Snow job on the Snowy River

But it then includes a very important rider, stating, “No estimate of the volume of water that escapes the Shire in the various river systems, where that water is not captured by the scheme, is available”.

You see, all the claims about absent flows, and so on, have been in relation to the minor portion of the river system immediately below the dams. And both the public, and the policy process, has been encouraged to assume that this applies to the entire river system. But as each additional tributary joins the river on its way to the sea the more “healthy” the river becomes.

Indeed, the East Gippsland Catchment Management Authority provides the first glimmer of evidence that the Snowy system is not quite as bad as it has been made out to be. It has a map showing entirely unmodified tributaries (listed for their heritage values) and a photo of what looks like a very healthy river.

It is not until we go to the Australian Natural Resource Atlas that we get closer to the real story on the Snowy River.

Total catchment area = 1,589,600 hectares
NSW catchment area = 894,000 ha
Victoria catchment area = 685,600 ha

NSW mean annual runoff = 1,317,000 megalitres of which 513,000Ml is captured in dams.
Victoria mean annual runoff = 863,000Ml plus 804,000Ml from NSW.

And this tells us that about 1,664,000 megalitres out of total catchment runoff of 2.18 million still makes it to the sea at Marlo. So we have a river system which has numerous tributaries that still exhibit zero disturbance in normal flows and allow the lower river to still deliver 76.3 per cent of total runoff into the sea.

The claimed requirement for another 330,000Ml, deemed by the above mentioned “expert panels” as the minimum required to restore the ecological function of the river, would send 91.5 per cent (1.99 million Ml) of total runoff into the sea.

Note that there is some discrepancy in the Alliance's maths. If 330,000Ml is 28 per cent of flow then total flow would only be 1.18 million Ml not the 1.317 million Ml reported by ANRA as the NSW share of the runoff. What we do know with absolute certainty is that no mandate would have been given by the public to undermine the efficiency of expensive infrastructure for the dubious benefits of lifting river flow from 76.3 per cent to 91.5 per cent.

But wait, there is more. The Victorian part of the catchment is still largely timbered so we can assume that the runoff volumes from the Victorian portion are close to the original pre-settlement volumes. The same cannot be said about the NSW portion where, outside of the National Parks and reserves, extensive clearing has increased the runoff volume from pre-settlement volumes.

The Australian Natural Resource Atlas has good, but apparently limited access, data on the extent and type of original vegetation and the extent of subsequent clearing. An exact area is not available but by visual estimate about 66 per cent of this part of the catchment has been cleared. And from this we can make a reasonable "guestimate" at the change in runoff volumes since settlement. (Link here. If you can't access this then please follow the links here to find out why.)

We also know the mean annual rainfall at Bombala is 645mm which is quite evenly distributed throughout the year. This even distribution is also present at Nimmitabel with mean annual rainfall of 690mm. And from the work on 21 Victorian catchments by Holmes and Sinclair in 1986, as reported in Vertessy et al, 1998, “Predicting water yield from Mountain Ash catchments”, we can determine the changes in yield with some accuracy.