ADCP in the Ogooué River Flood Management

1. Where does the Ogooué River flow?

The Ogooué River is among the major rivers in Central Africa. It flows through a large part of Gabon in central Africa. The source of the river is in the Congo - Brazzaville Highlands.

Geographically, it passes through rainforests and savannas. It passes through a number of major cities and towns in Gabon including Port-Gentil. This river is an important transportation means and also plays a significant role in the local ecosystem and economy.

As far as rainfall is concerned, the catchment area of the Ogooué River has a tropical climate. Rainfall is heavy for most parts of the year; the wet season normally lies between October and May. This heavy and consistent rainfall in the region acts as a vital factor that maintains the water volume of the river. Good rainfall ensures a fairly stable flow in the Ogooué River for most of the time.

2. What causes flooding in the Ogooué River?

There are various contributory factors to floods in the Ogooué River. The intense and long rainfall during the rainy season may cause the river to overflow. Since more water is received from the rain than what the river naturally carries, the water level rises to cause a flood.

The second aspect is topography, which dictates the nature of flooding in the river basin. Sometimes, the channel of this river will be pretty narrow, or it might only have low-lying areas adjacent to it. Such areas are easily flooded in case of an increase in water volume. Moreover, human interference-for example, the removal of forests in its basin area-might increase soil erosion. The mobilized soil is then deposited in the river, reducing its cross-sectional area, and hence its capacity to carry water-which predisposes it to flood.

ADCP current meter is an advanced more convenient way of measuring and managing the flow conditions of a river during flood events.

3. How Do ADCPs Using the Doppler Principle Work?

The working principle for Acoustic Doppler Current Profiler(ADCP) is the Doppler principle. An ADCP emits an acoustic signal in the water surrounding it. The water happens to be flowing, and its moving particles interact with the acoustic signal. On reflection back to the ADCP, the frequency of the reflected signal changes due to the Doppler effect.

ADCP measures the difference between the frequency of the emitted signal and that received. From this frequency shift, it also calculates the velocity of water at different depths. Most ADCP flow meter have several transducers, capable of emitting and receiving acoustic signals in various directions. This gives the ability to create a profile of the water velocity across a section of a river.

For example, the frequency of the reflected signal will be higher than that of the emitted signal if the water is moving towards the ADCP current profiler, whereas, if the water is flowing away from the ADCP, the reflected signal frequency will be lower. By measuring such changes in frequency with a great degree of accuracy and applying the right mathematical algorithms, the ADCP will be able to calculate with good accuracy the velocity at several points within its measurement range.

4. Applications of ADCP in flood of Ogooué River?

Velocity Measurement

ADCP's role during the flood events in the Ogooué River is indispensable for acquiring the water flow velocity with accuracy. It can do continuous monitoring of the water velocity at varied depths and locations to obtain current data about how fast the water is moving. Such information will be useful in knowing the dynamics of the floods, to wit, which direction and the intensity with which flood waters would move.

Flow Measurement Application

The ADCP allows determination of the Ogooué River flow rate. By combining the measured water velocities at different points across a section of the river, by known cross-sectional area of the river, it can calculate the total volume of water flowing through the section per unit time-what is the flow rate. This is essential information, necessary to understand the general volume of water in the case of a flood and the accompanying decisions with regard to control of the flood and water resources management.

Application in Sediment Transport Research

Other than flow and velocity, ADCP profiler is useful in researching sediment transport in the Ogooué River during flooding. While this water flows, it carries sediments. This is to say that ADCP will detect changes in the backscattered acoustic signal, the changes caused by sediments. Thus, based on such changes, it would be possible to estimate the quantity and motion of sediments that will result in finding out the long-term evolution of the bed and the flood consequences on the sedimentary environment of the river.

5. How can the data measured by ADCP contribute to flood warning and risk management of Ogooué River?

Flood Warning

Velocity and Discharge Data Monitoring: It continuously monitors the real-time velocity and flow data from acoustic doppler flow meter. If the threshold values of water velocity are more than expected or if there is a quick raise in the flow, then that could indicate the flood peak approaching, or the flood situation that is likely to occur. This can thus provide an early warning to the relevant authorities for taking precautionary measures, such as evacuation of people residing in lower lying areas or strengthening flood defenses. Water Level Prediction and Warning: Measured flow data, correlated with historical data of water level and appropriate hydrological models, can be used to predict future water levels from ADCP data. If the predicted water level is above the flood warning level, timely warnings can be issued to the public for preparation against flood.

Risk Management

Water Conservancy Project Scheduling Decision Support: The correct flow and velocity information provided by acoustic doppler velocity meter can aid decision-making processes related to the operation of water conservancy projects like dams and sluices. For instance, based on the measured flow of water, water release from a dam can be manipulated to regulate the water level in the Ogooué River and limit the extent of flooding.

Flood Disaster Assessment and Emergency Response: In the event of a flood, data collected through ADCP allows assessment of the flood event regarding the inundation extent, velocity of flow, and sediment deposition. This information is rather vital in formulating emergency response plans besides execution of post-flood reconstruction and rehabilitation works.

6. What is necessary for high-quality measurement of currents within the Ogooué River?

A few things need attention in regard to high-quality measurements of currents in the Ogooué River. First, it has to have reliable materials. The casing of the ADCP has to be of highest priority. It is suggested that the casing of the doppler current profiler should be made from titanium alloy. Titanium alloy possesses a lot of advantages. This will make it possible for the equipment to bear all the pressure and impacts of flowing water in the river. Besides, it is highly corrosion-resistant, given the nature of the Ogooué River's water, which may have a lot of corrosive stuff present.

Besides material reliability, the size and the weight of the equipment should be small and light. That would make the installation and operation of the ADCP easier at different locations along the river, especially in the most inaccessible reaches. Low power consumption is also imperative because it enables longer continuous operations without frequent battery replacement or a hookup to a power source. Besides, the cost of equipment must be relatively low to realize large-scale measurement. Lower cost allows the deployment of more ADCPs along the Ogooué River for comprehensively gathering data on flood management.

7. Comment Choisissez l'appareillage meus adapte pour la mesure de courant?

A number of aspects should be considered when choosing appropriate equipment for current measurement of the Ogooué River. First, according to the type of measurement to be required-horizontally in cross-section measurement-a HADCP should be selected; if vertically in cross-section, then a Vertical ADCP is appropriate.

Different water depth corresponds to different frequencies. For instance, a 600 kHz ADCP is suitable for a water depth within 70 m. If the water depth in the Ogooué River fits this depth and if the measurement requirements fit, then a 600 kHz ADCP could be put into consideration. This is quite appropriate for deeper waters, such as waters over 70 m up to 110 m, since it gives quite accurate measurements at such depth.

There are several well-known ADCP brands in the market, such as Teledyne RDI, Nortek, and Sontek. However, for those who are searching for a cost-effective option, China Sonar PandaADCP would be the best choice. It is made of all - titanium alloy material, which ensures its durability and reliability in the water environment. Moreover, it offers an incredible cost - performance ratio. You can find more information about it on its official website: (https://china-sonar.com/).

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