ADCP in the Shire River Flood Management

1. Where does the Shire River occur?

The Shire River is one of the great rivers in Africa; more precisely, it lies in Malawi. It originates from Lake Malawi.

Geographically, it courses through southern Malawi, passing through plains with some savannah. It also cuts across several towns and villages, hence being important both in local water supply and transportation.

This has a marked wet and dry season in rainfall. Normally, from November through April, the wet season is a time of much rain. It contributes to the volume of water in the Shire River by a great amount. However, the amount of rain that could be received may be highly variable from year to year. When there was a period of heavy and continued rain, the water in the river would increase hugely.

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

Many factors are involved in the development of floods in the Shire River. The first is that much rain, particularly during the wet season, is one of the reasons this occurs. If the rains are very heavy and continuous, the sudden reception of large volumes may be too much for the river to handle, and with rising water levels, flooding would occur.

The second factor that contributes is the aspect of topography in the river basin. In some areas of the Shire River, conditions of generally flat terrain can be found where water is more apt to lay relatively still. Human activities such as deforestation along the upper reaches of the river have contributed to increased soil erosion. This soil eventually deposits in the river channel and has reduced the carrying capacity within the river and thus makes it susceptible to flooding.

In addition, improper control of flood situations in certain areas of rivers works as an added factor towards increasing the flood situation. The development of technique acoustic doppler current meter, Acoustic Doppler Current Profiler, a more advanced and user-friendly measurement technique for assessing the flow conditions of the river during flood section applied.

3. How do the Doppler Principle based ADCPs work?

Acoustic Doppler Current Profiler(ADCP) work off the principle of Doppler. When the ADCP current meter sends out an acoustic signal into the water, the signal scatters off of moving water particles. Because the water is in flow, the reflected acoustic signal has a shift in frequency due to the Doppler effect.

The ADCP measures the difference between the emitted frequency and the received frequency of the acoustic signal. Thus, it can estimate from this frequency shift the velocity of the water at some depth. There are usually several transducers present in any device that can send and receive acoustic signals in various directions to obtain the profile of water velocity across a section of the river.

For example, if the water is moving toward the ADCP current profiler, then it would result in a higher frequency of the reflected signal than that emitted; vice versa would happen when the water is moving away from it. By measuring the frequency changes with millisecond accuracy and applying appropriate mathematical algorithms, the ADCP does an accurate measurement of velocity at different points within its range.

4. Application of ADCP to the floods of the Shire River

Measurement of Velocity

In flood events on the Shire River, ADCP flow meter plays an important part in recording water flow velocity accurately. It continuously monitors water velocity at depth and location, with real-time information on how fast the water is running. This will be of importance in understanding the dynamics of the flood-for example, being able to predict the direction and intensity of movement of the floodwaters.

Flow Measurement Application

The ADCP meter can also be used to measure the Shire River flow rate. By combining the measured water velocities at different points across a section of the river with the known cross-sectional area of the river, it can calculate the total volume of water flowing through the section per unit time-that is, the flow rate. This constitutes fundamental information for the general volume of water valuation in case of flooding, as well as for flooding control and decision-making with regard to water resource management.

Application in Sediment Transport Research

Besides flow and velocity measurements, ADCP profiler can be useful in sediment transport research along the Shire River during floods. During water flow, it transports sediments, and the variation in the backscattered acoustic signal can be recognizable by an ADCP due to the presence of these sediments. Researchers can estimate quantity and movement through such changes, which are important in comprehending the long-term evolution of the riverbed and the action of floods on the sedimentary environment of the river.

5. How would you utilize the data measured by ADCP in respect of flood warning and risk management of the Shire River?

Flood Warning

Velocity and Flow Data Monitoring: The ADCP continuously provides real-time velocity and flow data. When the water velocity is measured above the threshold or when the flow rate increases drastically, such a scenario could indicate that a flood peak or even flood might be arriving. Such early warning could allow the necessary authorities to undertake necessary action, such as the evacuation of people in low-lying areas or reinforcing flood defenses.

Prediction of Water Level and Warning: By relating the measured flow data to the historical water level data and using appropriate hydrological models, acoustic doppler velocity meter data can be used to predict the future water levels. In case this forecasted water level is expected to exceed the flood warning level, timely warnings can be issued to the public, enabling them to prepare for the flood.

Risk Management

Support for the Scheduling Decision of Water Conservancy Project: The precise flow and velocity data from ADCP can support the decision on the operability of water conservancy projects such as dams and sluices. As an example, the water quantity released from a dam can be adjusted based on the recorded water flow to control the level of water in the Shire River and create ways to minimize the effects of floods.

Assessment of flood disaster and emergency response: ADCP is able to be used in the assessment of the flood disasters on the severity of the flood inundation, velocity of the flood flow, and sediment deposition quantity after a specific flood event. This information is important in formulating emergency response plans, including post-flood reconstruction and rehabilitation works.

6. What is needed to ensure quality measurement for the currents of Shire River?

Quality measurement for the currents of Shire River demands addressing a number of factors. First, the equipment should be made from reliable materials. One of the important things is the casing of the ADCP. The casing is recommended to be made from titanium alloy. Titanium alloy has several advantages. With high strength, it can support the pressure and impact of flowing water in the river. Another important feature is that this is highly resistant to corrosion, given the water environment of the Shire River, which may contain a variety of corrosive substances.

Other than the material reliability, it is also important that the size and weight of equipment be as small and light as possible. This facilitates easier installation and operation of the doppler current profiler in various locations along the river, especially in areas that are not easy to access. The power consumption should also be low to allow for running continuously over a longer period without often changing batteries or its connection to a source of power. The equipment cost should also be relatively low to enable the measurement over a large extent. A lower cost has come to mean deploying more ADCPs along the Shire River for more comprehensive and detailed data for use in flood management.

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

In view of selecting the right equipment for current measurement in the Shire River, a variety of aspects should be considered: according to the measurement that needs to be taken, if it is for horizontal cross-section measurement, then a Horizontal ADCP must be selected. However, if it is for vertical cross-section measurement, then a Vertical ADCP should be appropriate.

The frequency, further, shall be selected based on different water depths. For instance, a 600 kHz ADCP shall be suitable for water depths within 70 m. If the water depth of Shire River falls within this range and meets the measurement requirements, then a 600 kHz ADCP shall be considered. In deeper waters than this, say to about 110 m, a 300 kHz ADCP would be more appropriate since it would yield better data in such depths.

Some of the famous brands of acoustic doppler profiler in the market are Teledyne RDI, Nortek, and Sontek. However, for people looking for more economic options, the China Sonar ​PandaADCP has been a good choice. It is made of all-titanium alloy material, which guarantees stability and dependability within the water environment. Besides that, it offers a great cost-performance ratio. You can find more about it on its official website: ​https://china-sonar.com/.

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