V-Notch Flow Meters

V-Notch Flow Meters

The Sisgeo V-Notch Flow Meters are widely used for monitoring water flow in open channels, particularly in environmental and geotechnical applications. These meters are designed to measure the leakage rate in dams, which is an essential indicator of their performance. Leakage monitoring helps in assessing the long-term stability of earth/rock-fill and concrete dams.

The V-Notch flow meters feature a triangular or rectangular notch plate made of stainless steel. The water flow is measured by determining the water level at the notch, which is then converted into an instantaneous flow rate based on a specific formula. The system is compatible with high-accuracy transducers and is easy to automate using Sisgeo's OMNIAlog logger family.

Operating Principle of V-Notch Flow Meters

The V-notch flow meter operates on the principle that an obstruction in a channel causes a hydraulic jump, which generates a high-water level behind the barrier with a low water current. The purpose of the V-notch weir is to convert the water level (head) in the upstream basin into instantaneous flow values for the channel where the weir is installed.

The flow rate is proportional to the water depth ("H") and depends on the shape of the notch. A specific formula is used to calculate this flow rate. For accurate measurements, the following conditions must be met:

• The upstream canal should have a gentle slope (1-3%) and a rectangular section for a length at least 10 times the width of the canal.
• The water head measurement point ("H") should be at least 4 times the height of the weir away from the weir.
• The air under the water after the weir must be in contact with barometric pressure.
• Accumulated sediments upstream of the equipment must be cleared regularly to maintain measurement accuracy.

Typically, the user should select bill of materials based on deployment scenario:

• V-Notch Weir Plate: Stainless steel plates with triangular or rectangular notches used to measure water flow by creating a controlled hydraulic jump.
• Pressure Transducer: Measures the water pressure and is connected to the V-notch weir to convert water head into flow rate.
• Water Level Transducer: Measures the water level at the V-notch to calculate flow rate.
• Staff Gauge: A graduated stainless-steel gauge used for manual measurement of water levels at the weir.
• Data Logging Interface: This is the interface that allows the V-Notch Flow Meters to connect with compatible data loggers for data collection and monitoring.

1. CRD-400 READOUT: CRD-400 is a new generation multipurpose readout designed to take readings of all instruments including vibrating wire.
2. OMNIAlog Datalogger: Centralized data collection for remote monitoring and analysis.
3. MIND Portable Readout: A compact, multichannel readout unit for local readings of Sisgeo instruments.
4. WR-Log Wireless Node: Wireless data transmission and remote monitoring through the node.

Applications of V-Notch Flow Meters

• Leakage measurement in earth/rock-fill and concrete dams.
• Measurement of open channel flow rates.
• Flow monitoring in drainage systems in tunnels and excavations.