3D determination of the scour evolution around a bridge pier by photogrammetric means

The three dimensional development of a scour has been measured by photogrammetric means. Therefore an experiment has been set up in the Hydromechanics Laboratory of the Technische Universität München (Pfleger et al. 2010a). In the center of a 1.20m wide rectangular flume a cylindrical pier (diameter 10 cm)was mounted.The river bed consisted of uniformsand (d50 =1.9 mm,Cu =d60/d10 ≈1.45) with a mixture of yellow, white and black corns in order to provide sufficient contrast or texture for the photogrammetric processing. The sand was leveled to a horizontal plain where five aluminium sticks with markers on top were set as ground control points. 15 cm above the river bed a plate of acrylic glass was installed in order to avoid minor waves and to receive a defined refraction during the experiment. On top of this plate another set of six ground control points were placed. All in all a sequence of 7200 pictures was taken with two 4 Mpx CCD cameras at a frame rate of 1 Hz. The height depending diffraction in the vicinity of the bridge pier was corrected by calibration measurements with a target that was positioned at different levels in the expected vertical range. The photogrammetric resultswere corrected accordingly.The experimentwas conducted at 80% of the critical section averaged velocity. Within this paper the experimental setup and the evaluation procedure are being presented together with the acquired data and some findings are being briefly discussed.