STUDY ON THE INFLUENCE OF WIND SPEED ON THE MEASUREMENT OF SURFACE VELOCITY

Surface velocimetry has been steadily increasing interest and research on its applicability to stationary discharge measurement due to its measurement efficiency and economy. However, it has not yet been widely used due to some uncertainties in the measurement of surface velocity. The first is the uncertainty of the relation between the surface and mean velocity, and the others is for wind effect on surface velocity.

In the case of measurement of water surface velocity, the direction and height of the wave on water surface can be changed by wind, which may cause an error in the surface velocity value. For higher velocity in flood flow, the influence of the wind speed is negligible on surface velocity, but as the velocity decreases, the influence of the wind effect on the surface velocity increases relatively.

In this study, in order to analyze the effect of wind speed and direction on the surface velocity under constant flow conditions when measuring discharge using surface velocity meter, wind direction anemometer(150WX of AIRMAR Co.) was installed with radar surface velocimetry(RQ-30 of SOMMER co.) in an test river.

From the results, speed and direction of wind was found to affect the measured surface velocity in low flow condition. Wind speeds of 2.5 m/s or more caused fluctuations of 20.0~71.4 % of the surface velocity depending on the wind direction, while the effect was not significant as 2.9~8.6 % at less than 1 m/s of wind speed. Therefore, for calculating the discharge by measuring the surface velocity, the effect of wind speed and direction should be considered, especially in low flow conditions where the influence of wind is relatively large.