ADCP in the Nen River Flood Management

1. Where is the Nen River?

The Nen River is a major river in Northeast China. The origin of the river is from the Greater Khingan Mountains.

Geographically, it flows through several provinces in Northeast China such as Heilongjiang, Inner Mongolia, and Jilin. With its own course, it flows through many cities and towns such as Qiqihar in Heilongjiang. It is pretty long with a meandering path over the open plains of Northeast China thus highly instrumental in the local water system and agriculture.

The amount of rainfall and the general climatic condition remain different in the area of the Nen River. Normally, there is a rather short but fully concentrated rainy season in this area that usually starts in June and goes up to August. During this period, heavy rainfall is possible, which strongly increases the water volume carried by the Nen River. Besides this, during spring the snowmelt from the surrounding mountains makes a contribution to the water supply of the river, even though it is less when compared to the rainy season.

2. Why does flooding take place in the Nen River?

There are a lot of factors contributing to the occurrence of floods in the Nen River. For one, heavy rainfall is the main reason during the rainy season. It can be observed that heavy downpours within a very short period can increase the water level in the river rapidly. If the river drainage capacity is unable to bear this sudden and large amount of water coming into it, then flooding will occur.

The second aspect is the topography of the river basin itself. Relatively flat plains, which the Nen River runs through, might impede the travel speed of the water in case a flood should occur and thus enable water to pile up more easily. In addition, human interference in the form of cutting down trees in the upper reaches of the river could reduce soil cohesion and enhance erosion. The eroded soil might settle into the channel of the river, diminishing its carrying capacity and making it easily flooded.

Besides, the insufficiency of the general flood control infrastructure in some parts of the river also contributes to the aggravated problem of flooding. ADCP profiler has become one of the more advanced and convenient measurement methods for better understanding and managing flow conditions during flood events.

3. How do ADCPs using the principle of Doppler work?

The Acoustic Doppler Current Profiler(ADCP) work on the basis of Doppler. When the ADCP meter sends an acoustic signal into the water, the signal scrambles with the moving particles of the water. Since water is flowing, due to the phenomenon of Doppler, the frequency of the reflected acoustic signal will change.

The ADCP measures the differential between the emitted frequency and the received frequency of the acoustic signal. With this kind of frequency shift analysis, it is able to estimate the water velocity at each depth. Most of these instruments have several transducers that send and receive acoustic signals in various directions so that it can receive a profile of the water velocity across a section of the river.

The reflected signal, for instance, will have a higher frequency compared to the emitted signal if the water is coming towards the ADCP flow meter, and vice versa if it is moving away from it. With this change in frequency, due to precise measurement and appropriate application of mathematical algorithms, the ADCP current profiler will be able to determine the very accurate velocity of the water at varied points within its range of measurement.

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

4.1 Measurement of Velocity

The ADCP current meter plays an important part in measuring the velocity of water flow in the event of floods in the Nen River. It continuously monitors the water velocity at various depths and locations and delivers real-time data on how fast the water is moving. This may be useful to understand the dynamics of floods, such as the pre-dictions of direction and intensity the flood waters could move.

4.2 Flow Measurement Application

It is also possible to measure with ADCP the flow rate of the Nen River. When the measured water velocities at different points across a section of the river are combined with the cross-sectional area of the river, the device is able to compute the total volume of water flowing through the section in every unit time-that is, the flow rate. This information becomes vital considering the total amount of water in a flood and decision-making about the management of floods and the planning of water resources.

4.3 Application in Sediment Transport Research

Aside from the flow and velocity measurements, ADCP can also be applicable to sediment transport research in the Nen River during a flood. This is because when there is flow, the water carries sediments with it, and thus the acoustic doppler velocity meter is able to detect changes in the backscattered acoustic signal related to the presence of the sediments. Such changes, once analyzed, enable estimation of the amount and movements of the sediments-a very important factor in understanding the long-term evolution of the riverbed and how floods would affect the river's sedimentary environment.

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

5.1 Flood Warning

Monitoring of Flow Velocity and Flow Data In real-time, it will watch the flow velocity and flow data continuously that are measured by an acoustic doppler flow meter. When the water berth's velocity exceeds the threshold or flow rate raises in a large scale, that can be viewed as an upcoming flood peak or the emergence of a flood. By doing so, the relevant departments will be able to take precautionary measures in advance, including moving people in the low-lying areas and reinforcing the dykes. Water Level Prediction and Warning: Measured flow data correlated with historical data of water level and appropriate hydrological models can help in predicting future water levels using ADCP data. If the predicted water level is above the flood warning level, timely warnings can be issued to the public for preparation against the flood.

5.2 Risk Management

Water Conservancy Project Scheduling Decision Support: Because of the accuracy of flow and velocity data provided by ADCP, it can provide support with suggestions concerning decisions related to the operation of water conservancy projects such as dams and sluices. For example, based on the measured water flow, water release from a dam can be used for controlling the water level in the Nen River to reduce flood disasters. -Flood Disaster Assessment and Emergency Response: The acoustic current meter data during the flood event would also be of great help during post-flood disaster assessment concerning the 'extent of inundation, velocity of the flood water, and amount of sediment deposition' aspects. This information is of prime importance for formulating the plans regarding emergency response and for carrying out post-flood reconstruction and rehabilitation work.

6. What is necessary for the realization of high-quality measurement of the Nen River currents?

High-quality measurement of the Nen River Currents would entail addressing a number of issues. First, the equipment used in carrying out the measurement should be made of materials that are reliable. This is where the ADCP casing is very critical. The casing should, to this end, be of titanium alloy. Titanium alloy has a number of advantages. It is a high-strength material, and the equipment must withstand the water pressure and impact it flows in the river. Besides, it is highly resistant to corrosion, which is highly important given the Nen River's water environment, which may contain substances corrosive to this material.

Besides material reliability, small and light size and weight must be attained. It shall facilitate operating an ADCP in difficult river accesses, as well as higher accessibility to various sites for installation and operation. The ADCP shall also use low power consumption to allow for longer continuous operations without being replaced or connected to a power source frequently. Of particular significance, it shall be comparatively low-cost equipment to make the measurement feasible on a large scale. The cheaper the better, because one can deploy more ADCPs along the Nen River, which is more comprehensive and detailed for flood management.

7. Selection of Equipment for Current Measurement?

Based on the selection of the equipment for the current measurement of the Nen River, several conditions should be considered. According to the type of measurement, when it falls into the category of horizontal cross-section measurement, a Horizontal ADCP ought to be chosen; otherwise, when the measurement is to take place within a vertical cross-section, a Vertical ADCP would be suitable.

Different frequencies suit different water depths. For instance, a 600 kHz ADCP is suitable for water within a depth of 70 m. In addition, if the water depth in the Nen River can be less than 70 m and fit this measurement requirement, then using a 600 kHz ADCP should be considered. If the water body is deeper than 70 m but up to 110 m, a 300 kHz ADCP can be more appropriate.

In the market, there are a couple of famous brands that sell ADCP, such as Teledyne RDI, Nortek, and Sontek. However, this China Sonar PandaADCP is a rather great choice for those who want it at a relatively cheap price. The all-titanium alloy material ensures the quality and reliability in the water environment. Besides, it can offer an extremely high cost-performance ratio. For more details, please refer to the official website: https://china-sonar.com/.

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