ANALYSIS OF EMBRIONIC SAND BARS (SUBMERGED) IN THE MIDDLE PARANÁ RIVER

PEREYRA, SOLEDAD; RAMONELL, CARLOS; LATRUBESSE, EDGARDO; SZUPIANY, RICARDO N.

Belem

Simposio; Anual Symposium IGCP 582-Tropical Rivers.; 2010

Sand bars and islands are conspicuous geophorms in the main channel of the Middle Paraná River. Their growth rates and enlargement modes have been studied since the seventies, but the primary origin of these forms is little known. We present some results concerning with the geometry and shifting of "embryonic" submerged bars, studied from satellite images of high spatial resolution (CBERS 2B and Google Earth ®) and 1:5,000 bathymetric charts. The influence of these bars in the origin of emerged bars during low and medium water stages of the river is also considered. The study was conduced between Corrientes (km 1208 of the navigation way) and Rosario (km 420) by means of images and bathymetries from the year 2002 to 2009. Several properties of embryonic bars were evaluated: frequency, displacement rates, relationship with emerged bars, and typical morphology (or 3D geometry). Submerged bars become evident in satellite images by "U" geometries in the water surface, with the "U" base pointing the water flow. The "U" geometry results from the 3D form of the embrionary bar, whose geometry is properly linguoid. The locally higher zones of a linguoid bar promote the trace in "U" advised from aerial views. The analysis of images from different times permit us the measurement of the downstream displacement of linguoids bars; shift rates up to some hundreds m/year were measured. The first-time emergence of "common" (emerged) isolated bars could be recorded as part of this multitemporal analysis. The geometry and location of emerged bars ratify the linguoid morphology of the embryonic bars. Chains of dunes were observed on the back of linguoid bars, and it is suggested that the bar acts like a ramp for these bedforms. Channel islands are more abundant than the emerged bars in the Paraná River during low-medium water stages or higher, but embryonic bars occur more frequently than island, up to 2:1. Embryonic or linguoid bars occurs isolated or as coalescent group, in the center of the main channel as well as near the channel and island banks. The morphological diversity of the emerged bars in the Middle Paraná River during an early stage of development is well explained by the migration, coalescence and juxtaposition of linguoid bars. Aerial photographs and satellite images are normally used in the study of bars and islands in the large rivers of the world, but this is the first time that they were used for the study of "embryonic" submerged bars. The application of this knowledge has a significant potential for the design and maintenance of waterway river engineering in this large fluvial system.