A method for extracting surface flow velocities and discharge volumes from video images in laboratory

• The mean surface velocity has been examined through artificial tracers.
• A new technique based on variance image to quantify surface velocities has been developed.
• An automatic algorithm to detect surface tracers in a flume has been implemented.
• Increasing the amount of flow surface tracers increases the accuracy of the velocity estimation.
• Video images are a reliable technique to quantify discharges in laboratory conditions.

The lack of hydrological data has been identified as one of the major obstacles facing the effective evaluation of hydraulic and hydrological interventions in the field. Traditional methods of data collection have proven to be generally expensive and particularly risky under high flow conditions. A method for quantifying hydrodynamic variables, such as surface flow velocity and discharge volume was developed in a laboratory setting using video images. This method explores several innovative image analysis techniques, specifically the Image Variance (IV) and Threshold Segmentation with Path Discretization (TSPD), where the basics steps comprise image capture, rectification and data extraction. Measurements obtained from conventional instruments and data extracted from video images were compared and exhibited less than 2.5% difference. It can be concluded that under laboratory conditions it is possible to obtain reliable velocities and discharges from video techniques, without being in contact with the flow.