ADCP's Application in Flood Management of Naryn River

1. Where is Naryn River?

The Naryn River is a major river in Central Asia. It is mainly located in Kyrgyzstan and is one of the main tributaries of the Syr Darya.

The river originates in the mountainous range of Tien Shan. Its upper parts flow through alpine and sub-alpine zones of beautiful glaciers, high-altitude meadows, and meager forests. Moving downstream, it takes the direction toward more arid valleys and plains.

The climate in the catchment area of the Naryn River varies from subzone to subzone according to the altitude. It is cold and alpine in the upper mountain areas, with heavy snowfalls during winter. These snow and ice reserves in the catchment area are considered the main source of water in the river. In the lower parts, the climate is more arid, with relatively scarce rainfall.

Cities and towns such as Naryn city are situated along the river. The river is an important water supply for the areas; domestic water supply, irrigation, and partly local hydro - power generation is supported by it as well.

2. What are the reasons for floods in Naryn River?

Snowmelt: The most prevalent cause of flooding in the Naryn River is snowmelt. Originating from mountainous areas, large amounts of snow accumulate during winter. During the spring and early summer, these snows, with increasing temperatures, start melting at an incredible rate. The sudden coming of a large volume of water from the melting snow can very easily exceed the natural carrying capacity of the river and thus floods occur.

Glacial Melting: The upper reaches also contain glaciers that add to the water volume of the Naryn River. Because of climate change, glaciers are melting at higher rates. Water from glacial melting adds to the flow of the river, and during periods of intense melting or in combination with heavy snowmelt, it can trigger flood events.

Heavy Rainfall: While the lower catchment areas of the basin are arid, in some seasons heavy rainfall is recorded in the upper mountainous areas. When this is combined with snowmelt or glacial melting, it can further contribute to the flood situation by adding more water to the river.

In the context of flood management, Acoustic Doppler Current Profiler (ADCP) provides a more accurate and efficient way of measuring the flow of the river compared to traditional methods.

3. How do Doppler Principle-based ADCPs work?

ADCPs work on the principle of the Doppler effect. They transmit acoustic signals-essentially, sound waves-into the water. These signals interact with moving particles in the water, such as sediment, organic matter, and water molecules that are flowing with the current.

These moving objects reflect the emitted waves back, causing a shift in frequency. This shift in frequency, commonly known as the Doppler shift, has a direct relationship with the velocity of the moving objects. ADCPs are normally fitted with several transducers, which send acoustic pulses in various directions.

For instance, a downward-looking ADCP meter is able to measure the velocity profile of the water column from the water surface down to the riverbed. By analyzing the Doppler shifts of the reflected signals from different depths within the water column, the ADCP current meter can calculate the velocity of the water flow at each depth.

Knowing the velocity at various depths, and with additional information on the cross-sectional area of the river (which can be measured or estimated), it becomes possible to calculate other important parameters, such as the flow rate of the river.

4. What are the applications of ADCP in floods of Naryn River?

Velocity Measurement: During flood events along the Naryn River, ADCP current profiler is able to record the actual velocity of water flow with high accuracy both in lateral and vertical directions. This gives a better idea of how fast the floodwaters are moving. It will give them a clue as to when the flood would reach agriculture fields, settlements, or infrastructures. Continuous monitoring of the same velocity helps authorities take preventive measures such as evacuation of people or embankment strengthening.

Flow Measurement Application: Through integration over the cross-sectional area of the river, ADCP flow meter is used in the computation of flow rates from velocity. The magnitudes of flood will then be determined. In doing this, it offers greater information in the perspective that when this will be greater, for example, it overhauls the capacity of various flow-control structures including levee and dam structures to implement effective measures concerning mitigations of the same flow or flood.

Sediment Transport Research Application: Being transported by the floodwaters of the Naryn River, ADCP profiler can analyze the backscattered acoustic signals to study the movement of these sediment particles. Sediment transport during floods is important to understand in regard to changes in the riverbed. Sediment deposition and erosion will change the depth, width, and stability of the river, which then affects future flood risks and the overall health of the river ecosystem.

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

Flood Warning

Velocity and Flow Data Monitoring: The ADCP current profiler allows continuous monitoring of the velocity and flow data to enable early detection of abnormal changes in the river's flow. The increase in speed suddenly or an extreme alteration in flow rate could reflect an imminent flood or increase in a flooding situation. This can be integrated into flood warning systems for the correct timing of warnings to the respective local communities, emergency preparedness teams, and authorities involved.

Water Level Prediction and Warning: Measured flow data by ADCP meter, combined with other factors like the cross-sectional geometry of the river and historical records of water level, can be used to predict future water levels. If the predicted water level is expected to exceed the flood level mark, warnings can be issued in advance to enable people to evacuate or take protective measures.

Risk Management

Water Conservancy Project Scheduling Decision Support: The data from ADCP flow meter provides valuable input for decision-making with regards to the operation of water-conservancy projects such as dams, reservoirs, and diversion channels on the Naryn River. For example, during a flood, the flow data can help determine the optimal release rate from a dam to mitigate the impact of the flood downstream.

Flood Disaster Assessment and Emergency Response: On the occurrence of a flood, ADCP data post-flood can be employed for assessing the damage caused due to the flood. For example, the high-velocity flow areas, silt deposition, etc. This information is useful for guiding emergency response and recovery efforts, such as search and rescue operations and post-flood rehabilitation of infrastructure and ecosystems.

6. What's needed for high-quality measurement of Naryn River currents?

For high-quality measurement of the Naryn River currents, several aspects need to be considered.

Reliable Equipment Materials: The ADCP current meter should be manufactured with materials that can resist the harsh conditions of the environment in the Naryn River. It should be resistant to corrosion from the river water, impacts from floating debris such as branches and ice (in the upper reaches), and abrasion by sediment particles.

Small Size, Light Weight, and Low Power Consumption: A lighter and smaller-sized ADCP is easier to install and deploy, especially in remote sections along the river. This low power consumption enables the ADCP flow meter to operate over longer periods of time with no need for frequent replacement or complex power supply arrangements; this is helpful in undertaking continuous and long-term monitoring.

Low Cost: It is desirable to have a lower-cost ADCP meter to be able to deploy hundreds of units for complete coverage of the river.

In regard to casing material, one of the best options is that of titanium alloy. With a high strength, the titanium alloy can resist external forces that the ADCP current meter can bear. The material shows excellent corrosion resistance, hence it can continue its performance in water without degradation for a long period. Its relatively low density helps reduce the overall weight of the device while still maintaining structural integrity.

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

When choosing equipment for current measurement in the Naryn River, consider the following:

Purpose of Use: Horizontal cross-sectional flow measurement will require the use of a Horizontal Acoustic Doppler Current Profiler (HADCP). The flow velocity and other parameters across a horizontal section of the river can be measured using it. For a vertical cross-section, a vertical ADCP will be appropriate as it measures the velocity profile from the water surface to the riverbed along a vertical line.

Frequency Selection: Different frequencies of ADCPs are used for different water-depth ranges. For instance, a 600 kHz frequency ADCP is generally suitable for a water depth within 70 meters, while an ADCP flow meter with a frequency of 300 kHz is more appropriate for water depths up to 110 meters. It ensures the accuracy and reliability of the measurement results when the right frequency is chosen according to the actual water depth of the Naryn River.

There are well - known ADCP profiler brands such as Teledyne RDI, Nortek, and Sontek. Additionally, there is a Chinese brand, China Sonar PandaADCP, which features a casing made of titanium alloy and offers a good cost-performance ratio. 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.