Natalia Bugajny

The goals of this study were the calibration of the XBeach model for moderate and weak hydrodynamic conditions in 2D mode and the determination of the volumetric changes induced by them. An evaluation of model performance was made based on the Brier Skill Score (BSS), the visual match of the profile shape (VMS), the absolute volumetric change error (m3/m) and the relative volumetric change error (%). An analysis of accuracy in determining volumetric changes in the dune coast, with XBeach applied, provided an average absolute error in determination of volumetric changes of 4.0 m3/m for a significant storm and 1.5 m3/m for moderate and weak hydrodynamic conditions in a 2D model calibration process. Simulations of morphological changes caused by moderate and weak hydrodynamic conditions for seven timeframes classified into three groups have been run in 2D mode. Within a validation process, the average absolute error in the determination of volumetric changes in the beach was ranging from 0.64 m3/m to 2.42 m3/m depending on the group of hydrodynamic conditions. A high value of the correlation coefficient (R) between the measured and modelled balance of volumetric changes (m3/m) for all timeframes – 0.79 and for the ‘strongest’ group no. 3 – 0.91 were revealed. For the remaining groups, i.e., group no. 1 and no. 2 of hydrodynamic conditions, no such correlation was observed. Furthermore, the temporal analysis of the sum of beach volumes proved that a rising trend was observed over 4 months. Thus, moderate and weak hydrodynamic conditions dominated the accumulation within the area of study. XBeach reflected this trend well, producing a difference between the measured and modelled sum of volumes at the end of the timeframe of 7.27 m3/m, which is close to the volume determination error by the model.

Bugajny, N. and Furmańczyk, K., 2020. Short-term volumetric changes of berm and beachface during storm calming. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 398–402. Coconut Creek (Florida), ISSN 0749-0208.The storm calming coastal processes are presented in the paper. Within these hydrodynamic conditions, the most intensive changes take place on the berm, the beachface and the nearshore, where erosion and accumulation processes are observed. This research was carried out along an approx. 300 m long section of the dune coast of the southern Baltic Sea, in the area of Dziwnow Spit. The measurements were taken using GPS RTK within four days, twice a day. Consecutive profiles were located in about 20 m distance from each other covering the most dynamic part of the beach and the shallow bottom to a depth of about 0.5 m. In order to compare volumetric changes in the profiles, a 1 m grid along every profile was created. Next, a rate of those changes was calculated for each grid. During the storm calming, the significant wave height changed from 1.0 m to 0.2 m from SW to SE direction, and the water level dropped down by 20 cm. A diversified rate of volumetric changes of the beach in time and space was identified, depending on profile location along the coast. Also, temporal and spatial differentiation of the beach volumetric change rate was found, depending on profile location and its parts. The beach accumulation rate did not exceed 0.012 m3/m/h, and erosion - 0.019 m3/m/h, while in the shallow bottom, the accumulation rate did not exceed 0.030 m3/m/h, and erosion rate - 0.020 m3/m/h. The diversity of these processes in time and space are observed and they are related to hydrodynamic conditions. The obtained results will help to understand the accumulation processes during the storm calming in non-tidal environments.

Bugajny, N. and Furmańczyk, K., 2017. Comparison of short-term changes caused by storms along natural and protected sections of the Dziwnow Spit, southern Baltic coast. This paper focuses on a comparison of changes caused by weak storms (significant wave height [Hs] <2.5 m) along a dune coast on a nontidal sea. Repeated observations were made along two 2 km long sections of the southern Baltic coast; one section is a natural coast, and the other features protective structures. Several real-time kinematic GPS surveys were carried out in 2012. The surveys included cross-shore profiles measured from the dune foot to a water depth of 1 m. The profiles were spaced at constant 100 m intervals. In addition, offshore wave data and water level data were collected. Using statistical methods, three types of hydrodynamic conditions were identified and the data grouped accordingly; these groups had different effects on the coast. The coastal changes that occurred along the natural and protected sections of th...

The process-based XBeach model has been used to simulate changes in beach and dune morphology in terms of influence of the significant storm event on the sandy Dziwnow Spit, located in the western part of the Polish coast. The research was carried out as part of the SatBałtyk project and represents the first stage of XBeach model application to create a system for recording the selected effects and hazards caused by current and expected storm events. The significant storm event, registered in 2009, was used for model calibration. Ten cross-shore profiles were selected and compared against preand post-storm morphological data. Model performance was verified on the basis of BSS values for the terrestrial part of the profiles. Verification of the results was performed using two different approaches: on the basis of the highest mean BSS value for all profiles together and for one set of parameters (approach no. 1) and on the basis of the highest BSS value for each profile and most adequate sets of parameters (approach no. 2). Additionally, the observed and modelled beach and dune volume changes were calculated. The research showed that the XBeach model is well capable of simulating the dune and beach erosion caused by the storm event, but the model requires site-specific calibration. High sensitivity of the XBeach model to the facua parameter was determined; the parameter defines the wave shape and affects the sediment transport. The best fit of the profiles was obtained for BSS, ranging between 0.71 and 0.93, with the parameter hmin = 0.01 or 0.05, facua = 0.2-0.5, wetslp = 0.2-0.4 and dryslp = 1 or 1.5. The volume estimation error ranged from + 0.6 m³ m^-1 to -7.7 m³ m^-1, which represents 2.7% to 31.6%.