Some notes on LLWS, don't waste your time reading this!

This is the exact definition of LLWS:

LLWS LaagLaagWaterSpring dient als basis voor reductievlakken van
zeekaarten. Het LLWS 1985.0 is het gemiddelde over 1980 --- 1984 van het
laagst opgetreden springlaagwater van elke maand. Per springtij gelden twee
laagwaters als springlaagwater.
Source: Getijtafels voor Nederland, 1999, Rijksinstituut voor Kust en Zee,
's Gravenhage.

My translation:
LLWS 1985.0 is the basis for sea-maps; in Dutch called "reductievlak".
LLWS 1985.0 is the average of the lowest spring-low-tide of each month over
the period 1980 -1984. Each springtide has two low-tides that count as
spring-low-tide.

LLWS is used as basis for sea-maps, because somebody on a ship needs to know
where water is deep enough, even at LLWS. Even though only twice per
lunar-month there is a spring-tide.
On these maps depth in meters are given compared to the reductievlak.

If one wants to walk over the dry seabed, to say .... Neuwerk, such a map is
not accurate enough because it does not show the details of the seafloor
between the LLWS (reductievlak) and the mean sea-level.
It is better to know the depth in meters compared to the Dutch NAP (Nieuw
Amsterdams Peil) which is mean sealavel.

One example to compare the both:
Lauwersoog (Waddenzee, northern part of NL). LLWS 1985.0 = NAP -170.
So a channel in the (dry) floor of the sea could be 1 mtr (- 100 cm) deep,
that means at low tide easy to pass.
On the sea-map the depth could be given as + 70, which is 70 cm higher then
the "reductievlak"; but such accuracy is not on these maps; because
everything "dryer" than LLWS is not interesting for ships.

In Germany for sea-maps KN (Kart Null) is used. I think it is the same as
the Dutch LLWS.
KN is lower than MNW Mittleres Niedrigwasser (mean low-tide).
B.t.w. MNW for Cuxhaven/Neuwerk is not given, because the seafloor is so
"high"; both compared to KN and also compared to NN (Normal Null = mean
sealevel, like NAP). So walking to Neuwerk is very save! (at low tide off
course).
Source: Gezeitenkalender 1998, Bundesamt für Seeschifffahrt und
hydrographie.

gl
Harry ten Veen