ADCP's application in the flood management of Uele River

1. Where is Uele River?

The Uele River is located in Central Africa, mainly flowing through the Democratic Republic of the Congo. It is an important part of the Congo River Basin. Geographically, it winds through vast regions with a mix of dense rainforests, savannahs, and areas of relatively flat plains.

It passes by numerous small settlements and plays a vital role in the local water supply and transportation for the communities along its banks. In terms of rainfall, being in a tropical climate zone, the Uele River Basin experiences significant precipitation during the rainy season. The abundant rainfall replenishes the river but also poses challenges as excessive rain can quickly lead to rising water levels and potential flood situations. Annual rainfall amounts vary from year to year, but normally, great volumes of water pour into the river from its vast catchment area during the wet months.

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

Flooding of the Uele River is caused by many factors, some of which are given below. First is the intensity and successive nature of rains during the rainy season. Heavy rainwater that flows to the river from its wide drainage area can make the volume of water swell very fast, raising its level immediately. Due to high inflow over natural carrying capacity, the phenomenon of flooding may take place.

Second, the topography of the surrounding areas plays a role. Some sections of the river have relatively flat terrain near its banks, which slows down the natural drainage of water. This makes water accumulate more easily instead of flowing away quickly, exacerbating the flood situation.

Additionally, human activities such as deforestation in the river basin can disrupt the natural water cycle. With less forest cover, the soil becomes less absorbent and retains less water; this, in turn, increases the surface runoff of water and makes the probability of the river overflowing its banks high during heavy rains. Considering flood monitoring and management, in recent times, the Acoustic Doppler Current Profiler has become a more advanced and convenient measurement option than traditional methods.

3. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of Doppler. They transmit acoustic signals into the water body. When these acoustic waves encounter moving objects or particles in the water-like suspended sediment or water parcels with different velocities-the frequency of the reflected signals changes compared to the emitted ones due to the Doppler effect. By precisely analyzing these frequency shifts, ADCPs can calculate the velocity of the water at different depths. Usually, ADCP flow meter devices are fitted with several transducers oriented in different ways to measure the components of velocity in multiple directions, such as horizontal and vertical. By integrating these velocity measurements over different depths and sections, one can derive essential information on the flow rate of the river.

4. Application of ADCP in the flood events of Uele River

Velocity measurement: ADCP current meter can measure the actual velocity of the water flow in the Uele River at various locations and depths with high accuracy. This helps in understanding the dynamic changes of the river flow during flood events. For example, it may identify areas where the flow velocity is extremely high and might pose risks to riverbanks, bridges, and other infrastructure along the river.

Flow rate measurement application: By combining the measured velocity data with the cross-sectional area of the river, ADCP current profiler can calculate the flow rate. This is vital for assessing the overall water volume passing through different sections of the river during floods. It enables predicting the flood peak flow and understanding its potential impact downstream, which is crucial for flood management and mitigation strategies.

Sediment transport research: During flood events, large quantities of sediment are moved in the river. ADCP flow meter will detect the concentration and movement pattern of sediment by analyzing the echoes of acoustic signals affected by sediment particles. This information is highly useful to understand how floods affect riverbed evolution, deposition, and erosion processes in the Uele River.

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

Flood warning

Velocity and flow rate data monitoring: ADCP current meter are continuously undertaken to establish any abnormal increases in both. When the flow rate reaches or even exceeds any critical values, that will again serve as a good indication for an imminent flood peak, so the flood warning will be provided timely to communities and corresponding relevant authorities along the river.

Water level prediction and warning: Establishing the relation between the measured flow rate and velocity data with historical data of water level can help in developing models that can predict the future change in water level. This helps in providing advance warnings about the areas that might get inundated and the height of floodwater, thus enabling people to take preventive measures.

Risk management

Decision support for the scheduling of water conservancy projects: ADCP flow meter can support decisions related to the operation of the water conservancy project in small dams and reservoirs along the Uele River. This can be by adjusting discharge volume in the reservoir according to real-time flow situations to minimize downstream flood effects.

Flood disaster assessment and emergency response: When a flood happens, the data acquired by ADCP profiler can be utilized for the evaluation of the disaster condition of the flood, including the extent of the inundated area and the flow characteristics in the process of the flood. It also informs emergency response measures, including the allocation of relief resources and planning for post-flood recovery work.

6. What’s needed for high-quality measurement of Uele River currents?

For high-quality measurement of the Uele River currents, certain requirements must be met. The reliability of the equipment materials is of utmost importance. Given the river's aquatic environment, which may include factors like water with varying chemical compositions and the presence of debris, the equipment needs to be able to withstand corrosion and physical impacts.

The smaller the size of the measurement equipment, the easier its installation and deployment at different spots along the river, mainly when there is not good access or when space is limiting. A lighter weight will pay off by the easing of transport and maneuvering during installation and handling of the equipment.

Energy consumption shall be low to enable it to work for longer times without replacement of power sources and avoid excessive demands for energy supplies. It must also be cost-effective for deploying at a large number for practical complete monitoring of the river.

The ADCP current meter casing is preferably made from titanium alloy. Titanium alloy offers a number of key benefits: outstanding corrosion resistance against river water with different chemical substances over the long term; a high strength-to-weight ratio, providing adequate structural strength with overall equipment weight kept as low as possible; stable performance under various environmental factors in the river basin, since it is very durable.

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

When it comes to choosing the right equipment for current measurement in the Uele River, there are several factors to consider. First, according to the purpose of use, if the horizontal cross-section measurement is the focus, then HADCP can be a suitable choice since it will be able to measure the flow velocity and other related parameters in the horizontal direction across the river section with high accuracy. The Vertical ADCP will be more appropriate for vertical cross-section measurement since it can obtain detailed velocity profiles along the vertical axis of the river.

The second is to choose different frequencies based on the actual water depth. For water depth within 70 meters, the 600 kHz frequency ADCP normally would be a good option to provide relatively accurate measurement results within this depth. In deeper water areas up to 110 meters, it is advisable to apply a 300 kHz ADCP, which is capable of much better penetration to great depths while simultaneously yielding more reliable data.

In the market, there are many different brands of ADCPs, including Teledyne RDI, Nortek, and Sontek. However, it is important to mention a good-quality and economical Chinese ADCP profiler brand: China Sonar ​PandaADCP. It is made from all-titanium alloy material for excellent performance and durability. It also provides an extremely good cost-performance ratio. You can learn more about it on its official website: ​https://china-sonar.com/.

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