There is a categorization for Hydrological Models which divides them into three groups: Empirical models, Physical Models and Conceptual Models.
The question is: Where exactly "Hydrodynamic Models" stand within this categorization?
Are those three types related to rainfall-runoff models and Hydrodynamic models are within a different group?
Or Hydrodynamic Models can be a combination of those three types (i.e. a combination of Empirical and Conceptual Models)?
I think hydrodynamic models could fall into any of the three categories. This however depends on the purpose for modelling and the input parameters during simulation processing.
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A hydrodynamic model uses a numerical approximation (e.g. finite element or finite difference methods) to solve a PDE (e.g. shallow water wave equation, Saint-Venant equations). As such, these are physically-based models (or physics-based models if you prefer). You might use the output of an empirical or conceptual model to give the flows at the upper part of a reach being studied (i.e. set a boundary condition for solving the PDE), but a hydrodynamic model is a physically-based model.
Note that I have used "physically-based model" rather than "physical model" - a "physical model" could refer a model built out of concrete, plaster etc. for running simulations in a laboratory (i.e. not in a computer). For example, a scaled model of a floodplain used to study flood characteristics by actually running water over it.
It could be argued that a hydrodynamic model is a "physics-based" model rather than a "physically-based" model.
@ Barry Croke :
Thank you for the response
I agree that "physiscs-based model" is a better representation of what we mean in such a discussion.
However, let's back to the main point of this question:
You mean a hydrodynamic model can be physics-based, right?
nd it probably can be a conceptual model in some cases..
but, my question arises from the fact that there are categorizations where distinguish Hydrodynamic models as a different group, for example the one attached. You mean you do not agree with the categorization shown in the attached file?
Hydrodynamic models are indeed physics-based (or physically-based) models as Barry Croke mentioned. They can be part of a completely or partly physics-based hydrological model (i.e. for simulation of the rainfall-runoff response of a catchment) and used for the simulation of overland flow and river flow. Other hydrological processes might then be modelled for instance based on the Richards equation (unsaturated zone) and Darcy equation (saturated zone). Also the term hydrodynamic model is often used for hydraulic models for river flow or flows in estuaries and (shallow) seas. Most of the latter models are hydrodynamic models, although also hydrological approaches (similar to flow routing models) are used in combination with hydrological models at the catchment scale.
This might partly explain the confusion about the figure Negin Binesh is referring to, since given the previous explanation, hydrodynamic models are one type of river flow models and part of one type (physics-based models) of rainfall-runoff models.
I am a naval architect with years of experience in hydrodynamics. In sciences and naval technologies hydrodynamics is the study of the nature of fluid flow interacting with the shapes/geometry about solid objects on the surface, submerged and internally through pipes, etc. Besides the solid geometry of shapes being studied it also includes the characteristics of fluids in in both their liquid and vapor states such as propeller cavitation.
Your last statement is right Binesh.
Empirical model is an equation like the determination of evaporation using a pan coefficient. Physical model is like constructing a surface and monitoring evaporation. Conceptual model is interaction of various parameters to give an outcome. Hydrodynamic model is a mathematical model which has conceptualized say evaporation and is water driven (inputs as water).
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