Poster Presentation NCGRT/IAH Australasian Groundwater Conference 2019

Assessing seawater intrusion vulnerability to sea level rise in Christchurch, New Zealand using GIS-based methods (546)

Irene Setiawan 1 , Leanne K. Morgan 1 2 , Crile Doscher 1
  1. Waterways Centre for Freshwater Management, Lincoln University and University of Canterbury, Christchurch, New Zealand
  2. Flinders University, Bedford Park, SA, Australia

The Christchurch coastal aquifer system provides one of the highest quality drinking water sources in the world, which local residents completely rely on for critical needs. Coastal aquifers are vulnerable to sea-level rise (SLR) through seawater intrusion (SWI), which is the landward movement of the saltwater-freshwater interface. In this study, we carry out a first-pass assessment of SWI vulnerability to SLR in the Christchurch coastal aquifer system using two GIS-based methods.

The assessment of SWI vulnerability using GIS is a useful first-pass approximation to highlight areas of highest possible risk to SLR. Here, the qualitative GIS-based GALDIT method (Lobo-Ferreira et al., 2007) was used to assess SWI vulnerability in the shallow confined Riccarton Gravel aquifer under various SLR scenarios. To overcome limitations of the GALDIT method, the analytic solutions of Werner et al. (2012), which predict the change in the saltwater-freshwater interface position under SLR, were applied within a GIS framework. These analytic solutions predict the change in the saltwater-freshwater interface position under SLR and are, arguably, more physically justifiable than GALDIT.

As expected, both methods showed greater SWI under increasing sea level. Interestingly, both methods highlighted similar areas of greatest SWI vulnerability to SLR, which occurred in areas of low groundwater heads. Brooklands (a suburb built on low-lying swampland), Woolston (where SWI has occurred previously) and Ferrymead (adjacent to the Avon-Heathcote estuary) had maximum SWI vulnerability under the simulated SLR scenarios. 

Analytic solutions, such as those developed by Werner et al. (2012) can be incorporated into a GIS framework to quantitatively assess SWI vulnerability to SLR and are a useful addition to traditional qualitative approaches such as GALDIT.

Lobo-Ferreira, J. P., Chachadi, A. G., Diamantino, C., & Henriques, M. J. (2007). Assessing aquifer vulnerability to seawater intrusion using the GALDIT method: part 1 - application to the Portuguese Monte Gordo aquifer. In J. P. Lobo-Ferreira & J. M. P. Viera (Eds.), Water in Celtic Countries: Quantity, Quality and Climate Variability (Vol. 310, pp. 161).

Werner, A. D., Ward, J. D., Morgan, L. K., Simmons, C. T., Robinson, N. I., Teubner, M. D. (2012) Vulnerability indicators of seawater intrusion, Groundwater 50(1), 48-58.