ADCP Applied in the Magdalena River Flood Management System

1. Where is the Magdalena River

The Magdalena River is located within the country of Colombia. It is the country's main river and is considered important in the system of South American waterways. It traverses different terrains of the country-from the mountain regions, plains, to valleys.

Passing through several significant cities, such as Bogotá (from its tributaries) and Barranquilla. The Magdalena River basin has a tropical climate with well-defined wet and dry seasons. The wet season, which usually falls between April and November, is very rainy. The snowmelt from the Andean mountains in the upper reaches also contributes to its water volume. The river is a vital water source for agriculture, industry, and transportation and also supports a rich biodiversity along its course.

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

There are various reasons for the flooding in the Magdalena River. The main one is heavy rainfall during the wet season. Heavy rains that fall within a short period or when the accumulated rainfall in a given time exceeds the normal capacity of the river to carry water raises the level of water in the river.

The topography of the catchment area is another important factor: flat plains and low-lying areas along the course of the river provide ample opportunity for the water to spread out easily during floods. Besides, the deforestation and changes in land use in the upper catchments can increase the surface runoff and reduce the natural water-holding capability of the land. Consequently, the Magdalena River is flood-prone, and accurate measurement of its flow characteristics becomes essential. Acoustic Doppler Current Profiler (ADCP) provides an advanced and efficient way of monitoring and managing the flow in the river in case of flood events.

3. How do ADCPs using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. This instrument emits acoustic signals into the water. The moving particles of water interact with these signals. When the acoustic waves, after striking the moving particles, bounce back, due to the Doppler effect the frequency of the reflected waves changes.

The ADCP current meter is equipped with multiple transducers that can send and receive acoustic signals in different directions. By precisely measuring 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 Magdalena River, it can measure the flow velocity from the riverbed to the water surface and across different widths of the river.

4. Application of ADCP to Magdalena River Floods

Flow Velocity Measurement: ADCP current profiler will be able to measure the flow velocity of the Magdalena River in cases of flooding with high accuracy. This becomes important in determining the speed at which water is flowing through different parts of the river. The flow velocity may denote regions where the water is running swiftly that could show the surge of a flood or change in flood behavior. For example, variations in flow velocity can be closely watched near the riverbanks or in the main channel.

This sensor enables one to calculate the flow rate of the river by combining it with the measured flow velocity, using the cross-sectional area of the river. Such data for the Magdalena River is very useful in estimating the total volume of water that passes through a section in every unit time, helpful for flood forecasting and understanding the general magnitude of the flood.

Sediment-transport Research: A considerable amount of sediment is usually transported along the Magdalena River during floods. The sediment particles' movements can be detected by ADCP profiler, as it analyzes the backscattered acoustic signals. In this way, the sediment-transfer patterns during floods can be studied, which is an important consideration for long-term modeling of the riverbed topography and related changes in the hydrological behavior of the river.

5. How can the data measured by ADCP be utilized for flood warning and risk management of the Magdalena River?

Flood Warning Aspect

• Flow-velocity and Flow-rate Data Monitoring: ADCP flow meter allows for continuous monitoring of flow velocity and flow rate. In case the flow velocity exceeds beyond a certain threshold or if the flow rate shows sudden increase, then that could trigger an early flood warning. This information can be relayed to local authorities and communities near the river.
• Water-level Prediction and Warning: Using the flow data obtained with ADCP in conjunction with other hydrological models, one may compute the water-level changes. Based on the relationship between the rate of flow and water-level, more accurate flood warnings can be issued, with particular emphasis on the easily flooded areas of the Magdalena River.

Risk Management Aspect

• Water-Conservancy Project Dispatching Decision Support: Accurate flow data from ADCP serves as a very valuable input to operate water-conservancy projects like dams and canals along the Magdalena River. This helps make more effective decisions on releasing or storing water to prevent flood risks further downstream.
• Flood-disaster Assessment and Emergency Response: After a flood event, the ADCP-measured data can be used to assess the extension and impact of the flood. This helps in formulating appropriate emergency-response strategies, including rescue operations and damage-assessment surveys.

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

For the measurement of high-quality current in the Magdalena River, the equipment should be manufactured with good materials. It must be resistant to such an aggressive aquatic environment: the water's corrosive effect and floating debris and sediment impact. It is also preferable for the size and weight of the equipment to be as small as possible, because this facilitates installation and the deployment of equipment in any part of the river.

It is also important to have low power consumption for continuous operation, especially 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 meter is preferably made of titanium alloy. Titanium alloy offers excellent corrosion resistance, which is important to withstand the corrosive effects of the water from the Magdalena River over time. It also offers a good strength-to-weight ratio, thus making the equipment more durable and easy to handle.

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

The measurement purpose should first be put into consideration when choosing the equipment for the current measurement in the Magdalena River. Horizontal ADCP can serve if the measurement of horizontal cross-section is to be done since it provides full flow-velocity information across the width. For the case of vertical cross-section measurement, the Vertical ADCP can best serve to measure the flow-velocity distribution from the riverbed to the water surface.

For the frequency of ADCP, in relatively shallower parts of the Magdalena River, for example, less than 70m, a 600kHz ADCP can provide accurate measurements. For deeper areas, around 110m, a 300kHz ADCP is more suitable. There are several brands of ADCPs available on the market, including some well-known ones like Teledyne RDI, Nortek, and Sontek. Besides, there is 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.