Sources
Where every number comes from
Watermark produces no data of its own. Every figure on this site comes from a public Australian dataset, and this page names each one, who keeps it, what licence it carries, and — more usefully — what it cannot tell you.
Satellite water observations
DEA Water Observations — Geoscience Australia
What it is. Every Landsat pass over Australia since 1986, processed so that each 30-metre square of the continent is classified on each pass as water, not water, cloud, cloud shadow, terrain shadow, or steep ground. This is the backbone of the site: it is a record of what a sensor in orbit actually saw, not a simulation of what water might do.
Custodian. Geoscience Australia, via Digital Earth Australia.
Licence. Creative Commons Attribution 4.0 (CC BY 4.0).
Coverage. The whole Australian continent, 1986 to the present.
What it cannot tell you. Landsat returns to the same place every eight to sixteen days, so water that arrived and drained between two passes was never seen by anything. Cloud hides the ground, and floods arrive with weather — so the passes during an event are the ones most likely to be obscured. A 30-metre pixel is about the footprint of a large house, so it cannot separate a flooded yard from a dry floor. Wet ground next to a river may be the river.
River gauge readings
Water Data Online — Bureau of Meteorology
What it is. Water level and flow readings from thousands of gauging stations across Australia, many with records going back decades and a few back to the 1800s. Watermark uses the quality-controlled daily series to rank a reading against a station's own history, and hourly readings where they exist to read the level at the hour the satellite passed over.
Custodian. Bureau of Meteorology.
Licence. Creative Commons Attribution 4.0 (CC BY 4.0).
What it cannot tell you. A gauge measures the river at the gauge, not the water at your house — the two are related by terrain this site does not model. Gauge heights are measured against local datums, so a reading of 10 metres at one station has no relationship to 10 metres at another. Quality-controlled readings run about ten days behind real time, which means the most recent event is usually the one still missing. Some stations were moved, rebuilt or re-levelled during their record.
Terrain
SRTM 1-arc-second elevation
What it is. Ground height, used for the 3D terrain, for the
height of your ground above the nearest watercourse, and for finding the lowest
point on each road out of an area. Delivered as height-encoded tiles from the AWS
elevation-tiles-prod open dataset; over Australia the underlying data is
SRTM at one arc-second.
Two things about it matter more than the accuracy figure. SRTM was flown by the Space Shuttle in February 2000. Nothing built since exists in it — not the replacement Windsor bridge, not twenty-five years of subdivisions, not a levee raised this century. And it is a surface model rather than a bare-earth one: over forest and dense housing it measures the canopy and the rooftops, which biases heights upward exactly where people live.
What it cannot tell you. Roughly ±5 m vertical and 30 m horizontal. That is enough to tell a floodplain from a hillside and to rank road low points against each other. It is nowhere near enough to compare a floor level to a kerb, and the interface says so wherever a height appears.
The clear upgrade is ELVIS, which publishes 1 m LiDAR over most Australian floodplains and urban areas under CC BY. Ingesting it catchment by catchment would turn every height here from indicative into actionable.
Roads and watercourses
OpenStreetMap
What it is. The road network used to work out the ways out of an area and where each one is lowest, the named watercourses used to check that a gauge is actually on your river, and the address search.
Custodian. OpenStreetMap contributors.
Licence. Open Database Licence (ODbL).
What it cannot tell you. OpenStreetMap is volunteer-mapped, so coverage is excellent in cities and patchy on remote holdings. A road that is not mapped does not exist as far as this site is concerned, and Watermark says "fewer than three roads are mapped near here" rather than "you have no way out".
Base map
CARTO, on OpenStreetMap data
The streets, coastlines and labels under everything else. Presentation only — no figure on this site is derived from it.
Warnings, which do not come from here at all
Watermark holds no warning data and never will. If you need to know what water is doing right now, the Bureau of Meteorology issues the warnings and your state emergency service runs the response. In an emergency call 000; for flood and storm help call 132 500.
Attribution and reuse
The source datasets are open, and their licences let you use them too — attribution is required in each case, and the ODbL has share-alike conditions for derived databases. The custodians above are not responsible for, and have not endorsed, anything Watermark does with their data.
Watermark's own working — how these are joined, and the rules it follows when they disagree — is written out at method. What the combination still cannot tell you is at limits.