CH Tides, Water Levels & Vertical Datums 4

Question 1

In areas with predominantly diurnal tides (e.g., portions of the Gulf of Mexico), the recommended chart datum is:

Accepted Answer

Mean Lower Low Water (MLLW)

Answer

MLLW remains the US chart datum even in diurnal tide areas because it adapts correctly to both semidiurnal and diurnal tidal regimes.

Question 2

The 'equilibrium argument' (V0 + u) used in harmonic tidal analysis represents:

Accepted Answer

The theoretical phase of a tidal constituent at the origin of the epoch from astronomical calculations

Answer

V0 + u is the equilibrium argument giving the theoretical phase of a tidal constituent at the start of the analysis period, derived from astronomical data.

Question 3

Sea level rise monitoring at NOAA tide gauges uses which statistical measure to track long-term trends?

Accepted Answer

Monthly mean sea level averaged over decadal periods

Answer

Long-term sea level trends are computed from monthly mean sea level values, which average out short-term meteorological and tidal variability.

Question 4

A 'co-tidal chart' displays lines of equal:

Accepted Answer

Time of tide (phase) at which high water occurs

Answer

Co-tidal lines (co-phase lines) connect points where high tide occurs at the same time, illustrating the progression of the tidal wave across a region.

Question 5

Which type of tide gauge is least susceptible to wave noise and therefore preferred for precise water level measurement in exposed locations?

Accepted Answer

Microwave radar gauge

Answer

Microwave radar gauges measure water level remotely without contact, and their signal averaging inherently rejects short-period wave noise in exposed conditions.

(CH) Certified Hydrographer Practice Test

(CH) Certified Hydrographer Practice Test

CH Tides, Water Levels & Vertical Datums 4