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

Abstract

Improved understanding of the relationship between groundwater outflows from Australian Great Arte-sian Basin (GAB) springs and the extent of wetlands they support is urgently needed given projectedincreasing impacts of land use and groundwater extractions for mining operations within the region. Thispaper demonstrates the use of wetland area derived from analysis of high-resolution satellite imageryas an indicator of groundwater flow from springs in the GAB. The method developed was tested on threespring groups in South Australia, encompassing a diversity of spring forms, spatial extents, geomor-phic and hydrogeological settings. The Normalised Difference Vegetation Index (NDVI) was computedfrom QuickBird and WorldView-2 satellite imagery captured to coincide with ground-based vegetationcover and spring discharge measurements. Significant linear relationships were established betweenimage NDVI and ground-based vegetation cover, and from these relationships NDVI thresholds weredetermined to delineate GAB-fed wetlands from surrounding dryland vegetation. There were strong lin-ear relationships between NDVI-derived wetland areas and spring flow rate measurements for selectedsprings (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 flowrate and wetland area that is transferable to a range of GAB springs, which vary in spatial scale, outflowrates, 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: arelatively consistent NDVI threshold can be used to differentiate wetland from dryland vegetation andspring flow rates can be determined from image-derived wetland extents. This approach provides naturalresource managers with an indicator of spring wetland response that can be used to monitor the impactsof land use, groundwater extractions and climate change over time for the GAB and potentially otheraquifers worldwide.