Case studies

1. Objective and operating principle

The flow measurement station aims to determine the amount of water passing through a river cross-section over a given period of time. The result is obtained by combining three types of data: the shape and area of the wetted section, the water level and the average flow velocity. Integrating these parameters allows for continuous and automatic flow estimation.

2. Bathymetric survey and section definition

The first step consists of the survey of the river section. This operation can be carried out using bathymetric instruments, pressure sensors, or manual surveys, depending on the site scale. Points collected along the river’s transverse line allow reconstruction of the bed profile and calculation of the wetted area corresponding to each water level. From these data, the so-called “section-level curve” is obtained, representing the relationship between the water surface elevation and the shape of the hydraulic section.

3. Installation of the level sensor

The level sensor is the core of the continuous measurement system. It can be piezometric, radar or ultrasonic, depending on environmental conditions and required accuracy. The sensor should be installed in a protected location, such as inside a stilling well or measurement pit, to reduce the effects of waves and turbulence. The data acquired are recorded by a data logger at regular intervals. Power can be supplied by a photovoltaic system with a backup battery to ensure long-term autonomy.

4. Measurement of current velocity

The velocity measurement can be performed using two complementary approaches. The first uses a fixed sensor, of Doppler or electromagnetic type, installed at a representative point of the section. This sensor provides a continuous measurement of local velocity, which can be correlated to the mean velocity through a calibration phase. The second approach involves sample measurement campaigns using portable instruments such as ADCP, current meters or submersible Doppler sensors. Measurements taken at several verticals and depths make it possible to estimate the velocity profile and define a conversion factor between local and mean velocity.

5. Calibration and discharge curve

Once several measurements under different hydraulic conditions are available, it is possible to construct the discharge curve, that is, the empirical relationship between level and flow rate. This curve allows automatic flow estimation over time based solely on the measured level. The initial calibration is a crucial step, as it reduces uncertainty and ensures long-term consistency of measurements.

6. Components and station configuration

A typical flow measurement station includes:

• a level sensor installed in a stilling well or pit;
• a Doppler or electromagnetic velocity sensor placed in a uniform flow area;
• a multichannel data logger with internal memory and remote transmission;
• a self-contained power system based on a solar panel and battery;
• a mechanical support made of stainless steel or aluminum, with flow-resistant fixtures;
• software for data processing and correlation curve construction.

7. Maintenance and quality control

To ensure long-term data reliability, it is necessary to perform periodic checks on sensor calibration and cleaning of measurement surfaces. It is recommended to schedule at least one annual velocity verification campaign and a visual inspection of installation stability after flood events. Preventive maintenance, combined with comparison against direct measurements, ensures the validity of flow time series and the continuity of monitoring.

8. Final result

By combining level and velocity measurements, the station allows real-time reconstruction of river flow trends. The system provides continuous and reliable data, useful for hydrological studies, water resource management and modeling of river processes.