Conservation Equations for Unsteady Flow

The description of nearshore currents is of primary importance to the development of littoral transport models. The bases are given here for the current models to be described in Chapter 15. A convenient starting point for the study of unsteady flow phenomenon is a statement of the general conservation equations of mass, momentum and energy, following, for example, Mei (1983). In the first part of this chapter, the conservation equations are examined and discussed. A basic element of the NSTS dynamics task was to develop longshore current formulae for the case of statistically stationary waves (statistics do not change with time) propagating over straight and parallel contours. Making these assumptions, the momentum balances are simplified and compared with some of the NSTS field data in the second part of this chapter.