TABLE OF CONTENTS Nearshore circulation is the term used for the complex nearshore currents generated by the short wave motion. These currents are determined by the depth integrated and time averaged equations of continuity and and momentum. In the classical approach the currents are assumed depth uniform. Since, however, it turns out that their depth variation is actually of significant importance for the way way in which the currents interact in the horizontal dimension we will avoid as long as possible in the derivations to make any assumptions about the variation over depth of the currents. However, after deriving the equations governing general depth varying currents the special case of depth uniform currents is analysed in detail. Various aspects of the depth variation of nearshore currents are then analysed in Sections 12.2 and 13.
The derivation of the general depth-integrated, time-averaged equations requires some care. The benefit, however, of such a derivation is a more clear understanding of which assumptions are involved and how the assumptions allow us to simplify the equations.
When we integrate the differential equations over the depth from the (fixed, sloping) bottom to the (moving) free surface, we will need to apply the relevant boundary conditions as well. Since we are talking about highly turbulent flows, there will of course be contributions from bottom friction, and similarly wind stresses (if any) on the surface will contribute to the stresses there. In all, this makes the boundary conditions somewhat more complicated than for simple potential flow wave motions.
