An examination of the potential of in-line holography for the study of biostabilisation of sediment erosion
Under controlled conditions in-line particle field holography can provide an effective and unique method of observing, following and measuring the erosion process close to the bed where the erosion actually occurs. A holographic image preserves the three-dimensionality, perspective and parallax properties of the original scene and possesses an image resolution of down to about 5 mm. Replaying the hologram in the real image mode allows interrogation of the entire recorded image volume using a video/CCD camera mounted on x-y-z micropositioning stages. The study presented in this thesis utilises in-line particle field holography to visualise and quantitatively analyse how the erosion processes are affected by the presence of organic matter. The main features of holographic recording and its use in particle sizing are discussed and reviewed before describing how the techniques may be used in sediment transport studies. Factors that affect the resolution, the quality of the holographic images and their influence on the data produced are also discussed. The organic matter selected for this work was xanthan gum which is a commercially available form of an extra-cellular polymeric substance (EPS) similar to that produced by diatoms on natural sediment. The biological aspects which are considered are the effect of EPS on the sediment-floc/aggregate size distributions, erosion threshold stress and the morphologies of the flocs/aggregates at the moment that erosion occurred. To control and change the hydrodynamic stress and introduce erosion on the surface of a pre-defined bed an erosion device, cohesive strength meter (CSM), was used. Results are compared and correlated with those previously obtained by methods such as low temperature scanning electron microscopy and laser diffraction particle sizing.