Seminar by Alexandre Christophe Hauet, Seksjon for geoinformasjon, NVE.
"Measuring flow velocities from videos"
Abstract
Classical measurement of water velocity or discharge, using current meters or ADCP for example, requires that the operators and/or the equipment are in contact with the water body. Such intrusive methods give precise flow measurements, but they have several limitations. First, intrusive methods cannot be deployed during flood, as high velocities and floating debris make the river too dangerous, and the typical duration of a discharge measurement (about 1h) is often not in adequation with the quick dynamic of flood flows. At very low flow, the shallow water depth and the slow velocities do not allow the use of intrusive devices. Last, classical methods have a very low spatial coverage, giving information of velocities for singles points or transect at best. This local scale is not enough for calibration or validation of hydraulic models, that represent large flow scales.
Image-based method is an interesting alternative that allow to compute large-scale, instantaneous, 2D free surface velocity fields from videos of the flow. In this seminar, the principles of Large-Scale PIV (LSPIV) are presented, and the advantages of this method are illustrated using several field and laboratory experiments, including
- (i) river flood measurement from hand- or drone-held cameras and from fixed stations
- (ii) large-scale velocity mapping for validation of 2D hydraulic models,
- (iii) urban runoff velocity measurement with very shallow flows and
- (iv) velocity measurement of water overflowing dam spillways and its application for dam safety.
We’ll see how to make videos in the field that can be analysed with LSPIV, and we’ll discuss how measuring flows from videos is an opportunity for crowd sourcing of environmental data.
About the seminar:
This seminar is offered by the Section for Geography and Hydrology, Dept. of Geosciences, University of Oslo. The GEOHYD-seminars are announced as lunch seminars so bring your lunch if you want to.
The seminars are open for everyone interested, and especially students are welcome.
The Lunch Seminar Team
– Désirée and Sigrid