How to measure the coastal currents of Matara?

1. Where is Matara?

Matara is a coastal city in southern Sri Lanka. It enjoys a scenic location along the shoreline of the Indian Ocean. This city is known for its beautiful beaches, such as the Polhena Beach, which attracts both locals and tourists alike. The long stretches of the sandy coast are punctuated by clear blue waters that gently lap against the shores.

Matara is rich in cultural heritage. The local architecture is characterized by the combination of Dutch and Portuguese colonial remains and other historical influences. There are also a number of ancient temples and places of worship which add to the cultural importance of the city. The nearby waters form an important part of the local economy, mainly because of fishing activities. A familiar sight is the fleet of fishing boats that leave the harbor daily as fishermen go about their work, bringing in a catch of many different types of fish and seafood.

The bay off Matara affords some protection for smaller craft. The underwater topography around the coastal area is varied, with shallow water close inshore, ideal for wading and swimming, and deeper water further out to sea. This variation in depth consequently affects the nature of the coastal currents as the water moves over different underwater landscapes. The city's location also makes it a strategic point for observing the broader oceanic processes that occur in the Indian Ocean.

2. What is the situation of the coastal currents near Matara?

The coastal currents around Matara are influenced by a variety of factors. The influence of the monsoon winds is considerable. The southwest monsoon, from May to September, brings strong winds that drive the surface currents. These winds can cause the water to flow in a particular direction, often parallel to the coast. The northeast monsoon, from December to February, also has an impact, albeit with different wind directions and current patterns.

The larger-scale ocean circulation patterns also play their part. The South Equatorial Current and the influence of the Indian Ocean Gyre provide the general movement of water in the area. Tidal forces are another important factor. The tides in the region cause the water to rise and fall, creating tidal currents that interact with the other ocean-driven currents. The shape of the coastline and the bathymetry near Matara can modify the currents, such as headlands and bays, which change direction and speed due to water being deflected or funneled.

3. How to observe the coastal water flow of Matara?

Surface Drift Buoy Method: A simple and effective means to observe the surface water flow involves a surface drift buoy. These buoys are deployed in the water and are carried along by the surface currents. The direction and speed of the surface currents can be calculated using GPS or other tracking systems that monitor the position of the buoys over time. However, this method mainly provides information about the surface layer and does not give a full understanding of the currents at different depths.

Anchor Boat Method: The water flow can be measured by an anchor boat. The boat will be anchored at a location, and from the boat, the current-measuring instruments will be deployed at different depths. In this way, it can measure the speed and direction of the currents at different vertical levels. However, this method is somewhat stationary and may not cover a large area efficiently.

ADCP profiler is an advanced and effective method for the measurement of coastal currents. It utilizes the Doppler effect to measure the velocity of water at various depths. By emitting an acoustic signal into the water, the Doppler shift in the reflected signals from particles in the water allows ADCP to provide a very detailed profile of the current from the surface to a specific depth. This will provide a better understanding of the vertical structure of the coastal currents near Matara.

4. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of the Doppler. They emit acoustic pulses into the water column. These pulses interact with the suspended particles in the water, like plankton, sand grains, or other small debris. As the water is in motion, the particles move with it. Due to the particles reflected back to the ADCP meter, there is a shift in frequency in the received signal compared to the emitted signal. It is this Doppler shift that is related to the water flow velocity.

The ADCP flow meter has a number of transducers capable of sending and receiving signals in different directions. Thus, by precisely measuring the Doppler shift of the received signals from different angles and depths, it can estimate the speed and direction of the water currents at various points in the water column. This allows for a three-dimensional representation of the current field, which yields important data on both horizontal and vertical components of coastal currents.

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

The equipment to be used for measuring the coastal currents in Matara should have some unique characteristics for high-quality measurement, the material of the equipment needs to be reliable and bear the corrosive effects of sea water and the harsh marine environment; small size and light weight are beneficial to make the equipment easy to handle and deploy on either a boat, buoy, or other platforms.

Low power consumption is also of the essence in long - term measurements. It can be operated continuously without the frequent replacements of batteries or large scale power supply. It shall also be cost-effective, Not so expensive to make its wide application in as many units possible in order to achieve comprehensive monitoring.

In the case of ADCPs, a casing made of titanium alloy is ideal. The reason is that this material is highly resistant to seawater corrosion and will hence ensure that the equipment has long-term durability. It has a high strength-to-weight ratio, meaning it can provide structural integrity while keeping the weight to a minimum. Besides, titanium alloy is resistant to high pressure; hence, it is also suitable for various water depth situations in the Matara coastal area.

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

When choosing the right equipment for current measurement in the Matara coastal waters, several factors need to be considered.

According to the purpose of use, there are various kinds of ADCPs. If the measurements are to be made from a moving vessel, then a ship-borne ADCP is adequate. It will measure the currents while the vessel is moving along the coast in a continuous manner. If the aim is to monitor the currents at a fixed location near the seabed, then a sit-bottom ADCP is adequate. It can be set on the ocean floor and record the water flow passing over it. When it is more convenient to operate an ADCP current profiler from a floating platform, a buoy - mounted ADCP should be employed.

With regards to ADCPs frequency, it will again depend on the depth of the water. The first choice for depths up to 70m should be 600kHz due to high resolutioning. The ADCPs in frequencies of 300kHz should be adequate to be used for a water body with depths up to 110m, whereas up to 1000m a frequency of 75kHz can perform better in current measurements with very good accuracy.

There are well - known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, for those seeking a cost - effective alternative, the China Sonar PandaADCP is a great option. It is made of titanium alloy and offers an excellent cost - performance ratio. You can find more information about it on its website: https://china-sonar.com/.

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