smallcatchments

Small catchment water yields under current land uses

Project Description: Development of an easy to use software modeling tool that can be used by land managers to predict the impact of major land use changes on the quantity of in-stream flow in small catchments (50-500has in size).

Type of Activity: Planning

Timing: September 2004 – October 2005

Region: Statewide

Priorities addressed through this project:
North - Sustainable Use of Water Resources

South - Managing water supplies, allocation and use

Cradle Coast - Unsustainable water use

Partners: Natural Heritage Trust, CSIRO Land and Water, DPIWE

Others involved: Tasmanian Framers and Graziers Association (TFGA), Forestry Tasmania, Burnie City Council

Form of Investment:

NHT $140,000

Forestry Tasmania, Burnie City Council, DPIWE and TFGA provided in-kind support by donating data, sitting on steering group and reviewing model.

Achievements:

Catchment studies from around the world were analysed with similarities to the land use changes occurring in rural Tasmania. Changes examined were:

the planting of pasture land to plantations;
the conversion of native forest to plantations;
and the harvest of native forest (which is a land use change by way of the change in the forest age structure).

The summary of this analysis found that generally stream flow increased when forest cover was reduced and decreased when forest cover was increased. However, the magnitude of these changes was strongly influenced by the forest age structure (young trees and very old trees use less water than rapidly growing trees). The net outcome for conversion of native forest to plantation and native forest harvest and regrowth may be an increase or decrease of stream flow, depending on rotation length and the age of the original native forest.

The analysis has helped produce a simple to use predictive tool for industry, government and community members who have basic computer skills. The tool is loaded with three sample Tasmanian catchments and a facility to load others.

The model predicts changes to mean annual flows and where stream flow has been measured historically, it also permits predictions of the change in the distribution of daily flows. It does not permit this second measure in ungauged catchments. The model is not suitable for prediction of land use changes such as forest thinning, or changes in pasture management. Also, it is not able to predict the time series of stream flows or the flow in a particular season.

How you can get involved:

The tool will be publically available at www.toolkit.net.au in late 2005, following peer review of both the model and documentation.

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