Variable gridded tidal model

The numerical modeller concerned with water flows in estuaries is often faced with the dilemma of choosing a coarser grid than is ideally need to resolve the details of his problem or accepting the higher computing costs demanded by a finer gridded model. The difficulties are alleviated if some flexibility can be introduced in the grid sizes to provide fine grid where local detail is required and a coarser grid further away to enable the boundary conditions to be prescribed outside the sphere of influence of the works being studies.