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save the Blue Tier

water catchment

Image of unnamed rock pool above Halls Falls

Limpid rock pool above Halls Falls on the Groom River which currently provides water for the St. Helens community; this is under threat from large scale forest practices.

- d. e. leaman, hydrologist

EFFECT OF LAND USE CHANGE ON WATER SUPPLY: BLUE TIER REGION, NORTHEAST TASMANIA - 16 July, 2003

SUMMARY

Review of the implications for local water supply as a result of proposed forest operations (clearing, regeneration, plantation) at Blue Tier in Northeast Tasmania has exposed the need for some general principles of water and land use management in Tasmania.

Problems arise, principally, because such forest operations are not subject to, nor preceded by, any environmental impact statement nor any assessment of the possible effects of such activities upon water supply.

Relevant Tasmanian legislation (Water, Environment, Forestry Acts) is weak, incomplete and inconsistent. Consequently, the Forest Practices Code derived from them wholly omits reference to quantitative maintenance of water supplies to individuals, farms, industries or towns in an affected catchment. The Code is quite useless in these respects: it does not, and can not, protect other users nor manage the water available and overlooks the reality that trees use water. The Code does include modest constraints for protection of water quality and some limitation on the area which can be transformed per year. Proper catchment assessment is essential: there must be major change in management approach.

Conversion of native forests to "other" forests leads to a substantial loss of catchment yield for decades. Where the "other" forests contain a significant proportion of plantation or forest under rotation, the yield continues to decline in perpetuity due to cumulative effects. The role of groundwater storage and its interactions with surface water in controlling both yield and quality is critical in these exchanges. This aspect of catchment hydrology is ignored by all current legislation and codes of practice with the inevitable result that many Tasmanians, and the countryside, are losing their share of the water available.

The two catchments examined on Blue Tier, Groom and Ransom Rivers, amount to about 40% of the catchment of the George River system. The George River supplies the town of St. Helens and associated agricultural lands.

The proposed ten year forest plan for these catchments would convert nearly all the available state forest within them - about two thirds of their total area - to new forest and plantations. This change will transform these permanent streams into intermittent streams at best with consequences for all water uses in, and beyond, the two catchments.

The effect on the George River is significant. Much of the George River catchment has already experienced forest conversion, with more to follow. The change in yield of the North and South George Rivers as a result of recent forestry is unknown and the full effects may not be known for up to twenty years. It can, however, be predicted with confidence that the yield will decrease noticeably. If, in this situation, the Groom and Ransom Rivers are reduced to intermittency then the George River will fail. St. Helens will become a dry town.

Either steps are taken now to avoid this occurrence by cessation of forest activity in the feeding catchments while it is possible to do so, or government must be prepared to provide an alternative supply in future.

The moral, ethical, economic and political issues raised by these forest schemes are related to current lax law, ignorance of hydrology and an absence of sound impact assessment procedures. Taxpayers of Tasmania will be required to restore supply to an affected community when poor legislation and practice has advantaged a few individuals or companies economically to the detriment of all other users or the public good. Forestry is not the only way in which catchment water could be utilized yet present laws act most unequally.

Any uncertainty in the predictions offered here reflects the almost total absence of relevant research in forest hydrology in Tasmanian conditions and yet current practices guarantee change in water supply. Forest operations should be modified in all catchments and restricted mainly to catchments which have yield to excess and no possible affected users, until the necessary evaluation has been completed. In the case of the George River catchment the critical point may already have been reached and further land use change will damage water supply and restrict future options

At Blue Tier, protection of the George River and supply to St. Helens requires that the catchments of Groom and Ransom Rivers be left in the present, or natural, state. Any other action, given present research information and risk indicators, would be shortsighted, lack any sense of duty of care or responsibility to communities involved, and be quite foolish.

The community itself must be prepared to undertake the necessary catchment studies if government agencies can or will not do so. Independent review is advised in any event and this work must begin immediately. The results of such analysis might then provide the basis of civil legal action for damages where changes in water supply lead to losses in productivity or amenity, or where water lost must be replaced by other methods.

D. E. Leaman, Ph.D., Hydrologist
Leaman Geophysics, Hobart, Tasmania

[Republished with permission of the author and editors of Upper Catchment Issues, which first published this in Vol.2#1B ISSN 1444-9560. The main report received some criticism from Forest Practices Board (FPB); we are happy to provide Leaman's response.]

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