ABSTRACT
The result is that many different numerical models of currents in surface waters currently exist. The primary difference between these models is usually the different length and time scales that the investigator believes is significant for the specific problem. For example, if the details of the flow in the vertical are not thought of as significant, one can use a two-dimensional, vertically integrated model; this may be either steady state or time dependent, depending on whether the time variation is considered significant. To investigate flows where vertical stratification due to temperature and/or salinity gradients is significant but horizontal flows in a transverse direction are not, a two-dimensional, horizontally integrated model is relatively simple and may be useful. More complex three-dimensional, time-dependent models may be necessary when flow fields vary significantly in all three directions and with time. In whatever numerical model chosen, for reasons of accuracy and stability, the grid sizes in both space and time must be smaller than the smallest space and time scales that are thought to be significant.
