Measurement of coastal currents: Hartlepool

1. Where is Sunderland?

Sunderland was amongst the main sea cities in North East England, within the metropolitan county of Tyne and Wear. It faces the North Sea along its shores, putting together a unique combination of industrial heritage and modern urban development. The city has a long-standing relationship with the sea, which has molded its history, economy, and culture.

History can be traced in Sunderland as far back as the Roman times with evidence of early settlements and trading activities. From over the centuries, it grew from a mere fishing village into a significant industrial port. The architecture in Sunderland is both a reflection of the past and the present. These historic buildings range from the 11th-century St. Peter's Church to the show of early roots within the city. It's a Victorian-era structure that testifies, along with other such structures, including the grand Sunderland Museum & Winter Gardens, to the growth of the city during that time. In recent times, the modern developments-the Sunderland Minster and contemporary waterfront apartments-have altered the face of the city. The local community is deeply associated with the sea. Shipbuilding was once a dominant industry in Sunderland, with the city being a major ship - building center in the 19th and 20th centuries. Although the shipbuilding industry has declined, the port still plays a role in trade and is also a popular area for leisure activities, including pleasure boating and fishing.

The beaches of Sunderland are not only a recreational destination for locals and tourists but also an important part of the local ecosystem. The adjacent waters of the North Sea are home to a diverse range of marine life. Seals can often be seen on the sandbanks offshore, and the seabed is populated with various fish species such as cod, haddock, and mackerel. The seabed topography consists of sandy areas, rocky outcrops, and underwater channels, which contribute to the rich biodiversity of the area and also influence the movement of water.

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

The coastal currents near Sunderland are influenced by a complex interplay of multiple factors. Tidal forces are a significant factor. The North Sea experiences semi - diurnal tides, with two high tides and two low tides each day. The tidal range can vary, and the resulting tidal currents can reach speeds of up to 2-3 knots in some areas, especially near the mouth of the River Wear, which flows into the North Sea at Sunderland. At high tide, water surges toward the shore, carrying nutrients and sediment from the open sea. At low tide, the water pulls back, exposing the intertidal zones where a host of shore-dwelling organisms reside.

Another critical factor is wind. Dominant south-westerly winds can push surface waters toward the coast, adding to the coastal currents. These winds can also produce waves interacting with the currents, which is more complex to understand. It is also shown that northerly winds are responsible for the offshore driving of water. This shape of coastline with bays, headlands, and an estuary formed by the River Wear makes these currents converge and diverge in some areas. More complications come in with sub-surface boulder outcrops and a general sand overbed. These features can either impede the flow or act as channels and thereby create turbulent and calm regions. Besides, the inflowing freshwater from the River Wear modifies the local current patterns. Due to the differences in density from the seawater, the fresh water forms a density-driven current that interacts with the tidal- and wind-induced currents.

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

Surface Drifting Buoy Method

Surface drifting buoys are one of the easiest devices used for observing currents at the surface level. These buoys have been designed with GPS or satellite-based tracking systems. After being discharged into the water, they drift due to the action of surface currents. The buoy movements are able to be followed by the scientists for periods of time, and the speed and direction of surface waters are able to be estimated with analysis of its path. This, however, describes only the top few meters of the water column and cannot necessarily reflect what deeper currents might be like.

Moored Ship Method

A ship in the moored ship method is taken and moored in one spot near the coast of Sunderland. Current-measuring instruments, such as electromagnetic current meters, are then deployed. These instruments can measure the flow of water at different depths, providing a detailed vertical profile of the current velocity and direction. But this method is restricted to a single location, and the presence of the ship can potentially disrupt the natural water flow, affecting the accuracy of the measurements.

Acoustic Doppler Current Profiler (ADCP) Method

ADCPs have completely changed the pattern of measurement in Sunderland for all aspects related to coastal currents. They can measure the velocity profile of the whole water column from surface to seabed. Basically, ADCPs use sound waves as a non-intrusive method for the measurement of water flow. They can work out the current velocity at different depths by emitting acoustic pulses and measuring the Doppler shift of the reflected signals from suspended particles in the water. This provides a comprehensive view of the current structure, making it highly suitable for studying the complex coastal current patterns in the waters around Sunderland.

4. How do ADCPs using the Doppler principle work?

ADCPs operate based on the Doppler effect. They emit high-frequency acoustic pulses into the water. When these pulses reach small particles in the water, like sediment, plankton, or even just bubbles, the particles reflect the acoustic signal back to the ADCP profiler. If the particles are moving with a water current, there will be a frequency shift in the reflected signal with respect to the transmitted one. This is called a Doppler shift and is proportional to the velocity of the particles relative to the ADCP. By measuring the Doppler shift at different depths in the water column, the ADCP can calculate the velocity of the water at those depths. Multiple transducers on the ADCP flow meter are used to measure the velocity components in different directions, allowing for the determination of the three-dimensional velocity vector of the water flow.

5. What’s needed for high-quality measurement of Sunderland coastal currents?

Equipment Material Reliability

For high-quality measurement of the coastal currents near Sunderland, the reliability of the equipment materials is crucial. The casing of the ADCP current meter should be made of a material that can withstand the harsh marine environment of the North Sea. Titanium alloy is an excellent choice. The high strength helps the material oppose impact due to strong water flow, collision, or other possibilities of floating debris and the ionic corrosion possibility of seawater. Its elastic modulus is lower to provide certain flexibility, enabling the material against mechanical stress resulting in damage. Moreover, such good corrosion resistance makes it certain that the ADCP can support long-term deployments in seawater with minimal deterioration in performance.

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

Smaller and lighter ADCPs are easier to install and handle on a small research vessel, on a buoy, or even on the seabed. There is also less disturbance on natural water circulation, and that will allow more accurate measurements. Low power consumption is of prime importance if long-term autonomous monitoring is intended and if battery-powered systems are in use. A low-cost ADCP enables large-scale deployment, which is necessary for comprehensively understanding the complex coastal current patterns around Sunderland.

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

Based on Usage

• Shipborne ADCP: Suitable for real-time current data along a ship's route near Sunderland, it can be used for oceanographic surveys, studying the general circulation in the area, and for optimizing shipping routes.
• Bottom-mounted ADCP: Suitable for long - term, fixed - point monitoring of the currents at the seabed. This is valuable for studying long - term trends in the coastal currents, such as the impact of climate change on the local marine ecosystem.
• Buoy-mounted ADCP: Well-suited for the monitoring of surface-level currents over a wide area as the buoy drifts with the water. It helps in understanding the spatial variability of the surface currents and how the coastal waters interact with the open North Sea.

Based on Water Depth

• 600kHz ADCP: Suitable for water depths of up to about 70m, providing high-resolution measurements in the relatively shallow waters near Sunderland.
• 300kHz ADCP: Suitable for water depths around 110m, which can be useful for areas with slightly deeper sections in the North Sea near the city.
• 75kHz ADCP: For deep-water applications. Although the waters around Sunderland are generally not very deep, it can be used for studies related to the deeper-layer currents or for areas with deeper channels; it can measure currents to depths up to 1000m.

Several famous brands exist in the global market for ADCP, such as Teledyne RDI, Nortek, and Sontek. If the budget is the matter, you will find China Sonar PandaADCP-a great balance between quality and price-made of all-titanium alloy. More about it can be found here: (https://china-sonar.com/).

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