Risk to Groundwater Quality in Coastal Aquifers under the Pressure of Climate Change

English Abstract:

In coastal regions, fresh groundwater is in direct contact with the ocean. The quality of the groundwater can be compromised due to saltwater intrusion (SWI) caused by various hazards related to pumping (due to development) and climate change (sea level rise, storm surge, changes in recharge). The goal of this research is to develop approaches for assessing and managing risk to groundwater quality in coastal aquifers. The Gulf Islands in British Columbia is the case study area. Chemical indicators of SWI were identified based on the analysis of an extensive water chemistry database available for the Gulf Islands. Various quantitative, graphical and statistical methods were used to chemically distinguish groundwaters that are impacted by saltwater intrusion, and to identify thresholds for several chemical parameters that could be used for monitoring purposes. The most appropriate indicators, based on available data, are chloride, electrical conductivity and total dissolved solids. Climate change related hazards, including sea level rise and storm surge overwash, were combined into floodplain maps for each island using projected sea level rise data for 2100 in combination with estimated storm surge data over a forty year period. The floodplain maps show the projected extent of coastal zone that may become inundated or impacted by storm overwash under future climate change, and thus more likely to be impacted by SWI. When combined with maps showing the density of pumping wells, coastal zones that may be at higher risk of SWI are identified for this particular coastal area of BC. The combination of chemical indicators and risk assessment maps are useful tools which can be used to improve decision-making related to monitoring and community development for this particular coastal area of BC.