I work at Deltares and have been involved in our WQ modelling system for many years. The name changes depending on the larger context, but I fondly call it DELWAQ 
Of course, now you have made me curious!
(Indeed, I think YAML files or any of the other formats are nice enough, but they were designed for very different goals)
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Ah great, I’ve certainly come across Deltares’s WQ modelling before! Is DELWAQ the model behind Delft3D? I’m not too far from you - I work at the UK Centre for Ecology & Hydrology. I’m not strictly a WQ modeller, more so environmental contaminant fate, but that does naturally include a fair amount of modelling water and its quality!
[Moderator note: WQ stands for Water Quality]
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