How to Measure Water Current of the Pearl River?

1. Where is the Pearl River?

The Pearl River is a major river in the southern part of China. Originating from three branches, namely the Xi River, the North River, and the East River, its drainage system covers a wide area in parts of Yunnan, Guizhou, Guangxi, and Guangdong provinces.

It passes through mountainous areas and karst landscapes in its upper reaches. The water is so clear and cold, fed by numerous springs and many tributaries. As it courses down through the more populated parts of Guangdong, it becomes an important transport route. Busy cities line the river, like Guangzhou and Foshan. These urban centers have promoted extensive port facilities and use the Pearl River as a hub of shipping, trade, and commerce.

The Pearl River Delta is one of the economically most dynamic and highly populated regions in the world. The estuary represents a polytrophic, productive ecosystem featuring high species diversity in fish and shellfish species. It provides nursery grounds for many marine organisms, with very diversified wetlands and tidal flats that serve as important migratory habitats for birds and host several plant species adapted to the brackish water environment.

2. What is the Pearl River Flow Rate Like?

Fundamentally, seasonal and regional factors determine the flow rate of the Pearl River. During the rainy season, heavy rain starting from April through September in southern China produces an extremely high rise in the flow of the upper catchment area. The river swells and the current becomes stronger. Thus, the water level can rise, and, at times, flooding can be experienced in low-lying areas.

During the dry season, which falls between October and March, the flow rate decreases. Its width may shrink, and the water level falls. However, with the big catchment area and release from some reservoirs, it has a certain flow. Even the average flow rate changes along the length of the river. In the reaches closer to the mountain sources, there is a relatively higher flow due to a greater gradient. This slows and spreads out on entering the area of the delta, which is flatter.

Human activities involving the Pearl River also include water extraction for agriculture and urban use, as well as the construction of dams and water-control structures that affect flow. Such influences may alter the flow behavior of the natural current and have their repercussions in terms of the ecology of the river itself and communities depending on it.

3. How to Measure Water Current of the Pearl River?

The water current of the Pearl River can be measured by using different methods.

Traditional Methods

Float Method: The most straightforward and traditional method for approximating water current is by a float. A buoyant object, like a block of wood or a plastic bottle, is let loose in the river. Knowing how much time it took to travel a known distance is very close to the surface current speed. However, the approach may be affected by wind and disturbances on the surface, which in any case gives only the surface current and not the one at different depth intervals.

Current Meters: Mechanical or electronic current meters can also be used in order to find the velocity at one particular point. Meters are positioned in a certain depth of water and record the speed of water that is passing by them; hence, they can find speed with greater precision compared to the float method at only one point within the water column. But they are limited to that depth and not giving a full picture about the current profile at the moment throughout the water column.

Advanced Method - Acoustic Doppler Current Profiler (ADCP)

ADCP doppler is a more advanced and efficient way of measuring the water current of the Pearl River.

3.1 How do ADCPs using the Doppler principle work?

Principle ADCP profiler operate based on the Doppler effect. The device sends acoustic pulses through the water. Those pulses, in their path, will interact with suspended particles in the water and all other substances, including sediment, plankton, and small pieces of debris. This determines a change in frequency because of moving water, reflected from acoustic signals.

This frequency shift is measured by the ADCP meter and converted, by means of the Doppler formula, to calculate the velocity of water at each depth. By sending out pulses in several directions and at different frequencies, the ADCP flow meter is able to produce a very detailed profile of the current in the whole water column. This offers a far more detailed insight into the structure of the current than the more traditional methods that either measure just from the surface or from one point in the column of water.

3.2 What is needed to perform a high-quality measurement of the Pearl River currents?

To get high-quality measurement of the Pearl River currents, the measuring instrument should be reliable. The instruments must be put into consideration that the climate of the place is humid and typical of high flow and sediment-laden water in the Pearl River.

In addition to the fact that the equipment should be pretty light and compact in size. Ease of deployment will be necessary, particularly in the areas that are not accessible, along riverbanks, or from boats. The power consumption of the equipment should be low so that it can keep running for long without necessarily changing batteries or external power sources. A further critical view is that of the costliness of most measurements, especially for large-scale or long-term measurements when monitoring river dynamics.

Using titanium alloy for the case in ADCP current profiler is advantageous. It is highly resistant to corrosion, which is important in a water-rich environment like that of the Pearl River. It's durable and strong enough to handle such physical forces from the river current and any impacts that may occur. Its light weight makes it more convenient for installation and transportation.

3.3 How to Choose the Right Equipment for Current Measurement?

 The choice for current measurement at Pearl River is based on the given requirements.

For Horizontal Measurements: Generally, horizontal measurements over a reach of the river can be done with an ADCP current meter in the horizontal setup-an HADCP. It would have a wide view of the current flow in a horizontal plane; this would give insight into general flow patterns of the river.

For Vertical Profile Measurement: Vertical profile measurement of current is more aptly done with a vertical ADCP, which can give highly detailed information about the velocity of water at different depths, important for the study of the stratification and mixing of the water column.

Frequency Selection: Considering frequency selection, for fairly shallow reaches of the Pearl River up to about 70 meters, the 600 kHz ADCP might be adequate. Where the reaches are deeper, about 110 meters, the 300 kHz ADCP is a better option.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option with good quality, the ChinaSonar PandaADCP is a great choice. It is made of all - titanium alloy, providing durability and resistance to the Pearl River's environment. It also offers an excellent price - performance ratio. You can visit https://china-sonar.com/ for more information.

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