How can we measure the coastal currents of Bournemouth

1. Where is Bournemouth?

Bournemouth is a resort city on the southern coast of England, in the county of Dorset. It enjoys a perfect setting along the shores of the English Channel, where the seven-mile stretch of beaches brings in millions of visitors into the city every year. This seaside location has made it significant to tourism, besides influencing much of its long-standing association with the sea.

It is a relatively modern town compared to its neighbors from other coastal developments. It went to develop extremely fast as a stylish seaside getaway during the 19th century. The building structure in Bournemouth is considered Victorian elegance alongside modern design; the seafront houses Victorian-era hotels and guesthouses, echoing nostalgic moments down to the newer, modern buildings that host shopping malls in the midst of the townsfolk. The ocean means so much to the local community; therefore, water sports are very popular with both locals and visitors alike, such as surfing, paddleboarding, and kayaking. Whereas traditional fishing is not as huge here as it perhaps is in some other coastal towns, the sea plays a vital part in the local economy through tourism-related marine activities.

The beaches of Bournemouth are not only a place for recreation but also a vital part of the local ecosystem. The waters of the English Channel, which are adjacent to these beaches, are home to a large number of marine species. Dolphins and porpoises can often be seen offshore, while the seabed is teeming with several species of fish, such as bream, pollock, and wrasse. The seabed topography comprises sandy bottoms, rocky reefs, and underwater caves, adding to the rich biodiversity in the area and influencing the movement of water.

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

The general setup of coastal currents near Bournemouth results from a complex interplay between a number of factors. Among these, tidal forces are the most important. The tide in the Channel is semi-diurnal; there are two high tides and two low tides each day. The range of tides varies but the resulting tidal current can attain certain speeds of 2 to 3 knots in some places, especially at the mouth of rivers running into the channel or where the channel gives way to constricted waterways. The tide forces water ashore, which adds nutrients and oxygen to benefit marine life at high tide, while at low tide, the water pulls back, exposing intertidal zones, the areas occupied by shore-dwelling organisms.

The second important factor is wind. Dominant south-westerly winds can force surface waters to push towards the coast, adding to the coastal currents. These winds can also give rise to waves interacting with the currents, thereby making the flow pattern far more complicated. Northerly winds can push the water away from the shore. These currents, due to the form of the coastline with gentle curvatures and minor headlands, tend to converge and diverge. The presence of underwater rocky reefs and sandbars further complicates the current patterns. These features may represent barriers or channels for the flow, which provides points of turbulence and calm. In addition to this, other variations within local current patterns occur due to the inflow of freshwater from such local rivers as the River Stour. Freshwater possesses different density compared with sea water, and hence that causes the emergence of the so-called density-driven currents that somehow interact with both tidal- and wind-induced ones.

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

Surface Drifting Buoy Method

Surface drifting buoys represent one of the simplest methods of observing surface level currents. The buoys are fitted with GPS or satellite-based tracking systems. Once they have been put in the water, they drift with the movement carved by the surface currents. By tracing its path with time, and from the trajectory of the buoy, scientists are able to calculate the speed and direction of the surface waters. This method can only be done within the top few meters of the water column and may not reflect the currents further down in the water.

Moored Ship Method

This method of determining the surface waters involves mooring a ship at a selected location near the coast of Bournemouth. Then, current meters, usually electromagnetic current meters are deployed. They can measure water flow at several depths and so provide a quite detailed vertical profile of the velocity and direction of the current. This method, however is limited to one place only, while the presence of the ship may disturb the normal flow of the water and, therefore, falsify the measurements.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCPs have revolutionized the measurement of coastal currents near Bournemouth by measuring the velocity profile of the entire water column from surface to seabed. An ADCP current profiler works non-intrusively with sound waves to measure the water flow. By emitting acoustic pulses and measuring the Doppler shift of the reflected signals from suspended particles in the water, they can calculate the current velocity at different depths. This provides a comprehensive view of the current structure and is very suitable for studies concerned with complicated coastal current patterns in waters around Bournemouth.

4. How do ADCPs using the principle of Doppler work?

Working of ADCPs is based on the Doppler effect. They emit high-frequency acoustic pulses into the water. When these pulses reach small particles in the water-sediment, plankton, or even bubbles-the particles reflect the acoustic signals back to the ADCP current meter. If the particles in the water are moving along with the current, then the frequency of the reflected signal will shift from that of the transmitted signal. This is a Doppler shift, proportional to the velocity of the particles relative to the ADCP. The Doppler shift, at various water column depths, allows the ADCP profiler to determine the water velocities at those depths. A number of different transducers are fitted on an ADCP-measuring components of velocity in different directions. Determination of these may allow calculation of the three-dimensional velocity vector of the flow of water.

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

Equipment Material Reliability

A few of the pertinent factors are listed below: Equipment materials: Equipment materials must ensure high-quality measurements of coastal currents near Bournemouth. The outer casing of ADCP must, therefore, be made from some material that may withstand the heavy marine environment inside the English Channel. Titanium alloy is an outstanding choice. With high strength, it will be able to bear the impact of strong water currents, collision that may possibly happen with floating debris, and the corrosive nature of seawater. Low elastic modulus imparts flexibility to the material and hence reduces chances of mechanical failure. Besides that, its excellent corrosion resistance will allow the ADCP meter to stay deployed in seawater for a long period for monitoring without deteriorating noticeably.

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

A small and light ADCP flow meter promotes ease of deployment and operation in a small research vessel attached on a buoy and laid on the seabed, and it does not impact greatly on the flow of water outside, hence measuring more accurately. Low power consumption is necessary, especially in an autonomous long-duration monitoring relying upon a battery-powered system. A low-cost ADCP will enable a large-scale deployment, which is very much required to understand the complex coastal current patterns around Bournemouth.

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

Based on Usage

• Shipborne ADCP: In this regard, it is ideal for the obtainment of real data on currents along a ship's route near Bournemouth in real time. It can be used for oceanographic surveys, study general circulation in the area and optimization of shipping routes.
• Bottom-mounted ADCP: Suitable for long-term, fixed-point monitoring of the currents at the seabed. This is useful in studying the long-term trends in the coastal currents, such as the impact of climate change on the local marine ecosystem.
• Buoy-mounted ADCP: It is very good at measuring surface level currents over a large area since the buoy will drift with the water. This helps understand the spatial variability of the surface currents and how the coastal waters interact with the open English Channel.

Based on Water Depth

• 600kHz ADCP: Shallower water, say up to about 70m, would provide high-resolution measurements in the relatively shallow waters near Bournemouth.
• 300kHz ADCP: For water depths of around 110m, it will be useful for areas with slightly deeper sections in the English Channel off the town.
• 75kHz ADCP: For deep-water applications. Even though the waters around Bournemouth are not generally deep, it can be used for studies that require the deeper-layer currents or for areas that have channels of greater depth. Capable of measuring currents to depths up to 1000m.

Some of the well-known brands of ADCP in the world market are Teledyne RDI, Nortek, and Sontek. If you want to have a reasonably priced ADCP, then the all-titanium alloy Sonar PandaADCP made by China is worth considering for value and quality. You can check it out at https://china-­sonar.com/.

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