Open Channel Flow Monitoring Solutions
Open Channel Flow Monitoring Solution Overview
Open channel flow monitoring requires different measurement technologies depending on channel geometry, water quality, civil engineering conditions, power supply and maintenance requirements. For standardized concrete channels and regulated discharge points, an ultrasonic weir or flume flow meter converts measured water level into flow using the calibrated relationship of a standard weir or flume. For natural rivers and irregular earth channels where constructing a weir is impractical, a radar flow meter measures surface velocity and water level without contacting the water. For turbid wastewater and sediment-laden small or medium channels, an ultrasonic Doppler open channel flow meter can directly measure flow velocity and water level with an immersed probe.
This solution is intended to help engineers, system integrators and project purchasers select an appropriate open channel flow measurement method according to the measuring point, medium condition, installation environment, communication requirement and maintenance capability.
Related instruments:Ultrasonic Open Channel Flow Meter |Radar Flow Meter |Flow Measurement Instruments
| Technology | Best-Fit Channel | Measurement Method | Main Selection Reason |
|---|---|---|---|
| Ultrasonic Open Channel Flow Meter | Standardized concrete channels, sewage outlets, irrigation channels | Water level + standard weir/flume calibration curve | High-accuracy measurement when standard civil works are available |
| Radar Flow Meter | Natural rivers, wide earth channels, ecological and flood monitoring points | Non-contact surface velocity + water level + cross-sectional parameters | No weir construction and no underwater sensor |
| Ultrasonic Doppler Open Channel Flow Meter | Turbid wastewater, sediment-laden tributaries, rainwater and sewage channels | Immersed probe measures velocity and matching liquid level | Direct velocity measurement without a weir; suitable for turbid water |
How to Select the Right Open Channel Flow Measurement Technology
1. Ultrasonic Open Channel Flow Meter (Weir Groove Type)
Ultrasonic liquid level measurement relies on the water level-flow calibration curve of standard weir grooves (Bacher groove, triangular weir or rectangular weir) to convert the flow rate, without directly measuring the flow velocity. It has the highest accuracy and must be matched with standard weir groove civil engineering.
2. Radar Flow Meter (Surface Velocity Type)
Microwave non-contact measurement simultaneously measures water surface velocity and water level. After cross-sectional parameters are entered, the instrument calculates flow rate by the velocity-area method. No weir is required, making this method suitable for irregular natural rivers and earth channels.
3. Ultrasonic Doppler Open Channel Flow Meter
An underwater immersion probe uses suspended particles or bubbles in water to reflect ultrasound and directly measure cross-sectional flow velocity and matching liquid level. The velocity-area method does not require weirs and is suitable for turbid sewage and sediment-laden channels. Measurement accuracy is poor in very clear water, and long-term immersion creates a risk of adhesion to the probe.
Application Scenarios, Medium Conditions and Selection Limits
| Instrument Type | Applicable Applications | Medium Characteristics | Core Problem to Be Solved | Not Applicable |
|---|---|---|---|---|
| Ultrasonic open channel flowmeter (weir type) | Municipal sewage plant discharge outlet, industrial sewage discharge, standardized concrete channels in irrigation areas, and online environmental monitoring | Sewage, clean water, and low sediment water bodies; water foam will interfere with ultrasonic liquid level measurement | High-precision compliant measurement requires environmental acceptance and accurate cumulative flow; regular canal sections can be renovated by civil engineering | Natural irregular river course, unable to construct weir and groove, no civil engineering conditions, or a large amount of thick foam on the water surface |
| Radar flowmeter | Natural river channels, wide earth channels, ecological flow monitoring, flood prevention, remote irrigation areas, and drainage channels | Clear water, slightly turbid water with a small amount of floating debris, and low sensitivity to water bubbles | No channel modification, non-contact and no underwater maintenance; suitable for sites without mains power, remote monitoring and irregular cross-sections where a weir cannot be built; better adaptability than ultrasound under winter icing conditions | Extremely shallow water level (<15cm), continuous severe fluctuation from strong wind and waves, or dense floating weeds obstructing the beam |
| Ultrasonic Doppler open channel flowmeter | Rainwater and sewage confluence channel, small and medium-sized flood discharge channel, high-sediment tributary, and sewage pipe network outlet | Turbid water bodies with suspended particles or bubbles | Direct measurement of flow velocity and flow rate without a weir; suitable for small and medium channels where cost needs to be controlled and the water remains turbid throughout the year | Extremely clear water without reflective particles, a large amount of fiber debris wrapping around the probe, or long-term deep water with strong corrosion |
Measurement Point Planning
Standardized concrete channel discharge outlet: Use an integrated flow and liquid-level measuring point at one weir-slot location. Reserve a straight upstream channel section of at least 3-5 times the channel width, without vortex or backwater.
