The long battle by locals to obtain a 28% release of water from the Jindabyne dam for the Snowy River could be partly or wholly negated by clearfelling its major sub-catchments, scientists have warned.
Two reports from the early 90s indicated that logging would cause reduced water yields. They were dully ignored by government, but a decade later their predictions are now coming back to haunt them.
Logging = Loss of Water
Evaluation of the Economic Values of Wood and Water for the Thompson Catchment (Read Sturgess and Assoc., June 1992) says that logging can reduce stream flows by 50% and it may take more than 100 years to restore original flows. Maximum stream flows occur in forests which are very young or very old. This means a 60-80 year logging cycle could create a permanent drought downstream. Under any cash flow analysis, old growth forests are high value as they produce maximum stream flows.
A second and more regionally relevant report, The Impact of Forest Harvesting on Water Yield: Modelling Hydrological Changes Detected by Pollen Analysis (Dr R.L. Wilby, University of Derby UK and Dr P.A.Gell, ,Adelaide University, 1994), supports the Read Sturgess findings.
Wilby and Gell analysed logging in the Delegate catchment, another major sub-catchment of the Snowy. They predicted a progressive reduction in annual yields resulting in a 20 to 55% loss of water by 1987-88 and an almost 100% reduction by 2005 (±6years). This serious reduction in water yield is due to increased forest transpiration from regrowth after logging.
Greatest impact since Ice Age
Both swamp core samples and climate data were used in the modelling to predict the decreased water yields. Reduced water runoff from bushfires and clearfelling create similar drought-related flowering reactions (pollen release). However, pollen records show these are much less severe after a bushfire, with clearfelling causing up to 100 times more drought stress than fire.
Analysing core samples dating back 10,000 years showed there had been more impact on two indicator plant species in the last 30 years (since clearfell logging began) than in the previous 10,000 years!
Water sponges by any name
NRE argues that, because most studies have been done on fast regenerating Ash forests, they cant be used to predict what catchments of other forest types will do. But forests in the upper Delagate catchment were tall wet mixed forests, dominated by Shining Gum and Cut-tail, with an occurrence of Alpine Ash. These Ash-type forests also regenerate very quickly and consume large amounts of water.
The Wilby and Gell report predicts that lowest flow rates will occur 30 years after severe catchment disturbance. This is similar to findings of other research carried out in Ash forests. It also suggests it would take over 100 years for normal flows to return.
Besides drying up the much abused and thirsty Snowy River, logging of the Delegate catchment is drying out and subjecting the nationally significant Delegate River alpine wetland to the threat of fire.
Onus of proof now on NRE
There is an urgent need for lengthy hydrological studies and data collection in sensitive catchments before any further clearfelling is approved. NRE is unable to show its management is NOT affecting water yields. It s not good enough to simply say they dont believe research that shows that it IS.
Government Pooh-poohd Reports
When the Wilby and Gell study was released, government officials thought it fanciful to suggest that logging could affect an area 6 km downstream. Even recently, we heard Peter McGauran claiming there was no science behind conservationists claims and that, anyway, “its more than 20 km from the Snowyand its not in a gully, its on a ridge”. !*??! And hes now Minister for Science!!!? He also stated the Yalmy was not connected to the Snowy. I wonder if he’s ever looked at a map of his electorate in the last 40 years.
Logging industry should pay water rates
Clearfelling old growth and mature forests is expected to continue until 2030, when all accessible areas will be in a young regrowth stage. The fast growing young eucalypts are then planned to supply the industry.
Clearfelling, coupled with the effects of climate change, could cause critical water shortages in the near future. As the logging industry can be seen as consumers of water, due to the uptake by the regrowth managed for its next rotation, they should pay as users of water, just as irrigators, domestic and commercial users do.
Sub-catchments need urgent protection
The Buchan and Murrindal Rivers upper headwaters, where they flow through wetter forests, have also been intensively logged and whats left is scheduled for more clearfelling. Relative to other forested high rainfall catchments, the Yalmy still has excellent high water yielding forest cover but is planned for extensive clearfelling over the next ten years.
Thorough research has already been carried out but has been conveniently ignored. It is now the governments responsibility to act on these reports and to monitor water yields, climate and rainfall to determine what likely future effects there will be, before they log. However, the governments legislated obligation to supply maximum volumes of sawlogs could hinder any chance of adopting recommendations from hydrology research. If this issue is not addressed, unaltered management by NRE could negate much of the Snowys hard-won environmental flow concessions.