Measuring the Coastal Currents of Holyhead

1. Where is Holyhead?

Holyhead is a significant seaside town on Anglesey Island, in Wales, which borders the Irish Sea. Its west coast position on the island has given it an age - old and vital connection with the sea, which has been at the heart of its history, economy, and way of life for its people.

Holyhead is also rich in history. It has been a major port for centuries as a major stopping point for ferries traveling between Wales and Ireland. The town's history also involves sea trade, fishing, and the military. Architecture in Holyhead is a mix of traditional Welsh classicism and functional modernity. Within the town center, there are typical stone-built houses with standard features. They have thick, durable walls, narrow-framed windows, slate-tiled roofs, and a distinct Welsh seashore atmosphere. The port area has modern ferry terminals and services capable of accommodating the dense stream of people and goods in transit on a daily basis. Down the high streets, there are high-street shops, cafes, and accommodations for both the permanent residents and the seasonal influx of visitors.

The people of Holyhead have an ancient bond with the sea. Fishing has always been a long-standing profession passed down through the generations. While the fishing industry has experienced its changes with the years, some of the local fishermen continue to sail out of the harbor. They bring back fish such as mackerel, herring, and other shellfish. Harbour is not just a transport hub and fishing center but also a widely accessed tourist area and settlement where people and tourists can take boat cruises. Tourists can experience the sea breeze, watch seagulls fly overhead, and enjoy Irish Sea views.

Shores and waters bordering Holyhead are rarely more important to the local environment. The Irish Sea waters in this area provide a biodiversity that is rich and varied. Seals can often be seen on the sandbanks, and seabirds such as gulls, terns, and puffins are common visitors. Sandy tracts with rocky outcrops and seafloor channels form the landscape of the seabed. These habitats support an opulent abundance of biodiversity and play a significant role in the water circulation.

2. What is the Status of the Coastal Currents Around Holyhead?

The coastal currents around Holyhead are influenced by several factors. The tidal forces are one of the most important factors. The Irish Sea has semi-diurnal tides, two high tides, and two low tides daily. The tidal range can be non-uniform and the resulting tidal currents can become as rapid as 2 - 3 knots in some locations, especially the mouth of little inlets or where there exists a well-developed coastal line. Water travels towards the coastline during high water, bringing nutrient and sediment carried from the outer ocean. It enriches the local marine fauna, providing nutrients and habitats for numerous sea creatures. During low tide, the water recedes, and intertidal zones are exposed, revealing sea anemones, little crabs, and seaweeds.

Wind also plays an important role. Powerful south - westerly winds can push surface water toward the coast, increasing coastal currents. The winds also generate waves that interact with the currents, increasing the complexity of the flow pattern. The northerly wind may drive water away from the shore. The construction of the coastline in terms of headlands and bays and the unorthodox shape of Anglesey's shoreline make the currents converge and diverge at various points. The submerged sandbars and rock outcrops are responsible for the challenges in the flow of currents. These may channel or block and divert the flow of water to create calm and turbulent water points. In addition, the contribution of freshwater from the small local streams could affect the local current patterns. The freshwater is less dense than seawater and floats on top, draining to the sea and responding to the tidal and wind - driven currents.

3. How to Observe the Coastal Water Flow of Holyhead?

Surface Drifting Buoy Method

Surface drifting buoys are a simple but effective way of tracking the surface - level currents in the vicinity of Holyhead. The buoys are equipped with GPS or satellite - based tracking equipment. When they are dropped into the sea, the surface currents carry them along. Scientists can track their trajectory over time. From the trajectory of the buoy, they can determine the speed and direction of the surface waters. But this technique is limited to the upper few meters of the water column. It can be quite different from what is actually happening in the deeper parts of the water, where the currents can be divergent due to reasons like temperature and salinity difference.

Moored Ship Method

In the moored ship method, a ship is moored at a fixed point near the coast of Holyhead. Then, there are current-measuring instruments like electromagnetic current meters. They can record the current at different depths. They provide an accurate vertical profile of velocity and direction of the current. However, this method is confined to a single point. Further, the ship's presence actually disrupts the free flow of water. The hull shape of the ship and its anchorage can create turbulence in water, which may affect the accuracy of the measurements.

Acoustic Doppler Current Profiler (ADCP) Method

ADCPs have facilitated the measurement of coastal currents off Holyhead with the ease. ADCPs are able to measure the velocity profile of the entire water column from seabed to the top. ADCPs use sound waves to measure the water flow non-intrusively. They emit acoustic pulses and record the Doppler shift of the backscattered reflections from suspended material within the water, such as sediment, plankton, or small bubbles. From this, they can infer current velocities at a range of depths. This gives a comprehensive description of the current structure, which is well-suited to investigating the complicated coastal current patterns in the area around Holyhead.

4. What are the Requirements for High-Quality Measurement of Holyhead Coastal Currents?

Equipment Material Reliability

Equipment material reliability is crucial for high-quality measurement of coastal currents off Holyhead. The ADCP casing should be made of a material that can withstand the Irish Sea's harsh marine environment. The most suitable option for this is titanium alloy. Its high strength allows it to resist the pressure of strong water currents, potential impact with floating debris, and corrosive seawater environment. Its low elastic modulus provides it with flexibility, reducing the likelihood of mechanical stress-related damage. In addition, its high corrosion resistance allows the ADCP to be submerged in water for long-term monitoring purposes without damaging much its effectiveness.

Light Weight, Low Cost, Low Power Consumption, and Compact Size

The ADCP is lighter in weight, lower in cost, power consumption, and size. It is easier to install and also to use. You can mount it on a small research vessel, suspend it from a buoy, or put it on the seabed. It also disturbs the natural water flow less, thereby leading to more accurate measurements. Low power consumption is important for independent monitoring over the long term, especially where battery-powered equipment is utilized. Mass deployment is possible using a low-cost ADCP. This is needed to get a complete understanding of the complex coastal current systems off Holyhead. With more ADCPs installed in different locations, we are better able to understand how the currents vary around the area.

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

By Application

• Shipborne ADCP: Applicable for obtaining real-time current data along a vessel track near Holyhead. It may be used for oceanographic surveys, general circulation studies in the area, and for shipping route optimization, especially in the context of Holyhead's prominence as a port.
• Bottom-mounted ADCP: Best used for fixed - point, long - term survey of the seabed currents. Best for studies on long - term trends within the coastal currents, e.g., how the climate change would impact the coastal marine environment.
• Mounted ADCP on buoy: Appropriate to study surface - level currents across an extensive area because the buoy retains the motion of the water. It helps reveal the spatial variance of the surface currents and the manner in which the coastal water influences the open Irish Sea.
• 600kHz ADCP: For depths up to around 70m, providing high-resolution measurements in relatively shallow Irish Sea waters off Holyhead.
• 300kHz ADCP: Best for depths of around 110m, which could be useful for patches of slightly higher depth in the Irish Sea near the town.
• 75kHz ADCP: It is appropriate for deep-water applications. While the waters around Holyhead are generally not deep, it can be utilized for investigations of the deeper-layer currents or where channels are deeper, and it can operate up to a depth of 1000m.

There are several very renowned ADCP manufacturers across the globe as well, namely Teledyne RDI, Nortek, and Sontek. For the financially constrained, there is ADCP manufacturer  China Sonar ​PandaADCP, all-titanium alloy, available with the ultimate blend of cost and quality. You can visit(​https://china-sonar.com/) to learn more about it.

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