How to Measure Water Current of the Han River?

1. Where is the Han River?

The Han River is one of China's most important water bodies and extremely important in geographical, economic, and cultural aspects. Originating from the Qinling Mountains in Shaanxi Province, the river follows a general southeastward course through several regions and cities in central China.

It passes through some important urban areas along its course: for example, Wuhan- a very large metropolis and transport center. The river splits Wuhan into three parts: Wuchang, Hankou, and Hanyang and stands as a silent witness to its growth and prosperity over the centuries. The Han River is also connected with many towns and villages, taking care of daily water needs and irrigation, even for industrial purposes.

Indeed, the views along its banks represent a beautiful mixture of parks, greenbelts, and historic sites. It is a favorite place for walking, boating, and angling among locals and tourists. Besides being the center of local ecosystems, the Han River contributes much to supporting all forms of aquatic life, from different fish species to amphibia and invertebrates. Wetlands and floodplains along its sides serve as a nature habitat and spawning area, basically to keep the ecological balance of the area.

2. What does the Flow Rate of the Han River Consist of?

In the course of different seasons, the flow rate in the Han River does change. For the rainy season, normally from April to August in the region, the river's flow rates increase due to increased rainfall and water runoff from upstream areas. Heavy precipitation in the Qinling Mountains and its catchment area causes a rush of water into the Han River, giving way to a relatively high flow rate.

During this period of high flow, water level maintenance, recharge of groundwater supplies, and sediment flushing occur. It further affects flood control and water resource management in the lower reaches. This flow rate is reduced during the dry season, which generally falls between September and March. However, the river still retains a base flow sufficient to support ecological functions and water demands within those areas the river passes through.

Whereas the dry season average flow rate stands at several hundred cubic meters per second, peak rainy seasons have achieved several thousand cubic meters per second. The volume of water carried by the Han River holds great importance in water supply to urban and rural areas, power generation, and shipping throughout its course.

3.Measurement of the Water Current of the Han River?

Velocity Meter Method

This old method consists of the use of a velocity meter in either mechanical or electronic type. The basic idea is to point the velocity meters at the right position in the river, directly measuring the speed of the water at that particular location. However, it requires correct positioning and multiple readings into various depths and positions in order to get the total understanding of the overall water current. In the case of Han River, which is pretty long and has differently structured parts, this method will be quite labor-intensive and long.

ADCP Method

The ADCP flow meter is a more modern and handy means for measuring water currents. It operates on the use of sound waves that trace the movement of the particles of water. By emitting acoustic signals and analyzing the Doppler shift of the reflected signals, it can measure the velocity of water at multiple depths simultaneously. This provides a very substantial profile of the water current for more accurate assessment of flow conditions along the entire river. ADCP profiler can be installed on boats, bridges, or even be deployed on buoys for continuous monitoring.

Buoy Method

In the buoy method, buoys with sensors that measure the movement of water around them are put into the river. These buoys float on the water surface and may indicate something about the surface current. They may not be so correct in fully representing the complexity of the water current like the above methods, especially in regard to variations in velocities at different depths.

Among those, ADCP meter ​is a more advanced and efficient option for the measurement of the water current of the Han River.

4. How Do Doppler Principle-based ADCPs Work?

The Acoustic Doppler Current Profiler (ADCP) work according to the principle of Doppler. In case an ADCP sends an acoustic signal through the water, it travels through the water, hits moving particles of water, and sends sound waves back again. The frequency will change due to the movement of the particles of water.

If the water particles are moving towards the ADCP current profiler, the reflected wave frequency would be higher than the emitted one. On the other hand, if the water particles are moving away from the acoustic doppler velocity meter, then the reflected wave frequency would be lower. By precisely measuring the change in this frequency, the ADCP can calculate the velocity of the water particles at different depths.

With these independent velocity measurements obtained at various depths, the current profiler would then ensemble to yield one complete profile of the water current. This provides a great deal in the detail of how the water is flowing, not at just the surface but throughout the entire vertical section of the river.

5. What's Needed for High-Quality Measurement of the Han River Currents?

There are various aspects related to the equipment necessary to conduct quality measurement of the currents of the Han River.

Reliability of the material is the first and most important aspect. Since the river's water, sediment, and temperature, in which the working environment of the equipment takes place, are unbearable, its facilities have to be tough enough to bear sudden changes of temperature in different seasons or other severe attacks by floods or other natural disasters in the area.

The desired characteristics are small size, lightweight, and low power consumption. A device with compact and lightweight design is easy to handle and deploy on a boat or attached to a buoy. Low power consumption makes the equipment operate for long hours without necessarily changing batteries or having access to a continuous power source.

Another important factor is the cost. The lesser the cost, the greater the applicability of the measurement equipment for wider coverage of the monitoring of the river.

The casing of the ADCP could be made with a titanium alloy. The advantages of using a titanium alloy are multiple. It is highly resistant to corrosion, important for operation in the water body like the Han River, because it is always in contact with water and possibly corrosive elements. Besides this, it is strong enough to resist possible physical impacts and pressure changes arising during deployment and operation. In addition, the density of the titanium alloy is relatively low, so it contributes to the general goal of making the equipment light.

6. How to Choose the Right Equipment for Current Measurement?

For choosing the right equipment for measuring the Han River's current, several factors have to be considered.

Based on the Purpose of Use

Where the intention is to measure the horizontal cross-section of the river current, one should prefer a horizontal ADCP. HADCPs are designed to measure with much accuracy the water flow in the horizontal plane, useful in ascertaining the overall movement of water across a particular section of the river.

On the other hand, a vertical ADCP should be selected if the focus is to measure the vertical cross-section of the river current. Vertical ADCPs can accurately measure the velocity of water at each depth and yield a detailed profile of how the water flows vertically in the river.

Based on the Frequency

The choice of frequency also depends on the depth of the water in the Han River. Water depths of up to 70 meters are usually sufficient with a 600 kHz ADCP. A frequency like this has very good resolution and accuracy when it comes to the measurement of the water current in case of relatively shallow waters.

For deeper waters, say in excess of 70 meters up to about 110 meters, an ADCP would be more appropriate operating at 300 kHz. The lower 300-kHz frequency can extend deeper into the water and can still do a good job of measuring the water current effectively.

There are several reputed brands available in the market, such as Teledyne RDI, Nortek, and Sontek. However, for cost-effective options with excellent quality, one can go for China Sonar PandaADCP. It is made of all-titanium alloy material, hence durable and reliable. Its incredible cost-performance ratio gives an alternative choice for the measurement of water current of the Han River. You can get more details from the official website: https://china-sonar.com/.

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