December 2023

Making The Most Of Ensemble Hydraulics Outputs

We are seeing a continued increase in the volume of hydraulic model outputs as more customers receive the outputs of ensemble hydraulic modelling.

This presents some interesting challenges not only due to the massive data storage requirements, but also in terms of the usability of the datasets.

Traditional hydraulic modelling involved first running multiple rainfall duration and intensity combinations (rainfall ensembles) to determine the critical duration for any given rainfall exceedance probability (eg 1% AEP) in various parts of the catchment.

This resulted in a large number of hydrologic model runs (which are computationally and storage "cheap"), followed by a comparatively limited number of "expensive" hydraulic model runs being contained to just those handful of critical durations.

Recent updates to the Australian Rainfall and Runoff (AR&R) guidelines have resulted in the increased use of hydraulic ensembles to capture the hydraulic subtleties associated with varying both rainfall patterns and intensity/durations.

Extraction of Flow Hydrographs - A Problem With Traditional Envelope Surfaces

In practice, this tends to mean that for any given probability (eg the 1% AEP design flood), there can be, say, 10 rainfall temporal patterns, each with 10 intensity/duration combinations, meaning that there are 100 model runs for just the 1% AEP flood.

Statistical processing of this information by modellers often results in a single deliverable surface being the worst case of the intensity/duration combinations for the median temporal pattern (ie an enveloped surface).

Whilst these envelope surfaces are useful for panning purposes, they do lose some value for those looking to understand the dynamic nature of flooding (eg emergency managers looking to determine the timing and duration of inundation) as well as those looking to investigate the hydraulic behaviour of the catchment in detail, such as extracting flow hydrographs at any location which cannot be calculated accurately using only peak hydraulic parameters.

To help overcome these limitations, we have developed two approaches to creating a representative time-varying flood surface:
   1) Fully automated ensemble processing
   2) Composite file driven "spatially clipped ensembles"

Unfortunately, whilst the first option is fully automated and delivers excellent outcomes, the sheer volume of data to process makes it impractical (from several days to a week per design event). However, we are confident that continued refinement of the process and some experimentation on some new powerful processing cloud servers will bring execution times down to a more reasonable timeframe. Stay tuned.

Given the current need of customers, we elected to release option 2 with the current waterRIDE version (10.98). Under this approach, users are able to utilise the "source" parameter of the enveloped hydraulic runs to create polygons representing areas impacted by the same simulation. Once created, this layer is then used to clip the individual time series results to create a seamless composite layer.

This usually results in a layer that has different time steps and flood durations in different parts of the catchment. However, this is managed seamlessly by waterRIDE.

The tool is available on the Process panel, as the Virtual Merge tool in the Drape and Merge section. Instructions and example screenshots are available in the online help.

waterRIDE v10.98 Released

Those with active annual maintenance plans will have received download links for the latest waterRIDE 10 release (v10.98).

If you have not received the link and believe your maintenance plan is current, please contact us to update your email preferences.

This release brings some key new features, a host of refinements, and a couple of important updates for TUFLOW and MIKE21 users running specific model types.

You can see the full list of features here.

End of Year Office Closure

As the end of another year rapidly approaches, we would like to say thank you to our users for your continued support, and wish everyone a safe and relaxing Christmas break.

We have some very exciting releases planned for next year, so keep your eye out for webinar invitations in early 2024 to see what we've got planned.

Our offices will be closed from Thursday 21st December, 2023 and reopen on Tuesday 2nd January, 2024.

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