Browsing by Author "Vousdoukas, M. I."
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- Comparisons of acoustic and optical sensors for suspended sediment concentration measurements under non-homogeneous solutionsPublication . Vousdoukas, M. I.; Aleksiadis, S.; Grenz, C.; Verney, R.A set of acoustic and optical turbidity sensors was tested and compared in laboratory conditions under suspended sediment concentrations of the range 0.1-10 g/l. Various well sorted, mixed, as well as natural sediments (including clay, mud and sand) were used to cover a wide range of conditions, with emphasis on bimodal sediments. All optical sensors showed good performance with post-calibration RMS errors typically below 10% of the range and R2 Pearson coefficients exceeding 95% (a=0.1). The Wetlabs produced the smallest RMS errors, followed by the Troll (overall average ~4.3% and 5.8%, respectively), but the differences were not significant. OBS-3+ performance was also good (overall average RMS error ~3%), while the Vector ADV produced measurements with average RMS errors ~10.7% of the range for SSC up to 1 g/l, above which signal saturation is likely to occur.
- Modelling storm-induced beach morphological change in a meso-tidal, reflective beach using XBeachPublication . Vousdoukas, M. I.; Almeida, L. P.; Ferreira, ÓscarExtensive XBeach testing took place against field topographic and bathymetric measurements of storm morphological impact at the mesotidal, reflective Faro Beach (S. Portugal). Five monitored events have been selected for XBeach calibration and sets of runs for 768 different set-ups, showed that alongshore profile morphology variations even for the same site, may require different calibration settings, in order to achieve optimal performance. XBeach performed better with higher facua and wetslope values at the reflective parts of the study area and with lower values at the less steep ones. Model sensitivity to calibration settings appeared to increase with beach slope; while the majority of the tested set-ups resulted in negative Brier Skill Scores (BSS). The main discrepancies compared to the field measurements were related to the overestimation of berm erosion and the intense avalanching/beach scarp formation; which rarely occur at the study site. Moreover, the simulations resulted in morphological change within a narrower profile section than observed; and did not accurately simulate offshore bar formation. The study highlights that predicting beach profile morphodynamic response during storm events at steep reflective beaches with XBeach may be more difficult than at intermediate beaches. However, the results can be satisfactory after proper calibration and for the present study the optimal cases resulted in BSS of the range 0.2-0.7. The best performance was obtained by deactivating long wave stirring, wave-current interaction and equilibrium sediment computation (lws=0, wci=0, turb=0, respectively); keeping directional spreading of long waves and groundwater flow on (nspr=1, gwf=1, respectively); and using the lower morfac, facua and wetslope parameters (at the present case morfac=5, facua=0.1 and wetslope=0.2).