Rzeki anastomozujące - procesy i modele sedymentacji..

Andrzej Karol Teisseyre

Abstrakt


ANASTOMOSING RIVERS - PROCESSES AND SEDIMENTARY MODELS

Summary
This paper is based on data taken from the literature and the author's own results. Anastomosing rivers (in the Australian sense) are common in the River Odra drainage basin, western Poland, both in sand-bed and gravel-bed rivers (60-62, 51, 53-55, 5; Fig. 1). Prior to the last river training at the beginning of the 20-th c., the River Kwisa and the Bóbr, Lower Silesia, had numerous anastomosing reaches (16% and 11 %, respectively). These were located mostly within successive basin-like valley expansions characterized by a low local slope. Mountain streams (e.g., the upper Bóbr in the Sudetes) have also been found to develop anastomosing reaches under similar circumstances. These reaches were characterized according to the classification by Brice et aI., (6; Fig. 3) and the results are shown in Figs 4 and 5. Two types of anastomosing landforms were distinguished, including anastomosing islands, which are channel forms, and interchannel areas, that are valley forms (Figs 4, 5, cf. 54, 55). Two original models of sedimentation have been briefly characterized, including a model for the suspended-load, gravel-bed upper Bóbr (Fig. 7) and the suspended-load, sand- or clay-bed upper River Oława (Fig. 8). In the former case, the deposits of the anastomosing river, underlain by deposits of meandering stream, comprise 3 types of sedimentary bodies: 1°tabular bodies of cohesive overbank sediments (deposits of inter channel areas), 2°shoestring bodies of over bank sediments (fillings of abandoned channels), and 3° accompanying shoestring-like bodies of gravel and sand (channel deposits, limited or no lateral accretion). In the latter case, the alluvium of the anastomosing river consists of shoestring bodies of sand and gravel (deposits of very stable anabranching channels, no lateral accretion) embedded in black clays and peats (deposits of inter channel areas and wetlands). In each case studied, anastomosing systems were the result of rivers adjustment to valley slope too low to permit the development of either meandering or braided patterns (Fig. 2).