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 km
2 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.
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.
This article deals with the results of seven years of measurements of sediment release from the flysch badlands in the Rokava River headwaters. Measurements of sediment production were carried out in ...erosion plots, and measurements of cliff (or rockwall) retreat using erosion pins. Selected meteorological time series from the Portorož Airport meteorological station were included in the analysis. The calculation showed that from 2008 to 2015 (149 measurements) sediment production was 36 kg/m² per year and the flysch cliff retreated by 146 mm or 21 mm per year. The amount of sediment produced is moderately positively correlated with the number of days between successive measurements (r = 0.51), with a recorded daily transition of air temperature over/below 0 °C (r = 0.56) and slightly more weakly correlated with the precipitation amount (r = 0.45). On the other hand, the amount of sediment produced has a low negative correlation with average air temperature (r = −0.29) and average minimum air temperature (r = −0.30). However, no statistically significant correlation was calculated between the amount of sediment produced and average wind speed.
Boundary-making in Istria is an old undertaking. It has actually never ceasesed, not even today. Istrian peninsula has thus undergone substantial boundary shifts during the last couple of centuries ...(especially after the Venetian demise in 1797). But Istria carries its worldwide fame also due to one of probably the harshest disputes on the post-war European grounds – the Trieste territory dispute. In author's perspective, this dispute is one of the four main corner-stones of the current Slovenian-Croatian boundary dispute. The remaining three include the Kozler's boundary around Dragonja (Rokava) River, the ungraspable notions of Austrian censuses in Istria, and the narratives of partisan settlements on military jurisdiction. However, there are other very important aspects which significantly shaped the development of the dispute, but we will focus at assessing the importance of the aforementioned ones. In this sense, the analysis of the effects of the outcome of the Trieste dispute and its implications to the contemporary interstate dispute is set forth. By unveiling its material and consequently its psychological effects upon the contemporary bilateral relations, its analyses simultaneously reveals backgrounds of never answered question, why Kozler's proposed linguistic boundary around Dragonja (Rokava) River turned out to become a boundary of national character. Though nowadays disputed, there is absolutely no chance for both involved parties to substantially draw away from once decisively drawn line of a layman. Despite the fierce battle of words in Slovenian public media on whether should the interstate boundary be placed on Mirna (Quieto) or Dragonja Rivers, it will be argued here that the actual choice of the Valley of Dragonja as a boundary is by all means Slovenian. The arguments are based on extensive analyses of cartographic materials, relevant literature, documents, and statistical data.
When studying the development of different geomorphic processes, floods, glaciers or even cultural heritage through time, one cannot rely only on regular photogrammetrical procedures and metrical ...images. In a majority of cases the only available images are the archive images with unknown parameters of interior orientation showing the object of interest in oblique view. With the help of modern high resolution digital elevation models derived from aerial or terrestrial laser scanning (lidar) or from photogrammetric stereo-images by automatic image-matching techniques even single nonmetric high or low oblique image from the past can be applied in the monoplotting procedure to enable 3D-data extraction of changes through time. The first step of the monoplotting procedure is the orientation of an image in the space by the help of digital elevation model (DEM). When using oblique images tie points between an image and DEM are usually too sparse to enable automatic exterior orientation, still the manual interactive orientation using common features can resolve such shortages. The manual interactive orientation can be very time consuming. Therefore, before the start of the manual interactive orientation one should be certain if one can expect useful results from the chosen image. But how to decide which image has the highest mapping potential before we introduce a certain oblique image in orientation procedure? The test examples presented in this paper enable guidance for the use of monoplotting method for different geoscience applications. The most important factors are the resolution of digital elevation model (the best are the lidar derived ones), the presence of appropriate common features and the incidence angle of the oblique images (low oblique images or almost vertical aerial images are better). First the very oblique example of riverbank erosion on Dragonja river, Slovenija, is presented. Than the test example of September 2010 floods on Ljubljana moor is discussed. Finally, case study from November 2012 floods is presented. During November 2012 floods an initiative was launched to gather as much non-metrical images of floods as possible from casual observers (volunteered image gathering). From all gathered images the guidelines presented before helped to pick out 21% images which were used for monoplotting.
In 2005 and 2006 intensive measurements were made of various erosion-denudation processes in the Dragonja River basin. The measurements included geomorphic processes in the badlands: the rockwall ...retreat of steep bare flysch slopes, movements of flysch debris along erosion gullies, and geomorphic processes on talus slopes. At the same time, measurements of soil erosion were made in three different land use areas: bare soil in an olive grove, an overgrown meadow, and a forest. The results are presented in two parts. Part One presents the measurements of soil erosion, and Part Two in the next issue of the journal (No. 49-2) will present geomorphic processes in the badlands. The measurements of soil erosion made on one-meter-square closed erosion plots south of the village of Marezige revealed that the greater part of the annual erosion was caused by only a few major erosion events. Between May 2005 and April 2006, interrill erosion amounted to 9,013 g/m2 (90 t/ha) on bare soil in an olive grove with an inclination of 5.5º and an average weekly proportion of specific runoff of 23%, 168 g/m2 (1.68 t/ha) on an overgrown meadow with an inclination of 9.4º and an average weekly proportion of specific runoff of 8%, and 391 g/m2 (3.91 t/ha) in a forest with an inclination of 7.8º and 415 g/m2 (4.15 t/ha) in a forest with an inclination of 21.4º with an average weekly proportion of specific runoff of 6% regardless of the inclination. The amount of precipitation during the reference year was slightly below the long-term average.
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