Geography K–10 · Years 7–8
Stream table: meanders, cut banks, point bars and a delta
Landscapes and landforms (ACARA Year 8 sub-strand); NSW Stage 4 focus area Landscapes and Landforms (2015 syllabus) and Landscapes and landforms (2024 syllabus)
The idea
Flowing water erodes where it moves fastest (outside of bends) and deposits where it slows (inside of bends and at the mouth), so a straight channel becomes a meandering one and builds a delta.
Safety card
Hazards
- water on the floor
- lifting the wet tub
Controls
- outdoors or on a tarp; drain 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 as in the hydrograph entry (tub 80 cm × 40 cm, 20 mm outlet 3 cm above the base at the low end, raised 5 cm at the high end for run 1)
- Washed play sand, damp, enough to lay 4 cm deep over the upper 65 cm of the tub (65 × 40 × 4 cm = 10.4 L of sand), leaving the lowest 15 cm around the outlet free of sand so that water stands there as a shallow lake up to the outlet level; a straight 1 cm groove cut from the top to the edge of the sand
- Water supply at a held rate: a 20 L container with a tap, kept topped up to a marked level so the head does not fall (gravity flow slows as the head drops, so a tap set once drifts through a run), with the rate checked by catching the flow in a measuring jug for 15 s at the start and every 2 minutes and the tap adjusted back to the target; a bucket under the outlet; stopwatch. A run at 2 L per minute uses 16 L, so the container is refilled between runs.
- Ruler; toothpicks as bank markers; a phone camera on a tripod for a photo every 60 s
- Small paper houses; 3 pebbles
How to do it
- Fill the lake at the low end with water up to the outlet level and photograph the straight groove. Start the flow at the top of the groove at 1 L per minute, set by catching 250 mL in the jug in 15 s, and check it the same way every 2 minutes through the run.
- Every 60 s take a photo and mark with toothpicks where the bank has retreated. Run for 8 minutes.
- Measure the widest channel width and the length of the longest bend; measure the delta where the channel enters the lake (width across and length out from the edge of the sand).
- Rebuild the groove and repeat at double the flow rate (2 L per minute) for the same time; measure again.
- Rebuild and repeat at the first flow rate with the tub raised to 10 cm (steeper).
- Place houses on the outside and inside of a developing bend and record which is undercut first; place pebbles in the channel and record where sand builds behind them.
What you should see
The straight channel widens, its banks retreat unevenly and bends grow; the outside of each bend is cut back while a bar of sand forms on the inside; sand carried out of the channel spreads into a fan-shaped delta where the channel enters the lake, and the delta grows through the run. Doubling the flow and steepening the slope are both expected to give a wider channel and a larger delta in the same time (the learner reports the measured widths and delta lengths in cm for the three runs). Houses on the outside of a bend are undercut first; a pebble creates a small deposit in its lee. Each run reports the flow rate measured through it, not the nominal setting.
What changes
- What you change
- flow rate, then slope
- What you measure
- channel width (cm), bend length (cm), delta length (cm) after 8 minutes
- What you keep the same
- sand depth and initial groove
- run time
- water temperature and source
- lake level at the outlet
- delivery rate checked with the jug every 2 minutes and held at the target
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Rivers erode evenly along both banks.
- A river gets narrower as it flows downstream because water soaks in.
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.GE4-2GE4-7
- Geography 7–10 Syllabus (2024), NESA; implementation from 2027, not yet taught; code read on this page on 22 September 2026GE4-PRI-01GE4-TAP-01
- Australian Curriculum v9AC9HG8K01AC9HG8K04AC9HG8S02
Sources
The pages the author read to write this activity.