Water Velocity and Flow Meters

In a global environment where water supply is an increasing concern, demand for water-flow monitoring equipment is also growing. Water scarcity affects every continent without exception, and for at least one month a year 2.8 billion people suffer the effects of the problem. Of these, 1.2 billion – one fifth of the world’s population – chronically lack secure access to clean potable water.

Water Velocity and Flow Meters

Climate change, specifically the effects of rising sea levels and increasing glacial flows, is also leading to expanding demand for water-flow monitoring equipment for a variety of applications. What specific types of devices are available, how do they work and what can they be used for?

Continuous Monitoring

Water-flow meters are generally divided into two categories: meters designed for continuous monitoring and meters for instant sampling of flow. Continuous-flow monitoring is used to gather scientific data over time, to track the development and changes of flows and to learn more about a hydrological system.

Such equipment has a wide range of uses alongside purely scientific investigation. Applications include those in the sewage treatment industry, where effluent off-flow and wastewater flows must be carefully monitored during water treatment operations. The agricultural sector also employs continuous-flow meters in contexts where irrigation channels require careful attention to produce the most profitable and efficient crops year after year.

Besides these specific uses, continuous-flow meters are used across many branches of industry where flow measurement and monitoring are required, including the pharmaceutical, chemical, and food and beverage industries. Specially designed flow meters have also been developed for use in highly conductive liquids.

Instantaneous Measurement

For instantly sampling the velocity and flow rate of a liquid, instantaneous meters are used. Predominantly employed by scientists, researchers and hydrologists, these devices can be used to monitor the flow rate and velocity of water in rivers, streams and canals, as well as to quickly and efficiently calculate water distribution throughout a hydrological system to determine flood risk, for example.

Both types of flow meter can feed data into other surveying tools and even into analytic software. When combined with a bathymetric surveying system, water velocity and flow meters can help provide a full picture as to the profile of a body of water as part of a hydrographic survey. Software can also be used to visualise water flows, transfer and distribution in 3D.

How Does It Work?

Water-flow meters use a variety of different technologies to provide the required data. Naturally, different collection techniques are necessary for monitoring flow in the deep ocean compared to small open channels or pipes. The most straightforward technology, used in small channel flow monitoring, is an impeller mechanism. This is a small propeller which spins as water flows around it, feeding data to a calibrated device which monitors and records flow velocity.

Ultrasonic beams or pulses can also be used. These pulses are projected into the moving body of liquid at two separate points, with suspended particles and bubbles acting as tracers to reflect the pulses back to the probe as they travel between the two measuring points. Velocity is calculated by examining the time spent to travel from the first point to the second. Calculating mean velocity requires a continuous flow meter and is deduced by analysing a velocity histogram.

Different configurations are suited for varying applications, from hand-held devices to measure streams and open channels all the way up to estuary and ocean current monitoring. Data can be transmitted wirelessly to a research station to enable fast, easy and accurate modelling and analysis.