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Recent developments in unmanned aerial vehicles (UAVs) have resulted in high-resolution digital elevation models (DEMs) of vulnerable coastal environments, including beach–foredune topography. If performed repetitively, they can offer an excellent tool to determine the spatial and temporal changes in the sediment budget, which may be required for proper land management. However, the quality of a UAV, slope parameters, and vegetation significantly influence DEM accuracy. The aim of this study is to compare precise GPS-RTK transects across a section of the South Baltic coast in Poland with those obtained from a DEM based on high-resolution and high-accuracy images obtained by a wind-resistant, high-quality fixed-wing UAV during beyond visual line of sight operation (BVLOS). Different land cover classes, slope inclination, and general curvature, as well as surface roughness, were taken into consideration as possible factors influencing the uncertainty. The study revealed that marram grass greatly affects the accuracy of the UAV-derived model and that the uncertainty of the UAV-derived DEM increases together with increasing slope inclination and, to a lesser degree, with increasing general slope curvature. We showed that sediment budget determinations with the use of a UAV-based DEM are correct only where grass cover is sparse, in our study, up to 20% of the area.

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Function of Agricultural Terraces in Mediterranean Conditions - Selected Examples From the Island of Ikaria (The Southern Sporades, Greece) The aim of the research was to define the influence of agricultural terraces on slope erosion. There have been selected three plots located on the Greek island Ikaria. On the plots detailed geomorphological mapping was done, spatial relief models were created based on the measurements taken using GPS RTK, georadar profiles were made using RAMAC/GPR and the extent of destruction of terrace resistance walls was evaluated. In comparison with similar forms on other Aegean islands, Ikarian terraces are narrow and high. Their stability depends on: lihtology, slope gradient, height and spatial arrangement of particular terrace steps and the current way of their usage. It was acknowledged that the most stable are the forms created on crystalline schists and gneisses, whereas the slopes, which erode the easiest, are the terraced ones consisting of carbonate rocks. The obtained results indicate that on Ikaria similarly to numerous other regions the most significant factor facilitating erosion on the terraced slopes is the cessation of their agricultural usage.

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Abstract. Ksours form a cultural landscape for most of the countries of North Africa. They are an important part of the cultural heritage of the desert areas in Algeria, Libya, Tunisia, Mali or Morocco. They also become an undeniable attraction for tourism. The article looks at the impact of tourism on the transformation of ksours. It is based on comparative field research in the Dadès-Drâa Valley (Southern Morocco), the region of the highest ksour concentration. The results show that despite being very close to most sustainable tourism indicators, the whole impact of tourism is rather negative. Tourism is creating social disproportions, being the first incentive to abandon the ksours by those who are not involved in the sector. This is leading to the destruction of particular houses first, and later to the destruction of the whole village. The revitalization of ksours remains a theoretical solution only; thus the author suggests paying greater attention to social equity in order to stop the transformation of ksours at the 2 nd stage of development.Contents:

The aim of this study is to review current knowledge on channels development in mountain basins in arid zones. The research was intended to describe the main triggering factors responsible for the development of ephemeral river channels in such areas. A detailed study was made of the Upper Dades basin located on the southern slopes of the High Atlas Mountains (Morocco). In this paper we analyse the morphometry of channels of different orders in three small basins chosen for a thorough study in order to present the details of channel characteristics.The results show that the development of stream channels of the same order may vary greatly. This is mainly due to variation between the basins in lithology, vegetation cover, precipitation amounts and hillslope sediment supply. We prove however that the key agents of stream channel development are the energy of water and associated mass gravity movements in the period when water is absent. The morphological component provides strong evidence for this conclusion. The results show that runoff energy generally compensates for the low amount of water in 2nd and 3rd order channels where erosion is dominant. The 4th order channels are therefore better adapted to evacuate significant discharges (weak slope, large channel) which therefore decreases the erosive capacity of their stream flows. In this paper we also discuss whether the impact of the limited hillslope vegetation and the supply of coarse-grained sediment in the channels are important in the development of channels in mountain basins in arid regions. We conclude that intense rainfall-runoff events that lead to short-lived but high-energy flash floods have a more significant impact in contemporary channel development. Channels, especially those of 3rd and higher order, tend to be very unstable during large floods. We show that channels located in small basins in mountains in arid zones are in a state of almost permanent non-equilibrium.