FIELD VERIFICATION OF A NUMERICAL MODEL OF BEACH TOPOGRAPHY CHANGE DUE TO NEARSHORE CURRENTS, UNDERTOW AND WAVES

A practical method for estimating the undertow velocity and its direction is developed and verified on the basis of field measurement data. It is found that a simple vector addition of nearshore current and undertow gives a good approximation. The actual bottom topography change during a year is simulated by the 3-D beach evolution model taking into account the cross-shore sediment transport due to waves and undertow as well as the transport due to nearshore currents. The results of both measurements and calculations show that the sediment transport due to nearshore current is predominant and the contribution of cross-shore sediment transports is cancelled for a long-term beach evolution.