This tool is designed to provide warning of potential tidal inundation (otherwise known as nuisance inundation or sunny day flooding) along the NSW coast. This type of inundation typically occurs during higher tides in some low-lying sites adjacent to estuaries (see Figure 1 for an example)

These inundation events involve minor, short lived (1-3hrs), flooding of roads, paths and driveways usually over successive days of the spring tide, although they suggest more widespread and significant impacts ahead as sea levels rise.

In many instances tidal waters are able to enter the stormwater system and emerge in street gutters flooding streets and paths. Some Councils in NSW already take action to warn of potential flooding associated with predicted king tides. Some have installed tidal gates or flaps to limit ingress of tidal waters into the stormwater system to limit the associated flooding.

The tool leverages the extensive network of tide gauges in NSW and enables users to investigate the potential implications of sea level rise using water level exceedance data from their local tide gauge.

The tool provides users with two water level forecasts. The first is a short term (7 day forecast) which combines astronomical tide prediction with a prediction of additional weather-related factors. The second is a longer-term astronomical tide forecast for the coming year.

The tool requires users to set a threshold level at which inundation is expected to occur. There are several options available to do this, including:

• First-hand observation of inundation and cross matching against measured inundation levels on the nearest gauge
• Cross match the date/time of photographs of tidal inundation (for example sourced by undertaking web searches or accessing sites like Witnesskingtides.org) against the measured inundation on the nearest gauge (see Figure 1)
• Local surveying to determine the levels of low points in streets and gutters and overland inundation thresholds
• High resolution mapping using LiDAR point could data which is available for NSW via ELVIS (elevation.fsdf.org.au)

Doing this enables users to forecast when inundation is likely to occur both over the short and longer term.

The below image shows a numbered diagram of the tool's interface, with a description of each component following:

1. Station selector: Choose from the dropdown which water level station to use for the forecast. A full list of all stations can be found on the MHL homepage. You can filter sites by typing either the station's number or name in the input field, then select the station by clicking on it.
2. Threshold selector: This field displays the currently selected flood threshold level. The plotted data relates the number of projected days where the tidal level will exceed this level. You can type the desired level into this field or use the slider in the following component.
3. Threshold slider: The slider provides an alternative way to select the desired flood threshold level, displayed in the threshold selector above. You can drag the slider bar up and down (or left and right on mobile) to select the desired flood threshold level. The box next to the slider will update with the currently selected level as you move it around, and the plot will update on release of the slider.
4. Forecast series selector: forecasts are provided the next 7 days based on an aggregated water level forecast which include both astronomical tide and weather related factors (excluding rainfall) and a longer term astronomical tide forecast for the coming year.
5. Download buttons: You can click this button to download the currently plotted data in CSV format for your own purposes. You will need to accept the disclaimer and user agreement before downloading will commence.