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The paper presents the results of a tracer experiment with the uranine tracer at the non-hazardous landfill of Dragonja. The purpose of the tracer test was to determine the dynamics of the potential pollutants from the landfill to the groundwater. The landfill lies on the thicker weathered layer of flysch rock that forms the slope of the hill. At the foot of the hill are silty clay and partly sandy alluvial sediments of the Dragonja River. The transport of uranine depends on the intensity and duration of precipitation, potential evapotranspiration, permeability, precipitation infiltration into the landfill, and saturation of the weathering layer of flysh. Uranine first appeared in the observation well P2, which is located downstream of the injection point, in the direction of water flow. Observation well P1 is not in the direction of direct flow and therefore only the edge of the dispersed tracer plume appeared in P1. The groundwater from the flysch weathered layer drains into the alluvial plain and the uranine concentrations are diluted in the groundwater. In the observation well P5 a slow increase and decrease of the uranium concentration was therefore observed. Due to the high evapotranspiration, the groundwater levels were falling until October, when they began to rise after autumnal precipitation events. The tracer experiment confirmed the heterogeneity and complexity of the geological structure of the landfill site.

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Predstavljene so meritve erozijsko-denudacijskih procesov v porečju Dragonje. Meritve so obsegale površinsko spiranje na treh različnih rabah tal, umikanje strmih golih flišnih pobočij, premikanje gradiva po erozijskem jarku in kemično denudacijo v porečju. Meritve so potekale od februarja 2005 do maja 2006. Namen članka je opozoriti na hitrost nekaterih geomorfnih procesov, zaradi katere bi bilo treba bolj poudariti njihov pomen pri oblikotvornosti površja.

Abstract: Under the influence of socio–economic changes in many regions in Europe, a trend of decreasing agricultural activity has been observed since the Second World War. The resulting reforestation profoundly changes water and sediment supply to river channels, deposition rates on the floodplains and erosion rates on the hillslopes. We studied these changes in the 91 km2 Dragonja catchment in southwestern Slovenia. With the spatially distributed erosion and sediment delivery model WATEM/SEDEM, the hillslope sediment delivery to the river channel was calculated on the basis of parameters (soil and precipitation parameters, a DEM and land use) measured in the field and laboratory in 2002 and land use maps based on aerial photographs from 1954, 1975, 1985 and 1994. For two independent calibrations WATEM/SEDEM modelled a sharp decline of 69% in total hillslope sediment delivery from 1954 to 2002. As the sub-catchments Rokava and Upper-Dragonja did not reforest in the same way, the sediment yield response is different as well. Separate calculations show the same reduction (45%) in sediment yield from 1954 to 1975. After 1975 the sediment yield was stable in the Rokava sub-catchment. In the Upper-Dragonja the trend continued, to a total reduction of 76% of sediment outflow since 1954. The sources of fine sediment were determined by analysing the hysteresis of the discharge waves, and the suspended sediment texture. The sediment that leaves the catchment originates from three sources: hillslopes, erosional bedrock banks and sedimentary riverbanks. The analysis of the suspended sediment texture suggests that during a discharge wave the suspended sediment originates predominantly from the hillslopes. During low stage the sparse sediment in the water column largely originates from large bedrock banks. The sedimentary riverbanks are not an important source of suspended sediment. [Copyright &y& Elsevier]

This article is a continuation of the article on soil erosion in submediterranean Slovene Istria from the first issue of the 2009 (49-1) journal. In this article we present geomorphic processes in the badlands of the same area (Dragonja River basin, SW Slovenia): sediment production from steep bare (Eocene) flysch slopes (rockwall retreat), movements of flysch debris along erosion gullies, and geomorphic processes on talus slopes. Sediment production of flysch rocks was determined by measurements on erosion plots and totals around 80 kg/m² per year on average, which means that steep bare flysch rockwalls retreat at a speed of 35 to 50 mm per year. The badlands not only contain flysch walls but also slopes already eroded by erosion rills and gullies. A dam in one of the erosion gullies with the catchment area of 0.1 ha captured 20 tons of debris in fourteen months. Monitoring on talus slopes of the badlands revealed their dual character because erosion here alternates with accumulation. [ABSTRACT FROM AUTHOR]

Changes in floodplain sediment dynamics have profound effects on riverine habitats and riparian biodiversity. Depopulation due to socio-economic changes in the Dragonja catchment (91 km²) in southwestern Slovenia resulted in the abandonment of agricultural fields, followed by natural reforestation since 1945. This profoundly changed the water and sediment supply to the streams, as well as floodplain sediment deposition. This paper presents a reconstruction of the development of the Dragonja floodplain due to these land use changes during the last 60 years. The reconstruction is based on dating of floodplain sediments using 137Cs profiles, measurement of actual sedimentation rates using artificial grass sedimentation mats, and linking this information to the present-day hydrological behaviour of the river. The sedimentation mats showed that floodplain sedimentation was restricted to peak flows of considerable magnitude. Due to the reforestation, the return period of such high flows increased from 0.31 year in the period 1960-1985 to 0.81 year between 1986 and 2003, with commensurate changes in sedimentation rates. At the 1.5 m river terrace (formed about 60 years ago), 137Cs-based sedimentation rates (1960-1986) were roughly twice the rates inferred from the artificial grass mats (2001-2003). This finding matches the increase in the return period for larger peak events during the 1986-2003 period, which caused fewer major inundations at this level. Conversely, sedimentation rates determined for the lowest terrace at 0.5 m were similar for both techniques (and periods) because the return periods of the peak events responsible for sediment deposition at this lower level did not change much over the period 1986-2003. [ABSTRACT FROM AUTHOR]

Abstract: The effects of increasing agricultural land use on fluvial morphology have received much attention in fluvial research. However, in several regions in Europe, a reversing trend of decreasing agricultural activity and land abandonment, followed by reforestation, is observed. The response of fluvial morphology deserves attention because of its large impacts on landscape and riverine habitats. With the help of geomorphological mapping, multi-date aerial photography and a range of dating techniques, we reconstructed the evolution of the morphology of the riverbed and the floodplain of the Dragonja river in southwestern Slovenia. The results of this study show that the fluvial morphology in this Mediterranean catchment has changed considerably as a result of shifts in agricultural land use, in particular large-scale land abandonment in the second half of the 20th century. Until the first half of the 19th century, floodplain aggradation prevailed. Probably around 1870, a large erosion event occurred from which the floodplain did not fully recover. A terrace standing 2.5 m above the present floodplain was formed. Natural reforestation, due to depopulation since World War II, caused a reduction in discharge and sediment supply to the river. The decreased intensity and frequency of floods allowed invasion of the riverbed by vegetation, causing narrowing and incision of the riverbed. This resulted in the formation of a terrace, which now stands 1.5 m above the present-day river. This terrace is about 60 years old. However, the largest increase in forest area occurred since 1975, which intensified this process of riverbed narrowing and incision, creating a local terrace at 0.5 m at 0.5 m above the presently meandering river. [Copyright &y& Elsevier]