A generalizable NDVI-based wetland delineation indicator for remote monitoring of groundwater flows in the Australian Great Artesian Basin

Improved understanding of the relationship between groundwater outflows from Australian Great Artesian Basin (GAB) springs and the extent of wetlands they support is urgently needed given projected increasing impacts of land use and groundwater extractions for mining operations within the region. This paper demonstrates the use of wetland area derived from analysis of high-resolution satellite imagery as an indicator of groundwater flow from springs in the GAB. The method developed was tested on three spring groups in South Australia, encompassing a diversity of spring forms, spatial extents, geomorphic and hydrogeological settings. The Normalised Difference Vegetation Index (NDVI) was computed from QuickBird and WorldView-2 satellite imagery captured to coincide with ground-based vegetation cover and spring discharge measurements. Significant linear relationships were established between image NDVI and ground-based vegetation cover, and from these relationships NDVI thresholds were determined to delineate GAB-fed wetlands from surrounding dryland vegetation. There were strong linear relationships between NDVI-derived wetland areas and spring flow rate measurements for selected springs (R2=0.92 to 0.99). Although there were some differences in this relationship for the three sites, they were not statistically significant. This research demonstrates a relationship between surface flow rate and wetland area that is transferable to a range of GAB springs, which vary in spatial scale, outflow rates, surface form, geomorphic setting and vegetation composition. The technique provides an objective, quantitative and accurate means of documenting the distribution and extent of spring-fed wetlands: a relatively consistent NDVI threshold can be used to differentiate wetland from dryland vegetation and spring flow rates can be determined from image-derived wetland extents. This approach provides natural resource managers with an indicator of spring wetland response that can be used to monitor the impacts of land use, groundwater extractions and climate change over time for the GAB and potentially other aquifers worldwide.