Autori: Ionita Ichim, Maria Radoane, Nicolae Radoane, Crina Miclaus

Editorial: Transactions, Japanese Geomorphological Union, 17-3, p.135-137, 1996.

Rezumat:

Reţeaua hidrograficã a României are o lungime totalã de 76 000 km , drenând o suprafaţã de 237 500 km². Este tributarã in proporţie de 97.8 % Dunãrii, are un debit mediu anual de 1300 m³/s şi in proportie de peste 80% izvoraste din Muntii Carpati. Ca geomorfologi, am abordat aceastã problemã în contextul analizei bilanţului aluviunilor dintr-un bazin hidrografic, al identificãrii unor particularitãţi de evoluţie a râurilor, al relaţiilor dintre variabilitatea depozitelor de albie şi unii factori de control specifici acestei regiuni din punct de vedere morfogenetic. Concret, ne vom referi la:a)forma profilului longitudinal in relatie cu dimensiunea materialului de albie;
b) spectrul granulometric al materialului de albie explicat în relaţie cu unele variabile ale bazinului hidrografic.
c) evidenţa empiricã a modalitãţii distribuţiilor granulometrice în profil longitudinal;d)variabilitatea petrografica a materialului de albie explicat in relatie cu alcatuirea litologica a ariei sursa.
Cercetarile noastre s-au concentrat asupra a sase rauri din Romania, a caror suprafata de drenaj este de 44 748 kmp, adica 18.8% din suprafata Romaniei.
The drainage network of the Romania’s territory has a total length of 76,000 km, characterising an area of 237,500 km². A weight of 97.8 % from this network is tributary to the Danube, the second river as size after Volga River from the Europe.
As geomorphologists, we approached gravel bed rivers in the context of relationships between channel deposits variability and some controlling factors characterising morphogenetically this region: i) longitudinal profile form related to the variation of bed material calibre; ii) grain size spectrum of bed material explained in relation with some drainage basin variables; iii) empirical evidence of the grain size modality in downstream direction; iv) petrographical variability of bed material explained in relation with the source area lithological composition. Our researches focused on the six rivers in Romania, whose drainage basins are 44,748 km², that is, 18.8 per cent of Romania’s surface.
The granulometrial spectrum of bed materials is disturbed by the discontinuities in longitudinal profile, by lateral input of sediment, by intersection of some relict landforms. There is a tendency of bed material segregation in the downstream direction controlled by geological – geomorphological units cut by the streams. Modality of the granulometrical distributions is the best described by including of three categories of fractions of bedmaterial: sand, gravel and the fraction 1 – 20 mm. Bimodality is determined by amounts under about 35 % of the fraction 1 – 20 mm. The petrographical composition of fluvial gravel reflects, differently, the petrographical types of source areas. The ratio river/source is a measure of the river efficiency in different lithological clast abrasion. This measure shows, for example, that magmatic, metamorphic and carbonate rocks are of 10 – 30 times better represented in river channel than in source area. Contrarily, the gravel from sandstone rocks is of better represented in the source area than in river channel.

Cuvinte cheie: rauri cu pat de pietris, distributii granulometrice, compozitie petrografica, Carpatii Orientali, Romania // river bed gravel, grain size distributions, modality, downstream variation, petrographical composition, Eastern Carpathians, Romania

URL: http://www.usv.ro/istgeo