ADCP's Application in Flood Management of the Dulong River

1. Where is the Dulong River?

The Dulong River is located in southwestern China. It is a significant watercourse in the mountainous regions of Yunnan. Originating from high - altitude areas, it flows through deep valleys and lush forests, carving its way through the rugged terrain.

It passes through some ethnic minority villages and small settlements. The climate in the Dulong River basin is very complicated, with the influence of altitude and monsoon. There is a distinct rainy season from around May to October, during which heavy rainfall is common. It is during these months that a large part of the water volume of the river is contributed by the rains. In contrast, the dry season, from November to April, is relatively less rainy. In addition to that, snowmelt from the higher mountainous regions also contributes to its water supply, especially when it is in transition from winter to spring.

2. What are the causes of flooding in Dulong River?

There are a number of factors that cause flooding in the Dulong River. The first is heavy rainfall during the wet season. Heavy and continuous rainfall can raise the water level of the river very fast. As many tributaries join the main river, the combined inflow of water can be greater than the natural carrying capacity of the river.

Another crucial factor is topography. It is set within the mountainous environment of steep slopes and narrow valleys where much water can flash down quickly at a high rate with volumes, leading to floods. More importantly, characteristics within the river channel can alter in accordance with landslides or debris flow, as well, which may cause obstruction or stricture of the riverbeds, thereby causing its flow into the surrounding regions: thus, flooding it.

Another factor is land cover change. Deforestation and inadequate land-use practices in the catchment area reduce the infiltrating capability of the ground and regulating runoff. Consequently, more water is likely to enter the river in a fairly short period, thus raising the flood risk.

In this respect, the Acoustic Doppler Current Profiler (ADCP) offers an advanced measurement technique that is superior to the traditional methods in efficiency, which is particularly required for better flood management.

3. How do ADCPs using the Doppler principle work?

The operating principle of ADCPs is based on the Doppler effect. ADCPs transmit acoustic pulses into the water. Moving particles in the water-like sediment, small aquatic organisms, and other suspended material-interact with these pulses. When acoustic waves that have hit moving objects return back, a frequency shift happens.

The magnitude of this frequency shift is directly related to the velocity of the moving objects and, thus, also the velocity of the water. For instance, an ADCP placed in the Dulong River, probably on a floating platform or fixed structure near the riverbank, transmits sound waves into the water column. The ADCP current profiler will analyze the received signals that are reflected back by the flowing water and its constituents to provide the speed and direction of the water flow at different levels.

4. What are the applications of ADCP in floods of the Dulong River?

Flow velocity measurement: ADCP flow meter is capable of measuring the actual velocity of water flow in the Dulong River. During flood events, this information will be helpful in understanding the speed of the floodwaters' movement. It helps predict the spread of the flood and helps in identifying areas where high-velocity flows may cause erosion or other damage.

Discharge measurement: By combining the measured velocities with the cross-sectional area of the river, which can also be determined using ADCP, one is able to calculate the flow rate of the river. In the event of a flood, knowing the rate of flow is crucial in judging the volume of water passing through any particular section of the river and predicting its impact downstream.

Sediment transport research: ADCP profiler can detect the movement of sediment particles along with the water flow. During floods, this provides valuable information about the amount of sediment being carried by the river. Understanding sediment transport helps in predicting changes in the riverbed, such as areas of sediment deposition or erosion, which can affect the stability of the river and its infrastructure.

5. How can the data measured by ADCP be used in flood warning and risk management of the Dulong River?

Flood warning

Flow velocity and flow rate data monitoring: With ADCP, continuous monitoring of flow velocities and flow rates allows for the detection of abnormal changes in advance, which may indicate an imminent flood. If the velocities or flow rates increase beyond normal levels, an alert can be triggered to allow timely warnings to communities along the riverbanks.

Water Level Prediction and Warning: Analyzing the relationship of flow rate, velocities, and the resulting water level using historic data and ADCP measurements will enable the prediction of future water levels. This will provide the necessary warnings for the residents with accurate warning time to take necessary precautions such as evacuation or flood-proofing.

Risk Management

Water Conservancy Project Scheduling Decision-Support: The ADCP data shall be useful to make a decision on the operation of dams, reservoirs, and other conservancy projects along the Dulong River. For instance, if the forecast of the flood, the release from the reservoirs can be regulated with the data of ADCP-measured to lessen the flood in the downstream areas and keep the structures safe.

Assessment of Flood Disaster and Emergency Response: In case a flood has occurred, this ADCP data helps estimate the aftermath of the process, which includes erosion in recent times, changes in the riverbed, and therefore the infrastructure. The emergency response was guided by that information, and further methods of avoiding floods were thereby built.

6. What's needed for high - quality measurement of the Dulong River currents?

The equipment should be made of reliable materials for high-quality measurement of the currents of the Dulong River. Small in size and light in weight, this is advantageous for easy deployment at every location along the river, even on boats or bridges. Low power consumption is necessary for long-term monitoring, especially in regions where power supply is limited. Low cost is also vital to make it deployable in many numbers for full coverage of monitoring.

The casing of ADCP is preferably made of titanium alloy. Titanium alloy provides excellent corrosion resistance, which is necessary when dealing with the Dulong River's water that may contain various minerals and salts. It also has a good strength-to-weight ratio, making the equipment durable and relatively easy to handle and install.

7. How to choose the right equipment for current measurement?

This could include the following when selecting appropriate equipment for current measurement along Dulong River: The equipment of choice for horizontal cross-section measurements is a horizontal ADCP. This will allow for the measurement of the flow velocities across a horizontal plane and thus yield clear insight into the overall pattern of flow in a certain reach of a river. In the case of vertical cross-section measurements, a Vertical ADCP is preferred as it profiles the velocities from the water surface to the riverbed along a vertical line.

In terms of frequencies, an ADCP with 600 kHz is quite suitable for water depths up to approximately 70m, while frequencies of 300 kHz are more appropriate for deeper sections with water depths up to about 110m.

There are well - known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, for a cost - effective option, the China Sonar PandaADCP is recommended. It is made of all - titanium alloy materials and offers a good cost - performance ratio. You can find more information at (https://china-sonar.com/).

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