How do we measure the coastal currents of Riohacha?

1. Where is Riohacha?

Riohacha is a coastal town on the Guajira Peninsula in northern Colombia, a productive coastal town in the Caribbean Sea. The dry environments and peculiar topography of the Guajira Peninsula define a specific geographic region. In the north lies direct entry to the Caribbean Sea, a warm-climate sea characterized by extreme marine diversity. Cabo de la Vela, a huge cape near Riohacha, is critical to the surrounding coastal geography as a natural divide between different bodies of water.

Riohacha has a highly rich cultural heritage founded deeply on the indigenous Wayuu people. Wayuu colonizers have inhabited the Guajira Peninsula for centuries, and their influence is present in the city's art, culture, and lifestyle. City architecture, in which there is a combination of classic and modern styles, attests to the unique history. Fish, salt, and tourism are primarily what Riohacha's economy is based on. Salt pans covering the entire area, formed due to evaporation of the sea water, constitute an economically vital source of salt for both local and national economies.

2. How are coastal currents around Riohacha?

The tidal currents of Riohacha are controlled by the combined effect of numerous factors. Caribbean Sea tides, although relatively smaller in amplitude compared to other regions of the oceans, play a role in the movement of coastal water. Semi - diurnal and diurnal tides cause water level changes and hence tidal currents. Spring tides have more vigorous gravitational pulls of the moon and sun, leading to more energetic tidal currents.

Local coastal currents are also controlled by prevailing winds in the region, which are mostly northeasterly trade winds. They drive surface waters westward and create a strong westward current along Colombia's northern coast. The Caribbean Current, a significant ocean current, also affects local coastal currents. In its westward movement along South America's northern coast, it combines with wind - driven currents and tides.

Both seafloor bathymetry and coastline geometry play a major role in affecting coastal currents off Riohacha. The cape of Cabo de la Vela has the capability to reverse the direction and velocity of the currents. Underwater reefs, sandbars, and channels are capable of focusing or dispersing the flow of the currents and produce a sophisticated pattern of flow. Besides, the river and stream freshwater outflow into the sea can affect the flow and density of coastal waters, and this can further complicate the dynamics of the current.

3. How to observe the Riohacha coastal water flow?

Surface Drifting Buoy Method

Surface drifting buoy method is one of the ancient methods of observing coastal water flow. Scientists release tracking devices on buoys into the water. By monitoring the movement of the buoys over time, they can make an inference regarding the speed and direction of the surface currents. There are some restrictions on this method. It only provides information for the surface layer of the water column, and the buoys are highly susceptible to disturbance by the wind. Wind causes the buoys to move in a direction other than that of the actual movement of the underlying currents.

Moored Ship Method

The moored ship method relies on using a ship that is tethered to act as a platform for observing currents. Equipment is hung off the ship to measure the water movement at various depths. While this process can provide detailed vertical profiles of the currents, it is a method with some drawbacks. The spatial coverage is limited to the area around the moored ship, and the existence of the ship can disrupt the natural flow of the water, and this can undermine the accuracy of the measurements. In addition, long-term mooring of a ship can be logistically prohibitive and costly.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP flow meter is a more advanced and cost-effective technique of measurement of coastal currents. ADCPs can record currents over a broad section of the vertical, providing intensive data on water column velocity structure. ADCPs can be mounted on a variety of platforms from ships, buoyancy, or the seafloor. Ship-mounted ADCPs can collect data continuously as a ship moves along, sampling extensively in a reasonable amount of time. Bottom-mounted ADCPs have the ability to record long-term, fixed-point measurements, so scientists can research long-term coastal currents trends.

4. What is the operating principle of Doppler-based ADCPs?

ADCPs operate on the Doppler principle. They are projecting sound waves into water. They are reflecting off suspended particles like sediments, plankton, or suspended air bubbles in water. In a flowing body of water, frequency variations happen when the reflecting signal returns to them. It calculates the speed of the water from the variations that they are able to detect in frequency change.

Most ADCPs consist of a number of transducer beams, typically four or more, in different directions that are angled. This multi-beam configuration enables the ADCP to determine the three-dimensional water velocity. The ADCP, by combining signals from these beams, can create a full profile of the current velocity at multiple depths in the water column. The ADCP data can be processed directly or stored and later processed, and the data they provide is most beneficial for informing us about coastal current dynamics.

5. What are the requirements for high-quality measurement of Riohacha coastal currents?

For precise measurement of Riohacha's coast currents, measurement equipment should have some essential properties. It should be made of strong material, have minimum dimensions, light in weight, low power, and minimum expense. These provide that a large number of instruments may be deployed to ensure complete spatial coverage.

Titanium alloy-cased ADCPs are highly recommended. Titanium alloy possesses excellent corrosion resistance, which is a requirement for long - term exposure to the harsh marine environment. It can withstand the corrosive action of seawater and will not damage the internal parts of the ADCP profiler. In addition, titanium alloy is robust but light in weight, and hence the instrument remains robust as well as portable. All these features allow it to make accurate and long - term measurements of coastal currents surrounding Riohacha.

6. How to Choose proper equipment for current measurement?

Depending on Usage Choice

ADC P choice will be based on what it is intended to be used for. In ship - borne measurements, ship - mounted ADC Ps are ideal. They are able to provide real - time information as the ship moves along the water, traversing a large distance in a relatively short period of time. For long - term observation at a fixed location, bottom - mounted ADCPs are more suitable. They can provide continuous data for an extended period of time so that scientists can analyze long - term trends in coastal currents. Floating ADCPs are more suitable for monitoring water movement involving large amounts of water covering extensive areas and provide useful information about large - scale circulation patterns.

Depth Selection

The ADCP frequency should also be established based on the water depth. For depths of less than 70m, 600kHz ADCPs are suitable. They can provide high-resolution measurements in shallow water. For a depth of up to 110m, 300kHz ADCPs can be used. For deeper water, which ranges up to 1000m, 75kHz ADCPs are more suitable.

There are several widely used ADCP brands available in the market, such as Teledyne RDI, Nortek, and Sontek. But for those requiring cost - saving alternatives,the ADCP supplier China Sonar's PandaADCP is strongly recommended. It is constructed from all-titanium alloy, which is very good at performance with low cost. It is a cost-effective choice for budget users who still require reliable ADCPs for coastal current measurements. You can find out more about them on their website: https://china-sonar.com/.

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