A Regional Scale Approach to Assessing Current and Potential Future Exposure to Tidal Inundation in Different Types of Estuaries

David J Hanslow,Michael A Kinsela,Bradley D Morris,Edwina Foulsham

doi:10.1038/s41598-018-25410-y

Abstract

Broad scale assessments of impacts associated with sea level rise have mainly been undertaken using ocean water level data from tide gauges located in harbours and ports assuming that these can be applied directly in mapping inundation throughout estuaries. On many coasts, however, exposure to sea level rise comes about through inundation adjacent to rivers and estuaries, in many instances far from the ocean. In this study, we examine the potential impacts of sea level rise within the diverse estuaries of South East Australia. We use an extensive and long-term water level data set, which show that water levels within the different types of estuaries vary from ocean water levels. We map potential inundation scenarios for each estuary using an approach which improves on the commonly used bath tub method by allowing for variation in tidal processes both between and along estuaries. We identify considerable exposure to future sea level rise, and variable suitability of the bath tub method within different estuaries. Exposure is particularly high around tidal lake systems, where reduced tidal ranges have allowed development to occur in relative proximity to present sea level, and around larger coastal rivers, which feature extensive low-lying plains exposed to potential inundation.

Highlights

Beyond 2100, the Intergovernmental Panel on Climate Change (IPCC)[4] conclude that it is virtually certain that global mean sea level rise will continue for many centuries due to thermal expansion of the oceans and ongoing contributions from the loss of mass from ice sheets
To evaluate and refine previous assessments of potential impacts from sea level rise in South Eastern Australia, we describe an improved method to quantify current and potential future exposure of property and infrastructure, which addresses the variation in tidal water levels within different types of estuaries
The finding that water levels within different estuary types vary from those seen in the ocean is not new[41,43,45,46] but does not seem to have been widely appreciated or applied in many broad scale sea level rise risk assessments

Summary

Introduction

Beyond 2100, the Intergovernmental Panel on Climate Change (IPCC)[4] conclude that it is virtually certain that global mean sea level rise will continue for many centuries due to thermal expansion of the oceans and (probably underestimated) ongoing contributions from the loss of mass from ice sheets. The IPCC4 predict warming greater than a threshold above 1 °C but less than about 4 °C would lead to the near-complete loss of the Greenland ice sheet This would result in a global mean sea level rise of up to 7 m over a millennium or more. Recent modelling suggests that collapse is inevitable under mid to high range global warming scenarios[6], and that www.nature.com/scientificreports/ This area could contribute significantly to sea level rise in the decades and centuries to come[6]. There is usually some level of natural defence against ocean inundation, typically through the presence of headlands and coastal beach-dune barrier systems This has, to date, generally limited significant impacts to only the more extreme events. The creeping effects of sea level rise are becoming apparent through the growing frequency of ‘nuisance inundation’ or ‘sunny day flooding’[14,21,22]

Methods

Results

Conclusion