FORMATION OF THE FLOODPLAINS OF THE SELENGA RIVER DELTA
E.A. ILYICHEVA1, M.V. PAVLOV1, B. MCELROY2, D.A. NITTROUER3, T.Y. DONG4
1V.B. Sochava Institute of Geography, Siberian Branch, Russian Academy of Sciences, 664033, Irkutsk, ul. Ulan-Batorskaya, 1, Russia
lenail3663@mail.ru
2Wyoming University, 82070, Wyoming, Laramie, 22nd Street, 222, USA
bmcelroy@uwyo.edu
3Rice University, 6100, Texas, Houston, Main Street, 126, USA
nittrouer@rice.edu
4University of Texas at Austin, 78712, Texas, Austin, 23rd Street, 305 E, USA
tian.y.dong@utexas.edu
Keywords: morphogenesis, morphodynamics, stages of water discharge, Baikal, Late Holocene, mapping
Abstract
Results of geomorphological investigations in the estuarine region of the Selenga river for the last 10 years are presented. Within the Ust’-Selenginskaya depression, the modern estuarine region of the Selenga has been identified on the basis of assess ing the interaction of the fluvial flow with the banks and the riverbed for the technogenic stage of development - from the begin ning of the Irkutsk reservoir filling. A geomorphological analysis of cartographic material from different times was made to identify the floodplain complex of terraces an abandoned stretches of channels that emerged in different periods of discharges in the basin. It was found that during the stage under consideration the Lake Baikal drainage basin showed at least three anoma lies of the river runoff which were responsible for the onset of low- and high-water periods. Furthermore, we determined the areas of the islands and banks which were unaffected by erosion-accumulative activity of the delta by-channels and inundations. Such areas include high islands and banks, on the surface of which there occur abandoned channels, hollows and oxbows pro ducing a network of fans of wandering of the relict channel network. It is established that some negative forms are filled with water and have no direct hydraulic connection with the modern channel network. A dating of bank deposits and bottom sediments of the oxbows was carried out by the radiocarbon method. It was found that the bottom sediments of the oxbows are represented by gyttja which often occurs on the riverbed alluvium. The bank sections are similar in structure and are composed of different facies of alluvial deposits intercalating with paleosoil horizons. The modern floodplain deposits are represented by silty sands with sparse fine well-rounded pebble.
|
