How do we measure Cabimas' coastal currents?

1. Where is Cabimas?

Cabimas, in northwestern Venezuela in Zulia state, is a city located strategically on the west coast of Lake Maracaibo. Lake Maracaibo is South America's largest lake, and it's connected to the Caribbean Sea by a thin strait, thus the unique coastal ecosystem. Due to its location near the lake, the city has the advantage of having easy access to a gigantic body of water, which heavily influences its economic, social, and environmental life.

Geologically, the region is notable for its flat - lying nature, with vast tracts of mangrove forests and wetlands. The marshes create a natural buffer belt between the land and lake, protecting the coast from devastation and offering sustenance to diverse flora and fauna. Cabimas possesses a long-lasting history. The area was originally inhabited by the native people, whose legacy might still be traceable in neighborhood legend, art, and culture. They were followed by Spanish settlers, who brought new farming and business methods.

Cabimas economy is presently controlled by the oil sector. The region is rich in oil deposits, and there are numerous oil platforms on the surface of the lake. Oil drilling and refining have not only affected the regional economy but also the regional population and infrastructure. Tourism is on the rise too, with travelers visiting the region's natural scenic attractions like its peaceful lake landscape and varied ecosystems.

2. How are the coastal currents in the Cabimas region?

The coastal currents in the Cabimas region are governed by an array of conditions. The exchange of water between Lake Maracaibo and the Caribbean Sea through the strait is the governing factor. The difference in water level, salinity, and temperature between the sea and lake causes a pressure gradient, which creates the movement of water. During the rainy season, abundant rain in the lake basin causes more freshwater to outflow into the sea, affecting the flow and density of coastal waters.

Caribbean Sea tides also affect the Cabimas coastal currents. The diurnal and semi-diurnal tidal currents generate water level variations at the strait entrance. These, consequently, influence in-and-out movement of water into the lake. The northeasterly prevailing trade winds propel the surface water westward. Wind-driven current interacts with water exchange through the strait as well as tidal currents to establish a complicated pattern of water motion.

Lake Maracaibo's bathymetry and the presence of underwater structure such as reefs, channels, and sandbars significantly control coastal currents. They have a tendency to disrupt or channel the path of the current and produce eddies as well as more complex flow patterns. The presence of oil rigs and other human-made structures on the lake controls the path of the currents away from the normal flow regime.

3. How is coastal water flow of Cabimas traced?

Surface Drifting Buoy Method

The surface drifting buoy method is a traditional method of tracing coastal water flow. Scientists release buoys with tracking devices into the sea. By tracing the drifting of buoys over time, scientists determine the direction and speed of the surface current. It is a restricted method. It is only in contact with the surface layer of the water column, and also quite susceptible to interference from winds. The buoys may be pushed in a direction other than the way currents move in deeper waters by the wind.

Moored Ship Method

The use of an anchored ship as a current-measurement platform is referred to as moored ship method. Gear is let down off the ship to track the flow of water at varying depths. As much as the method can return detailed vertical profiles of the currents, the method is fraught with a series of faults. The spatial coverage exists only in the area surrounding the moored vessel, and the existence of the vessel has the potential to slow the unmoored free passage of the water and compromise measurement quality. Besides that, extended mooring of a ship can be logistically challenging and costly.

Acoustic Doppler Current Profiler (ADCP) Technique

ADCP is a newer and better method of coastal current measurement. ADCPs can measure currents in water over a broad vertical range with high resolution on the structure of water velocity. ADCPs can be installed on numerous different platforms, such as ships, buoys, and the seafloor. Ship-mounted ADCPs can take continuous measurements as the ship moves, sweeping across a large area in a relatively short time. Bottom-mounted ADCPs can take point-long-time measurements, allowing researchers to monitor long-term coastal current trends.

4. How do Doppler-based ADCPs work?

ADCPs operate on the Doppler principle. ADCPs send out acoustic pulses into the water. The pulses bounce off suspended material such as sediment, plankton, or water bubbles. The frequency shift of the bounced signals when the water is moving. The ADCP takes this frequency shift and computes the relative water velocity to the instrument.

The majority of ADCPs consist of a number of transducer beams, typically four or more, pointed in different angles. With the multi-beam configuration, it is possible to compute the three-dimensional water velocity. With an integration of the signals of the different beams, the ADCP is capable of presenting a full profile of the current velocity at different levels of the water column. The information gauged by the ADCP may either be processed in real-time or archived for subsequent analysis to yield worthwhile information regarding the dynamics of the coastal currents.

5. What is required for high-quality measurement of Cabimas coastal currents?

For an effective quality measurement of Cabimas coastal currents, the equipment to be utilized must possess certain attributes. The equipment must be durable as far as materials are concerned, small in size, light as far as weight is concerned, power, and cost. They will facilitate the deployment of a large number of instruments with extensive spatial coverage.

Most desirable are ADCPs with titanium alloy housings. Titanium alloy offers enhanced corrosion resistance, which is essential for long-term deployment in the corrosive marine environment. It resists the corrosive nature of seawater, keeping the internal ADCP components safe from corrosion. Titanium alloy is lightweight but tough, offering strength and portability to the instrument. This combination of properties allows accurate and long-term measurement of the coastal currents in Cabimas.

6. How to Select the appropriate equipment for current measurement?

Selection Based on Utilization

The selection of ADCP is based on its application. For ship-borne measurements, ship-mounted ADCPs are most suitable. They can give real-time information while the ship moves in the water in a big area in a fairly short period of time. For long-term observation at a stationary point, bottom-mounted ADCPs are best suited. They can deliver continuous data over a long period of time, enabling researchers to analyze long-term trends in coastal currents. Floating ADCPs are effective in monitoring the path of water masses over large areas, offering useful information regarding large-scale circulation patterns.

Selection Based on Depth

The ADCP frequency should also be established based on water depth. In water less than 70m, 600kHz ADCPs are used. These can be used to measure shallow waters at high resolution. In waters up to 110m deep, 300kHz ADCPs have to be used. In deeper water, up to 1000m, 75kHz ADCPs are used.

There are many well-known ADCP brands on the market, such as Teledyne RDI, Nortek, and Sontek. However, for users with limited funds, the ADCP supplier China Sonar's PandaADCP is highly recommended. Made entirely of titanium alloy, it has better performance but is economical. It is especially suitable for cost-conscious users but still requires precise ADCPs in coastal current measurement. You can learn more about them on their official website: https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and models.