How to measure the coastal currents of Hastings

1. Where is Hastings?

Hastings is an historic coastal town situated on the south - east coast of England in the county of East Sussex. With its blend of historical charm and natural beauty, it faces the English Channel in a prime position. The place has gained such importance due to this strategic location since time immemorial and is attached with the sea since ages.

This town has quite an eventful history and is mostly known for the Battle of Hastings in 1066, one battle that drastically altered the course of English history. Most of the architecture contained within Hastings shows evidence of a very long-standing past. The Old Town contains remarkably well-preserved medieval-style buildings with narrow, winding streets lined with timber-framed houses. These stand in contrast to more modern structures that have been built over the years. The local community has a long history related to the ocean. Fishing has traditionally been a vital occupation for several centuries, and the Hastings Fishermen's Museum illustrates the town's long historical fishing tradition. Even today, a small but active fishing fleet operates from the beach-launched boats in the old fishing quarter.

The beaches at Hastings are nothing but part of the local ecosystems that attract lots of tourists here. The English Channel waters here have a myriad of marine lives. One finds seals often sitting offshore on boulders in the water; there are so many fish-species such as mackerel, herring, and different types of fish like sole who call the bottom of the ocean their home. It also comprises a sandy seabed with rocky reefs and underwater ledges that further allow rich biodiversity but at the same time influence water movement.

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

Coastal currents near Hastings influence a rather complex interplay of several different variables. Among all, tidal forces are the main factor. The tide in the English Channel is of a semi-diurnal type. It means there are two high tides and two low tides every day. Various tidal ranges may be considered, together with tidal currents resulting up to 2 - 3 knots in some locations, such as near the entrance of the River Rother discharging into the Channel. High tide forces water ashore, bringing with it nutrient-rich water and sediment from the open sea. At low tide, the water pulls back, exposing the intertidal zones and their many shore-dwelling organisms.

Wind is also an important factor. Dominant south-westerly winds can push surface waters toward the shore, augmenting the coastal currents. These winds also create waves that interact with the currents to give a more complicated flow pattern. The northerly winds will push the water offshore. Converging and diverging of the currents, due to a coastline shape of bays and headlands with the particular arrangement of the old fishing harbor, adds to the complication. There are also underwater rocky reefs and sandbars which further complicate the current patterns. These may act as either obstructive features or channels, therefore deflecting the flow of water and creating areas of turbulence and still water. Another modifying factor is the input of freshwater from the River Rother, since this will have an impact on the local current patterns. The freshwater is less dense than the sea water, and density - driven currents will develop which will interact with the tidal and wind - induced currents.

3. How to observe the Hastings coastal water flow?

Surface Drifting Buoy Method

Surface drifting buoys are one of the easy and practical means to observe the surface-level currents. The buoys are prepared with GPS or satellite-based tracking systems. These buoys, once dropped into the water, drift with the surface currents. By tracking the path of a buoy, scientists can estimate how fast and in what direction the surface waters are moving. However, this technique gives information only about the top few metres of the water column and may not be representative of deeper currents.

Moored Ship Method

In the moored ship method, a ship is anchored at a specific location near Hastings' coast. Presently, the measuring instruments are deployed, including electromagnetic current meters. These can measure the water flow at varied depths, offering a highly resolved vertical profile in the current velocity and direction. However, this technique is applicable to only one location, with the added disadvantage of the ship itself disturbing the natural water flow, which may be reflected in the measurement results.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCPs have revolutionized the measurement of coastal currents around Hastings by their ability to measure the velocity profile of the whole water column from surface to seabed. These instruments use sound waves to make non-intrusive measurements of water flow. They can estimate 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 gives a complete representation of the structure that exists and, thus, is perfectly suited for a study of the elaborately patterned currents in waters off Hastings.

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

The ADCPs operate based on the Doppler effect. They emit high-frequency acoustic pulses into the water. These pulses, as they travel through water, get reflected back through the small particles in the water-sediment, plankton, or even bubbles-to the ADCP. If these particles are moving with the current of water, due to Doppler shift there would be a frequency shift in the reflected signal with respect to the transmitted signal proportional to the velocity of the particles relative to the ADCP flow meter. By measuring the Doppler shift at different depths in the water column, the ADCP is able to calculate the velocity of the water at those depths. An ADCP does this with a set of multiple transducers which measure the different components of the velocity vector, so the three-dimensional velocity vector of the flow of water is obtained.

5. What's required for high-quality measurement of Hastings coastal currents?

Reliability of the Equipment Material

In its turn, for the high-quality measurement of the coastal currents near Hastings, the reliability of the equipment materials is crucial. The casing of the ADCP current profiler should be made from the material resistant to extreme conditions of the marine environment of the English Channel. Titanium alloy will be ideal. Its high strength is enough to withstand strong water currents, collision with floating debris, and the corrosive action of seawater. Its low elastic modulus imparts flexibility on the material such that mechanical damage due to elastical stress would be minimal. Besides, its excellent corrosion resistance allows the ADCP meter for long-term deployment in seawater without significant deterioration. The instrument shall be compact in size and lightweight for easy transport, with low power consumption and at a very low cost.

A compact and lightweight ADCP current meter is easier to install and operate, whether on a small research vessel, attached to a buoy, or placed on the seabed. It also has less impact on the natural water flow, leading to more accurate measurements. Low power consumption is important for long-term autonomous monitoring, especially when relying on battery-powered systems. A low-cost ADCP enables large-scale deployment, which, in turn, is considered necessary for adequately understanding the complicated coastal current patterns around Hastings.

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

Based on Usage

• Shipborne ADCP: This will be applicable for real-time current data along a ship's route near Hastings. It can be used for oceanographic surveys, studying the general circulation in the area, and for optimizing shipping routes.
• Bottom-mounted ADCP: This is fine to go for long-term fixed-point monitoring of the currents at the seabed, being very useful in studying the long-term trends of the coastal currents, like the influence of climate change on the local marine ecosystem.
• Buoy-mounted ADCP: Ideal for monitoring the surface-level currents over a large area while the buoy drifts with the water. It provides insight into the spatial variability of the surface currents and how the coastal waters interact with the open English Channel.

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 Hastings.
• 300kHz ADCP: Suitable for water depths of about 110m, which can be useful for areas with slightly deeper sections in the English Channel off the town.
• 75kHz ADCP: For deep-water applications. The waters around Hastings are not usually very deep; this instrument, however, can be used in the study of the deeper layer currents or when channels in areas of study are deeper and is capable of current measurements up to 1000m.

There are some famous brands of ADCP in the market, such as Teledyne RDI, Nortek, and Sontek. For those who want to save money, the China Sonar PandaADCP, made of all-titanium alloy, is a great balance of quality and price. You can learn more about it at [https://china-sonar.com/].

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