South Sister St. Marys, Tasmania
February 7, 2005
Mr. D. Clement,
You have asked how comparable are the springs and hydro-geological settings at Koonya and South Sister, and could there be good reason as to why the protective zones assigned in each case should be so different. I am familiar with, and have inspected, both sites.
The two situations are geologically similar; both involve dolerite on high ground, slopes draped in dolerite-derived debris of variable thickness - some of which have suffered slope failure, and all overlying Triassic sandstones and mudstones (no coal). Seepages and springs are associated with old failures or where slope cover is thin and pinched toward the surface. The springs are perennial (at present) and supply a very small number of households.
As a result of substantial local debate and investigations reported by Forest Practices Board (Dec 2003), plus a report from S. Forsyth of MRT, the Assistant Manager of Derwent District, Forestry Tasmania (B. Haywood) publicly declared in October 2004 that 'Forestry Tasmania will use low soil impact harvesting methods and will not harvest within 300 m upslope from the three known springs'. This is a wise and sensible approach.
I cannot, therefore, understand why a mere 10m should be considered adequate at South Sister. This decision is made more strange given the peaked mature of South Sister (and hence less storage and more chance of damage) and the greater demands (many more people depend on the south sister springs). I can see no good reason for any difference in prescription.
In fact, as I have previously advised, the risks to both water quality and quantity are such that South Sister should be treated as a supply catchment and not unnecessarily disturbed in any way.
Yours faithfully,
D. E. Leaman, Ph.D., Hydrologist
Leaman Geophysics, Hobart, Tasmania
23 November, 2003
5275 (2, 12, 29, 60)