Sonar survey of shallow water bodies has challenged scientists for a long time. Although these water courses are small, still they have an increasing ecological, touristic and economical role. As maritime sonars are non-ideal tools for shallow waters, the bathymetric survey of these rivers has been taken with cross-sectional methods. Due to recent developments, interferometric surveying technology have also burst into the market of recreational-grade fish-finders. The objective of the current study was the development of a novel, complex and integrated surveying technique which is affordable, robust and applicable even at low water levels. A recreational-grade sonar system was assembled and mounted on a double-hull vessel and connected with a geodetic Global Navigation Satellite System (GNSS) device. We have developed a novel software which enables the bridging between a closed sonar file format and the commonly used Geographic Information System (GIS) datasets. As a result, the several month-long conventional bathymetric survey of the 146 km-long reach of the Drava River was reduced to 20 days and provided channel bathymetry of many orders of magnitude higher than the classical methods. Additionally, a large number of spatial derivatives were generated which enables the analysis of channel morphology, textural variation of channel sediments and the accurate delineation of navigational routes.

Constructions of dams influence river courses by cutting off sediment delivery and altering flow regime. We conducted flume experiments to study how sediment starvation, flow deficit and occurrence of series of floods with sediment load influence the evolution of channel planform. Results indicated that reduced flow caused a transition from a braided to incised single-thread planform with remains of inactive channels. The planform resembled rivers suffering from flow reduction caused by dams and constructions of irrigation canals (e.g., Central Platte River, USA). Simulation of series of floods with no sediment delivery caused the formation of an anabranching planform with incised main channel, alluvial islands, and side channels active at high flows. This evolution corresponds to river courses altered by sediment starvation and series of floods (e.g., the lower Drava River, Hungary). Floods with delivery of fines created a single-thread, incised channel with terraces along banks. Such channels are formed by rivers closed by dams, and compensating sediment deficit by sediment load from tributaries and/or floodplains (e.g., the Green River, USA). The flume tests demonstrated how flow and sediment deficit influence river channels and that the potential for restoration strongly depends on possibilities for the activation of sediment supply. However, restoration of pre-dam conditions is often impossible owing to other hydro technical works and land use changes. The highest restoration potential refers to the rivers compensating sediment delivery blocked by dams with tributary and floodplain resources.

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Climate change is expected to have a significant impact on changing the flow regime of the lower Drava River. Four flume experiments were run to see how stabilized, increased and decreased flow and the occurrence of a series of floods affect channel planform evolution. Constant discharge produced alternate bars that subsequently merged into bigger bedforms, bedform migration, and a higher sinuosity of the channel. While merging and migration of bedforms may happen in the lower reaches of Drava, its sinuosity is unchanged due to river regulation. Reduced flow initiated transition from a braided to incised single-thread planform, with the formation of dormant channels. Drava already has a single-thread planform (because of dikes) and, in cases of flow reduction, will have the remnant of inactive channels. Increased discharge showed greater erosion and reworking of channel banks, a decrease of sinuosity ratio and active high bluff zones. On Drava sinuosity ratio is more difficult to change because of levees, but erosion, reworking of banks, and increased high bluff risks are possible. Floods simulation generated the construction of an anabranching planform alongside the incised main channel with terraces along banks (active during floods), bars, alluvial islands, and side channels (active during low flows). On the lower Drava River, this situation correlates with past floods.

Small-scale modelling is a widespread method for the simulation of large-scale natural processes in the fields of hydrology, hydraulics, geology, geomorphology and river mechanics. At the University of Pécs a computer-controlled sand table (hydrologic and tectonic geomodel) was put into operation in 2014 for both research and educational purposes. The table can be tilted at any arbitrary angle between ±7.5° along its longitudinal axis, and by ±10° along its transversal axis. Lateral deformation of the medium is simulated through the displacement of four lateral pushblades to the extent of 100 mm. The four interior units can be uplifted to model orogenic processes. All motions in the flume are executed by computer-governed electroengines. Geomodels, flumes and stream tables may ease the understanding of geographic processes through problem-oriented based teaching methods and hand-on-experiences. The benefits of problem-based learning (PBL) have also been confirmed during the visits of various age groups at the geomodel. Our observation during these demonstration sessions revealed one of the major weaknesses of the Hungarian educational system, i.e. teachers are forced to follow the conventional geographical curricula, therefore hindering their adaptation to cutting-edge educational methods and the learning-by-doing approach of the Western European and North American syllabi.Keywords: computer-controlled geomodel, problem-based learning, geography education, popular science BevezetésA világban történt eseményekről szinte azonnal tájékozódunk a médiának köszönhetően, így a természeti katasztrófákról is. Arról azonban kevés információt szerezhetünk, hogy mekkora felelőssége van ebben az emberiségnek, pedig már kutatások bizonyították, hogy az antropogén hatások teljesen átformálták, egyre inkább átformálják környeze-tünket, növelik a természeti veszélyeket és hozzájárulnak az éghajlatváltozáshoz. E téren a földrajzoktatásra komoly feladat hárul; a médiában terjedő álhírekkel szemben a leját-szódó folyamatok okainak és következményeinek feltárására kell fókuszálnia. Azonban