An image processing technique for measuring free surface of dam-break flows

This paper describes an imaging method for measuring water surface in rapidly varying flows based on light absorption. After preliminary spatially distributed calibration, the water depth field is obtained by processing the images of the free surface captured by a digital camera looking downstream at a back-lighted device. The water body is coloured so that it acts as a variable-density filter. This method was used to detect the topography of water surface in a series of laboratory dam-break tests. Its validity was assessed by locally comparing the water depth time series derived from images with the ones returned by six ultrasonic distance metres. The experimental results obtained starting from two different image formats show that the accuracy of this technique is comparable to that of conventional ultrasonic transducers. Therefore, the method can be considered as an effective tool for collecting high-resolution spatial distributed experimental data useful to validate numerical models.