Farmland main canals for water quantity measurement and water-price calculation: Measure flow velocity and liquid level. Give priority to straight canal sections without bends or turbulent flow after gates.
Natural irregular rivers and earth channels: Measure section flow and water level in a straight section. For wide river channels, multiple velocity measuring points are recommended for weighted velocity calculation. A separate backup water-level measuring point can also be used for flood warning.
Rainwater and sewage confluence or high-sediment branch channels: Use integrated flow and liquid-level measurement while avoiding debris collection and vortex areas.
Culvert outlet: Measure flow velocity and liquid level in the open-flow section at the outlet. Do not install the measuring point in the turbulent-flow area of a full pipe.
Adapting the Solution to Difficult Field Conditions
Channel Form
Regular concrete channel: A Bacher groove can be used, with priority given to the ultrasonic weir-groove type for optimal accuracy.
Natural earth channel or irregular river channel: Where the section is subject to erosion and changes over time, a weir-and-channel scheme should not be used. Radar should be given priority. Doppler can be selected for small and medium-sized turbid tributaries.
Power Supply
Where no 220V mains power is available in the field, a low-power radar or Doppler version is preferred and can be powered by solar panels and lithium batteries. The power consumption of the weir-groove ultrasonic host is relatively higher, so the required solar configuration capacity and cost will also be higher.
Remote Communication
If a central-control PLC is nearby: RS485 Modbus or 4-20mA wired communication can be used.
For long-distance field sites: 4G/NB-IoT wireless transmission can be used.
Recommended Instrument by Measurement Point
| Measurement Point Type | Recommended Instrument | Reasons for Selection | Reference for Water Level / Flow Range |
|---|---|---|---|
| Standardized sewage outlets, regular concrete channels, and environmental measurement | Ultrasonic open channel flowmeter equipped with Bacher groove / triangular weir | Weir calibration with an accuracy of ±5% FS, meeting environmental protection online measurement requirements; non-contact air ultrasound keeps the sensor out of sewage; mature and stable measurement with high data recognition | Water level 0.13m; flow rate 0.01 tens of m³/s, determined by the specifications of the weir channel |
| Natural irregular river channels, wide earth channels, ecological flow, unmanned wilderness, and applications where underwater probes are not desired | Radar flowmeter | No need to construct weirs, no contact with the water body, and no sedimentation or entanglement. Microwave measurement is not affected by sediment and mild foam. Low power consumption is compatible with solar power supply. Suitable for irregular river sections. Surface velocity and water level are measured directly and flow is calculated by the velocity-area method. | Water level 0.156m; flow rate 0.025m/s |
| Rainwater and sewage confluence channel, small and medium high-sediment branch channel, limited budget, and sites where regular underwater maintenance is possible | Ultrasonic Doppler open channel flowmeter | No weir is required. Suitable for perennial turbid water bodies. The integrated probe simultaneously measures flow velocity and liquid level. Equipment procurement cost is lower than radar and is suitable for small and medium channel sections. | Water level ≥0.15m; flow velocity 0.03~5m/s; prohibited under clear-water conditions |
Installation, Power Supply and System Integration
Ultrasonic Open Channel Flow Meter
Installation: Fix the ultrasonic probe on the top bracket of the canal and align it vertically with the water surface of the weir. Standard Bacher troughs must be poured in advance, with the upstream straight section being at least 5 times the width of the canal. Stay away from backflow and eddies.
Power supply: 220VAC is preferred. Where mains power is unavailable, solar 12V can be used, but higher power consumption requires increased photovoltaic capacity.
Signal output: 4-20mA, RS485 Modbus RTU.
System access: Direct connection to PLC and environmental data acquisition instruments; can connect with environmental protection platforms.
Remote transmission: Can be paired with an RTU module to achieve 4G/NB-IoT platform upload.
Radar Flow Meter
Installation: Install on a channel-top or bridge-pole support, with the beam diagonally aligned with the water surface. It is non-contact and does not require stopping the water for construction. Wide river channels can use multiple distributed deployment stations. Installation height is adjustable from 0.5 to 6m.
