The vast majority of boundaries within the littoral zone are based on one of the many possible tidal lines. These tidal lines are defined by the line of intersection between a particular tidal datum and the land mass. The difficulty with boundaries defined on the basis of a tidal datum is that the rigorous and consistent realisation of the line of intersection between a nominated tidal datum and the land mass is notoriously difficult, creating spatial uncertainty and the potential for conflict and dispute.

This paper describes and discusses some fundamental issues in defining and realising tidal lines, with particular interest in their relevance and application to the development of a marine cadastre. A technical solution for realising the line of intersection between any given tidal datum and the foreshore terrain is presented. Particular attention is paid to the modelling of the water and terrain surfaces as the two fundamental datasets required for the intersection computations. The methodology and results of a case study in New South Wales, Australia, are presented, along with some initial findings.