How can we measure the coastal currents of Folkestone

1. Where is Folkestone?

Folkestone, a charming coastal town, is situated on the southeastern coast of England within the county of Kent. This prime location on the English Channel not only endows it with breathtaking sea views but also has shaped its long - standing maritime heritage.

Steeped in history, archaeological evidence shows that Folkestone was occupied by the Romans and thus laid early foundations for being connected to the sea. In the town of Folkestone, the architectures are a harmonic blend of all different eras: Victorian-era buildings along the seafront harken back to its bygone days of prosperity as a favorite seaside resort. These elegant structures, with their ornate facades and characteristic bay windows, add to the town's old-world charm. The local community is deeply connected with the ocean, as fishing has been the traditional source of livelihood for generations, with skills and knowledge passed down through time. Up to this day, this place is seriously in sight, as many fishing boats are leaving and coming to the harbor; it is part of being a town with a maritime identity.

The port of Folkestone has contributed much to the local economy. It caters for a wide variety of vessels, from small fishing boats to cross-channel ferries plying passengers and goods between the UK and mainland Europe. The waters around the English Channel are teeming with life. A diverse range of marine life-from seahorses inhabiting shallow seagrass beds to the playful dolphins quite often spotted off the coast to a variety of fish species like bass, mackerel, and sole-abounds here. The seabed in this area is characterized by a complex topography of chalky cliffs, sandbanks, and rocky outcrops. These underwater features not only provide habitats for marine organisms but also play a crucial role in influencing the movement of water.

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

The coastal currents near Folkestone result from a combination of many different factors. Tidal forces are one of the dominant influences. The English Channel is subject to semi-diurnal tides, where there are two high tides and two low tides in a day. These tides can cause big changes in water level, with the resulting tidal currents reaching 3-4 knots in certain areas. High tide forces the water towards the shore, washing in nutrients and sediment, beneficial to the marine ecosystem in that area. At low tide, the water pulls back, revealing the intertidal zone, and a dynamic environment for the shore-dwelling organisms.

The other major contributing factor involves the wind. Dominant south-westerly winds push surface waters toward the coast, making coastal currents stronger. This can also build up waves from these winds interacting with currents and creates an even more complicated flow pattern. On the other hand, the northerly winds could push the water away from the shore. The irregular coastline contains bays, headlands, and coves which make the currents diverge and converge. Such underwater features as sandbanks and rocky outcrops further complicate the pattern of currents. These naturally act like barriers or channels in the bottom, causing the water to divert and tumbling sections of turbulence and calm. The mixing of water from different sources, such as those from the North Sea and local river outflows, creates density-driven currents that interact with tidal and wind-induced currents.

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

Surface Drifting Buoy Method

Surface drifting buoys are among the easiest to use but efficient tools in observing surface-level currents. These buoys are fitted with state-of-the-art GPS tracking devices. Once they are thrown into the water, they drift with the surface currents. Scientists can track where the buoy goes in real time, and by following its path over a period of time, they can roughly determine how fast and in which direction the surface waters are moving. However, this method is restricted to the upper few meters of the water column and may not be representative of the currents at greater depths.

Moored Ship Method

The moored ship technique consists of mooring a ship in a fixed position off the coast of Folkestone. The current-measuring instruments, including 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. However, this method is limited to one location alone, and the presence of a ship could disrupt the natural flow of water itself, which may affect accuracy.

Acoustic Doppler Current Profiler (ADCP) Method

ADCPs have really transformed the way one measures the currents near the coastlines in Folkestone. They can also estimate the velocity profile of the entire water column, from the surface to the seabed. The ADCPs utilize sound waves in order not to disturb or destroy the measurements; hence, measurement is contact-free. Each operates by sending an acoustic pulse out, measuring back the frequency changes, i.e., the Doppler shifts in the reflection off suspended particulate matter over different depths with flow. This gives a complete picture of the existing structure and thus is very ideal for the study of the present costal patterns that are very complicated in the English Channel near Folkestone.

4. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of the Doppler effect. They transmit high-frequency acoustic pulses into the water. These pulses, when intercepted by small particles in the water-like sediment, plankton, or even bubbles-reflect the acoustic signals back to the ADCP flow meter. If the particles are moving with the water current, there will be a shift in the frequency of the reflected signal compared to the transmitted signal. This Doppler shift is directly proportional to the velocity of the particles relative to the ADCP current meter. Using different Doppler shift measurements at depths in the column of water enables the ADCP to determine depth velocity. Measurement of velocity in different directions via multiple transducers on the ADCP is undertaken to establish even the three-vector dimensions of a flow of water.

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

Equipment Material Reliability

In making high-quality measurements of the coastal currents near Folkestone, the reliability of the equipment materials is paramount. The casing of the ADCP meter should be able to withstand the harsh marine environment of the English Channel. The best material can be a certain type of titanium alloy. High strength imparts resistance to impact from strong water currents, any possible collision with floating debris, and the corrosive nature of seawater. Meanwhile, a low elastic modulus offers flexibility with low risk from mechanical damage. Furthermore, very good corrosion resistance can enable long ADCP deployment in seawater without performance degradation.

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

Smaller and lighter, an ADCP is easier to install and operate whether from a small research vessel, on a buoy, or on the seabed. It has much less impact on the natural flow of water and thus provides far more accurate results. Low power consumption is critical for long-term autonomous monitoring when relying on battery-powered systems. The low cost of ADCPs allows for an en masse deployment, a configuration necessary to comprehend the complex pattern of coastal currents around Folkestone.

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

Based on Usage

• Shipborne ADCP: This is perfect for real-time current information over a ship's route near Folkestone. It can be used for oceanographic surveys studying the general circulation in the English Channel near the town and for optimizing shipping routes.
• Bottom-mounted ADCP: Suitable for long-term, fixed-point monitoring of the currents at the seabed. This is valuable in studying long-term trends in the coastal currents, for example, studying the impact of climate change on the local marine ecosystem.
• Buoy-mounted ADCP: More suited for measurement of the currents at surface levels over an extended area of water, which would be accompanied by the drifting of the buoy itself. In addition, this makes it quite effective in terms of the comprehension of the surface current's spatial variation and its interaction with open English Channel waters.

Water Depth Based

• 600kHz ADCP: For water depths of up to about 70m, this will be very appropriate to give high-resolution measurements in the relatively shallow waters off Folkestone.
• 300kHz ADCP: Suited for water depths of about 110m, it can be helpful for places that could have slightly deeper areas in the English Channel off the town.
• 75kHz ADCP: For deep-water applications. The English Channel is not that deep for most parts around Folkestone, but this could be useful for studies relating to the deeper-layer currents or for areas with deeper channels. It has the capability of measuring currents up to 1000m.

There are some very well-known brands in the ADCP global market: Teledyne RDI, Nortek, and Sontek. For those looking for a cheaper solution, the China Sonar PandaADCP made of all-titanium alloy is outstanding in price vs. quality. You can see it at (https://china-sonar.com/).

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