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Our ability to predict the tidal levels and currents through coastal
waterways is of great importance to a number of human activities. The
beneficiaries of this information include commercial and recreational users,
the Navy and a host of others. Sea
level monitoring also provides key data for coastal authorities responsible
for the determination of property boundaries, and for planners and
engineers in the construction of waterfront buildings, bridges, and
jetties.
It may be argued that for tidal prediction it is no longer necessary to
continuously monitor sea level. Indeed, the greater part of the tidal
fluctuations are regulated so closely by clockwork-like astronomical
variations that the tides can be predicted with a high degree of
precision for many years into the future. Nonetheless, the monitoring of
sea level and currents remains an essential task, even in tide
prediction, which is only as good as the data on which it is based, and
is continuously improved as the data set lengthens. One reason for this
is that water level and currents are controlled by transient environmental
factors as well as astronomical motions, and accurate records of both are
often required in retrospect for legal, scientific, environmental,
maritime safety, and planning purposes. From a broader perspective, we
might consider that the global ocean, so closely tied to climate, is very
sparsely sampled, and so we must do all in our power to maintain the best
possible record of its variability at our shorelines.
Over the past several decades, sea level monitoring has taken on a new and
important role in climate prediction, particularly for the El Niņo
Southern Oscillation (ENSO) and the estimation of long-term sea level
variability. In the early 1990's, the advent of reliable satellite
altimeter data, combined with numerical models, gave rise to the belief
among some that conventional tide gauges would soon become obsolete.
However, this has not proven to be the case. Tide gauges have proven to
be the most reliable and accurate source of coastal sea level data, and
have even turned the tables on satellite altimeters, providing evidence
of drift in the latter technology.
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