Tidal Terms

Question 1

Chart datum

Answer 1

a level so low that the tide will very rarely fall below it.
predicted by astronomers with current astronomical conditions.
not lowest ride will ever reach as storm surges may lower the level.

Question 2

HAT

Answer 2

Highest Astronomical Tide

highest level of tide astronomers can predict given current astronomical conditions.
not lowest ride will ever reach as storm surges may Raise the level.

Question 3

MHWS

Answer 3

The average height of successive high waters during the period when the tail range is a maximum
usually obtained over a year

Question 4

MHWN

Answer 4

The average height of two successive high waters when the tidal range is a minimum

Question 5

MLWS

Answer 5

The average height of successive low waters during the period when the tidal range is a maximum

Question 6

MLWN

Answer 6

The average height of two successive high waters when the tidal range is a minimum

Question 7

MTL

Answer 7

Mean Tidal Level

The average tidal heights of MHWS,MLWS,MHWN,MLWN
from observations over a period of time

Question 8

MSL

Answer 8

Mean Sea Level

the average level of the sea surface from observations over a long period of time at least 18.6 years, of the average height of the sea surface in the absence of tides e.g. the baltic

Question 9

CD

Answer 9

Chartered Depth

Depth of water below chart datum

Question 10

HOT

Answer 10

Height of Tide

Height of sea surface above chart datum at a particular instant in time

Question 11

Sounding

Answer 11

The depth of water below the sea surface at a particular instant in time
CD+HOT

Question 12

Chartered height

Answer 12

Height of an object above above level of HAT

Question 13

Chartered Elevation

Answer 13

The elevation of a light or tower above the level of MHWS.
Lights always the height go the centre of the focal plane of the lantern above MHWS

Question 14

Tide Coming in
Tide Going out
High Tide

Answer 14

Flood
Ebbing
High Tide