Terrain Rivers
Rain falls on a little height map. Water runs downhill, fast streams pick up sediment and slow ones drop it — so valleys deepen and lakes silt up as you watch.
Sculpt a small landscape and watch rain gather into streams that carve and fill it.
FreeOn this device
Which way does the water leave the ridge — and where do the first channels form?
Ground height
- 0–0.3
- 0.3–0.6
- 0.6–0.9
- 0.9–1.2
- 1.2–1.5
- 1.5–1.8
- 1.8–2.1
- over 2.1
- water (darker = deeper, relative to the deepest now)
| Ground | 1.5981 |
|---|---|
| Water | 0.0000 |
| Sediment | 0.0000 |
A visual toy on a 96 × 64 grid with made-up units — not a flood, erosion or landscape prediction. Terrain is generated here from a seed; nothing is downloaded.
Controls
- Run, Pause and Step move time on; Rain switches the rain on and off; Reset terrain goes back to the experiment's starting landscape.
- Raise, Lower and Smooth sculpt the ground. Drag on the map, or focus the map, move the pink cursor with the arrow keys (Shift for 5 cells) and press Enter.
- Gentle, Medium and Strong set the brush strength. The cross-section slider picks the row drawn underneath.
- Export saves a PNG picture or the ground as JSON; Import loads a JSON height field of the same size.
The rules
- Each tick, rain adds the same depth everywhere. Every cell sends water to lower neighbours, a quarter of the height difference at most, and never more than it holds.
- Water carries sediment. Where fast water carries less than it could, up to 0.01 ground is picked up; where it carries too much, some settles.
- 1% of the water evaporates each tick. Open edges let water and sediment leave the map; the totals count what left.
Scoring, saving and limits
No score — each experiment asks a question to explore. The totals show water, carried sediment and what has left the map.
The experiment, your sculpted or eroded ground and the rain and contour settings are kept on this device. Water starts fresh after a reload.
A visual toy with made-up units on a 96 × 64 grid — not a flood, erosion or landscape prediction.
Questions
- Why does the lake never drain?
- It sits in a hollow with no lower exit. Lower a notch in the rim and watch it spill.
- Why do colours change while it runs?
- Erosion lowers the ground along streams and deposition raises it where they slow — the bands follow the new heights.
- Can I see exact numbers?
- Yes: the cell readout shows ground, water and sediment under the cursor, and the cross-section draws a whole row.