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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
GULLIES, GOOGLE EARTH AND THE GREAT BARRIER REEF: A REMOTE 
SENSING METHODOLOGY FOR MAPPING GULLIES OVER EXTENSIVE AREAS 
U. Gilad, R. Denham and D. Tindall 
Remote Sensing Centre, Queensland Dept. of Environment and Resource Management, ESP, GPO Box 2454, Brisbane, 
QLD, 4001, Australia - (uri.gilad, robert.denham, dan.tindall)@derm.qld.gov.au 
KEY WORDS: Environment, Geomorphology, Mapping, GIS, Prediction, Modelling, Imagery 
ABSTRACT: 
Recent work suggests that gully erosion is the main contributor of sediments to the Great Barrier Reef, Australia. The objectives of 
this study were to identify the location of gullies as well as the landscape characteristics associated with gully presence in the 
Burdekin Catchment. Data were collected by random sampling using Google Earth. A spatial-statistical analysis allowed the 
exclusion of areas where gullies were less likely to be present. The remaining gully sensitive areas were then manually mapped by 
using Google Earth, assisting in the creation of a predictive map. A semi-quantitative gully presence map was also created by 
visually inspecting imagery at 5 km x 5 km grid cell scale. Results show a strong relationship between gully presence and drainage 
features, low tree cover and low slopes. The resulting predictive map has correctly allocated more than 90% of gullies within less 
than 20% of the Burdekin’s area, yet uncertainties still remain. The manually derived mapping product comprises the most 
comprehensive gully data available for the Burdekin, while the high-resolution predictive map and the 5 km x 5 km grid map will 
allow better targeting of gullied areas in later stages of this research. This study also provides a methodology that can be applied to 
mapping gullies over extensive areas. It demonstrates how Google Earth could be used as a reliable platform for mapping gullies and 
discusses the limitations in the use of remotely sensed data for gully mapping and modelling. 
1. INTODUCTION 
Until recently, hillslope erosion was thought to be the dominant 
contributor of sediments to the Great Barrier Reef (GBR). 
However, recent work is challenging this assumption, with 
suggestions that in some subcatchments most of the sediment 
load is being derived from gully erosion (Bartley et al., 2007). 
Evidence also suggests that fine sediment particles are of most 
concern to reef water quality and significant amounts of these 
are derived from gullies. Consequently, it is important to know 
where gullies occur in the contributing catchments, as well as to 
identify the types of landscapes and environmental factors that 
are associated with gully formation. In the last few years efforts 
have focused on the Burdekin Catchment (130,000 km?), the 
fifth largest river catchment in Australia (Bartley et al., 2007) 
which is the largest contributor of sediments to the Reef. The 
Remote Sensing Centre of the Queensland Department of 
Environment and Resource Management, supported by the 
QScape program, has been undertaking this study aiming to 
identify the location of gullies and the environmental conditions 
associated with gully formation in the Burdekin Catchment. 
2. STUDY AREA 
The Burdekin Catchment in central Queensland, Australia, 
covers 130,000 km? consisting of almost a third of the total 
Reef drainage area (Figure 1). The climate of the Burdekin is 
defined as dry-tropical, ranging between 500-1500mm a year 
(Dight, 2009). The most prevalent land use is grazing which 
accounts for about 90% of the sediments and nutrients exported 
to the reef (Brodie et al., 2003). At the heart of the catchment is 
the Burdekin Falls Dam which captures about 60% of the 
sediments that reach the Lake Dalrymple during flood events 
(Bainbridge et al., 2008). The dam's location and ability to trap 
sediments reduces the volume of sediments that arrive from 
above the dam to only about 20% of the total sediment load that 
is exported from the catchment. The remaining 80% of the load 
is being transported from the river systems below the dam, in 
particular the Bowen and Broken rivers (Figure 1). 
  
   
    
  
    
  
Burdekin Catchment (above dam) 
RASE Burdekin Catchment (below dam) | 
Other GBR catchment 
Non:GBR catchment 
GBR Marine Park 
SÉ» Lake Dalrymple E 
  
  
  
  
Figure 1. Queensland catchments and the Great Barrier Reef 
Marine Park boundary.