Groundwater dependent ecosystem mapping: the role of modelling in defining GDE under varying land use and climate

Abstract

This paper describes a proposed approach to enhance potential GDE mapping to likely GDE extent by the application of a physically-based groundwater model. The paper also compares the estimated change in shallow watertable area and, by association, the change in GDE extent under pre-European conditions and under 2030 climate change conditions. The objectives of this paper are to (1) describe the groundwater model used which accounts for land use recharge and evapotranspiration plus surface water/groundwater interactions (2) analyse the simulated depth to watertable surface with pre-existing potential GDE mapping and (3) to present a supplementary methodology for better defining GDE map units. The impact on GDE extent under climate change and pre- European vegetation conditions are also considered. The paper presents a linked surface-water/groundwater catchment model (Catchment Analysis Tool, CAT) to describe the temporal soil moisture profile and groundwater dynamics within the Loddon Catchment of North Central Victoria. Results indicate that the current potential GDE mapping techniques have a high correlation with vegetation transpiration from the unsaturated zone and soil moisture status within the root zone, but poorly correlate with simulated depth to watertable. This paper concludes that the extent of existing potential GDE mapping is more than double the likely GDE extent based on estimates derived using a distributed groundwater model. The application of a distributed groundwater model is shown to provide a more robust representation of the likely locations of a GDE when used in conjunction with the existing potential GDE layer. The reduction in the area of likely GDE assuming a dry period (2030 climate change) and pre-European landuse relative to current environmental conditions is estimated to be a factor of 1.4 and 2.2 respectively.