EGU2020-9943
https://doi.org/10.5194/egusphere-egu2020-9943
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Wind effect on image-based river surface velocity measurements

Salvador Peña-Haro1, Beat Lüthi1, Robert Lukes2, and Maxence Carrel1
Salvador Peña-Haro et al.
  • 1photrack ag, Zurich, Switzerland (pena@photrack.ch)
  • 2Federal Office for the Environment FOEN, Bern, Switzerland

Image-based methods for measuring surface flow velocities in rivers have several advantages, one of them being that the sensor (camera) is not in contact with the water and its mounting position is very flexible hence there is no need of expensive structures to mount it. Additionally, it is possible to measure the whole river width. On the other hand, environmental factors, like wind, can affect the surface velocity and the have an impact on the accuracy of the measurements.

Herein we present an analysis of the wind effect on the image based surface velocity at Rhine river, at the border between Switzerland and Austria. At this location the river width is of approximately 100 meters under low flow conditions, while the width of its floodplain is of about 200 m. An ATMOS 22 ultrasonic anemometer was installed at the site to measure the wind intensity as well as its direction.

A time series of flow velocities and wind from May to October 2019 was analyzed. During this period, the average discharge was 320 m3/s and the average flow velocity 1.7 m/s. While the average wind velocity was of 2.3m/s which roughly follows the same direction of the river flow.

A rating curve following a power law function was fitted to the image based surface flow measurements. It was found that for maximum wind speeds of 10 m/s, blowing in the opposite direction of the river flow, there was a deviation of 8%. For the average wind speed of 2.3m/s, the deviation was found to be 3%.

How to cite: Peña-Haro, S., Lüthi, B., Lukes, R., and Carrel, M.: Wind effect on image-based river surface velocity measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9943, https://doi.org/10.5194/egusphere-egu2020-9943, 2020

Display materials

Display file

Comments on the display material

AC: Author Comment | CC: Community Comment | Report abuse

Display material version 1 – uploaded on 30 Apr 2020
  • CC1: Comment on EGU2020-9943, Jérôme Le Coz, 03 May 2020

    Thanks Salvador, very neat presentation and very interesting results on an important issue for all surface velocity methods. We observed similar problems at a site equipped with surface velocity radars.

    Slide 9: it would be interesting to estimate the uncertainty of the rating curve and compare it with the observed discharge deviations. I guess the RC uncertainty is not so small compared to the discharge deviations, actually.

    Slides 10-11: I wonder whether the discharge deviations are due to surface velocity measurement errors (due to wind-induced ripples or gravity waves for instance) or to a modification of the actual vertical velocity profile, hence of the coefficient. Or both? or another effect?