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GPHA invites bids for tidal gauge installation

By: Maclean Kwofi
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The Ghana Ports and Harbours Authority (GPHA) is taking steps to install new tidal gauges with integrated weather stations at the Tema and Takoradi seaports.
The Ghana Ports and Harbours Authority (GPHA) is taking steps to install new tidal gauges with integrated weather stations at the Tema and Takoradi seaports.

THE Ghana Ports and Harbours Authority (GPHA) is asking interested firms and organisations to bid for the supply, installation and commissioning of tidal gauges with integrated weather stations.

The new device, which is expected to be installed at the Tema and Takoradi seaports, is to measure changes in the sea level relative to a vertical datum.

A tide gauge, which is one component of a modern water level monitoring station, is fitted with sensors that continuously record the height of the surrounding water level.

This data is critical for many coastal activities, including safe navigation, sound engineering, and habitat restoration and preservation.

The port authority in a public advertisement in the Daily Graphic on Thursday, February 22, observed that organisations must express their interest before April 4 this year.

Shortlisting of the organisations will be in accordance with the Public Procurement Act, 2003 (Act 663) and in the Public Procurement (Amendment) Act, 2016 (Act 914).

According to the GPHA, interested and eligible organisations are to note that this is not a request for proposal but rather expression of interest.

For this reason, shortlisted organisations will be invited to submit their proposals through letters of invitation which will include specific terms, after review of correspondence for expression of interest.

General specifications
Touching on the general specifications, the port authority said the new station must be able to automatically and continuously record tidal and weather information, and must have the capacity to store data over a relatively long period of time.

It must also have options for integrating other oceanographic sensors in the future. It should be able to transmit real-time data telemetry across various networks to a dedicated display monitor.

The equipment must be of global sea level observing system (GLOSS) standards.

Analogue tidal gauge
Before, computers were used to record water levels through what is described as special "tide houses" sheltered permanent tide gauges. Housed inside was the instrumentation—including a well and a mechanical pen-and-ink (analogue) recorder—while attached outside was a tide or tidal staff.

Essentially a giant measuring stick, the tide staff, allowed scientists to manually observe tidal levels and then compare them to readings taken every six minutes by the recorder.

Tide houses and the data which is recorded required monthly maintenance, when scientists would collect the data tapes and mail them to headquarters for manual processing.

The computer age led to tide gauges that use microprocessor-based technologies to collect sea-level data. While older tide-measuring stations used mechanical floats and recorders, modern monitoring stations use advanced acoustics and electronics.

Modern tidal gauge
Today's recorders send an audio signal down a half-inch-wide "sounding tube" and measure the time it takes for the reflected signal to travel back from the water's surface.

Data is still collected every six minutes, but while the old recording stations used mechanical timers to tell them when to take a reading, a geostationary operational environmental satellite (GOES) controls the timing at these stations.

In addition to measuring tidal heights more accurately, modern water level stations are capable of measuring 11 other oceanographic and meteorological parameters, including wind speed and direction, air and water temperature, and barometric pressure.

The port authority uses this information for many purposes, among them to ensure safe navigation, record and predict sea-level trends and other oceanographic conditions via now-casts and fore-casts, and publish annual tide predictions.GB