Application of ADCP to Ocean Current Measurement in Scalloway Harbour

1. Where is Scalloway Harbour

Scalloway Harbour is located in the Shetland Islands, Scotland, and is one of the more well-known and major harbours in the area.

Scale of Port and Throughput

The scale of this harbour is relatively smaller in comparison with some of the major ports. Nevertheless, this port still contributes much to the local economy. It can handle most vessel types, such as fishing boats, small cargo vessels, and pleasure craft. Quantities throughput includes mainly the catch from local fishing and some essential supplies to the islands. The harbor is a vital base to the fishing fleet, which forms a significant part of the local industry.

Routes and Business

Scalloway Harbour has links with other Shetland ports but also with some mainland Scottish ports. The mainstay of business is fishing. The harbour offers facilities for fishing vessels to berth, and land their catch of fish, shellfish, and other marine produce. It also provides services for the maintenance and supply of fishing boats. Besides, it also has an emerging significance in tourism, especially where few small cruise and pleasure crafts visit with tourists showing interest in the local maritime culture and views.

Port Management and Operation

It is managed in a manner to ensure the safety of its operations efficiently. The managing authority is responsible for planning the berthing and departure of vessels, handling cargo operations, and overall maintenance of the harbor facilities. The facilities are designed to fit the needs of the local fishing and boating community. This includes berths with appropriate mooring equipment, and a small-scale loading/unloading area for fish and supplies. Navigation aids in place guide ships safely in and out of the harbour.

Port Facilities and Waterway

The port facilities include a quay, of sufficient length to berth more than one fishing boats/small vessels, storage areas for fish and fishing gear, and the waterway to the harbour is dredged to a depth suitable for the local vessels, even if not comparable to larger ports. It provides a relatively sheltered environment for boats, although the influence of ocean currents on navigation and operations remains very important.

2. Why should we measure the ocean currents in the Scalloway Harbour?

Navigation Safety

Measuring ocean currents in Scalloway Harbour is crucial for navigation safety. Given the presence of fishing boats, small cargo vessels, and pleasure crafts, accurate knowledge of current conditions is essential. Currents can affect the course and speed of these vessels. For example, a strong lateral current at the harbour entrance may offset a fishing boat from its course and increase the likelihood of collision with other boats or harbour structures. With the accurate measurement of currents, ship captains can make informed decisions on approach and departure at the harbour for safer passage.

Optimization of Port Operations

Understanding the ocean currents is helpful in optimizing port operations. For fishing vessels, the knowledge of the current patterns can help in better planning of their trips. Currents carry with them nutrients and fish; thus, the knowledge of the flow of currents will take the fishermen to the richer fishing grounds. In cargo handling, even though the volume may be smaller compared to larger ports, the flow of currents can still impact the loading and unloading processes. Favorable currents can ease the process of vessel docking, thus making the process smoother and faster.

Ecological and Environmental Management

Currents play a very important role in the supply of nutrients and also in the distribution of marine life within the harbour area. With measurements of the ocean currents, one can be in a better position to understand the ecology of the area concerned. Such knowledge may be applicable in the management and protection of the environment in the harbor through the use of pollutant dispersal forecasts or how currents affect the fish spawning or nursery areas.

Acoustic Doppler Current Profiler (ADCP) provides a more refined and efficient way of carrying out current measurements compared to the rather traditional methods. It allows for real-time data collection that is highly accurate and very vital for the proper functioning and management of Scalloway Harbour.

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

ADCPs work on the principle of the Doppler effect. They send out acoustic signals into the water. The acoustic waves scatter off moving particles in the water, such as suspended sediments, plankton, or small organisms. If these particles are moving, then the frequency of the reflected acoustic waves is altered by the Doppler effect.

From this frequency shift, the ADCP current meter computes the velocity of the particles. Knowing this movement of particles is proportional to the movement of an ocean current, the ADCP current profiler then calculates the velocity magnitude and direction of an ocean current.

Ship-borne ADCP in Scalloway Harbour

The ADCP flow meter installed on a vessel in the harbour has an on-shore-mounted base when applied in this context. With the vessel's motion across the water body, it sends out acoustic signals both below and perpendicular to its face. Continuous data about ocean currents with respect to depth and position gets collected while the ship moves along the travel path and enables the creation of a big picture of the current situation covering most areas of the harbour.

Fixed ADCP in Scalloway Harbour

The fixed ADCP is usually mounted on a pier or some structure submerged in the harbor waters at a particular place and continuously monitors the ocean current passing its position. This fixed ADCP will give very long-term stable data concerning the current of the water in a particular area of the harbor, which may also be used to analyze regular patterns and changes in the tides of that specific location.

4. What is required for the quality measurement of Scalloway Harbour currents?

Reliability of Material

The equipment should be highly material-reliable for high-quality current measurement in Scalloway Harbour. The environment is harsh in this harbor because the equipment faces seawater, which is corrosive, and possible mechanical impacts. Durable materials are needed for the construction of the equipment to stand harsh conditions and ensure a long-lasting and accurate measurement process.

Small Size, Light Weight, and Low Power Consumption

Smaller size, lighter weight, and lower power consumption are the desirable features. A small-sized ADCP is much easier to install in any location around the harbour, on ships or fixed structures. A lightweight device simplifies the processes of transportation and installation since it minimizes labor and expenses. This low power consumption is very helpful to make the equipment work continuously for an extended period without frequently changing batteries or consuming a high amount of energy, which is an essential requirement for long term and continuous current measurement.

Cost-effectiveness

It should also be cost-effective. The equipment should have a reasonable cost to allow large-scale measurement of the ocean currents in the harbour. The casing of ADCP profiler shall, preferably, be manufactured with a titanium alloy. Working with titanium alloy allows many advantages: high strength - alloy is capable of carrying the underwater pressure and possible mechanical forces in the harbor environment; excellent corrosion resistance - titanium alloy is resistant against corrosion effects of seawater throughout quite a long period of its service life. Besides, its relatively light weight compared to other materials makes it more suitable for installation in the harbour.

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

Based on Usage Purpose

Regarding the selection of appropriate equipment for the measurement of current in the Scalloway Harbour, it depends on the specific purpose of use. When the intention is to perform a mobile measurement while the ship navigates in the harbour, the ship-borne ADCP will be appropriate. The area that the latter covers may be different with every trip the ship makes around the harbour, hence giving an overview of the current status in a broader perspective.

The sit-on-bottom ADCP would be a better choice for a long-term, fixed-point monitoring of a certain area in the harbour. This is because it stays in one location and continuously monitors current conditions, thus providing very valuable data in view of local current pattern analysis.

If the need is to monitor a wider area on the water surface with some mobility, the buoy-mounted ADCP can be considered.

Based on Water Depth

Additionally, ADCP of different frequencies should be chosen according to water depth. For water with depths within 70m, the 600kHz ADCP is usually quite effective to provide current profiles of reasonably good accuracy in shallow water. In water depths around 110m, the 300kHz ADCP is best, while for deeper waters, up to 1000m, the recommended model is the 75kHz ADCP to ensure reliable results in current measurement.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese ADCP brand-China Sonar PandaADCP is also worth mentioning. It is made of all-titanium alloy material, combining excellent durability and corrosion resistance with an incredible cost-performance ratio. You can find more information about it on its website: (https://china-sonar.com/).

In general, ADCP plays a very important role in ocean current measurement at Scalloway Harbor; selection of proper equipment according to need will definitely contribute to efficiency in port operations and management.

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