Open Channel Flowmeters

Open channel flow meters are used to measure flow in non-pressurised systems where liquid moves through channels, flumes, weirs, partially filled structures or gravity-fed water lines. Unlike closed-pipe flowmeters, open channel systems do not operate under full pipe pressure. Instead, flow is typically calculated by measuring the liquid level at a defined point and converting that level into a flow rate according to the channel, flume or weir geometry.

Reinmeer open channel flow measurement instruments are suitable for applications where water flow measurement, wastewater flow measurement and industrial discharge monitoring are required. These systems are commonly used in wastewater treatment plants, water infrastructure projects, drainage channels, irrigation systems, industrial effluent lines and environmental monitoring points.

In open channel applications, the accuracy of the measurement depends not only on the instrument but also on the hydraulic structure. The channel shape, flow profile, approach conditions, turbulence, sediment, foam, debris and installation point can all affect the relationship between level and flow. For this reason, open channel flow measurement should be evaluated together with site conditions and hydraulic design.

As part of Reinmeer’s industrial flow meter portfolio, open channel flowmeters support applications where liquid flow must be monitored without a fully pressurised pipe system. For closed pipe applications, other technologies such as ultrasonic or electromagnetic flow measurement may be more suitable depending on the medium and installation requirements.

Wastewater and Water Infrastructure Applications

Open channel flowmeters are widely used in wastewater systems because many treatment and discharge points operate in non-pressurised channels. They can be installed at inlet channels, outlet channels, treatment process stages, effluent discharge points and monitoring stations where continuous wastewater flow measurement is required.

In water infrastructure, open channel measurement can support irrigation canals, drainage networks, stormwater systems, river diversion points and gravity-fed water distribution structures. These applications often require reliable measurement under changing environmental and hydraulic conditions.

Industrial facilities may use open channel flow measurement for process water discharge, treated effluent monitoring or compliance-related reporting. In these environments, stable measurement helps improve visibility over discharge volumes and supports better process supervision. Site conditions such as sediment build-up, foam, floating debris and channel maintenance should be considered during selection and installation.

Level-Based Flow Calculation in Open Channels

Many open channel flow meters calculate flow from level measurement. The instrument measures the liquid height at a defined point, then converts this level into flow rate using the hydraulic characteristics of the flume, weir or channel. This means that level measurement is a central part of open channel flow measurement.

The level signal may be obtained using ultrasonic, radar or other non-contact level measurement technologies depending on the system design and site conditions. Non-contact measurement is often preferred because the sensor does not need to touch the liquid, which can be useful in wastewater, contaminated water or outdoor channel applications.

For reliable calculation, the level measurement point must be installed correctly. The sensor should be positioned where the water surface is representative and not heavily disturbed by turbulence, foam, inlet flow or obstructions. Incorrect level measurement can directly affect the calculated flow value.