How to Measure the Coastal Currents of Port St Mary

1. Where is Port St Mary?

Port St Mary is a picturesque coastal village on the southern coast of the Isle of Man, within the Irish Sea. The village's picturesque location has fostered a deep-rooted relationship between the village and the sea, which has played a crucial role in its development, economy, and lifestyle of its inhabitants.

The village has a rich and long history. It has long been a significant fishing harbour, with its heritage roots firmly linked with the sea. Port St Mary's architecture consists of a combination of old Manx charm and modern practicality. There are stone-built quaint old-fashioned cottages in the centre of the village. They have thick and strong walls, small-framed windows, and steeply sloping roofs, with an atmosphere of timelessness about them. They are a reminder of the history of the village, reliving the stories of fishermen and their families through generations. In and around the harbor and on the main streets, there have emerged modern buildings. There are contemporary shops, welcoming cafes, and soothing accommodation, catering to the needs of both the local population and the tourists who are drawn to the seashore beauty of the village all year round.

The residents of Port St Mary share a deep connection with the sea. Fishing has long been a traditional activity that has been handed down through generations. Though the fishing industry has evolved over the years, some local fishermen continue to set out on their morning trips from the harbor. They return with mackerel, herring, and other types of shellfish in their nets. The harbour is not only a focal point for fishing but also a holiday destination for boat tours. Fresh sea air, flying seabirds, and spectacular Irish Sea views are there to enjoy.

Port St Mary's beaches and the sea waters are of extreme importance for the ecosystem around the place. Irish Sea waters here abound in diverse species of sea creatures. The seals tend to lay around on sandbanks and typically the gulls, terns, and the puffins appear in view hovering overhead. Varied topography of the ocean bed appears here, ranging from sandy periods to detached outlying rock surfaces as well as subsurface channels. These features grant an extremely abundant biodiversity in conjunction with an influencing impact upon movement in water.

2. What is the State of the Coastal Currents Surrounding Port St Mary?

Coastal currents surrounding Port St Mary are influenced by a number of factors. Tidal forces are significant. The Irish Sea experiences semi-diurnal tides, two high tides and two low tides every day. The tidal range is also not constant, with the consequential tidal currents developing up to 2 - 3 knots over some sections, especially where small inlets mouths or a significant coastal profile exists. During high tide, seaward flow towards the coast, including nutrients and sediments imported from the open ocean, takes place. It enriches the marine community nearby, providing sea life with food and shelter. If the tide is out, the water runs away and the intertidal areas become exposed, revealing miniature crabs, sea anemones, and other seaweeds.

Wind is also a significant factor. Prevailing south-westerly winds are capable of forcing surface waters ashore, increasing the coastal currents. These winds also generate waves that interact with the currents to create a more complex flow pattern. Northerly winds can force the water off the coast. The shape of the coastline, bays, headlands, and the characteristics of the Isle of Man's southern coast cause converging and diverging currents in different areas. Rocky sea outcrops and sandbars contribute to current complexity. These can also act as a barrier or channel, diverting the water and creating areas with calm or turbulent water. Additionally, the input of fresh water from small local creeks can also affect the local current patterns. The fresh water, being lighter than seawater, serves as a lid on the surface and flows towards the sea, interacting with the tidal and wind-driven currents.

3. How to Monitor the Coastal Water Current of Port St Mary?

Surface Drifting Buoy Technique

Surface drifting buoys are a simple but useful technique to observe the surface - level currents near Port St Mary. GPS or satellite - based tracking systems are mounted on the buoys. Released in the ocean, surface currents carry them along. Researchers can track their movement over time. By observing the direction of the buoy, they can estimate the speed and direction of the surface waters. This method is only applicable to the top few meters of the water column. It might not be what is happening in the deeper parts of the water, where the currents could be different due to variations in temperature and salinity.

Moored Ship Method

In the moored ship method, a ship is anchored at a single location on the shore off the coast of Port St Mary. Then, current-measuring equipment like electromagnetic current meters are lowered down. They record the speed of the flow of water at different depths. They provide a detailed vertical profile of the current speed and direction. But the method can only be applied at one location. Secondly, the presence of the ship can potentially disrupt the natural movement of water. The ship's hull and how it is anchored has the effect of creating turbulence in the water, which can affect the accuracy of the measurements.

Acoustic Doppler Current Profiler (ADCP) Method

ADCPs have revolutionized the measurement of coastal currents off Port St Mary. They are able to measure the velocity profile of the entire water column from the surface all the way to the seabed. ADCPs use sound waves to quantitatively measure the water current non-invasively. They emit acoustic pulses and measure the Doppler shift of the echoes from suspended items in the water, such as sediment, plankton, or small bubbles. From this, they can estimate the current speed at different depths. This gives a general idea of the current shape and is thus extremely appropriate to investigate the complex patterns of coastal currents in Port St Mary.

4. What Does High-Quality Measurement of Port St Mary Coastal Currents Require?

Reliability of Equipment Material

To obtain high-quality measurement of coastal currents near Port St Mary, reliability of equipment material is necessary. The casing of the ADCP current meter should be of material that is capable of withstanding the harsh marine environment of the Irish Sea. The most suitable material would be titanium alloy. Its tensile strength is strong enough to be able to handle intense impact from water current force, potential impact with passing rubbish, and seawater corrosion. Its relatively low elastic modulus allows the material to be resilient and flexible to prevent mechanical damage stress. Further, its strong resistance to corrosion ensures that it is feasible to expose the ADCP meter to continuous water contact while still maintaining normal functions for quite some time.

Light Weight, Small Size, Low Cost, Low Power

A small size and light weight ADCP flow meter is easier to install and operate. You can install it in a small research vessel, attach it to a buoy, or place it on the seafloor. It will also create less disturbance to the natural water flow, leading to improved measurements. Low power consumption is essential for long-term stand-alone monitoring, especially with battery - powered systems. A low-cost ADCP facilitates large-scale deployment. This is necessary to fully understand the complex coastal current patterns around Port St Mary. With more ADCPs at different locations, we can understand the difference in currents in the region better.

5. How to Choose the Right Equipment for Current Measurement?

Based on Application

• Shipborne ADCP: Ideally suited for measuring real-time current data along the route of a ship near Port St Mary. It can be used in oceanographic surveys, studying the overall circulation in the area, and for streamlining shipping routes, if any in the area.
• Bottom-mounted ADCP: Ideal for long - term, fixed - point monitoring of seabed currents. This is useful for observing the long - term trends in coastal currents, e.g., the effect of climate change on the coastal marine ecosystem.
• Buoy-mounted ADCP: Appropriate to monitor surface - level currents over an extensive spatial area since the buoy is carried by the water. It helps to understand the spatial variability of the surface currents as well as the way coastal waters interact with open Irish Sea.

Based on Water Depth

• 600kHz ADCP: Appropriate for water depths of approximately 70m, with high-resolution readings in the relatively shallow waters off Port St Mary.
• 300kHz ADCP: More suitable for water depths of approximately 110m, which may suit areas of the Irish Sea off the village that have slightly deeper sections.
• 75kHz ADCP: Designed for deep-water use. Even though the seas off Port St Mary are not actually very deep, it can be used to apply to research on the deeper-layer flows or for places with deeper channels, which can measure currents up to 1000m in depth.

There are several well-known ADCP brands in the global market, such as Teledyne RDI, Nortek, and Sontek. For those who are looking for a low-cost one, the China Sonar PandaADCP, made of all-titanium alloy, offers good quality and price ratio. You can learn more about it at (https://china-sonar.com/).

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