Application of Neumann boundary condition in hydrodynamic modelling

Abstract

      It is very important to choose the right boundary condition when applying any numerical model. For coastal region, due to a combination of processes acting on the model domain, a certain water level or velocity distribution will develop in cross-shore direction. The boundary condition has to match this distribution to prevent the development of boundary disturbances. A good solution is to impose the along shore water gradient (a so called Neumann boundary condition) instead of a fixed water level or velocity (Roelvink and Walstra, 2004). This paper presents the results the application of Neumann boundary condition in hydrodynamic modelling at the Egmond coast, the Netherlands using Delft3D. It is shown that the calculated water levels at all stations match nearly exactly with the measurements. The model reproduces significant wave heights very well. Considering the longshore velocities, the model results are in good agreement with the observations.