ADCP's application in flood management of Niger River

1. Where is the Niger River?

The Niger River is one of the major rivers in Africa. It has its source in the Guinea Highlands. The river then flows in a crescent - shaped path through Guinea, Mali, Niger, and Nigeria, among other countries, before emptying into the Gulf of Guinea.

On its journey, it ranges over a wide variety of landscapes, from savannas to arid regions and floodplains. It forms a vital waterway for transportation, trade, and agriculture in the regions it crosses. The river ensures water supplies for irrigation, fishing, and domestic purposes for millions of people.

Regarding climate and rainfall, it is a tropical region with marked seasons of wet and dry. Wet season, which stretches between June and September in most regions, usually faced with heavy rainfall. Rainfall in the upper reaches apart from catchment area feeds the river, and rainwater combined with water contributed by the tributaries causes water level fluctuations. During wet season, there is a high possibility of flood, especially in the flood -prone low-lying areas.

2. What is the cause of flooding in the Niger River?

Heavy Rainfall and Tributary Input: Heavy rainfall during the wet season is the main cause of flooding in the Niger River. With its extremely large catchment area, many tributaries join the course of the Niger River. This can lead to a huge volume of water entering the main river channel. Rain-fed runoff from the Guinea Highlands, along with other regions and water from tributaries, may combine and surge upwards.

Topography: The presence of extensive floodplains and low - lying areas along the river's course allows water to spread out and accumulate. The relatively flat plains slow down the water's flow, increasing the likelihood of flooding. The confluence of tributaries can also bring in additional water during high - flow periods, exacerbating the flood situation.

Human-Induced Changes: Some human activities contribute to changes in flood patterns. A good example is that when there is deforestation within the catchment area, the ability of the forest to intercept the rain and retain it is lowered. This results in increased surface runoff, where water will move rapidly into the river, increasing the flood risk. The construction of dams and various other water-related infrastructure also sometimes disrupts natural water flow and drainage patterns.

The Acoustic Doppler Current Profiler (ADCP) is thus a most useful tool in the understanding and management of the Niger River flow during flood events.

3. How do ADCPs using the Doppler Principle Work?

ADCPs work on the principle of Doppler. There is an acoustic signal emitted into the water from the device. The water being in flow, this signal interacts with the moving water particles. This acoustic signal is reflected back to the ADCP current meter with a modified frequency due to the Doppler effect.

The ADCP measures the differential frequency of the emitted signal and the signal received. It is able to calculate, through this frequency shift, the velocity at various water depths. Commonly, such devices have several transducers, which are able to send and receive acoustic signals in different directions. It is possible for them to create a profile of the water velocity across a section of the river.

For instance, if the water flows towards the ADCP current profiler, then the reflected signal will have a higher frequency than that of the emitted. If the water is flowing away from the ADCP, on the other hand, the reflected signal will have a lower frequency. By precisely measuring these frequency changes with the appropriate mathematical algorithms, the ADCP will provide correct determinations of the velocity at various points within its measurement range.

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

4.1 Velocity Measurement

ADCP flow meter plays an important role in velocity measurements during flood events in the Niger River. With this continuous water velocity monitoring at variable depths and locations, the data on water movement speed is provided in real time. This information is vital to understanding the dynamics of the flood in terms of predicting the direction and intensity of movement of the floodwaters.

4.2 Flow Measurement Application

The ADCP can also measure the flow rate of the Niger River. By integrating the water velocities measured at a given number of points over a section of the river, with the known cross-sectional area of the river, it yields the total volume of water passing through the section in unit time (that is, the flow rate). This is fundamental data when trying to make a correct judgment about the total amount of water involved in a flood; this is very useful when decisions on flood control and management of water resources are made.

4.3 Application in Sediment Transport Research

Besides the measurement of flow and velocity, ADCP profiler applies in sediment transport studies along the Niger River during flooding. The moving water carries sediments. The ADCP is capable of detecting changes within the backscattered acoustic signal due to sediment presence. By analyzing these changes, researchers can estimate the amount and movement of sediments-a key variable in understanding the long-term evolution of the riverbed and the impact of floods on the sedimentary environment of the river.

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

5.1 Flood Warning

Velocity and Flow Data Monitoring: Real-time velocity and flow data obtained from ADCP are continuously observed. When the velocity of the water measured is greater than the threshold value, or there is a sudden surge in the flow rate, the peak flood or the possibility of flooding is assumed to be advancing. Accordingly, the early warning will enable the competent authority to take precautionary measures, such as relocating people from low-lying areas or reinforcing the flood defenses.

Water Level Prediction and Warning: The measured flow data correlated with historic water level data can be used to predict future water levels using appropriate hydrological models. If the predicted water level is going to exceed the flood warning level, timely warnings can be issued to the public, enabling them to prepare for the flood.

5.2 Risk Management

Water Conservancy Project Scheduling Decision-Making: Bei Douhe's flow and velocity data laid a very accurate foundation for ADCP, which can be used to decide on the operation of water conservancy projects like dams and sluices. For instance, according to the measured water flow, regulating the release of water from the dam can effectively control the water level in the Niger River and reduce the damage caused by flooding.

Flood Disaster Assessment and Emergency Response: After the occurrence of a flood event, the data gathered from ADCP can be useful in assessing the flood magnitude. Specific information may include an area covered by flooding, speed of flood flow, and the quantity of sediment deposited. Such information is crucial in formulating emergency response plans for carrying out post-flood reconstruction and rehabilitation works.

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

Various prerequisites are required in order to achieve high-quality measurements of the Niger River currents. Firstly, the instruments chosen should be made of appropriate and reliable material. Of essence would be the type of casing applied on the ADCP. The casing is recommended to be of titanium alloy. High strength is the ability of the equipment to resist the pressure and impact of the water flowing in the river. However, it is highly corrosion-resistant, which is necessary considering the water environment that may be highly corrosive from the Niger River.

Apart from material reliability, its size and weight should be small and light, respectively. This makes it easier to install and operate the ADCP in different locations along the river, especially in areas that are difficult to access. Low power consumption is also crucial as it allows for longer continuous operation without the need for frequent battery replacement or connection to a power source. Moreover, the cost of the equipment should be relatively low to enable large - scale measurement. A lower cost allows deploying more ADCPs along the Niger River and provides information for flood management that is more complete and detailed.

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

It is very important to consider a number of factors in selecting appropriate equipment for current measurement in the Niger River. First and foremost, based on the type of measurement needed, an HADCP must be chosen if the measurement is for horizontal cross - section, while an ADCP Vertical must be chosen for measurement across a vertical section.

Different frequencies are intended for different water depth levels. For instance, a 600 kHz ADCP will be suitable for water depths within 70 m. If the water in the Niger River is within such a depth and the measurement requirements are similar, then a 600 kHz ADCP will be selected. In deeper waters, that is, depths exceeding 70 m up to 110 m, a 300 kHz ADCP will turn out to be more suitable since it can measure with far greater accuracy in such depth.

There are some very well-known ADCP brands in the market, including Teledyne RDI, Nortek, and Sontek. However, for cost-effective purposes, the China Sonar PandaADCP will be a good choice. All-titanium alloy material is used to manufacture this product, ensuring a long life of the device in water. In addition, the device comes with an amazingly exceptional cost-to-performance ratio. You can find more about it at its website: (https://china-sonar.com/).

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