How to measure the coastal currents of Lahad Datu?

1. Where is Lahad Datu?

Lahad Datu is a coastal town in eastern Sabah, Malaysia, with a coast holding rich natural and cultural heritage.

This town is bounded by the Celebes Sea, part of the western Pacific Ocean. Extensive rainforests surround Lahad Datu, which are home to a wide variety of flora and fauna. These rainforests are part of the global ecosystem that is very vital, but to the local indigenous groups, they mean livelihood and attachment to ancestral lands and resources.

The coast of the district of Lahad Datu features sandy beaches and mangrove forests. Mangroves are an important ecological sector, and they protect the shores from erosion while at the same time acting as a perfect place for many marine species to breed and have their nursery. Shallow waters off the coast are nutrient-rich, thus providing conditions for various types of shellfish and small fish. Farther out at sea, the waters deepen, and there are areas important for fishing and shipping activities.

The people of Lahad Datu come from various ethnic groups consisting of the Bajau, as well as other inland tribes. Their traditional way of life, being closely associated with the sea, involves much fishing and sailing, which has become quite significant in their culture.

2. What is the situation of the coastal currents near Lahad Datu?

The coastal currents near Lahad Datu are affected by a number of factors. The effect of monsoon winds is immense. Strong winds during the seasonal southwest monsoon push the surface currents in one direction. This at times may bring warm waters from elsewhere with nutrients into this region and affect the local marine ecosystem. In contrast, the northeast monsoon pulls a different current and often brings cooler waters, which can alter the distribution of marine organisms.

Topography of the ocean floor also plays a very important role. Underwater ridges, valleys, and reefs may deflect or speed up the currents. For example, around a coral reef, water is deflected, leading to other areas with possible upwelling or downwelling. Such areas are very important in the nutrient cycle because deep waters that contain a lot of nutrients rise to the surface, where phytoplankton and other primary producers start their life.

Another important factor influencing the latter is freshwater input from land rivers and streams. Such discharge may eventually change the salinity of coastal waters, thus creating different density gradients able to generate different water masses and steer the mixing and flow of currents.

3. How to Observe Coastal Water Flow in Lahad Datu?

Surface Drifting Buoy Method: This method involves deploying buoys on the water surface. The buoys are left to drift according to the currents and their movements are tracked by satellite-based positioning systems. From the track of the buoys, the direction and speed of the currents at the surface are obtained. However, this method provides data mainly for the surface layer and cannot provide a complete insight into the currents throughout the water column.

Anchored Ship Method: In this, the ship is anchored in the coastal waters and from it current-measuring instruments are lowered at various depths in the water. This measures the characteristics of the current at different levels. But it may happen that the presence of the ship interferes with the natural flow of water and long continuous measurement might be economically not that good.

Acoustic Doppler Current Profiler (ADCP) Method: These are higher-order and more efficient ways of measuring the coastal currents. They are able to provide a detailed profile of the current velocities right from the surface to a certain depth, therefore giving full detail of the flow patterns within the water column.

4. How do ADCPs using the Doppler principle work?

The working principle of ADCP profiler is based on the Doppler effect. They send acoustic pulses into the water. This interacts with the moving particles in the water, such as sediment particles and small organisms that move along with the water. Because of the motion of the water, the frequency of the reflected pulses will change due to the Doppler effect. The frequency shift is measured by the ADCP meter, and it calculates the velocity of the water at a number of depth points. The instrument is fitted with a number of transducers capable of transmitting and receiving acoustic signals in several directions; hence, the measurement of the current three-dimensional velocity structure of the water column is possible.

5. What is required for good quality measurements of the currents off the coast of Lahad Datu?

Good quality of instrument materials will assure equipment quality only, as measurement in the coastal currents around Lahad Datu is concerned. Those materials should be able to withstand corrosive seawater and mechanical forces created by waves and currents. Small size and lightweight are advantageous for easy deployment from either a boat, buoy, or seabed.

Low power consumption: this is very important when doing long-term measurements at places where no one is around. Cost-effectiveness: the equipment should be such that doing large-scale measurement is financially viable. Casing: For ADCP flow meter, the casing made of titanium alloy is preferred. The corrosion resistance of the titanium alloy is very good which becomes vital in the marine environment. The material is also very strong and durable to bear the harshness of the sea while it is comparatively lightweight.

6. How to Choose the right equipment for current measurement?

Usage scenario: The choice of equipment for the measurement of currents near the shore at Lahad Datu will depend upon the usage scenario. In the case of ship-based measurement, a ship-mounted ADCP will do the work. It can be installed on the hull of any ship and measure the currents while the ship is sailing or stationary.

It would be ideal to measure the currents near the seabed with an ADCP current profiler that sits on the bottom of the ocean. This can easily be placed on the seabed and give detailed, accurate measurements of the current close to the bottom.

In floating applications, a buoy-mounted ADCP shall be fitting. This can be fixed to a buoy for the measurement of currents at varied depth displacement as the buoy floats.

As for the frequency of ADCPs, their action can normally be effective in water depths up to 70m at 600kHz. For depths up to 110m, a 300kHz ADCP offers better possibilities; for deeper waters to 1000m, a 75kHz ADCP can effectively measure the water currents.

There are several well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a highly recommended Chinese ADCP brand is China Sonar PandaADCP. It is made of all - titanium alloy material, ensuring excellent performance and durability in the marine environment. It also offers an outstanding cost - performance ratio. You can find more information on its website: https://china-sonar.com/.

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