Florina Grecu

Sediment Transport and River Channel Dynamics in Romania – Variability and Control Factors

Sediment transport and river channel dynamics are the result of the complex interaction between natural and human factors, at both local and regional scale. The study of sediment transport and river channel dynamics may be an important way to better know and understand the mechanisms that rule the functioning of fluvial system, allowing forecasts of its future evolution to be made and appropriate adaptation measures to be taken by society in front of the risks related to the fluvial dynamics and sediment transfer. The purpose of this chapter is to present specific aspects concerning the sediment transport and river channel dynamics in Romania and to reveal the role of various control factors. Our contribution consists mainly in regional analyses that highlight the following aspects: i) the spatial and temporal variability of suspended sediment transport; ii) the relationships between suspended sediment yield/load and some control variables (precipitation, water discharge, catchments characteristics, and human activities), and iii) the vertical and lateral dynamics of selected river channels. The chapter summarizes a part of the significant results of our previous studies and some more recent researches in the field of sediment transport and channel dynamics in Romania. It also includes new issues and approaches, based especially on case studies, which further develop the proposed topic. The analyses focus preeminently on two areas: the Carpathian’s Curvature region, and the central part of the Romanian Plain (Fig. 1A). We have chosen the first area because it has the highest sediment yield in Romania: over 20 – 25 t ha-1 yr-1, meaning more than 10 times the average sediment yield on a national scale, which is about 2 t ha-1 yr-1 (Mociorniţă & Birtu, 1997). The central part of the Romanian Plain is characterized by an intense lateral dynamics of the river channels, making it vulnerable to the risks induced by fluvial dynamics, because of the economic importance of the area and the significant density of population and settlements. The data used and the methodologies employed are mentioned in the text. This chapter is structured in four main parts concerning: i) previous researches on sediment transport and fluvial dynamics in Romania; ii) sediment transport and control variables; iii) river channel dynamics and iii) human impact on sediment transfer.

Floods and Flash-Floods Related to River Channel Dynamics

Floods and flash-floods are a major factor in hydrogeomorphological river dynamics. This chapter has two main aims: (i) to analyse the characteristics of floods in Romania, based on their origin, frequency and magnitude; (ii) to present case studies on the relation between river channel dynamics and floods. In most cases, in Romania, floods occur in spring and summer (up to 3/4 of the total number of floods) and have mostly pluvial origins. Rivers from the External Curvature (Carpathians, Subcarpathians and Romanian Plain) suffered historical floods in 2005, reflected by a slight extension of the river channel (for example, Putna and Buzău watercourses). Rivers from Banat Plain also recorded floods in 2005; a high volume of water created breaches in dikes and the long stagnation of water determined morphological modifications of the floodplain. The Danube River registered historical floods in 2006; due to the morphometry of the floodplain, the river overflowed the banks and the dikes, covering the floodplain between Rast and Bistreţ towards the homonym lake. The flash-flood from Ilisua River basin in June 2006 generated some modifications in the river channel morphology due to fine materials accumulation, with a thickness of 0.2–1.5 m, and coarser ones, which created bars with heights of 0.5–1 m; materials came from landslides and bank collapse. The interactions between hydrological phenomena and morphological processes may have consequences with ephemeral character, reversible on short-term, but also on long-term, with a potential impact on the environment and on the society. This analysis underlines the applied character of hydrogeomorphology.

InterGEO. A digital platform for university education on geomorphological heritage.

The project InterGEO was carried out with the objective to disseminate knowledge on geomorphological heritage by developing a digital learning platform. It aims at improving students’ autonomy by the reduction of face-to-face teaching and increasing autonomous learning as well as promoting international interactions between students interested in geomorphological heritage. A completely free-access virtual course on geomorphosites was developed with the Learning Management System Moodle. The course is divided into 24 thematic chapters, each of them containing a short description, a list of references and selected publications, as well as other educational material (videos, virtual fieldtrips, etc.). In particular, several videos allow presenting in a dynamic way concepts and examples. The paper presents the tool and its use in academic programmes in six European universities, where it was tested, in various contexts (Bachelors’ and Masters’ programmes; students in geography or geology; general courses in geomorphology and specific courses on geoheritage and geoconservation), before discussing the advantages and challenges the tool is facing. The InterGEO platform is an easy-to-use and friendly educational tool, which allows developing blended learning activities; it is flexible and adaptable in various learning contexts.

The dynamics of the Danube channel over the last 150 years (Giurgiu - Călărași sector. Preliminary data)

The dynamics of a river channel targets the interdependency relations between water, relief and sediments, as well as their effects within the fluvial system. This paper presents the dynamics of some fluvial islands (islets) from the river channel of the Danube between Giurgiu-Russe and Călăraşi-Silistra localities, corresponding to a part of the lower sector of the Danube, which constitutes the border between Romania and Bulgaria. The islets are fixed sedimentary deposits, stabilized, with a vegetation cover depending on the soil formation degree. We use the term “ostrov”, as specified on the cartographic materials published in Romanian. The objectives of the study are defined by the main work phases: 1) identification and mapping of islets on maps of 1864, 1910, 1980 and on orthophotoplans of 2009, 2) design of a typology of these islets based on various criteria, 3) determination of the surface evolution of some islets relevant both as position and as morphogenetic environment. The analysis highlights the ascending variation of the surface of the islets both in time and in space, in respect to the sedimentary input of the Danube. A conclusive example is the Kosuy islet, situated upstream of the Argeș-Danube confluence (between kilometers 427-423 on the Danube), with an area which increased over five times in the last 150 years. Keywords— dynamics; morphometry; mapping; fluvial island; the Danube; Romania

Geomorphologic Hazard in Romania. Typology and Areal Distribution

The general physiographic arrangements of the relief are characterized by a quasi-concentric disposal of altitudes, and the characteristics of the geomorphologic hazards are shaped accordingly. An essential feature of the geomorphologic hazards is their cohabitation with the pedologic processes, deriving long-lasting effects on elements at risk through land degradation. In Romania, the hills and the plateau regions are the most prone to geomorphologic hazards, particularly to landslides and erosion. The specificity of the geomorphologic hazards is given by their genesis and long-term evolution; thus, their impact upon the elements at risk manifests less direct with risk effects (human and material damages, respectively). In Romania, one can distinguish geomorphic hazards induced by slope processes, by river channel dynamics and by other various processes. The gravitational hazards include avalanches and rock falls landslides, collapses, suffusion and compaction phenomena. In their turn, the pluvial–torrential systems are highly frequent for the lands deprived of wood vegetation in sedimentary hilly, plateau and mountain areas. The hazards induced by channel processes occur mainly in the hills, lowlands and mountain depression areas. They are associated with high silting, channel wandering, braiding, side erosion and meandering in plains and subsidence areas. The hazards induced by various processes refer to the marine geomorphic system of the Black Sea coast and to the aeolian systems developed on sandy areas and at high altitudes. Geomorphologic hazards affect the Romanian territory with various degrees of intensity, thus contributing to land and soil degradation, with long-lasting effects on population.