Review of imaging-based measurement techniques for free surface flows involving sediment transport and morphological changes

In order to validate the numerical methods aimed at the simulation of fast transient flows involving sediment transport and morphological changes, data are required. However, field data are scarce, or, if existing, are often inaccurate or incomplete, due to the difficulty of taking reliable measurements in such difficult flow conditions. Laboratory experiments constitute a good alternative to obtain validation data for numerical models. When performing simplified experiments, a limited number of well-identified flow features can be highlighted if appropriate measurements are taken. Advances in experimental techniques in the last decades have significantly enlarged the field of possible data acquisition, especially thanks to the development of non-intrusive techniques such as digital imagery. Non-intrusive techniques are of paramount importance when considering sediment transport because a measurement device interacting with the flow would also modify the observed morphological features. In this paper, several imaging-based techniques are presented for waterlevel and bed evolution measurements. The key features and advantages are discussed but also the drawbacks of those techniques. The discussion is illustrated by different examples that have resulted in data sets commonly used by scientists all over the world to test their numerical simulation tools.