How to Measure Water Current of Ganale Dorya?

1. Where is Ganale Dorya?

The Ganale Dorya is a river in the Horn of Africa. It is located in Ethiopia and Somalia.

In Ethiopia, the river rises in the highlands and flows through a region composed of agricultural areas as well as semi-arid landscapes. This river is very essential as a source of water for the local people. It supports the growth of crops such as maize, sorghum, and other cereals through irrigation. Areas along its banks are also home to various species of birds down to small mammals.

As it enters Somalia, it continues through a more arid environment. It remains here an important water supply for both human and animal consumption. The course is part of the local topography and has shaped ways of life for those living off it.

2. What is the Flow Rate of the Ganale Dorya like?

This, therefore, means that seasonal rainfall greatly influences the flow rate of the Ganale Dorya. During the wet season, normally between March and June in the highlands of Ethiopia, there is a very high increase in flow in the river. The water level rises; likewise, the current becomes stronger. The high-flow period is very vital in recharging groundwater for the irrigation of agricultural fields, therefore ensuring that the ecological functions of both the river and its wetlands are maintained.

This would mean that during the dry period, which may be taken by a large part of the year, the flow rate decreases. The river shallows and narrows, with some parts of the river drying up in the downstream areas of Somalia if extreme conditions are experienced in a more arid area. The flow rate is also impacted by human activities like the extraction of water for both agriculture and domestic use, and also the construction of small-scale water management structures such as dams and canals.

3. How to Measure Water Current of Ganale Dorya?

There are several ways to measure the water current of the Ganale Dorya:

Velocity Meter Method: Conventionally, this method applies mechanical or electrical velocity meters. The conventional velocity meters normally contain a mechanical rotating element, such as a propeller, which rotates with the water flow at a speed related to the water velocity. These meters are installed at discrete points within the river and are often attached to bridges, piers, or other fixed installations. This method requires multiple installations at different locations and depths to get a comprehensive understanding of the overall flow. This may be rather tiresome and labor-intensive since the course of Ganale Dorya is long, considering the sometimes difficult-to-reach areas.

Acoustic Doppler Current Profiler (ADCP) Method: Much higher in sophistication and ease relative to the former is the ADCP current meter method for water current measurement. With this, acoustic waves work to measure the velocity at any number of points within a water column all at once. It can give a very minute detail of the water current from the surface to the riverbed by emitting sound pulses and analyzing the Doppler shift of the reflected signals. ADCPs can be mounted on boats or fixed structures near the river. Compared to the velocity meter method, this method allows for a more accurate and comprehensive view of the flow patterns.

Buoy Method: Buoys are available that can be deployed at the surface of the Ganale Dorya. These buoys have sensors that can record the surface current as it travels with the flow. Such records give information on direction and speed of the surface movement. The major disadvantage is that it largely focuses on the surface layer and cannot give in-depth details of the flow within more inner levels of the river.

Of these, the ADCP method is gaining more and more favor because it can provide detailed and extensive data with relatively less effort and in a shorter duration.

4. How Do ADCPs Using the Doppler Principle Work?

The working principle of ADCPs is based on the Doppler principle. When an ADCP current profiler is used in the measurement of the water current of the Ganale Dorya, it sends acoustic pulses into the water. These pulses interact with particles in the water, such as sediment particles, small aquatic organisms, or other suspended matter.

Once in motion, these particles develop a shift in the frequency of the reflected sound waves, through a process known as the Doppler effect. The frequency of the reflected waves is higher than the frequency emitted when the particles move towards the ADCP profiler, while the frequency is lower if they move away from the device. This is what the ADCP precisely measures and calculates, with complex algorithms, to derive the water's velocity at various points across its measurable distance range.

Besides velocity measurement, an ADCP flow meter is also capable of ascertaining the direction of the flow by analyzing phase shifts of the reflected signals from different directions. These permit detailed velocity profiles of the water flow at depth and across sections of the river.

5. What's Needed for High-Quality Measurement of Ganale Dorya Currents?

For high measurement quality of the Ganale Dorya currents, some characteristics should be ensured within the equipment.

Reliability of materials with the violent conditions of the environment that the river may expose is necessary. The arid and semi-arid regions that fall within the course of the Ganale Dorya imply high temperatures, dust, and sediment-laden water. A small size and lightweight is advantageous, especially in the view of easy deployment and retrieval at areas along the river, which can be remote and sometimes difficult to access.

Since most parts of the river's surroundings are not equipped with extensive power infrastructure, the equipment needs to operate over long periods with minimum power consumption to ensure continued and reliable data collection. Cost-effectiveness is another major consideration. Affordable equipment without sacrificing quality is a critical need in conducting comprehensive measurements across the river.

For the casing of the ADCP meter, titanium alloy is a perfect choice. The material has great corrosion-resistant properties, something very important as the equipment will be in contact with river water at all times. It also has a good strength-to-weight ratio, which means it can provide a durable casing while keeping the overall weight of the equipment relatively low. This helps in the protection of the internal components and in ease of handling during deployment and retrieval.

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

While selecting appropriate equipment for current measurement at Ganale Dorya, two main factors shall be considered.

Depending on the purpose of usage, the horizontal ADCP-HADCP-shall be a suitable one for horizontal cross-section measurements. It is a measure of the flow velocity across a horizontal plane and provides valuable information on the lateral movement of water in the river. In case of vertical cross-section, the vertical ADCP shall be more appropriate because this will present the flow velocity from the surface to the riverbed along a vertical line, thus being useful for understanding the nature of flow vertically.

In terms of frequency, different frequencies apply for different water depths. An ADCP with a frequency of 600 kHz, for instance, is well-suited for water depths within 70 m. It would yield accurate measurements in relatively shallow parts of the Ganale Dorya. Meanwhile, an ADCP with a frequency of 300 kHz is more appropriate for water depths up to 110 m and can handle the deeper sections of the river where the flow patterns may be more complex.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. Additionally, a Chinese ADCP brand, China Sonar PandaADCP, is highly recommended. It has a casing made entirely of titanium alloy, which provides excellent durability and corrosion resistance. It also offers an incredible cost-performance ratio. You can find more information about it on its official website: https://china-sonar.com/.

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