ADCP Application in the Flood Management of Okavango (Cubango) River

1. Where is Okavango(Cubango) River?

Okavango (Cubango) River is one of the major watercourses in southern Africa. It rises in the highlands of Angola and flows through Angola and Namibia. The river forms a huge inland delta in Botswana called the Okavango Delta, which is a world - famous wetland area.

This river passes through cities and towns such as Rundu in Namibia. In terms of rainfall, the upper reaches of the river in Angola receive more rainfall due to its location in a relatively wetter climatic zone. The annual rainfall can vary, but generally, the wet season brings abundant precipitation that feeds the river. The Okavango River is a source of vital water in surrounding arid and semi-arid regions, with a resulting rich variety of flora and fauna in the delta area.

2. What are the reasons for floods in Okavango (Cubango) river?

The flooding in the Okavango River results from a combination of many factors. Heavy rainfall over the upper catchment is one of the reasons for flooding. During the rainy season, the river's water can increase rapidly due to the intensity of the precipitation. Topography also influences the flow regime of the river. The relatively flat terrain in the delta area slows down the water flow and hence allows the water to easily build up and cause flooding.

Another factor is the soil type and land cover in the basin. In some areas, the low permeability of the soil may not allow water to infiltrate the ground quickly, leading to surface runoff and contributing to flood conditions. Since traditional measurement methods have limitations in accurately assessing the complex flood-causing factors and dynamic flow conditions, the ADCP has become a more efficient and accurate measurement tool for flood management.

3. How do ADCPs making use of the Doppler Principle work?

The working of an ADCP is based on the Doppler effect. It sends acoustic pulses into the water from the instrument. In turn, the pulses interact with the moving water particles, changing the frequency of the reflected sound waves. By precisely measuring this frequency shift, the velocity of the water flow can be determined. The ADCP has several transducers that emit and receive acoustic signals in different directions, hence capable of measuring the velocity at different depths and angles of water flow through a river cross-section. For instance, in the Okavango River Delta, it will give a full profile of flow velocity from the bed to the water surface.

4. What are the applications of ADCP in floods of Okavango (Cubango) river?

Flow Velocity Measurement: ADCP can give correct flow velocity measurement of Okavango (Cubango) River during floods. This is vital in terms of ascertaining the speed at which water is moving through a section of the river. For example, it can locate those areas where the flow velocity is increasing at a fast rate, and this can be indicative of a probable flood surge.

Flow-rate Measurement Application: The flow velocity is measured in conjunction with the cross-sectional area of the river to calculate the flow rate. In this case, it will help in the estimation of the Okavango River floods regarding the volume of water that passes through a section per unit time. This is vital in flood forecasting and understanding the overall flood magnitude.

Sediment-transport research: The Okavango River carries a huge amount of sediment during flooding. It is possible for ADCP profiler to identify the movements of sediment particles by analyzing backscattered acoustic signals. Consequently, in this way, researchers can investigate sediment-transport patterns during floods, which is considered important knowledge to understand the long-term evolution of the riverbed and the delta area.

5. How can the data measured by ADCP be used in flood warning and risk management of Okavango Cubango river?

Flood Warning Aspect

Flow-velocity and Flow-rate Data Monitoring: ADCP provides for the continuous monitoring of flow velocity and flow rate. For detection of abnormal changes, if the flow velocity exceeds over a certain threshold or if the flow rate shows any sudden increase, it may trigger an early flood warning. The information may be relayed to the local authorities and communities in the vicinity of the river.

Water-level Prediction and Warning: The flow data derived from ADCP meter can be input into other hydrological models to predict variations in water level. Study of the relation between the flow rate and the water level will provide more accurate flood warnings, especially in the flood-prone Okavango Delta area.

Risk Management Aspect

Water Conservancy Project Dispatching Decision Support: Accurate flow data from ADCP flow meter supplies very important inputs for operating decisions regarding water conservancy projects along the Okavango River, like dams and channels. Decisions on the release or impoundment of water can be done in an efficient way to reduce flood hazards further downstream.

Flood - disaster Assessment and Emergency Response: Subsequent to a flood event, the ADCP-measured data are applied in assessing the flood magnitude and the area affected. This aids in developing the appropriate emergency-response measures involving rescue operations and damage-assessment surveys.

6. What's needed for high - quality measurement of Okavango Cubango river currents?

For the Okavango (Cubango) River current measurement with high quality, the equipment requires materials that are reliable. It should be resistant to the harsh aquatic environment, including sediment-laden water and possible chemical substances in the water. A small size and lightweight are desirable features; they enhance the installation and deployment of the equipment at various locations along the river.

Low power consumption is also essential to ensure continuous operation in remote areas where power supply may be limited. Cost - effectiveness is another factor, as large - scale deployment may be required for comprehensive river - current monitoring. The casing of ADCP current profiler is preferably made of titanium alloy. Titanium alloy offers excellent corrosion resistance, which is crucial for withstanding the corrosive effects of the river water over time. It also provides a good strength-to-weight ratio, which makes the equipment durable and easier to handle.

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

Equipment selection for current measurement in the Okavango (Cubango) River should be based on the purpose of the measurement. In horizontal cross-section measurement, the HADCP is ideal, as it provides detailed flow-velocity information across the width of the river. For vertical cross-section measurement, a Vertical ADCP current meter is more appropriate to measure the flow-velocity distribution from the riverbed to the water surface.

ADCP Frequency-For relatively shallower parts of the Okavango River, for example, water depth less than 70m, 600kHz ADCP can be used to measure accurately. For deeper areas, for instance, around 110m, it is better to use 300kHz ADCPs. There are different types of ADCP brands available, such as well-known ones Teledyne RDI, Nortek, and Sontek. There is also a recommended Chinese ADCP brand, China Sonar PandaADCP. It is made of all - titanium alloy material and offers excellent performance and cost - effectiveness. You can visit its website (https://china-sonar.com/) for more information.

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