How to Measure the Coastal Currents of Exmouth

1. Where is Exmouth?

Exmouth is a quaint seaside town in Devon, England, along the southern coastline on the border of the English Channel. Its position has created a long-established and deep-rooted relationship with the sea that has greatly affected its history, economy, and lifestyle of the residents.

Exmouth has an illustrious past. It boasts a history embedded in fishing, trade, and tourism. The buildings in Exmouth are a combination of old - fashioned English seaside character and contemporary designs. Within the town center, there are stone - built, old - fashioned houses with typical features. Such houses usually feature thick, strong walls, small - framed windows, and tiled roofs, radiating an old - fashioned English seaside charm. The coastal region boasts modern promenades, hotels, and restaurants to cater to the massive influx of tourists who throng annually. Along the main roads, there are contemporary shops, cafes, and boutiques catering to both tourists and local residents.

The locals of Exmouth live close to the sea. Fishing has been a traditional occupation passed down through generations. Although the size of the fishing industry has varied over history, there remain some local fishermen who set out from the harbour. They bring back catches of mackerel, cod, and other shellfish. The harbour is not only a focus for fishing but a popular haunt for locals and tourists alike to take boat trips. People can unwind in the fresh sea air, see seabirds flying overhead, and be rewarded with picturesque views of the English Channel.

The sea and beaches at Exmouth are extremely significant to the local ecosystem. The English Channel waters here abound with a diverse marine fauna. Seals can often be seen on sandbanks, and seabirds such as gulls, terns, and cormorants can often be seen. The seabed is topographically intricate with sandy parts, individual rocky outcrops, and channels under water. These offer a rich biodiversity and play an important role in the transport of the water.

2. What's the State of the Coastal Currents Off Exmouth?

The coastal currents off Exmouth are regulated by a number of factors. Forces due to tides are a major force. The English Channel experiences semi-diurnal tides with two highs and two lows per day. The tidal range is not constant, and the tidal currents that ensue become as much as 2 - 3 knots in places, especially near the mouth of small inlets or around headlands. Water surges up onto the beach at high tide, bringing nutrients and sediment from the open ocean. This enhances the local marine environment, providing food and shelter for numerous sea creatures. At low tide, the water recedes, and the intertidal zones are exposed, revealing tiny crabs, sea anemones, and other types of seaweed.

Wind is also a significant factor. Prevailing south - westerly winds can push surface waters onto the coast, strengthening the coastal currents. They also create waves that mingle with the currents, generating a more complicated flow pattern. The northerly winds may drive the water offshore. The configuration of the Devon coastline with headlands and bays and the unusual features of the south-west English coast causes the currents to converge and diverge in different areas. The rocky outcrops and submerged sandbars make the current flows even more complicated. These can be barriers or conduits, diverting the flow of water and creating areas with calm or turbulent water. Further, the input of freshwater from small local streams can affect local currents. The freshwater is denser than seawater and constitutes a surface layer and drains away to the sea, combining with the tidal and wind - driven currents.

3. Monitoring the Exmouth Coastal Water Flow

Surface Drifting Buoy Technique

Surface drifting buoys are a simple yet efficient way of observing surface - level currents at or near Exmouth. GPS or satellite - based tracking devices are attached to the buoys. As they are sent into the water, the surface currents push them along. Scientists can track their trajectory over time. By observing the trajectory of the buoy, they can estimate the speed and direction of the surface water. This method is limited to the upper few meters of water. It might not be what really happens in the deeper parts of water, where the currents may be different according to temperature and salinity differences.

Moored Ship Method

In the ship-moored technique, a ship is moored at a specific position near Exmouth's coast. Then, current-measuring instruments like electromagnetic current meters are deployed. These instruments are able to measure the movement of water at different depths. They provide a very accurate vertical profile of the velocity and direction of current. However, this method is restricted to a single location. Also, the ship's presence can actually interfere with the natural flow of water. The hull of the ship and how it is moored can cause turbulence in the water, which can impact the precision of the measurements.

Acoustic Doppler Current Profiler (ADCP) Method

ADCPs have transformed the measurement of coastal currents off Exmouth. They are able to measure the velocity profile of the entire water column from the surface down to the seabed. ADCPs quantify water flow non-intrusively with the sound waves. They emit acoustic pulses and calculate the Doppler shift of the backscattered signals off suspended matter in the water, such as sediment, plankton, or small bubbles. From this, they calculate the current velocity at different depths. This gives a general image of the current structure, and is therefore extremely well suited to exploring the complex coastal current dynamics off Exmouth.

4. What is Needed for High-Quality Measurement of Exmouth Coastal Currents?

Equipment Material Reliability

Equipment material reliability is most critical for high - quality measurement of the coastal currents off Exmouth. The casing of the ADCP current meter needs to be made of a material that is robust enough to withstand the harsh marine environment of the English Channel. A titanium alloy would be a great choice. Its high strength allows it to survive strong water currents, collisions with floating debris, and the corrosive nature of seawater. Its low elastic modulus makes it flexible and thus resilient to mechanical damage. In addition, its superior corrosion resistance allows the ADCP current profiler to be submerged in water for extended periods of long-term monitoring without significant degradation.

Small Size, Light Weight, Low Power, and Low Cost

It is easier to install and operate a small and light ADCP meter. You can attach it to a small research ship, place it on a buoy, or place it on the seafloor. It also has a less disturbing influence on the natural flow of water, leading to more accurate measurements. Low power consumption is essential for extended autonomous monitoring, especially when it comes to the use of battery - driven systems. Low-cost ADCP allows for bulk deployment. We need this so that we will be able to fully grasp the complex coastal current patterns around Exmouth. We can see better how the currents vary around the area with other ADCPs planted in other positions.

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

Based on Application

• Shipborne ADCP: Applicable for obtaining real-time current data along a vessel track near Exmouth. It can be used for oceanographic surveys, studies on the overall circulation in the area, and for optimization of shipping routes, if any, in the region.
• Bottom-mounted ADCP: Ideal for long - term, fixed - point observation of the seabed currents. This is useful for examining long - term trends in the coastal currents, e.g., the effect of climate change on the local marine ecosystem.
• Buoy-mounted ADCP: Well-suited to monitor surface-level currents throughout a wide area as the buoy is transported with the water. It helps in understanding the spatial variation of the surface currents and the way the coastal waters interact with the open English Channel.

Based on Water Depth

• 600kHz ADCP: Ideal for water depths of up to approximately 70m, providing high-resolution measurements in the comparatively shallow water off Exmouth.
• 300kHz ADCP: Ideally suited to water depths of approximately 110m, which can be used for slightly deeper areas in the English Channel near the town.
• 75kHz ADCP: Designed for deep - water applications. Even though the waters near Exmouth are generally not extremely deep, it can be used for studies related to the deeper - layer currents or for areas with deeper channels, capable of measuring currents at depths of up to 1000m.

There are several of the most popular ADCP brands in the global market, such as Teledyne RDI, Nortek, and Sontek. For someone who wishes to be thrifty, China Sonar PandaADCP, all-titanium alloy, is a compromise between price and quality. You can learn more from it at (https://china-sonar.com/).

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