ADCP's Application in Flood Management of Senegal River

1. Where is Senegal River?

The Senegal River is in West Africa. It rises in the Fouta Djallon highlands of Guinea and flows northwestward through Mali, Mauritania, and Senegal before emptying into the Atlantic Ocean.

Geographically, it cuts across a diverse range of savannas, semi-arid areas, and floodplains. Major cities like Saint-Louis in Senegal are found along its banks. The river is an essential water avenue into agriculture, especially in irrigation for crops like millet, sorghum, and rice. It also hosts a rich ecosystem that has various species of fish, crocodiles, and hippos.

The Senegal River Basin experiences a semi-arid to tropical climate in terms of rainfall. The upper reaches in Guinea are more tropical with more rainfall, while the lower parts in Senegal and Mauritania are semi-arid. The rainfall is concentrated in the wet season, which generally falls between June and October. Snowmelt from the Fouta Djallon highlands during the warmer months also influences the volume of water in the river.

2. Why Are There Floods in Senegal River?

Heavy Rainfall: Heavy rainfall from the wet season is the most principal reason for floods in the Senegal River. With its big catchment, it means a large volume of water is collected to it. In cases of rainfall being intense and continuous, river capacity may easily be overcome in such instances.

Tributary Inflows: The Senegal River has a number of tributaries. When these also have high levels of water due to heavy rainfall, they can add substantially to the main channel. The collective action of these tributaries, in conjunction with the water from the main river, often raises the level of water quickly enough to cause flooding.

Topography and Drainage: In its course, the river contains portions with nearly flat floodplains apart from a number of constrictions. The nearly flat floodplains can impede the flow of water, which can spread out and cause flooding into adjoining areas. On the other hand, constrictions hinder the normal flow of water and are thus piled up to raise the water level upstream. In addition, poor drainage in some areas exacerbates the flood situation, as water has nowhere to go but to collect and flood.

Land Use Changes: Human activities like deforestation, expansion of agriculture, and urbanization have altered the flood behavior of the river. Deforestation decreases the land's water-absorbing capacity, hence increasing surface runoff. Agricultural activities compact the soil and alter the natural drainage. Urban development with its paved surfaces and stormwater drainage systems can also disrupt the natural hydrologic cycle and contribute to flooding. The use of ADCP profiler provides a more advanced and efficient way to measure and manage flood-related situations compared to the traditional methods.

3. How do Doppler Principle ADCPs Work?

ADCPs work on the principle of Doppler. They transmit acoustic signals into the water. When these acoustic waves encounter moving particles in the water-sediments, debris, and water parcels with different velocities-the frequency of the reflected signals, compared to the emitted signals, changes due to the Doppler effect.

The ADCP measures these frequency shifts and, using the known speed of sound in water and the angles of the emitted and received signals, calculates the velocity of the water at different depths. Multiple transducers in the ADCP flow meter are arranged to measure velocity components in different directions. Integrating these velocity measurements over different depths and different cross-sectional areas of the river determines the flow rate and other important hydrological parameters.

4. What are the Applications of ADCP in Floods of Senegal River?

Velocity Measurement: ADCP current meter could give correct measurements of the velocities of the water flow in different parts of the Senegal River from various locations and depths. In the cases of flood events, this information helps a great deal in understanding flood dynamics. It helps the identification of areas where flow is rapid and could be hazardous to riverbanks, bridges, and other infrastructure. It enables monitoring of how the velocity of flow changes with time as the flood progresses.

Flow Rate Measurement Application: Combining the measured velocity data with the cross-sectional area of the river, ADCP current profiler can calculate the flow rate. This is very crucial in predicting the volume of water that will pass through different sections of the river during a flood. It allows the anticipation of the flood peak and its impact downstream, which is important for flood management strategies.

Sediment Transport Research: Flooding in the Senegal River can carry a quite high amount of sediment. ADCP can analyze the movement of sediment by detecting the echoes of acoustic signals affected by sediment particles. This shall provide cardinal knowledge about how floods affect the riverbed evolution regarding sediment depositions and erosion processes, which is of essence in maintaining the stability of the channel and its surrounding ecosystem.

5. How can the Data Measured by ADCP be Utilized for Flood Warning and Risk Management of Senegal River?

Flood Warning

Velocity and Flow Rate Data Monitoring: ADCP profiler continuously monitors the velocity and flow rate data to enable the early detection of abnormal increases in the parameters. When the flow rate approaches or exceeds certain critical values, it serves to indicate an imminent flood peak and thus allows timely flood warnings to be issued to the communities and relevant authorities along the river.

Water Level Prediction and Warning: By correlating the measured flow rate and velocity data with historical water level records, models can be developed to predict future water level changes. This helps in providing advance warnings about potential inundation areas and the height of the floodwaters.

Risk Management

Water Conservancy Project Scheduling Decision Support: The ADCP data will be helpful in decision-making for the operation of water conservancy projects like dams and reservoirs in the Senegal River Basin. For instance, it helps to decide when and how much water should be released from the reservoirs to reduce the flood impact on the lower reaches.

Flood Disaster Assessment and Emergency Response: ADCP-measured data can be used after the flood event to establish the flood extent and inundation area and the characteristics of the flow during flooding. These will help in planning the scale of emergency responses, the amount of relief needed, and post-flood recovery works.

6. What Is Required for High-Quality Measurement of Currents in the Senegal River?

Only a highly reliable material can ensure such highly qualitative measurement of Senegal River currents. The casing shall be resistant to the unfavorable impact of the river, the impacts of floating debris, to corrosive water with different chemical compositions because of the landscapes it passes through, to the wide temperature range in this region.

The size of the equipment should be small enough for easy installation and deployment at different locations in the river. Lightweight design is also beneficial for easy transportation and installation. Low power consumption is necessary to allow the sensor nodes to operate for extended periods without the requirement to change batteries frequently, and also to avoid the need for high-energy power sources. Cost-effectiveness will allow for large-scale deployment, thus enabling comprehensive monitoring.

The ADCP meter housing is preferably made of a titanium alloy. Some outstanding merits of the application of the titanium alloy include that it has excellent corrosion resistance to bear the long-term effects from the river water; the material exhibits a high strength-to-weight ratio that keeps the equipment strong while limiting its weight within a good level. In such conditions, this durable material allows performance in the most diverse environments encountered within the Senegal River Basin.

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

In selecting the appropriate type of equipment for the measurement of water current in the Senegal River, quite a number of factors have to be considered. For instance, HADCP is a desirable option in case horizontal section measurement is required, for horizontal measurement of flow velocity and all other parameters across the river section. For vertical cross-section measurement, the Vertical ADCP is more appropriate since it can obtain detailed velocity profiles along the vertical axis of the river.

The frequency should be chosen based on the actual water depth. Within 70 meters, the 600 kHz frequency ADCP is usually a good option since it provides relatively accurate measurement results in this depth range. When considering deeper water areas up to 110 meters, an ADCP with a frequency of 300 kHz may be better since it would be more penetrative to such greater depths with more reliable data.

There are various ADCP brands available in the market, such as Teledyne RDI, Nortek, and Sontek. However, it is worth highlighting a high-quality and cost-effective Chinese ADCP brand-China Sonar PandaADCP. It is made of all-titanium alloy material, ensuring excellent performance and durability. You can find more information on its website: (https://china-sonar.com/)

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