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- Title
Nemuno upės salos ir jų raida.
- Authors
Baubinienė, Aldona
- Abstract
River islands are accumulations of bottom sediments and particulate material generated by processes taking place in the riverbed, valley or the entire basin, morphometric parameters of riverbed, flow hydraulics, and physical / geographical conditions of the watercourse territory. They represent one of the most characteristic morphological forms of riverbed. Formation of islands and shoals in the riverbed may change its type or cause meandering and bifurcation into branches. An increasing number of islands and shoals implies that a large amount of particulate material is transported by the flow. Field measurement of bottom sediments discharge is quite a difficult task. In Lithuania, the discharge of particulate material is measured only in two WMS: on the Nemunas River at Salininkai and the Neris River at Jonava. The transformations of river-bed may be predicted based on investigations of the secondary morphological forms - river islands, which best reflect the evolution of the river. In the territory of Lithuania, the Nemunas River is divided into two stretches: Middle Nemunas between the Lithuanian-Byelorussian border and Kaunas HEPP and Lower Nemunas between Kaunas HEPP and Curonian Lagoon. During the time frame 1970-2005, the number of islands in the Nemunas stretch between the Lithuanian-Byelorussian border and Strėva mouth increased from 0.10 islands per km to 0.15; from 1.9% to 2.6%. 60% of the investigated islands in this stretch have increased in size. The average width of islands increased from 2.3 ha in 1970 to 3.7 ha in 2005. The total area of islands in the mentioned stretch has increased by 25 ha. The area of islands eroded during the mentioned time span amounted to 1.70 ha. In the mentioned stretch, sediment accumulation takes place under the influence of natural factors (climatic, geological, lithological, and hydrological). The Nemunas River head plays a significant role in deposition of particulate material. In thirty years, the size of the island in the Nemunas River head, not far from the Strėva River mouth, increased by 11 ha. During the mentioned time frame, the number of islands in the stretch Kaunas HEPP-Skirvytė decreased by 18%. In 1970, the number of islands per km was 0.17 whereas in 2005 it was 0.15, i. e. it decreased from 5.7% to 4.5%. The average size of islands increased from 6 ha (1970) to 7 ha (2005). Before the construction of Kaunas HEPP in 1960, Lower Nemunas was distinguished for deposition of particulate material. After the construction of Kaunas HEPP water reservoir, river bed self-lining has been taking place in the downstream reach. The bed processes are also affected by other kinds of economic activity: riverbed regulation by removing the newly formed shoals and islands and building of groynes for improvement of navigation conditions.
- Subjects
NEMAN River; MARINE sediments; HYDRAULICS; RIVER channels; GEOLOGICAL formations; PARAMETER estimation; BANKS (Oceanography); BIFURCATION theory
- Publication
Geografija, 2013, Vol 49, Issue 1, p1
- ISSN
1392-1096
- Publication type
Article