ADCP's Application in Flood Management of the Pecos River

1. Where does the Pecos River lie?

The Pecos River lies in the southwestern United States. Originating from the Sangre de Cristo Mountains of New Mexico, it flows through New Mexico and Texas. It cuts through arid and semi-arid landscapes, playing an important role in an otherwise water - scarce region.

It passes through several small towns and ranches. The Pecos River basin has a semi-arid climate based on rainfall. Rainfall is generally scanty and not well distributed throughout the year. The river water volume is also supplemented by mountain snowmelt in spring. The Pecos River is significant for agricultural irrigation, besides giving water to livestock and certain industrial uses in the area.

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

Floods in the Pecos River can be caused by a combination of factors. Intense rainfall events, although rare in this semi - arid region, can lead to a rapid increase in water levels. When heavy rains occur over a short period, the river's capacity can be overwhelmed.

Snowmelt in the spring is another significant factor. A sudden and large-scale snowmelt in the upper reaches can send a large volume of water downstream. The topography of the river valley is also such that the narrow canyons, and relatively flat floodplains in some places, result in easy backup or spread of water. Overland flow, on the other hand, may be generated by changes in land use, such as over-grazing and urban development, each of which reduces the natural water-holding capacity of the land and increases surface runoff. In view of the importance of flood management, Acoustic Doppler Current Profiler (ADCP) offers a more accurate and efficient way of measuring and managing the flow of the river during flood events.

3. How do ADCPs using the Doppler principle work?

The working of ADCPs is based on the Doppler effect. The instrument emits acoustic signals into the water. The moving water particles interact with these signals. When acoustic waves, after interaction with moving particles, bounce back, then due to the Doppler effect, the frequency of the reflected waves changes.

The ADCP current meter has several transducers, each capable of transmitting and receiving acoustic signals in various directions. With the precise measurement of the frequency shift of the reflected signals, the velocity of the water flow at different depths and across different sections of the river cross-section can be determined. For example, in the Pecos River, it can measure the flow velocity from the riverbed to the water surface and across different widths of the river.

4. Applications of ADCP in Pecos River floods.

Flow Velocity Measurement: In regard to measuring flow velocity, ADCP current profiler would accurately determine the flow of water in the Pecos River during a flood. It will help explain the speed at which water is moving through various parts of the river. We will, by the flow velocity, be able to see where the water is flowing at a fast rate, hence showing potential flood surge or change in the behavior of the flood. For example, near the riverbanks or in the main channel, changes in flow velocity can be monitored closely.

Flow-rate Measurement Application: The flow rate can be determined by integrating the measured flow velocity and the cross-sectional area of the river. In the context of the Pecos River floods, this information is crucial for estimating the total volume of water passing through a particular section per unit time. This helps in flood forecasting and understanding the overall magnitude of the flood.

Sediment-Transport Research: A lot of sediment is transported in the Pecos River during flooding. In this context, ADCP flow meter can identify the movement of particles through the analysis of the backscattered acoustic signals. This enables sediment - transport research during the flood that is very important to study the long-term evolution of the river bed and, correspondingly, its impact on the hydrological features of the river.

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

Flood Warning Aspect

• Flow-Velocity and Flow-Rate Data Monitoring: The ADCP profiler provides for the continuous monitoring of flow velocity and flow-rate to enable the detection of abnormal changes. If the flow velocity is higher than the threshold or the flow rate rises sharply, then the early flood warning can be triggered. The information can also be conveyed to the local government and communities residing along the banks of the river.
• Water-level Prediction and Warning: The flow data obtained from ADCP meter can be used in conjunction with other hydrological models to predict water-level changes. By analyzing the relation between flow rate and water level, more accurate flood warnings can be issued, especially in the flood-prone areas of the Pecos River.

Risk Management Aspect

• Water-Conservancy Project Dispatching Decision Support: The precise flow data from ADCP will serve as very useful input in the operation of water-conservancy projects like dams and canals along Pecos River. Decisions on water release or storage can be made more efficiently to avoid flood risks downstream.
• Flood-disaster Assessment and Emergency Response: In the event of a flood, the data measured by ADCP is used to assess the flood event and its impact. This helps in formulating appropriate emergency-response strategies, including rescue operations and damage-assessment surveys.

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

The equipment should be made of reliable materials for high-quality current measurement of the Pecos River. It should be able to resist the harsh aquatic environment, including the corrosive effects of the water and potential impacts from floating debris and sediment. Small size and light weight are advantageous, as they facilitate the installation and deployment of the equipment in different locations along the river.

It is also important to ensure low power consumption, so that continuous operation can be ensured, especially in remote areas where power supply may be limited. It should be cost-effective since a large-scale deployment may be necessary for comprehensive river-current monitoring. Titanium alloy is preferred for making the casing of ADCP. The corrosion resistance of the titanium alloy is excellent, which is required to withstand the action of the Pecos River water over time. It also provides a good strength-to-weight ratio, which will make the equipment more durable and easier to handle.

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

For current measurement equipment selection in Pecos River, the purpose of the measurement has to be brought into consideration. In case horizontal cross-section measurement will be conducted, HADCP should be considered the appropriate equipment since it produces a good and detailed flow-velocity information across the width of a river. A Vertical ADCP would be more appropriate for making the flow-velocity distribution from the riverbed to water surface for vertical cross-section measurements.

For relatively shallower parts of the Pecos River, say, with water depth less than 70m, a 600kHz ADCP can work well. For deeper areas of around 110m, it is better to use a 300kHz ADCP. The ADCPs available in the market include some well-known brands like Teledyne RDI, Nortek, and Sontek, among others. Recommended Chinese brand for ADCP is 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.