IN-CHANNEL ACCRETIONARY MACROFORMS IN THE MODERN ANASTOMOSING SYSTEM OF THE UPPER NAREW RIVER, NE POLAND

Ryszard GRADZIŃSKI (1), Janusz BARYŁA (2), Marek DOKTOR (1), Dariusz GMUR (1),Michał GRADZIŃSKI (3), Artur KĘDZIOR (1), Mariusz PASZKOWSKI (1), Roman SOJA (4),Tomasz ZIELIŃSKI (5) & Sławomir ŻUREK (6)

1) Institute of Geological Sciences (Cracow Research Centre), Polish Academy of Sciences, Senacka 1, 31-002 Kraków, Poland, e-mail: ndgradzi@cyf-kr.edu.pl
2) Ojców National Park, 32-047 Ojców, Poland
3) Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, 30-063 Kraków, Poland
4) Institute of Geography and Spatial Organization, Polish Academy of Sciences, św. Jana 22, 31-016 Kraków, Poland
5) Faculty of Earth Sciences, University of Silesia, Będzińska 60, 41-200 Sosnowiec, Poland
6) Geographical Institute, Pedagogic University, Konopnickiej 15, 25-406 Kielce, Poland

Gradziński, R., Baryła, J., Doktor, M., Gmur, D., Gradziński, M., Kędzior, A., Paszkowski, M., Soja, R., Zieliński, T. & Żurek, S., 2003. In-channel accretionary macroforms in the modern anastomosing system of the upper Narew River, NE Poland. Annales Societatis Geologorum Poloniae, 73: 35-53.

Key words: anastomosing river, sand bars, vegetation, Poland.
Abstract: Predomination of sandy bedload is typical of the anastomosing channels of the Narew River. Several types of in-channel accretionary macroforms have been found in these channels: side bars, concave-bank bars, plug bars, point bars, linguoid bars, and mid-channel bars. The first three types are relatively rare, point bars occur only exceptionally, while linguoid bars and mid-channel bars are quite common. The bars usually occur in main channels, which are the master routes of sand transport in the whole anastomosing system of the Narew. The lower parts of the bars are built of coarse- and medium-grained sand, similarly to the sediments in the deeper parts of the channels. Fine-grained sand, locally alternating with organic-rich muddy sand, predominates usually in the upper parts; peat with high content of sand is present in the highest parts of some bars.
All bars are rapidly colonised and stabilised by plants. It is for this reason and due to the low energy of the river that the bar sediments have a high preservation potential. The development of bars is usually not accompanied by lateral migration of channels. Consequently, sediment accretion in bars is one of the factors leading to gradual narrowing of channels. Deposits of some sand-bars, when preserved in fossil record, may probably be represented by characteristic "wings" in the outer parts of ribbon-like sand bodies.
Annales
Societatis
Geologorum
Poloniae

 

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