Tips for Sydneysiders.

Notes on graphs and data in our Dam Statistics page

This page contains notes about the data and graphs that we use in our Sydney Dam Statistics Page.

Where do you get your data?

The raw data is provided on the Sydney Catchment Authority website, and we thank them for providing this service.

Can I use your graphs and data on my site?

We are more than happy for you to use the graphs etcetera if you provide a link to our dam statistics page. Any queries about this should go to the webmaster (at)

I can see some irregularities on the graphs, what is happening?

This happens for a couple of reasons. Firstly the data that the SCA provides on a daily basis is only given to the nearest 500ML. The data about individual dams is given on a weekly basis and with a finer resolution, as is the daily supply. This provides a few quirks that tend to eve themselves out over time. It is also interesting to note that the sum of the available capacities in the dams does not equal the overall capacity available for some reason.

How can the dams have negative inflow?

The inflow on our graphs is calculated by comparing the amount of water in the dams by the usage amount. Hence evaporation within the dams counts against inflow, and can in extremely dry circumstances be considered negative.

How do you calculate the amount of rain needed to fill the dams

Very approximately! The actual amount of rain required is very dependent on where the rain falls and the exact pattern of rainfall, and other recent rainfalls that may go towards saturating the ground (which we have not taken into account). In addition, to fill the dams, each catchment will need a different amount of rainfall. If anyone feels they have a better formula that is easily calculable, we would love to hear about it.

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