Power supply: DC12/24V low-power supply. Solar energy plus a lithium battery is the mainstream field solution.
Signal output: RS485 Modbus RTU. Some models include built-in 4G/NB-IoT modules.
System access: Direct connection to PLC and hydrological monitoring platforms.
Ultrasonic Doppler Open Channel Flow Meter
Installation: Fix an L-shaped bracket at the bottom or side wall of the channel and submerge the probe in the main flow area, avoiding the riverbed siltation zone. Water supply may need to be stopped or a cofferdam used during installation. Biological attachment and debris entanglement should be cleaned regularly.
Power supply: DC12/24V low power; solar lithium battery is suitable for outdoor use.
Signal output: RS485 Modbus, 4-20mA.
Protocol: Modbus is the main protocol and can use an external RTU for conversion to a hydrological protocol.
System access: PLC and regional water platforms.
Commissioning, Calibration, Maintenance and After-Sales Support
Ultrasonic Open Channel Flow Meter
Debugging: Enter the parameters of the weir slot, including Bacher slot number and weir type.
Calibration: Conduct on-site water-level comparison once a year.
Maintenance: Very little maintenance is required. Regularly clean dust from the probe surface and check thick foam on the water surface. There are no underwater components.
After-sales: Regular warranty of 1-2 years; remote parameter debugging and on-site fault replacement probe.
Radar Flow Meter
Debugging: Enter channel section parameters such as trapezoidal, rectangular or irregular section coordinates. Set the surface flow-velocity correction coefficient and beam angle. The flow-velocity correction coefficient is especially important in river channels and must be manually measured and calibrated on site, otherwise the error may be too large.
Calibration: Manual flow-rate comparison and calibration are required for initial installation. Review the cross-section and coefficient once a year before the flood season.
Maintenance: Almost maintenance-free. Clear weeds that block the beam range. The absence of underwater components provides a strong advantage in field applications.
After-sales: 1-year warranty; Bluetooth local configuration and remote platform debugging.
Ultrasonic Doppler Open Channel Flow Meter
Debugging: Enter cross-sectional parameters, set flow-velocity filtering, avoid strong turbulence zones and confirm that the water body contains sufficient suspended particles.
Calibration: Perform the first manual flow-rate comparison, check the probe signal every six months and regularly retest under clean-water conditions.
Maintenance: Clean algae, silt and fiber entanglement from the underwater probe every 3-6 months. Double the maintenance frequency for locations with a large amount of debris during the flood season.
After-sales: 1-year warranty. Underwater probes are prone to wear and spare parts are required.
Open Channel Flow Monitoring Project Cases
Case 1: Municipal Sewage Plant Discharge Outlet
Instrument: GLP-5A ultrasonic open channel flowmeter + 304 stainless steel Bacher groove.
Operating conditions: Rectangular concrete channel, 1.2m wide, sewage discharge, online environmental monitoring, 220V power supply, and 4-20mA access to the factory.
Operating time: 2 years of stable operation.
On-site installation: Ultrasonic probes installed on the top support of the channel, a prefabricated standard Bacher groove in the middle of the channel, and a matching data collection box uploading data to the environmental protection platform.
Case 2: Ecological Flow Monitoring of a Natural River Channel
Instrument: GRD-900 integrated radar open channel flowmeter.
Operating conditions: Irregular earth river channel, no mains power, solar lithium battery power supply, 4G remote transmission to a water-conservancy platform, and RS485 Modbus protocol.
Operating time: 3 years.
On-site installation: Integrated radar installed on the vertical pole of the river bridge, with no underwater equipment and the communication module installed in a field waterproof monitoring box.
Case 3: Township Rainwater and Sewage Confluence Branch Channel
Instrument: GLP-LS5A Doppler open channel flowmeter.
Operating conditions: Rectangular concrete branch canal, no weir groove, solar power supply, and RS485 connection to a township water platform.
Operating time: 2.5 years, with quarterly underwater cleaning of probe attachments.
On-site installation: An L-shaped channel-wall bracket fixes the underwater Doppler probe, matched with a field measurement and control box.
Choosing an Open Channel Flow Monitoring Solution
Before selecting an instrument, confirm the channel geometry, expected water level and flow range, water clarity or sediment concentration, availability of civil works, power supply, communication distance and maintenance conditions. Standardized channels generally favor an ultrasonic weir or flume solution; irregular natural rivers generally favor non-contact radar; and turbid small or medium channels can use an ultrasonic Doppler solution where regular underwater maintenance is acceptable.
