WATER S.O.S TASMANIA - Catchment Stability
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Catchment Stability
The Role of Forests in Maintaining Stable Catchments.
 The long term productivity of water catchments is wholly dependent on the stability of the forests in those catchments. Where ever clearfelling and roading takes place there is significant erosion and loss of topsoil resulting in the siltation and organic matter contamination of rivers and streams, this problem is compounded in steep terrain.
Catchment Stability
 Photo by Geoff Lea
Rainforest Tasmania
The binding action of deep rooting trees and plants in forests promotes soil particle aggregation and stability which together with the leaf litter inhibit run-off and encourage the deep filtration of water.

This deep water storage and filtration in turn enables rivers and streams to maintain relatively constant flows during periods of low rainfall as groundwater percolates out slowly over a long period.

Contamination of rivers and streams from unstable catchments with organic matter and silt, destroys the water quality, quantity and potability.
Forestry Road into Pristine Area Tasmania
Road into old-growth forest, Upper Florentine Valley. Zoned for logging.
The depletion of oxygen in waterways from decomposing organic matter together with sedimentation, are an important determinant of the viability of invertebrate communities within those waterways.
Algal contamination is indicative a nutrient
 build-up due to organic matter and or fertilisers
(i.e., nitrates and phosphates) entering rivers and streams.
Algae Tasmania
Following forestry operations, water run-off initially increases then gradually decreases as vigorously growing plantations or re-growth with their high corresponding evapo transpiration rates decrease run-off by up to 50% at around 40-50 years. Relative stability returns to water catchments at about 150 years plus.
Where logging rotations of less than 50 years takes place, catchments and water production are destroyed forever.
Catchments with large areas of young trees whose underdeveloped root systems and low soil organic matter, unlike old forests, do not have the ability to store water for dry time flows, consequently their high water demands leaves less for streams or may dry them up altogether.  

 The Tasmanian forest practices code does not recognise as necessary buffer zones around small ephemeral streams, channels or steep slopes which may facilitate the prevention of the contamination of waterways.
Clearfell piles Tasmania
 Photo by Brenda Rosser
Research which has been carried out highlighting the detrimental effects of logging on water yield :
Ref : Kuczera 1985.
Ref : O’Shaughnessy & Jayasuriya, 1991
Ref : O’Shaughnessy et al., 1995.
Ref : Doug and Koehn, 1990.