Applying numerical modelling techniques to surface water bodies often requires the addition of man-made structures such as embankments or dredged shipping lanes to the natural bathymetric conditions. The application of the model may be to determine the specifications of these structures, such as size and location. Therefore, multiple variations of the structure must be evaluated. Interactive methods to easily create these structures in grids used by numerical models are presented that show great promise in reducing the time and effort required to consider multiple scenarios for modelling and management. The methods presented utilize a conceptual representation of the domain. Features in this conceptual model are used to derive grid elements for the numerical model. The resulting numerical models provide information for decision support based on multiple design considerations.