About
Why this exists
Insurers hold detailed flood data on roughly 14 million Australian homes. Households do not. Watermark is an attempt to build the public version out of data that was already public, and to give it away.
This is not a warning service. It is a record of what has already happened. In an emergency call 000. For flood and storm help, call the SES on 132 500. For current warnings, go to the Bureau of Meteorology.
The problem this is trying to solve
If you want to know whether the ground under an Australian house has been under water, the information exists — but it is spread across a few hundred councils, eight states and territories, two federal agencies and several commercial vendors, in formats that mostly assume you are a planner.
Most of what you can find is modelled: a hydraulic simulation of where water would go in a hypothetical storm of a given size. Those models are careful and useful, and they are not the same thing as a record of what happened. A model can tell you a street is in a 1-in-100 flood planning area. It cannot tell you that water was sitting on that street on 9 March 2022.
Meanwhile the observations that would tell you that have been collected continuously since 1986 and published openly the whole time. Landsat satellites pass over every part of Australia about every eight to sixteen days. Geoscience Australia processes every one of those passes and publishes, for every 30-metre square of the continent, whether it saw water there. The Bureau of Meteorology publishes river gauge readings from thousands of stations going back, in some cases, to the 1880s.
Nobody had put those two things side by side for an ordinary address and made it free to look at. That is all this is.
What it actually does
You type an address. Watermark finds the 30-metre square it sits in, asks Geoscience Australia what forty years of satellite passes saw on that square, and asks the Bureau what the nearest river gauge was reading on each of the days water was seen. Then it shows you both, with dates.
The one number that is genuinely hard to get anywhere else
Where the record allows it, Watermark works out the range between the highest gauge reading on a day this ground was seen dry and the lowest reading on a day it was seen wet. Somewhere in that range is the level at which water first arrives on that particular piece of ground.
It is not a prediction and it is not a guarantee. It is an observation about one river gauge and one patch of dirt, and it is the kind of thing a person can actually act on: a number to watch on the Bureau's own gauge page during the next event.
Who made it, and why it is free
Watermark is an independent project. It is not a government service, not the Bureau of Meteorology, not Geoscience Australia, and not connected to any council or state emergency service. It republishes their open data and speaks for none of them.
It is not run for profit. There are no ads, no accounts, no subscriptions, no paywall, no upsell to a paid report, and nothing about you is sold or shared with anyone. There is no business model here, because there is not meant to be one. It was built because the data was sitting there and nobody had made it usable for the people it is about.
It is also deliberately cheap to run. Every answer that can be stored is stored, so the same question is never asked of Geoscience Australia or the Bureau twice. That keeps the site fast for you and keeps the load off public infrastructure that other people depend on.
What it refuses to do
A site about flooding built on government data gets mistaken for a government service, and a household that mistakes this for the Bureau might wait for a warning that will never come. So the rules it holds itself to are worth stating plainly:
- It never issues a warning or a forecast. Everything on it is in the past tense.
- It never gives a risk score. No stars, no grades, no "high risk" label on somebody's home. It reports observations and lets you read them.
- It never says what water will do. Where it reports a height difference, that is a measurement. What water does with it depends on hydraulics this site does not model and will not pretend to.
- It says when it does not know. There is a real difference between "we asked and there was nothing there" and "we could not ask", and the interface is built to never let the second one be shown as the first.
- It does not treat a clean record as a guarantee. A satellite passes every week or two. Water that arrived and drained between two passes was never seen by anything.
Who it is for
People in Australia — householders, renters, people about to buy, and people trying to work out after an event whether what happened to them has happened before. It is available in English, Thai, Chinese, Vietnamese and Arabic, because the parts of Australia that flood are not monolingual.
If a number here is wrong
It might be. This joins two independent datasets by date and location, and both of them have edges. If Watermark says something about your own address that you know to be wrong, you are the only person who can see that — please tell me. A record with no way to be corrected is not really a record.
If you want to check the working rather than take it on trust, the method is written out in full, and every source is named with its licence.