Field Guide: Fire in Dry Eucalypt Forest

Fuel Assessment and Fire Behaviour Prediction in Dry Eucalypt Forest

JS Gould, WL McCaw, NP Cheney, PF Ellis, S Matthews

• Publisher: CSIRO PUBLISHING
• Year: 2008
• Print ISBN: 9780643096172
• eBook ISBN: 9780643102767
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

An effective response to bushfires relies on accurate predictions of fire behaviour, particularly the rate of spread, intensity and 'spotting'. This field guide has been developed to provide a systematic method for assessing fuel hazard and predicting potential fire behaviour in dry eucalypt forest. It will assist in making vital decisions that ensure the protection of fire crews and the community.

This guide integrates Project Vesta research findings with the Victorian Overall Fuel Hazard Guide and is applicable to dry eucalypt forests throughout southern Australia. Fuel assessment is based on the hazard scoring system employed during Project Vesta which investigated the effects of fuel age and understorey vegetation structure on fire behaviour in these forests.

Information provided in this guide can be used to: Define and identify different fuel layers and components of fuel structure and hazard; Determine the hazard score of surface and near-surface fuel layers and the height of the near-surface fuel for fire spread prediction; Determine elevated fuel height for flame height prediction; and determine surface fuel hazard score and bark hazard score for spotting distance prediction.

The Field Guide provides tables to predict the potential rate of spread of a bushfire burning in dry eucalypt forest under summer conditions, and can also be used to predict flame height and maximum spotting distance. The guide also allows users to determine the moisture content of fine dead fuels throughout the day, and to account for the effect of slope on the rate of spread of a fire.

Rate of Spread

Rate of Spread Tables [R]

The fire behaviour tables are a systematic method for predicting forest fire behaviour in dry eucalypt forest. They are derived from mathematical equations relating wind, fuel structure, fuel moisture and slope for different fuel hazard ratings (scores). This guide is intended mainly to be used as a field reference. Certain simplifications were made so that the fire behaviour predictions could be presented in tabular form.

A complete technical description of the dry eucalypt forest fire behaviour prediction system is given in the technical report Gould JS, McCaw WL, Cheney NP, Ellis PF, Knight IK, Sullivan AL. (2007) Project Vesta – Fire in Dry Eucalypt Forest: fuel structure, fuel dynamics and fire behaviour. Ensis–CSIRO, Canberra, ACT and Department of Environment and Conservation, Pert, WA.

Use of the Fire Behaviour Tables

1. Select the appropriate fuel hazard score for the surface fuel and near–surface fuel from Table F1 and F2 and the estimated near–surface fuel height (cm).

2. Input the mean wind speed at height of 10 m in the open over level ground for a period of 15–20 minutes. You may need to use a measurement made at an appropriate nearby weather station, or a reliable forecast of wind speed. Measurements of wind at 2 m in the open can be adjusted to 10 m wind speed by multiplying by 1.25 (i.e. ratio between wind at 10 m in the open and wind speed at 2 m in the open is 10:8).

Measurement of wind in the forest is not recommended because of the great difficulty in finding a site that represents the mean of the variations induced by the topography and the vegetation.

If you must do it you will need an appropriate ratio to determine the standard 10 m wind speed above the canopy:

• Measure the wind speed on a windward slope at 2 m in a location away from tall shrubs or tree trunks for 20 minutes.

• Multiply the average reading by 3.0.

One of the major sources of error in the application of any fire spread model based on wind in the forest is the selection of an appropriate ratio to relate the wind in the open or above canopy to the wind in the forest. We would expect the model to over–predict fire spread in tall dense forest where the ratio of the wind above the canopy to the wind at 2 m in the forest to is likely be 5:1 or even 6:1.

If an anemometer is not available, a trained observer may assess wind speed with reasonable accuracy by means of the Beaufort scale, which relates the movement of objects to wind speed. Reproduction of th...

Table of contents

• Cover
• Title
• Copyright
• About this Guide
• Fuel Assessment
• Rate of Spread
• Fuel Moisture Content
• Slope Correction
• Maximum Spotting Distance
• References
• Acknowledgements