How to Measure Coastal Currents of Dalian

1. Location and Geographical Features of Dalian

Dalian is a coastal city situated at the southern tip of the Liaodong Peninsula in Liaoning Province, bordering the Yellow Sea and the Bohai Sea. As one of the very important port cities in China, it is also a well-known tourist destination.

Dalian represents a warm-temperate monsoon climate: it has comparatively mild winters and cool summers due to sea moderation. The rainfall is moderate, supporting a wide range of vegetation from forests to coastal shrubs.

Dalian has a very long and indented coastline, with a lot of beautiful bays, sandy beaches, and rocky shores. The seas around it are very helpful for the economy, culture, and transport of this city. The topography of the seabed around Dalian is complicated: shallow coastal parts alternate with submarine ridges and deeper areas further from the coasts.

2. The Situation of Coastal Currents near Dalian

The coastal currents near Dalian are influenced by many factors.

Monsoon Climate

The huge factor is the monsoon climate. The southeast monsoon during summer may push the surface waters in one or another direction, determining the direction and velocity of the coastal currents. This is very favorable for the activities related to sailing and fishing. During winter, the pattern of the current will be altered by the northwest monsoon. Winds at this period of the year can result in stronger and more variable currents.

Sea Floor Topography

Also, topography within the sea floor forms a crucial role. The presence of any underwater ridges may deflect the water and hence create different flow patterns. The flow can be slower-moving in shallow regions and stronger, with greater variability in deeper, more structurally complicated seabed areas. Above the shoals, for example, the waters might be retarded by the shallower depth, whereas, in the troughs, the current may be stronger with a more complicated circulation pattern.

Tides

Tides are another important factor. Due to the periodic ebb and flow of the tides in the Yellow Sea and Bohai Sea, great tidal currents are generated. The tidal currents are especially strong near estuaries and narrow channels. They are very important for the transportation of sediments, nutrients, and marine organisms. These tidal currents also contribute to coastal erosion and deposition of sediments, which again shapes the coastline and the distribution of marine life.

Interaction with Ocean Currents

Interaction with larger-scale ocean currents from the Yellow Sea and the Bohai Sea may also alter coastal currents near Dalian. The large ocean currents can introduce water masses of different temperatures and salinities, thus modifying the current dynamics locally. For example, the intrusion of warmer or colder water masses into the coastal waters changes their temperature-a factor that has implications for the local marine ecosystem and weather patterns.

3. Methods of Measuring Coastal Currents in Dalian

Traditional Methods

• Buoys: Buoy is a simple and traditional device which can measure the currents. They can be set in the water, which may give the information on direction and rough speed of the surface current. However, their precision is relatively poor, and they usually only measure at one depth-the surface.
• Current Meters: Current meters can be installed on fixed structures such as piers or directly deployed onto the ocean floor. They provide a measurement of the current speed and direction at a single point. Like buoys, they also suffer from some problems in coverage and measurement of simultaneous multi-depths.

Advanced Method - Acoustic Doppler Current Profiler (ADCP)

How ADCPs Work

The Doppler principle is the basis for the measurement of water flow velocity by an ADCP profiler. They emit sound waves into the water. Moving particles in the water, like suspended sediments and small organisms, interact with the emitted sound waves. These reflected sound waves have their frequency shifted by the motion of the particles. This shift is related to the velocity of the water current.

It emits and receives sound waves through the transducer array in different directions. By analyzing the frequency shifts of the reflected waves in multiple directions, the ADCP meter calculates the speed and direction of the current at different depths. It covers three dimensions in understanding the structure of the current.

Requirements for High-Quality Measurement

• • Reliability of Equipment: ADCP flow meter is an instrument that should be made with materials capable of resisting the adverse conditions at sea. The casings of the ADCP doppler could be made from Titanium alloy, which is an excellent material, highly resistant to corrosion, in particular, when it comes to saltwater along coasts. It also resists the corrosive effects of sea water and marine organisms, therefore assuring equipment performance for long durations. Also, titanium alloy is solid and light. Since it is powerful, it can bear physical strains in the sea environment; because of its small weight, it can be handled easily and installed.
  • Other Desirable Properties: Besides the material reliability, low weight, smaller size, low power consumption, and lower cost are other desirable properties. A compact and light ADCP current profiler is more comfortable to carry and deploy, thus it can measure in a wider range of locations. Low consumption allows operating longer without frequent battery replacement or large power supply. Cost-effectiveness for the deployment on a large scale allows for more comprehensive monitoring of the coastal area.

Choice of Equipment Based on Intended Use

• Ship-mounted ADCP: These are for measurements from a moving vessel. A ship-mounted ADCP would be quite apt since it can provide current conditions in real time as the vessel moves along the coast, thus enabling the continuation of current conditions. -Bottom-mounted ADCP: When the measurements must be taken from a specific point on the ocean floor, then a bottom-mounted ADCP is more in place; it can also be deployed from any point and offers long-term stable measurements of the current at that particular location.
• Buoy-mounted ADCP: When open water applications or in-stream installations are not feasible, a buoy-mounted ADCP should be considered. The buoy-mounted ADCP measures the larger area of current and will radio its results wirelessly.
• Based on Water Depth: From the point of view of selecting the frequency, as for each water depth, a certain frequency will do. Water depth up to 70 meters requires a 600 kHz ADCP. For 70 to 110 meters, it is better to apply the ADCP current meter with 300 kHz. For waters reaching up to 1000 meters in depth, a 75 kHz should be put into service.

When it comes to choosing an ADCP brand, well - known international brands such as Teledyne RDI, Nortek, and Sontek are popular options. However, for those seeking a cost - effective yet high - quality alternative, the China Sonar PandaADCP is worth considering. Made entirely of titanium alloy, it combines durability and reliability with an excellent price - performance ratio. You can find more information about it at https://china-sonar.com.

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