Geografie 1961, 66, 23-30
Evidence of Pleistocene Aggradation in the Valley of the Sázava
The remnants of the old abandoned valley ascertained in the middle course of the Sázava near Zruč and Chabeřice provide evidence of a strong Pleistocene aggradation. These deposits indicate that the accumulations of terrace gravels established on the lower Vltava extended up to the canyon-shaped valleys in central Bohemia. In the successive phases of erosion the gravels were removed almost completely from the narrow valleys in which very little evidence of the aggradation was left behind. From the longitudinal profile of the Sázava it is evident that the reaches of steep gradient between Pikovice and Týnec, and upstream of Ledeč furnish important criteria for the development of the valley, particularly if compared with the longitudinal profile of the Vltava and the system of the Vltava terraces. The headward erosion proceeding from the Vltava valley into the valley of the Sázava had been retained on resistant eruptive rocks of the Jílové zone and on the granodiorite downstream of Týnec, before terraces of the group III. and IV. were deposited. This obstruction in the river channel formed a local base-level of erosion for the middle course of the stream. The older erosion phase previous to the aggradation of the II. terrace proceeded up to Ledeč where a further step developed on the compact Lipnice granite. In our opinion, there is no reason to interprete the breaks in the longitudinal profile tectonically; the investigations did not reveal any evidence which would account for young tectonic movements. As concerns the age of the aggradation in the old Sázava valley, it is regarded as contemporaneous with the Vltava terrace IIIb. The overdeepened river channel south of Zruč represents a scarce instance of old river floor preserved together with the accumulation of sandy gravels on the concave bank of the river meander. The river was shifted towards the right bank by deluvial sediments which descended down the steep slope above the left bank, in the level of the highest aggradation. It is due to these talus deposits that the old overdeepened river valley with the original infilling has been preserved. The measured profiles of the abandoned valley of the Sázava point to the importance of the methods used for the study of the river terraces. The study of terraces and development of the river valleys without the reconstruction of cross-sections and analysis of the longitudinal profile, based only on the morphological criteria, cannot lead to the correct views on the development of the river valleys.
