Hydraulic modeling is used to evaluate important elements of free surface fluid flow. Generally, hydraulic modeling can refer to both numeric modeling (in which a simulation is performed on a computer), or physical modeling (where the physical flow geometry is scaled in such a way that it can be modeled in the laboratory). Numeric models are usually two- or three-dimensional, whereas physical hydraulic models are always three-dimensional. Geometry is sometimes easier to manipulate and modify in a numeric model, and wider areas (larger volumes) can often be more cost-effectively simulated in a numeric model. Physical hydraulic modeling, however, must be used when unsteady vortex dynamics is a concern, such as in pump or turbine intakes. Hydraulic modeling is often most cost effective when the two methods are used together, simulating wide areas with a numeric model, using results to develop boundary conditions for a smaller physical hydraulic model in locations where vortexing or some other physical phenomena not easily captured by numeric modeling is of interest.