How can we measure the coastal currents of Ja - Ela?

1. Where is Ja - Ela?

Ja - Ela is a town in Sri Lanka. It is located in the Western Province and is relatively close to the coast. The area is a part of a region that combines urban and suburban landscapes with natural elements.

It is also enveloped in a combination of a residential area, agriculture, and greenery patches. The city falls within a zone under the influence of the sea, with the climate controlled by its vicinity to the sea. Local waterways and canals drain into the general water system of the coast.

It is close to the Negombo Lagoon and the Indian Ocean in terms of geographical relation to the sea. The lagoon is vital in the local ecosystem as it provides a habitat for several species of birds, fish, and other aquatic life. The coastline around is basically sandy beaches and, thus, forms part of the recreational and economic activities such as fishing and tourism within the region.

2. What is the situation of the coastal currents near Ja - Ela?

A number of factors influence the coastal currents near Ja - Ela. The monsoon winds are a major determinant. During the southwest monsoon, which extends from May to September, strong winds push the surface waters in a northeasterly direction. In contrast, during the northeast monsoon from December to February, the winds drive the currents in a southwesterly direction.

The topography of the seafloor off the coast also affects current patterns. Underwater ridges, sandbars, and channels may cause the currents to accelerate, decelerate, or change direction. In addition, the shape and depth of the entrance to the Negombo Lagoon and its linkage with the ocean currents also play a role. Another significant factor involves tidal currents. The area has semi - diurnal tides, with two high and two low tides recorded daily. As a result, the tidal ebbs and flows could contribute to great variations in the velocity of the currents and their directions within the study area, particularly in the lagoon area and along the creeks joining the lagoon to the open ocean.

3. How to observe the coastal water flow of Ja - Ela?

Surface Drifter Buoy Method

Surface drifter buoys are an easy and practical method to observe the flow of surface water. The buoys are put onto the surface of the water and carried away by the currents. By using satellite-based tracking systems or other positioning methods, the movement of the buoys can be monitored over time. This gives information about the direction and speed of the surface currents. This, however, yields information concerning the surface layer only and might not provide a proper insight into the current structure of the whole water column.

Moored Ship Method

The ship in this method is moored-that is, kept anchored-at a certain point nearshore. The instruments onboard the ship measure the flow of water at various depths. In this way, it can measure continuously at one fixed point. But it has its limitations. The ship's own movement due to waves and wind can introduce errors into the measurements. Also, it only provides data for the area around the moored ship and may not represent the overall coastal current situation.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP profiler method is a more advanced and comprehensive way to measure coastal currents. ADCPs work by broadcasting acoustic pulses through the water and analyzing the frequency shifted or Doppler-shifted echoes returning from the analysis volume. They can estimate water velocity at several depths simultaneously in this way. This gives a high resolution current profile from near the surface to a certain depth depending on the instrument. It gives a more complete picture of the current behavior of the water column and is an excellent choice for studying the coastal currents near Ja - Ela.

4. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of Doppler. They send high-frequency acoustic signals into the water. As these signals reach moving particles in the water, like suspended sediments or small organisms, the frequency of the reflected signal changes owing to the Doppler effect.

If the particles are moving towards the ADCP meter, the frequency of the reflected signal is higher than the emitted frequency; if they are moving away, it is lower. By measuring these frequency shifts at different angles and depths, the ADCP can calculate the velocity of the water at various points in the water column. This enables it to give a detailed current profile that is a representation of the speed and direction of the water movement at various depths. Data from ADCPs can be used to analyze the spatial and temporal variability of the coastal currents.

5. What's needed for high - quality measurement of Ja - Ela coastal currents?

The equipment for measurement of coastal currents near Ja - Ela with high quality needs to be of reliable materials. It must be able to withstand seawater, which is corrosive, and the marine environment. It should also be compact in size, lightweight, and with low power consumption.

A small and lightweight device is much easier to deploy and retrieve, both from boats and from coastal installations. The low power consumption will provide the possibility of long-term monitoring without frequent replacements of batteries. Cost-effectiveness is also very important in many measurement projects of a larger scale.

The casing of the ADCP flow meter is preferably made of titanium alloy. The reason is that the metal has very excellent properties of corrosion resistance, thus it's well suited in the marine environment. It also features a good strength-to-weight ratio, enabling it to provide the needed structural integrity while keeping the device relatively light.

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

Based on Usage

Ship - borne ADCP: If the measurements are to be taken from a moving vessel, a ship - borne ADCP is quite adequate. It can give continuous data as the ship travels along the coast, thus enabling a better understanding of the spatial variability of the currents.

• Bottom-mounted ADCP: A bottom-mounted ADCP current profiler is a good option for long-term and fixed-point measurements near the seabed. It can provide a detailed current profile at a specific location, which is useful for studying the local current behavior.
• Buoy - mounted ADCP: When flexibility in deployment and measurement of surface and upper - water - column currents is required, a buoy - mounted ADCP is the way to go.

Based on Frequency

The choice of frequency depends on the water depth. A 600kHz ADCP should usually suffice for relatively shallow waters of up to 70m, while a 300kHz ADCP should be a better fit for water depths between 70m and 110m. For deeper waters, like the ones that might occur near Ja - Ela in some places, a 75kHz ADCP can be used to measure right up to about 1000m depth.

There are well - known ADCP current meter brands like Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option with excellent quality, the China Sonar PandaADCP is a good alternative. It is made of titanium alloy and offers a great price - performance ratio. You can find more information at https://china-sonar.com/.

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