For example at the seaward side the morphology of the sea bed is an important factor. The line up to where the sediment processes are significant may act as the coastal zone boundary. At the landward side, the end of dune formation may act as a boundary. However, situations exist where (parts of) river basins must be included in the 'coastal zone' because of the influence of their discharge and transported matter on the problems considered. In such cases, the extent of the considered area enlarges considerable and may cross international boundaries.