Legal Definitions - mean low tide

Mean low tide refers to the average height of all low tides observed over a specific, long-term period. This period is typically 19 years, known as a tidal epoch, which accounts for various astronomical cycles influencing tides. It serves as a critical baseline for measuring water depths, establishing property boundaries along coastlines, and defining jurisdictional limits.

Here are some examples illustrating how "mean low tide" is applied:

• Property Boundaries: Imagine a coastal property owner whose land borders the ocean. The legal boundary of their property on the seaward side is often defined by the mean low tide line. This means their ownership extends to the average lowest point the water reaches, and anything below that line, such as the submerged seabed, might be considered public land or under state jurisdiction. This clarity helps prevent disputes over access and development rights along the shore.

• Navigational Charts and Dredging: A port authority is planning to deepen a shipping channel to accommodate larger cargo vessels. When creating navigational charts or planning dredging operations, engineers use the mean low tide as a reference point. By ensuring the channel is deep enough at mean low tide, they guarantee that ships can safely navigate the waterway even during average low water conditions, significantly reducing the risk of groundings and ensuring efficient maritime trade.

• Environmental Permitting and Construction: A developer proposes to build a new pier or a protective seawall along a bay. Environmental regulations often require that such structures be built above or below the mean low tide line to protect sensitive intertidal habitats (the areas exposed between high and low tides) or to ensure public access to the foreshore. Regulators use the mean low tide as a consistent, scientifically determined benchmark to assess the environmental impact and approve or deny construction permits.