The definition of dynamic is “(of a process or system) characterized by constant change, activity, or progress.” It shows up throughout the H&H world, for example, HEC-RAS is a “hydrodynamic” model. Meaning it models the dynamics (i.e., changes) of a hydraulic system.
I would not get too caught up in it’s use or where it ‘fits’. Dynamic generally refers to unsteady flow modeling with a hydraulic model (e.g., HEC-RAS). The word ‘dynamic’ is sometimes followed by the word ‘routing’, because the model is routing (i.e., moving) flow through the system while accounting for changes in conveyance (flow) and storage (volume) ‘dynamically’ in space and time. So I think the word ‘dynamic’ is used loosely as a catch all for a model that simulates changes or a system that experiences changes over time and space.
Instead of focusing on the word dynamic, focus on learning the difference between Unsteady state hydraulic routing (i.e. typically this is what dynamic routing / modeling refers to) and hydrologic routing (for example using Modified Puls in HEC-HMS). Hydrologic routing is generally a simplified ‘version’ of Unsteady state hydraulic analysis, but can give similar results depending on the situation. In some situations where the system (i.e. river, etc.) is complex, hydrologic routing simply can not model the complex ‘dynamics’ of how water moves through and is stored in the system, so you then use Unsteady state hydraulics.
Hope that helps. If anyone else wants to chime in to give a more specific answer / opinion, I’d be interested to see what others think.
Regards,
Lee