How to Measure the Coastal Currents of Copenhagen

1. Where is Copenhagen?

Its capital city, Copenhagen, sits on the eastern edge of Zealand island where Øresund Strait intersects it. Situated strategically, separating the Baltic Sea from Kattegat and the North Sea, the city has been a strong maritime city with a history spanning more than a thousand years. City growth has had a close connection with the sea, which affected its economy, culture, as well as citizens' daily lives.

Copenhagen is well-off in that it has a very rich history. It began as a fishing village founded by Vikings but nowadays is a booming city. Copenhagen is an architecturally designed city in which one can see in its appearance, medieval warmth, Renaissance magnificence, and modern chic. Dominating the heart of Copenhagen is the 17th-century Rundetårn (Round Tower), standing as witness to Copenhagen's scientific and astronomical tradition. The Nyhavn canal quarter is lined with brightly colored 17th - and 18th - century townhouses, which once housed sailors and merchants. Now the buildings contain cafes, restaurants, and shops that welcome visitors from all over the globe. The modern waterfront neighborhoods, such as the Copenhagen Harbour, are characterized by high - end architecture, symbolized by the iconic Opera House and the innovative Amager Bakke waste - to - energy plant.

The Copenhageners have a strong affinity with the sea. Even though commercial fishing has decreased in recent years, the Copenhagen port is still an important connection for global trade. The city is also a port of call for cruise ships, which takes tourists to the city from all over the world. Sailing, swimming, and kayaking are some of the most popular sports of the residents. The city commemorates its sea-faring history in a number of festivals throughout the year.

The sea off the coast close to Copenhagen is an important part of the local ecosystem. The Øresund Strait holds a rich mix of sea life, including seals, porpoises, and many species of fish. The ocean floor itself is a diverse terrain with sandy and muddy bottoms and ridges and channels under the water. These give a dense support matrix for biodiversity and also help significantly in water movement.

2. What is the State of the Coastal Currents around Copenhagen?

The coastal currents around Copenhagen are influenced by a range of factors:

• Tidal Forces: The Øresund Strait experiences semi-diurnal tides with a tidal range of 0.5 to 1.5 meters. The generated tidal currents range from 1 - 2 knots in certain areas, specifically around the constricted parts of the strait. During high tide, water also flows into Copenhagen Harbour from the open sea with sediment and nutrients. This brings inshore marine conditions to feeding grounds and refuge grounds for millions of marine creatures. During low tide, water leaves Copenhagen Harbour, and exposed intertidal areas are left behind, leaving miniature crabs, sea anemones, and other seaweeds exposed.
• Wind Patterns: The westerly prevailing winds are capable of forcing the surface water onto the coast and hence increase the coastal currents. The winds also generate waves that interact with the currents to produce a more complex pattern of flow. The water can be forced away from the coast by easterly winds. Bayment, headland-dominated features of the Zealand coast combined with the Øresund Strait idiosyncrasies and consequently result in converging and diverging currents in different sections.
• Freshwater Inputs: The city of Copenhagen is drained by a number of small rivers and streams that flow freshwater into the Øresund Strait. This freshwater, due to its lower density compared to seawater, creates a surface layer and moves seaward, mixed with the tidal and wind - driven currents. The occurrence of this freshwater may also influence the coastal waters' salinity as well as temperature, which consequently might influence the current patterns.

3. Monitoring the Coastal Water Current of Copenhagen

Surface Drifting Buoy Method

Surface drifting buoys with GPS or satellite-based tracking gear are a simple but effective means of monitoring surface-level currents around Copenhagen. Once released in the water, surface currents carry these buoys. Researchers can track their path over a period of time and observe the buoy's track to estimate surface water speed and direction. The method is suitable for only the upper few meters of the water column and may not represent deeper - layer currents, which could be influenced by salinity and temperature gradients.

Moored Ship Method

In the moored ship technique, a ship is moored off Copenhagen's coast at a fixed point. Current meters, such as electromagnetic current meters, are then lowered down. Such instruments have the ability to measure the flow of water at several depths, providing an extensive vertical profile of the direction and speed of the current. But such a technique is constrained to some extent and the ship presence might even disrupt the free flow of water, generating turbulences which would distort the readings.

Acoustic Doppler Current Profiler (ADCP) Method

ADCPs have revolutionized measurement of coastal currents in Copenhagen. These systems can measure the water column velocity profile from the sea surface to the bottom of the sea. ADCPs use sound waves to quantify the water flow without penetrating the water. They emit acoustic pulses and measure the Doppler shift of the backscattered signals of suspended particles in the water, such as sediment, plankton, or minute bubbles. They are able to infer the current velocity at different depths and hence give a comprehensive picture of the current structure. This renders ADCPs highly suitable for study of the complex coastal current patterns near Copenhagen.

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

Equipment Material Reliability

Equipment material reliability is paramount in high-quality measurement of the coastal currents near Copenhagen. The ADCP current meter should be housed in a material that can withstand the harsh marine environment of the Øresund Strait. Titanium alloy is a good option because it is very strong, capable of withstanding the power of strong currents of water, chances of collision with floating wreckage, and the corrosive properties of seawater. It has low elastic modulus, which gives it some elasticity, so it won't be damaged easily by mechanical stress. Besides that, its fine corrosion resistance assures that the ADCP current profiler can last in the water for long stretches of monitoring with little degradation.

Portable Size, Low Weight, Reduced Power Consumption, and Low Expense

A small and light weight ADCP flow meter is easier to set up and to run. It can be put on a minor research vessel, installed on a buoy, or set on the seafloor with relative simplicity. Such a system is also less interfering with natural water flow, and therefore the measurements are more accurate. Low power consumption is of particular importance for long-term self-sustained monitoring, especially where battery-driven systems are deployed. Low-cost ADCP facilitates deployment at a large scale, as in the case needed to obtain an overview of the complex coastal current regime around Copenhagen. With more ADCPs installed at other locations, we will have an understanding of how the currents vary from location to location in the area.

5. What is the Correct Equipment for Measuring Current?

Depending on Use

• Shipborne ADCP: Appropriate for obtaining current data in real time along a ship track near Copenhagen. It can be used for oceanographic surveys, researching the overall circulation in the area, and shipping route optimization, as Øresund Strait is highly trafficked.
• Bottom - mounted ADCP: Suitable for long - term, fixed - point monitoring of the seabed currents. This is applicable for studying long - term trends in the coastal currents, e.g., the impact of climate change on the local marine ecosystem.
• Buoy-mounted ADCP: Appropriately well-suited to monitor surface-level currents in a wide area as the buoy floats along with the water. Helps in understanding the spatial variability of the surface currents and how the coastal waters exchange with the open Øresund Strait.

Depending on Water Depth

• 600kHz ADCP: Ideal for up to about 70m water depth, providing high-resolution measurements in comparatively shallow water off the coast in and around Copenhagen.
• 300kHz ADCP: Best for about 110m water depth, useful for the slightly deeper areas in the Øresund Strait near the city.
• 75kHz ADCP: Designed for deep-water applications. Although waters along Copenhagen shores are generally shallow, it can be used in the event of studies on currents in the deeper layer or within areas with more extensive channels and has the capacity to measure depths up to 1000m.

There are several well-known ADCP brands available in the global market, such as Teledyne RDI, Nortek, and Sontek. For people who need an economical choice, the China Sonar PandaADCP made of all - titanium alloy is a fair compromise between cost and quality. You can learn more about it at (https://china-sonar.com/).

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