Flood-Ready Town: Where Does the Storm Water Go?
See flooding as a budget: rain that cannot soak in runs off at once, drains have a fixed capacity, wetlands store the surplus, and the rest stands in the streets.
Before you try
What if a city kept all its ponds and wetlands? Would it still flood in a big storm?
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What happened?
Move a control to see what changes and why.
A lumped town with rounded run-off, storage and drain rates; real drainage depends on slopes and pipe sizes.
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Try these ideas
- Run the default 120 mm storm, then the same storm with the wetland removed.
- Find the smallest number of drain levels that keeps every house dry in a 200 mm storm.
- Pave the whole town and see how little rain it takes to flood it.
Why it works
When rain falls on a field, most of it soaks in. When it falls on concrete and tarmac, almost all of it runs off at once and arrives in the drains together. Drains can only carry so much an hour; anything beyond that stands in the streets. Wetlands, ponds and parks act as sponges that hold the surplus and release it slowly, which is why filling them in makes floods worse.
Chennai in 2015 and Mumbai most monsoons show the pattern: a very heavy storm on a heavily paved city whose lakes and creeks have been built over. In this simulator you set the storm, the paved share, the drain capacity, the wetland area and the river embankment, run the hours, and watch the water in the streets rise and fall. Houses flood at 25 cm.
Check your understanding
Question 1 of 4
Cities flood more easily than fields because
A wetland park helps in a storm by
Drains rated for 3 cm an hour receive 10 cm of run-off in an hour. The streets
An embankment
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
What will you discover next?
Try Groundwater Explorer: Will the Well Run Dry? next.
For parents & teachers
- Pour a cup of water on soil and then on a paving slab and compare.
- Ask: where did the old lakes and ponds of your town go?
- Find your area on a flood map and discuss the safest routes.