SWAN GIS Getting Input Data

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Introduction

This page guides you through the process of obtaining the bathymetric, wind and wave data required to develop our wave model. It is the second component of our SWAN GIS Tools step by step guide.

Please note this data is already included in the tutorial download Complete_Model\DATA folder, so if you want to this section can be optionally skipped. We do, however, highly recommend working through this process as you will likely need to complete these steps when you start to build your own project.

Bathymetry Data

The SWAN GIS plugin is designed to work with all GDAL compatible raster formats as well as UGRID and Aquaveo SMS TIN mesh formats.

Coarse bathymetry can be sourced from the global GEBCO dataset. Go to https://download.gebco.net/ and follow these steps:

1. Enter the subset extents: longitude (149.27, 162.53), latitude (-31.00, -22.43)
2. Tick the GeoTIFF Grid format option
3. Click the 'Add to basket' button
4. Click the 'View basket' button
5. Click the 'Download your data' button
6. Save the data to your \Moreton_Bay_Waves\DATA\BATHY folder

For near-shore wave modelling, the GEBCO data set is typically too coarse, therefore it is best to have a higher resolution data set for the area of interest. For our near-shore areas, we will overwrite the GEBCO data set with more accurate data from an Australian Digital Terrain Model (DTM) database accessed via https://elevation.fsdf.org.au/. Go to the webpage and follow these steps:

1. Enter the subset extents: longitude (152.79, 153.99), latitude (-28.16, -26.56)
2. Tick the 'High-resolution depth model for the Great Barrier Reef' option
3. Click the 'Download selected datasets' button
4. Set the output coordinate system to WGS84
5. Set the output format to GeoTIFF
6. Enter user credentials
7. Click 'Start extract of datasets' button
8. Save the data to your \Moreton_Bay_Waves\DATA\BATHY folder

Wind Data

The SWAN GIS plugin is designed to utilise gridded wind data from the European Centre for Medium Range Weather Forecasting (ECMWF) Reanalysis 5 (ERA5) dataset in netCDF4 format or alternatively a spatially constant time series in CSV format. This section shows how to download ERA5 wind data from the Copernicus Climate Data Store (CDS). Before the application can be accessed you will need to create a Climate Data Store account here.

Login to your CDS account and navigate to this webpage. To request the data follow these steps:

1. Tick 'Reanalysis' product type
2. Select variables 10m u-component of wind and 10m v-component of wind
3. Select the year 2018
4. Select months September and August
5. Select all days
6. Select all times
7. Enter the subset extents: longitude (149, 162), latitude (-31, -22)
8. Tick NetCDF4 format
9. Click 'Submit Form' button

The CDS server will now process the request. The status of the request should be monitored here. When the request has been processed, click the download button for the request as shown below:

Save the wind data to your Moreton_Bay_Waves\DATA\WIND folder.

Wind Timeseries Data

As an alternative to gridded ERA5 wind data, a time series of U and V wind components can be input to the SWAN Model Builder. The format required is csv. The first row specifies the X and Y location of the data point, the second row the header, rows 3-n are the data points.

For example:
153.250000,-27.000000
TIME,U10,V10
01/09/2018 00:00:00,3.64,0.27
01/09/2018 01:00:00,3.06,0.04
01/09/2018 02:00:00,2.12,-0.39
...
...

Where the date and time format is dd/mm/yyyy HH:MM:SS and U10 and V10 vector components are output in cartesian convention. i.e. the direction to where the vector points, measured counter-clockwise from due East. For example <-1U, 0V> will be wind coming from the east and heading west.

The wind data csv can either be developed from ERA5 using the post processing ERA5 Time Series Extractor Tool or you can develop an input csv manually using a custom dataset, provided that you generate the csv in the same format as shown above.

Wave Data

The SWAN GIS plugin is designed to work with gridded spectral wave parameter data from the ERA5 dataset in netCDF4 format. To download the wave data, follow the procedure outlined in the Wind Data section, however alter the selected variables to:

• Peak wave period
• Significant height of combined wind waves and swell
• Mean wave direction
• Mean wave period
• Wave spectral directional width

Save the wind data to your Moreton_Bay_Waves\DATA\WIND folder.

Conclusion

You have now obtained your input bathymetry, wind and wave data. We can move to Step 3 of our SWAN GIS Tools step by step guide: Building the Model in QGIS.