NSW Estuarine Inundation - 2025

This dataset comprises spatial inundation layers for all estuaries in New South Wales (NSW), representing both current (2020 baseline) and projected future inundation from a range of tidal water level exceedances at decadal intervals from 2020 through to 2150, under a range of sea level rise (SLR) scenarios associated with the Intergovernmental Panel on Climate Change’s shared socio-economic pathways (i.e. SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5 medium confidence and SSP5-8.5 low confidence). The inundation mapping is underpinned by a comprehensive estuarine tide gauge database, a water surface fitting methodology that accounts for spatial variability in water levels both between and along individual estuaries, and the most recent digital elevation model (DEM) with 5 m horizontal resolution.

Daily maximum water levels were analysed to derive empirical exceedance frequencies, enabling the delineation of inundation extents for a series of exceedance thresholds. The focus is on relatively frequent tidal inundation events (i.e. 1 day/year, 3.6 days/year, 36.5 days/year and 182.5 days/year) rather than flood events, which require more complex hydrological modelling. To isolate tidal influences, records affected by flooding were systematically removed prior to analysis using a threshold-based method. In estuaries lacking direct gauge data (ungauged estuaries), proxy data from hydrologically and geomorphologically similar nearby estuaries were utilised.

Future inundation conditions were estimated at decadal intervals through to 2150, incorporating probabilistic SLR projections derived from the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6), as accessed via NASA’s AR6 sea level rise projection tool. Sea level rise was added to the existing water level time series, randomly sampled from future sea level rise distributions fitted to the AR6 IPCC projection data. In estuaries with available hydrodynamic models, modifications to tidal dynamics under SLR (i.e., amplification or attenuation) were also considered through the application of estuary-specific adjustment factors. 

Water-level surface layers were constructed from the water-level exceedance distributions for indicative exceedance frequencies (1 day/year, 3.6 days/year, 36.5 days/year and 182.5 days/year). Inundation was mapped by overlaying the water-level surface layers onto a 5-metre resolution digital elevation model derived from the best available high-resolution LiDAR data. Each scenario is represented by two polygon layers: one depicting primary inundation (areas hydrologically connected to the estuary), and the other depicting isolated inundation (low-lying areas disconnected by more than 5 metres, yet potentially connected through stormwater infrastructure).

Detailed information on file naming conventions, directory structure, shapefile attributes, and layer descriptions is provided in the accompanying ReadMe documentation. Readers are also encouraged to refer to the accompanying technical report (NSW Coastal Erosion and Inundation Hazards and Exposure Assessment – Technical Report, 2025) for detailed information on the methodology, assumptions, and modelling procedures.

The primary purpose of this dataset is to inform strategic coastal and estuarine land use planning, early-stage risk assessment, and the prioritisation of adaptation needs across NSW. Its consistency across the state facilitates comparative exposure analysis and regional prioritisation. However, while the mapping provides a scientifically robust basis for understanding tidal inundation risk, it is not a substitute for detailed, local-scale flood or inundation modelling required for statutory planning or engineering design purposes.

Tags: Coastal Management, Estuary Inundation, Marine Hazards, Water Wetlands and Coastal
Organization: NSW Department of Climate Change, Energy, the Environment and Water