With InfoWorks ICM and InfoWorks ICMLive it is easy to apply spatial rainfall data to a model. This data can be used to apply observed and forecast radar data as well as Thiessen polygon generated rainfall areas directly to a model. When these data sources are applied using the ‘spatial rain sources’ page of the Polygons grid, it possible to prioritize these sources.
Applying radar rainfall to a model is surprisingly easy, just so long as you have some radar data and that data is in a format that we support. As far as the UK is concerned we support both the Nimrod and Nowcast formats that the UKMO generate and for the wider world we support GRIB1 and GRIB2 formats.
To create a radar source you need to create a Spatial Time Series Database (TSDB). To create a TSDB you will need to have a TSDB license (you get one with either ICMLive or InfoWorks ICM Suite). When the TSDB is created you need to specify the type of TSDB you’re going to use (observed or forecast) and the type of data. In the screenshot we have used the US National Weather Service (NWS) digital precipitation 176 data. Next we need to give an example file to the software. We then specify a projection that we wish to convert the data to. This is the projection that our model is in; in this case we have used a US state plane projection. Finally we need to specify a data interval and any conversion factor to move the data into an appropriate intensity (mm/hr or in/hr). When we click OK the software checks that the radar file is what the software is expecting. We can then tell the TSDB to update with all the remaining files.
One of the nice things about the TSDB functionality is that you can drag the TSDB directly onto a network and check that it is where you think it should be. You can also check that the rainfall values are what you expect. (You’ll need to change a couple of settings on the Properties and Themes dialog)
ICM automatically calculates which subcatchments lie under which cell and applies the rainfall directly from the radar image onto that subcatchment. Where a subcatchment lies under two or more cells the subcatchment centroid is used. By using the ‘Area Averaged Rainfall’ check-box on the subcatchment you can tell the software to work out the contributions from all the cells that lie over the subcatchment. This is especially useful in very large catchments.
To use the TSDB in a run you simply need to check the box ‘Use TSDBs’ in the run dialog. This allows the user to drop the TSDB into the drop target. All the other non-time varying inputs (wastewater, trade waste etc.) work as before but note that if you were using inflow or level events they’ll need to be added into a non-spatial or scalar TSDB; this will be discussed in a later blog entry.
For any questions or further information on TSDBs get in touch at email@example.com.