Tidal Datum Conversion example

Let's take the Malakal-B station in the Republic of Palau as an example. The values provided for this station allow us to convert between different tidal datums.

The values for Mean Higher High Water (MHHW) and Mean Lower Low Water (MLLW) at the Malakal-B station are 2.162 meters and 0.753 meters respectively, both relative to the station datum. The Mean Sea Level (MSL) at this station is 1.532 meters.

To convert the MHHW and MLLW values to be relative to MSL, you would subtract the MSL value from the MHHW and MLLW values. Here's how:

1. MHHW relative to MSL: 2.162m (MHHW) - 1.532m (MSL) = 0.630m. This means the Mean Higher High Water is 0.630m above the Mean Sea Level.
2. MLLW relative to MSL: 0.753m (MLLW) - 1.532m (MSL) = -0.779m. This means the Mean Lower Low Water is 0.779m below the Mean Sea Level.
3. To convert tide gauge water level observations to be with respect to MSL, you would subtract the MSL value from the observed water level value.

Remember, this example is specific to the Malakal-B station based on the values provided. The specific values and therefore the calculations would be different for other stations. It's important to use the correct values for the station you're interested in. The metadata provided about the tide gauge station, such as its geographical coordinates and the instrument types used, can also provide useful context for interpreting the data.

Tidal Datums Helper (AI)

Benchmarks example - Malakal Station, Palau

Name	Level above station zero (m)	Coordinates
UH4 (PRIMARY)	6.834	Latitude: 7.32921 Longitude: 134.45079
UH5	3.105	Latitude: 7.32857 Longitude: 134.45013

Description (PRIMARY): THIS MARK IS 80 PACES FROM UH3A BEARING 120 DEGREES UP A SMALL RISE TOWARDS A SEWAGE SETTLING BASIN AREA. THE MARK IS ABOUT 3 FEET ABOVE A CEMENT CULVERT RUNNING BETWEEN THE SEWAGE SETTLING AREA AND THE MOUNTAIN. THE MARK IS A 1” ROUNDED BRASS DISK SET IN A BOULDER AT THE MOUNTAIN BASE. THE BOULDER IS PARTIALLY COVERED BY THE CONCRETE CULVERT AT THE WEST END OF THE CULVERT.

Photos (PRIMARY)

How to relate datums to a benchmark:

To relate datums to a benchmark, you will first need to know the datum value and the benchmark level. Subtract the benchmark level from the observed water level to get the water level relative to the benchmark.

Map

Sea Level Data Users - Frequently Asked Questions

NOAA's Tides and Currents site provides definitions of Tidal Datums referred to here: https://tidesandcurrents.noaa.gov/datum_options.html#

See also the FAQ column on the UHSLC website: https://uhslc.soest.hawaii.edu/datainfo/