How is Mean Lower Low Water (MLLW) calculated?

Mean Lower Low Water (MLLW) is defined as the average height of the lowest tide recorded at a tide station over a specified period, typically 19 years, known as the National Tidal Datum Epoch. This definition specifically focuses on the average of the lower of the two low tides that occur each day. Therefore, the process involves identifying the minimum water level reached during the lower of the two low tides across this extensive time frame, which is crucial for various navigational and engineering purposes.

The significance of MLLW lies in its application as a reference datum for creating nautical charts and for marine navigation. By standardizing the low water level, it allows mariners to better understand tidal variations and plan their navigation accordingly, especially in regions where tides play a significant role in water depth.

In contrast, the other methods mentioned do not accurately reflect the concept of MLLW because they either focus on high tides or do not specifically average the lower of the two low tides. This specificity is what makes the correct choice distinctly accurate in the context of tidal calculations and marine navigation standards.