What defines the boundary line between the seashore and the upland estate?

The boundary line between the seashore and the upland estate is defined by the line of mean high tide. This line is significant because it represents the average height of the high water over a specific period, typically calculated over a 19-year cycle, known as the National Tidal Datum Epoch. Since this line indicates the highest point reached by regular tidal action, it serves as an important demarcation for property rights and land use, particularly in coastal areas.

Understanding this boundary is critical for landowners and surveyors because it affects ownership rights, land development, and environmental regulations. The mean high tide line is used to establish where private property ends and public land, or navigable waters, begins, which is vital in legal disputes or land assessments.

The other choices reflect various tidal benchmarks, but they do not serve the same purpose as the line of mean high tide in delineating the boundary between seashore and upland. Specifically, the line of mean low tide indicates the lowest regular tide level, while the line of average tide represents a mean of all tidal measurements, both of which do not delineate property boundaries as accurately as the mean high tide line. The line of extreme high tide refers to the highest tide that can occur, but