Laboratory Geosciences: Modelling Surface Processes

Created by: Nones Michael

The reproduction of landscape evolution at the laboratory scale can be tracked using new measurement techniques, depending on factors like the phenomena under study (rapidity, required detail, etc.), the scientific skills of the investigators and, obviously, the available budget.

Image-processing techniques are becoming paramount in tracking the changes typically observed in fluvial environments, involving relatively easy-to-use but very reliable methods. Indeed images can be handled to describe the dynamics associated with very small sediments, but also to track the movements of coarser material.

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In the last decades, new and advanced measurement techniques have been developed to track the dynamics of surface processes and the formation of river bedforms, bars and island as well as complex fluvial networks, gullies and rills by means of small-scale laboratory experiments, aiming to integrate and support mathematical models and field observations. In fact, to date, many numerical codes can dynamically reproduce the evolution of fluvial environments and landscapes in general as forced by atmospheric drivers like rainfall and flowing water, but only a very scarce research is available on the reproduction of the involved phenomena from a physical point of view, with a particular emphasis on the laboratory scale. To fill this gap, new measurement techniques (e.g., structure-from-motion, LiDAR, motion and depth detectors, image processing, high-resolution cameras, PIV/PTV techniques, etc.) can be adopted, designing appropriate laboratory experiments that can provide additional insights into the dynamic evolution of landscapes, possibly involving low-cost apparatus. However, more effort is needed to appropriately address the spatiotemporal scales and for the elaboration of the results,
extrapolating physically-based relationships and general approaches that can be extended beyond the single experiment, evaluated and applied in different contexts[1].

At the laboratory scale, the reproduction of the propagation of aggrading and degrading sediment fronts requires the simultaneous measurement of the sediment feeding rate, the profile of the free surface, and the flume bed elevation. An experiment done at the Polytechnic University of Milan, Italy, showed that this can be performed using five action cameras and different image-processing techniques that automatically measure all the quantities with an adequate temporal resolution[2]. The preliminary results of this prototypal experiment pointed out that there are many opportunities to develop the technique to be eventually applied in different fields.

The evaluation of the erosion of cohesive sediments or cohesive/non-cohesive sediment mixtures presents many challenges, and new methodologies are currently under study. One of them, developed at the University of Stuttgart, Germany, is based on high-resolution photogrammetry (PHOTOSED). Even if it is at its initial stage of development, preliminary applications already showed good capabilities in tracking erosive trends of cohesive sediments in lab-scale experiments[3], but further tests involving cohesive/non-cohesive sediment mixtures are required to corroborate such outcomes.

Image-processing methods like large-scale particle image velocimetry (LSPIV) are frequently adopted to remotely monitor the surface velocity and performs discharge estimates both in the laboratory and in the field. However, despite being a relatively well-tested methodology, several errors associated with the dimension of the interrogation area and the acquisition time are intrinsically embedded, and therefore require additional research[4]. As described in this work, indeed, hyper-concentrated flows reproduced in flume at the University of Palermo, Italy, were used to test the methodology and discuss pros and cons, showing the need for further research.

References

  1. Nones, M.; Special Issue “Laboratory Geosciences: Modelling Surface Processes”. Geosciences 2018, 8(11), 386, 10.3390/geosciences8110386 .
  2. Radice, A.; Zanchi, B.; Multicamera, Multimethod Measurements for Hydromorphologic Laboratory Experiments.. Geosciences 2018, 8(5), 172, 10.3390/geosciences8050172.
  3. Noack, M.; Schmid, G.; Beckers, F.; Haun, S.; Wieprecht, S.; PHOTOSED-PHOTOgrammetric Sediment Erosion Detection. Geosciences 2018, 8(7), 243, 10.3390/geosciences8070243.
  4. Termini, D.; Di Leonardo, A.; Efficiency of a Digital Particle Image Velocimetry (DPIV) Method for Monitoring the Surface Velocity of Hyper-Concentrated Flows. Geosciences 2018, 8(10), 383, 10.3390/geosciences8100383.