ADCP's Application in Flood Management of Blue Nile

1. Where is Blue Nile?

The Blue Nile is the main tributary to the Nile River, taking its source from Lake Tana in Ethiopia. The river flows through a wide range of topographies: from steep mountainous slopes in Ethiopia to plains in Sudan.

Geographically, the upper reaches in Ethiopia are underlaid by a highland with great biodiversity. As it enters Sudan, it becomes a vital source for irrigation agriculture in the arid and semi-arid regions. Along its banks, many towns and villages are sustained by it for their water supply, fishing, and transportation.

From the perspective of rainfall, it has a tropical climate with the Ethiopian highlands gaining significant rainfall during the wet season from June to September. Rainfall in this basin is primarily caused by the monsoon winds. In Sudan, the state of the climate is arid, and the flow is very crucial in maintaining water in this area.

2. What are the Reasons for Floods in Blue Nile?

Heavy Rainfall: Heavy rainfall in the highlands of Ethiopia contributes to a large portion of the flooding during wet seasons. With such a large catchment area, much water from different locations converges into one river. In such cases, when the rain is heavy and continuous, it easily exceeds the carrying capacity of the river, causing floods.

Tributary Inflows: The Blue Nile has a number of tributaries. When these tributaries also receive heavy rainfall and have high water levels, they contribute a lot of water to the main channel. This has a cumulative effect with the water from the main river, which raises the level rapidly and can thus flood.

Relief and Drainage: The course of the river consists of a relatively flat floodplain with some constrictions in its course. The relatively flat floodplains may slow down the flow of water, allowing it to fan out and flood areas on either side of it. Constrictions to the course will hamper the natural flow and cause water to back up, raising the level of water upstream. Besides this, the type of soil and its permeability in the surrounding areas contribute to drainage and hence flooding.

Land Use Changes: Human activities related to the expansion of agriculture and deforestation have affected the flood pattern of the river. Deforestation reduces the land's ability to absorb water, increasing surface runoff. Agricultural activities can lead to soil compaction and changes in the natural drainage. In this context, Acoustic Doppler Current Profiler (ADCP) represents a more sophisticated and efficient form of measurement for flood-related data than traditional methods.

3. How Do ADCPs Using the Doppler Principle Work?

ADCPs work on the principle of the Doppler. They send acoustic signals into the water. These acoustic waves interact with moving particles in the water, like sediment, debris, and water parcels with different velocities. When the emitted waves bounce back after hitting these moving objects, the frequency of the reflected waves changes due to the Doppler effect.

This frequency shift is measured by the ADCP meter. With knowledge of the speed of sound in water and the angles of the emitted and received signals, it can calculate the velocity of the water at different depths. Multiple transducers in the ADCP are used to measure the velocity in different directions. By integrating these velocity measurements over different depths and cross-sectional areas of the river, the flow rate and other important hydrological parameters can be determined.

4. What are the applications of ADCP in Floods of Blue Nile?

Velocity Measurement: ADCP current meter can measure the actual velocity of water flow in the Blue Nile at different locations and depths. This is highly crucial during flood events in an effort to understand the flood dynamics. It identifies the location where the flow is rapid and can be harmful to riverbanks, bridges, and other structures. Additionally, it allows monitoring of time-series changes in flow velocity over time, as the flood progresses.

Flow Rate Measurement Application: The ADCP can use the measured velocity and cross-sectional area of the river to compute the flow rate. This is a requirement for predicting the volume of water passing through various sections of the river in case of a flood. It enables anticipation of the flood peak and its impact downstream, which is important for flood management strategies.

Sediment Transport Research: Flooding in the Blue Nile normally carries a considerable amount of sediment. ADCP can analyze the movement of sediment by detecting the echoes of acoustic signals affected by sediment particles. This provides further insight into how floods affect the development of the riverbed, sediment deposition, and erosion processes; this is important for maintaining the stability of the river channel and its surrounding ecosystem.

5. How can the Data Measured by ADCP be used in Flood Warning and Risk Management of Blue Nile?

Flood Warning

Velocity and Flow Rate Data Monitoring: ADCP current profiler continuously monitors the velocity and flow rate data in order to determine the abnormality of such a rise. The flow rate reaching or just about surpassing certain critical values becomes indicative of an imminent flood peak for early issuance of timely flood warnings to communities and relevant authorities along the course of the river.

Water Level Prediction and Warning: Measured flow rate and velocity data are correlated with the historical water level records to develop a model for prediction of future changes in water levels. This would help provide an advance warning about inundation areas and floodwater height.

Risk Management

Water Conservancy Project Scheduling Decision Support: The data from ADCP can be useful in making decisions regarding the operation of water conservancy projects such as dams and reservoirs along the Blue Nile. For example, it will help to identify when and how much water to release from the reservoirs to mitigate the impact of floods downstream.

Flood Disaster Assessment and Emergency Response: In case of a flood, the data measured by ADCP can be used to analyze the actual situation of the flood disaster, like the range of flooded area and flow characteristics during a flood. It would be taken as a reference in organizing rescue work and planning post-flood recovery.

6. What’s Needed for High-Quality Measurement of Blue Nile Currents?

To be able to measure the Blue Nile currents with a high quality, the equipment should have reliable materials. The casing of the device should withstand harsh conditions such as impacts of floating debris, corrosion of water in different chemical composition due to the range of landscape it passes, and a wide temperature range in the region.

The size of the equipment should be small enough to be installed and deployed easily at different locations in the river. A lightweight design is also beneficial for ease of transportation and installation. Low power consumption is necessary to operate continuously over extended periods without frequent battery replacements or high-energy power sources. Cost-effectiveness is another important factor to enable large-scale deployment for comprehensive monitoring.

The casing of ADCP profiler should be made of titanium alloy. Titanium alloy has several outstanding advantages: it has excellent corrosion resistance, which is very important to ensure resistance against long-term attack by river water; it has a high strength-to-weight ratio, which provides enough strength with reasonable weight for the equipment. This material's durability ensures stable performance under the diverse environmental conditions of the Blue Nile Basin.

7. How to Choose the Right Equipment for Current Measurement?

Based on Measurement Purpose: In the case of horizontal cross-section measurement of the river, the Horizontal ADCP (HADCP) will be appropriate because it will measure the flow velocity and other parameters in the horizontal direction across the river section. For vertical cross-section measurement, a Vertical ADCP is more suitable to obtain detailed velocity profiles along the vertical axis of the river.

Based on Water Depth: Different frequencies of ADCPs are suitable for different water depths. For water depths up to 70 meters, an ADCP with a frequency of 600 kHz can provide very good measurement results. In the case of deeper water, up to 110 meters, an ADCP with a frequency of 300 kHz works better because it can go deeper and yield reliable data.

There are well-known ADCP brands like Teledyne RDI, Nortek, and Sontek. Additionally, a cost-effective Chinese brand, China Sonar PandaADCP, is worth considering. 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.