Mean High Water Neaps (MHWN)

The average height of high tides during neap tide cycles, which occur when the tidal range is at its smallest.

Mean High Water Neaps (MHWN) is a concept in tidal studies and marine navigation. It represents the average level reached by high tides during neap tide periods, which occur approximately twice a month when the gravitational forces of the Moon and Sun are at right angles to each other relative to Earth. This alignment reduces the tidal range, resulting in less pronounced high and low tides compared to spring tides. MHWN is calculated over a long-term period, typically 19 years, to account for variations caused by lunar and solar cycles.

MHWN is particularly significant for chart datum and coastal engineering. In nautical charts, it helps mariners understand the expected maximum water levels during neap tides, aiding in safe passage planning, anchorage selection, and avoiding potential hazards such as submerged rocks or shallow areas. For coastal infrastructure, MHWN provides a reference for designing structures like sea walls, jetties, and harbours, ensuring they can withstand typical tidal conditions without being excessively over-engineered.

Understanding MHWN is also essential for ecological studies, as it influences intertidal zones where marine life thrives. These zones are shaped by the frequency and duration of tidal inundation, which directly impacts the distribution of plant and animal species. By knowing MHWN, scientists can better predict habitat conditions and monitor changes due to sea-level rise or human intervention.