Mean Low Water Neaps (MLWN)

The average height of low tides during neap tide cycles, which occur when the tidal range is at its smallest due to the reduced gravitational pull of the sun and moon.

Mean Low Water Neaps (MLWN) is a tidal datum used in marine navigation and coastal management to describe the average level of low water during neap tides. Neap tides occur approximately twice a month, during the first and third quarters of the lunar cycle, when the gravitational forces of the moon and the sun are at right angles to each other. This alignment results in a smaller tidal range compared to spring tides, which occur during the full and new moon phases. MLWN is calculated by averaging the heights of all low waters recorded during these neap tide periods over a defined time span, typically 19 years, to account for long-term tidal variations.

This datum is particularly important for mariners and harbour authorities, as it provides a reference point for understanding the minimum depth of water that can be expected during neap tides. It is often used in conjunction with other tidal datums, such as Mean High Water Neaps (MHWN) or Mean Low Water Springs (MLWS), to provide a comprehensive understanding of tidal behaviour in a specific area. MLWN is also crucial in the design and maintenance of coastal infrastructure, such as piers, docks, and dredged channels, ensuring safe navigation and operational efficiency. Understanding MLWN helps mariners avoid grounding and ensures that vessels can safely access ports and harbours during neap tide conditions.