How to Measure the Water Current of the Lerma River

1. Where is the Lerma River?

The Lerma River lies in central Mexico. It is considered one of the main important rivers in the hydrological system of this country.

The river flows through an area that has agricultural areas, towns, and some mountainous places. It is an extremely important water source for various communities and agricultural activities in those areas. The Lerma River waters the great crops of wheat, corn, and vegetables; it supplies water for urban and industrial uses in the various cities and towns along its course. Its riverbanks are homes to a wide variety of wildlife that includes fish species like carp and catfish, and avifauna like herons and egrets. These are the balancing factors of nature, including floodplains and wetlands, that provide a site for breeding and feeding grounds for many species.

2. What is the flow rate of the Lerma River?

The flow rate of the Lerma River varies significantly with season and climate. During the rainy season, normally during the summer rains and snowmelt in the mountains of its upper reaches, the flow rate of the river increases considerably. The river swells and is able to carry a large volume of water.

In the dry season, it has a lower flow rate. Still, it possesses a base flow that might be important for the survival of fish and other aquatic life and to support fishing and limited irrigation. The average flow rate may vary from a few cubic meters per second in the dry season to hundreds of cubic meters per second in the peak of the wet season.

3. How to measure water current of the Lerma River?

Velocity Meter Method

This traditional method makes use of mechanical or electronic velocity meters. These are installed at selected points along the river, which directly measure the velocity of the water at that particular point. However, to have a proper understanding of the overall water current, several measurements must be taken across different depths and sections of the river. Considering the length and changing conditions of the Lerma River, this method is labor-intensive and time-consuming.

ADCP Method

ADCP current meter represents a more advanced and comfortable variant of water current measurement. It employs sound waves to identify the movement of water particles. It is capable of measuring the velocity of water at several depths simultaneously by transmitting acoustic signals and analyzing the Doppler shift of the reflected signal. This gives a highly detailed profile of the water current and allows for a more accurate assessment of the flow conditions throughout the river. ADCPs can be mounted on boats if the river is navigable, on bridges if available, or deployed on buoys for continuous monitoring.

Buoy Method

In the buoy method, buoys with sensors are submerged in the river to estimate the displacement of water around the buoys. They can float on the surface and give an indication of the current in the surface. However, these may not be as true representatives of the actual water current and the variations in velocity at different depths as provided by the other methods.

Among these, the ADCP current profiler is more advanced and efficient in measuring the water current of the Lerma River.

4. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of the Doppler effect. An ADCP flow meter sends an acoustic signal into the water, and as the sound waves travel through the water, they interact with the moving particles of water. Due to the movement of the water particles, the frequency of the reflected sound waves changes by the Doppler effect.

If the water particles move towards the ADCP profiler, this frequency of the reflected wave will be higher than the one emitted. On the other hand, if the water particles move away from the ADCP, the reflected wave frequency will be lower. Since the change in frequency is measured correctly, the ADCP can evaluate the velocity of the particles of water at different profundity.

Individual velocity measurements are then combined by the ADCP meter at many depths to provide a complete profile of the water current. This helps the researchers to understand the nature of water flow, not only on the surface, but throughout the vertical section of the river.

5. What's needed for high - quality measurement of the Lerma river currents?

For high - quality measurement of the Lerma River currents, the equipment should have the following characteristics.

The equipment should be highly reliable in material. It has to resist adverse conditions of the river environment, such as being in water and sediment and under variable temperatures. The variable flow of the Lerma River and the presence of debris in high - flow periods require durable equipment.

Other desirable characteristics include a small size, light weight, and low power consumption. A small and light device is easier to manipulate and launch, whether it is in a boat or attached to a buoy. Low power consumption means equipment can operate for long periods without necessarily needing immediate battery replacement or access to a continuous power source.

Cost - effectiveness is an important factor. The lower the cost, the more widespread use of the measurement equipment and hence a better monitoring of the river.

The casing of the ADCP flow meter can be done using the Titanium alloy. Titanium alloy is highly resistant to the corrosive action of the water and other substances that this equipment will be in constant contact with in the Lerma River. It is a strong and resilient material with high resistance to physical impacts and also to pressure changes that could happen during the deployment and operation of this equipment. Additionally, the density of the titanium alloy is relatively low, and this contributes to the general aim of keeping the equipment lightweight.

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

There are various things that one should consider in selecting appropriate equipment to measure the current of the Lerma River.

Based on the Purpose of Use

If the intention is to measure the horizontal cross-section of the river current, then an HADCP should be used. HADCPs are designed to provide accurate measurements of the water flow in the horizontal plane, which is useful for understanding the overall movement of water across a particular section of the river.

If the focus is to measure the vertical cross-section of the river current, then a vertical ADCP current profiler should be selected. Vertical ADCPs are able to measure the velocity of the water at different depths with high accuracy, providing a detailed profile of how the water is flowing vertically within the river.

Based on Frequency

Frequency will be chosen depending on the water depth in the Lerma River. Generally, a 600 kHz ADCP should suffice for depths up to 70 meters. The frequency of 600 kHz will yield a good resolution and accuracy of measurement in the water current of the relatively shallower waters.

For deeper waters, such as those exceeding 70 meters up to around 110 meters, a 300 kHz ADCP is more appropriate. The lower frequency of 300 kHz can penetrate deeper into the water and still provide reliable measurements of the water current.

There are well-known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, for those seeking a cost - effective option with excellent quality, the China Sonar PandaADCP is worth considering. It is made of all - titanium alloy material, ensuring durability and reliability. With its remarkable cost - performance ratio, it provides a great alternative for measuring the water current of the Lerma River. 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.