the rose over the upper half of the catchment in exactly 30 s. Swap the container every 15 s from the start of pouring until the outlet drips less than one drop per 5 s, adding containers if needed; label each with its interval.
- Measure each container (mL) and plot mL per 15 s against time: the hydrograph. Record time to peak and the peak volume.
- Rebuild the same shape; lay sponges across the valley floor as a wetland and repeat the pour and the containers.
- Repeat with turf on the upper slopes. Compare time to peak, peak volume and total outflow across the three runs.
What you should see
The bare run is expected to peak during or just after the 30 s pour and fall back towards zero within minutes; the sponge and turf runs peak later and lower and keep dripping longer, and their total outflow is smaller because the sponges and soil hold water. Total outflow should not exceed the 2 L poured; if it does, the sand was still draining from the previous run. The missing water is what stayed in the sand and sponges. Time to peak and peak volume are read from the learner's containers, in seconds and mL. Sand in a container means the clear zone round the outlet needs widening before the next run.
What changes
- What you change
- surface storage (bare, sponge wetland, turf)
- What you measure
- time to peak (s), peak outflow (mL per 15 s), total outflow (mL)
- What you keep the same
- 2 L in 30 s through the same rose
- same sand shape and slope
- same starting wetness
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- All the rain that falls comes straight out of the catchment.
- Wetlands make floods worse because they are already full of water.
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.GE4-2GE4-3
- Geography 7–10 Syllabus (2024), NESA; implementation from 2027, not yet taught; code read on this page on 22 September 2026GE4-PRI-01GE4-MAN-01
- Australian Curriculum v9AC9HG7K04AC9HG7S02AC9HG7S04
Sources
The pages the author read to write this activity.