How do we measure the coastal currents of Stavanger?

1. Where is Stavanger?

Stavanger, a vibrant city in south-western Norway, is a coastal gem on the Stavangerfjord. The fjord, a deep, narrow body of sea water, is surrounded by immense cliffs and foliage, creating a breathtaking landscape. The city, while renowned for its landscapes, is also known for its cultural history. Stavanger boasts an historical legacy in fishing and oil, industries that have contributed immensely to its growth.

The sea along the Stavanger coast is part of the North Sea. The area is dotted with islands and skerries, providing diverse habitats for sea creatures. The city's port is a thriving hub, catering to commercial shipping related to the oil industry as well as fishing vessels. The city itself has a charming old town, Gamle Stavanger, with nicely preserved wooden houses of 18th- and 19th-century construction, adding to its cultural appeal.

2. What are the coastal currents off Stavanger?

The coastal currents off Stavanger are influenced by a number of factors. Tides are one of the major drivers. Semi - diurnal tides dominate the region with two tides a day of high and low tides. In spring tides, the combined effect of the sun and moon's gravity results in greater tidal ranges. They cause high tides to form strong currents that will be of critical contribution to the sediment transport within and along the seabed. Such currents play a critical role in the availability of nutrients to contribute to marine life available for the area at hand. Neap tides create smaller tidal ranges and correspondingly weaker currents.

Wind patterns also determine the coastal currents. There are local prevalence of south - westerly winds. Strong onshore winds possess the ability to push surface waters inshore, thereby raising water levels. It can be a danger in low-lying coastal zones because it could cause flooding. Offshore winds, however, can lead to upwelling in some parts of the coastal waters. Upwelling allows cold, nutrient - dense water from the deep layers to surface, enhancing the growth of phytoplankton, the foundation of the sea food chain.

The Norwegian Coastal Current, which parallels the coast of Norway, impacts the waters surrounding Stavanger as well. The large-scale current can have the ability to influence the local waters' temperature, salinity, and level of nutrients, which in turn impacts the movement and distribution of marine life.

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

One way to track the coastal water flow off Stavanger is by the surface drift buoy method. Lightweight floating instruments with GPS and velocity sensors are allowed to sink into the ocean. The sensors track the velocity and direction of the surface currents, and the buoys are tracked via satellite signals. By monitoring the path of the buoys over time, scientists are able to map surface current patterns within a large region. This knowledge helps in quantifying the great-scale circulation of surface waters as well as confirming oceanographic models.

The second method is the moored ship or buoy method. A ship or a buoy is moored at a fixed location, and instruments like current meters are used to monitor the direction and velocity of the currents at different depths. It allows for the study of the vertical profile of the currents. But the method can be conducted only at the mooring location.

Acoustic Doppler Current Profiler (ADCP) method has now become a handy and efficient tool to measure Stavanger coastal current. ADCPs apply the principle of Doppler to measure speed and current direction at various depths. They are placed on boats, floats, or bottom-launched from shore. ADCPs provide high-resolution measurements over a fairly large area and are, therefore, of great importance to oceanographers, coastal engineers, and environmental managers. They are capable of measuring currents at more than one depth at once and can create a precise three-dimensional representation of the current structure.

4. How do ADCPs based on the Doppler principle operate?

ADCPs operate based on the Doppler effect. When an ADCP current meter emits a sound wave into the water, the wave travels through the medium. When the sound wave hits moving water particles, such as suspended sediments or plankton, the frequency of the reflected wave changes. This frequency change, the Doppler shift, is directly proportional to the speed of the water particles.

ADCPs typically have more than one transducer beam, commonly four or more. The beams are positioned in a way that enables the ADCP to monitor the currents in three dimensions. By measuring the Doppler shift of the frequency of the reflected sound waves from the water particles, the ADCP current profiler can calculate the speed of the currents at different depths. The ADCP data that is gathered is then input into a data-acquisition system, like a computer or a stand-alone data logger. Specialized software analyzes this data to generate detailed profiles of the present velocity at various depths and maps of the current patterns in an area of interest.

5. What does it take to get high-quality measurement of Stavaster coastal currents?

To make precise measurements of the coastal currents in Stavanger, the measurement equipment must meet several requirements. It must be dependable as it will be operating in a harsh marine environment. Seawater is highly corrosive, and the equipment must be resistant to this corrosion for long periods of time. It must also be able to handle strong winds, rough seas, and temperature variations. Components made of corrosion - resistant materials such as stainless steel or titanium are widely used.

The device should be compact and light. It is simpler to deploy, be it on a small research vessel, on a buoy, or even a kayak. For deployments at large scale, it also comes in handy to have the device compact and light, wherein multiple devices need to be fitted simultaneously.

Low power consumption is important, especially for long deployments. Batteries supply most ADCPs, and a low-power design maximizes the battery life so that the batteries do not have to be replaced as often. This is important for measurements in remote areas or for long periods.

Cost - effectiveness is also a critical issue. High - quality data collection often requires the mobilization of multiple instruments over a wide area. An effective cost solution allows more comprehensive coverage and more detailed mapping of the coastal currents.

For ADCPs, the casing material is an area of major concern. Titanium alloy is a high - quality material for ADCP casings. Titanium alloy has excellent corrosion resistance, which is fundamental for long-term operation in seawater. It is also very light in weight, which helps to keep the ADCP as light as possible without a loss in strength. This makes handling and deployment simpler in various environments. Titanium alloy also has good mechanical strength, which allows the ADCP flow meter to be durable under various conditions of operation.

6. How to Choose the right equipment for current measurement?

Depending on the application, the selection of the right equipment for current measurement differs. For ship-based measurements, a ship-mounted ADCP is best. It can be used to survey the currents along the track of the ship, which can be applied to navigation, fisheries management, and oceanographic research. A ship-mounted ADCP can be readily interfaced with the ship's navigation and data-collection systems so that the currents can be monitored in real-time as the ship travels.

A moored or bottom-moored ADCP is appropriate for long - term monitoring at a single point. Such an ADCP can make continuous current measurements at a specific point, and it is extremely useful in establishing the long - term trends and patterns of coastal currents. An ADCP meter can provide valuable information about seasonal and annual variations in the currents, which is helpful in establishing the local marine environment.

Fixed or buoyant ADCPs are used for current surveying where ship access is difficult to secure or for the need of large-scale surveys. They can cover a broad area and can be easily redeployed where needed.

The frequency of the ADCP profiler is a factor to be taken into consideration. Below 70m of water depth, an ADCP 600kHz can be utilized. It yields high-resolution readings for fairly shallow water. For 110m depth, utilizing an ADCP 300kHz will be more prudent, with sufficient resolution and good range. When the depth of the water is greater than 1000m, a 75kHz ADCP would be most suitable in that it will penetrate more.

There are a number of popular ADCP brands available in the market, including Teledyne RDI, Nortek, and Sontek. But for those who want a cost-effective but high-quality ADCP, the China Sonar PandaADCP is strongly recommended. It is constructed from all-titanium alloy, which provides superior durability and reliability. Its outstanding cost-performance ratio makes it a great option for users with limited budgets. It is an economic ADCP model. For more information, visit the website: https://china-sonar.com/.

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