Przyczynek do znajomości tarasów rzecznych

Krzysztof Schoeneich



The paper presents a project of classification of river terraces. The river erosional processes taking place on the continent form a continental river valley, those governing in a stagnant water basin are responsible for production of a subaqueous river valley being a continuation of the continental one. The river accumulation processes taking place on the continent cause the formation of a river cone, those manifesting themselves in a stagnant water basin contribute to the formation of river delta. The continental river valley appears to represent the most common surface form developed as a result of the activity of dynamical river processes. Valley slope and river terraces are its structural elements, the valley bottom being the lowermost terrace of the river. The river terrace formed under conditions of deepening the river valley, i.e. during the prevalence of erosion over accumulation, represents an errosional terrace (Figs 3, 4 and 5). Both surface inclination towards the river and slight thickness of underlying river grounds, always smaller than the depth of river, are its characteristic features. Accumulation river terrace formed under conditions of a temporary predominance of accumulation over erosion, is characterized by a horizontal surface, locally slightly inclined towards the valley slopes, and by a thickness of river grounds, greater than the depth of river (Figs 6 and 7). An accumulation terrace exists until the previously eroded valley is completely buried.
The river terrace, both accumulation and erosional, consists of two parts. Lower part, for which the name "terrace socle" is proposed, is built up of loose river grounds formed due to the sedimentation of traction material (stones, gravels, sand-gravel mix and sands), and upper part, the so-called terrace cover, consists of coherent and organic grounds formed due to the sedimentation of suspension material (alluvial deposits, tills, silty sands and silts). In terraces formed under conditions of unchanged dynamical river regime, the terrace cover rests above, and the terrace socle below the mean water. A different occurrence form proves the changing of regime either during the formation of terrace. or already after its accumulation.

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