Assessment of the Impact of Forest Logging
Abstract
The West Victorian Regional Forest Agreement, signed in March 2000, promotes long term sustainable management of forests in western Victoria of which the Otway forests are the most notable. In response to community concerns, research into the hydrology of the Otway forests was commissioned to evaluate the impact of timber harvesting on stream flow and water quality. This paper describes a part of the research undertaken, specifically the modelling framework used to estimate stream flow. A numerical model is developed and applied to three key catchments using data from geographic information systems as input. The model relies on functions relating forest age and stream flow for the two most dominant forest types; mountain ash (Eucalyptus regnans) and eucalypt mixed species. These functions are developed from a large body of research carried out in the Melbourne water supply catchments and elsewhere. Using the functions and applying logging schedules proposed for the next 100 years, demonstrates that only minimal changes to the current mean annual stream flow of test catchments are likely. By comparison, a large wildfire causes a brief increase in stream flow in test catchments, followed by a significant decrease with reduced flows being sustained for up to 60 years. The stream flow from forests undisturbed for the next 100 years is estimated to be about 50 mm greater than that generated when logging schedules are applied. The approach described provides objective estimates of stream flow under different forest management scenarios and provides a basis
from which to develop appropriate management policy.
Authors
Carl Daamen, Peter Hill, Seth Munday, Rory Nathan,
Sinclair Knight Merz, P.O.Box 2500, Armadale, VIC 3144, Australia.
P.M. Cornish
Landuse Hydrology Pty. Ltd.