How to Measure the Coastal Currents of Dandong

1. Location and General Information about Dandong

Dandong is a coastal city in Liaoning Province, China. It is at the easternmost end of the Liaodong Peninsula, next to the Yalu River and the Yellow Sea. This important border city also boasts rich history and a unique geographical location.

Dandong has a monsoon-type warm temperate climate with comparatively mild winters and warm summers. The sea and the river to a certain degree moderate the local climate. The amount of rainfall is moderate, which permits various vegetation to grow from forests to coastal shrubs.

The location of Dandong at the mouth of the Yalu River and on the Yellow Sea is of crucial strategic and economic importance. Local fisheries and navigation have a long tradition. The bottom topography of waters off Dandong is complicated: combined shallow and deeper waters around an estuary along a coastline. That itself is influenced by a number of factors including tides, river outflows, and oceanic currents from the Yellow Sea.

2. The Situation of Coastal Currents near Dandong

Influence of River Discharge: Another important factor affecting the current in this particular coastline could be discharges from the Yalu River into the sea. The freshwater water coming from the river can create various differences in density with the salt water, inducing a peculiar pattern of current, for example, estuarine circulation. Definitely, the exchange between the river and the sea could influence the direction or speed of the coastal currents.

Monsoon Climate: This again is the other major contributing factor. During summer, the southeast monsoon could push the surface waters in one direction or strength of flow of coastal currents. It thus bears relevance to fishing and shipping. The current pattern is altered during winter as the northwest monsoon kicks in. Winds in this season can give rise to stronger and more variable currents. Sea Floor Topography: The topography is another important factor related to the sea floor. The ridges, troughs, and shoals underwater will contribute to the water's flow in different directions and at different velocities. Shallow areas, such as near the estuary, may have slower-moving currents, while stronger, more complex flows occur over deeper regions.

• Tides: The tides in the Yellow Sea are the most predominant driving forces that determine the currents in the coastline of the Yellow Sea. Due to the periodic rise and fall of the sea level, the tidal current generated can be very high. Near the estuary and narrow channels, the tidal currents become very violent. They help in transportation of sediments, nutrients, and marine organisms. Besides, the tidal current regulates coastal erosion and deposition, thereby affecting the topography of the coastline and further distribution of marine life.
• Interaction with Ocean Currents: The interaction with larger - scale ocean currents from the Yellow Sea and other adjacent regions can also modify the coastal currents near Dandong. These oceanic currents can introduce water masses with different temperatures and salinities, further affecting the local current dynamics.

3. Measurement of Dandong Coastal Currents

• Traditional Methods Buoys: These are very traditional mechanisms for observing coastal water flow. They are placed in the water, which can record with elementary information on the direction and rough speed of the surface current. However, the data they would provide is somewhat inaccurate. And mostly these buoys will measure the current at a single level, the surface.
• Current meters: Current meters can be attached to fixed structures like piers or laid on the seabed. They give the velocity and direction of the current at one point. However, similar to buoys, they may involve certain inadequacies concerning area coverage, providing simultaneous measurements at varied depths.

3.1 Advanced Method - Acoustic Doppler Current Profilers (ADCPs)

Principle of ADCPs: Their working principle is linked with the Doppler principle; hence, these are called ADCPs. They emit sound waves into the water. These sound waves interact with the moving particles in the water, such as suspended sediments and small organisms. During this process, while the particles move, the frequency of the reflected sound waves change. This frequency shift is related to the velocity of the water current. The transducer array sends and receives sound waves in different directions. By processing the frequency shifts of the reflected waves in the multiple directions the ADCP can compute the current speed and direction at various depths and correspondingly allow a three-dimensional understanding of the current structure.

3.2 Requirements for High Quality Measurement

Equipment reliability: The ADCP needs to be built with materials capable of sustaining the hazardous conditions at sea.

Titanium alloy is an excellent material for ADCPs casing. It is extremely resistant to corrosion, which becomes crucial in the saltwater surrounding the coasts. It resists well the corrosion of seawater and marine organisms and provides long-term performance of the equipment. Additionally, it is strong yet at the same time light. The strength of the material can withstand the physical demands related to the use in the marine environment, and its light weight helps in easier handling and installation of the item. 

Other Advantageous Properties: In addition to material reliability, other properties are also advantageous. Examples are small size, light weight, low power consumption, and low cost. A compact, lightweight ADCP can be carried and deployed more easily and thus enable measurements in many more locations.

Low power consumption allows it to operate for longer without needing frequent replacement of its batteries or an unduly large power supply. This is particularly essential for cost-effectiveness at large-scale deployment in order to achieve more comprehensive coastal area monitoring.

3.3 Choice of Hardware Based on Intended Use: Ship-mounted ADCP

This equipment is used for measuring currents from a moving vessel. It can display the real-time current data as the vessel moves along the coast, permitting continuous monitoring of the current conditions.

• Bottom-mounted ADCP: If the measurement needs to be at a fixed location on the seabed, then the bottom-mounted ADCP is the device for that. It can be installed at that particular point and provide long-term stable measurements of the current at that location.
• Buoy-mounted ADCP: This is done on open waters or areas where a fixed installation can't be done; it measures over a greater area of current and wirelessly transmits data. Water Depth Dependence: For the selection of the frequency, different frequencies apply in waters of different depths. For water up to 70 meters deep, one can generally apply a 600 kHz ADCP. From 70 to 110 meters, there should be a 300 kHz ADCP applied. For deeper waters, of up to 1000 meters, one should use a 75 kHz ADCP.

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.