HYDROLOGICAL REGIME(DIET) AND ASPECTS OF THE MORPHOHYDRAULIC BEHAVIOR OF THE ARAGUAIA RIVER

With drainage area of 377,000 km2 and a mean annual discharge of 6,100 m3/s the Araguaia Rivers is the most important fluvial system draining the Cerrado biome of Brazil. In this paper we analyze water discharge, drainage area, cross-sections, width, depth and flow velocity data obtained from nine gauge stations in of the Araguaia River. In general terms the hydrologic regime depends of the dominant climate (tropical wet-dry) with floods from January to May (rain period) and low water between June and September. The peaks of maximum discharge are smoothed because the occurrence of secondary peaks. In the upper and lower courses there is a high variation between maximum and minimum peaks because the under developing of the floodplain, while in the medium course the flow peaks are smoothed by the presence of a well developed river floodplain. In general, the hydrological regime of the Araguaia River is simple. Was possible to conclude that the particular geomorphology of the drainage basin produces characteristic effects in river hydrology and that the hydrological regime is controlled by the characteristics of the bed (rocky in the upper and lower reach) as well as by the development of the floodplain (middle reach). However, doing more detailed analyses, the river presents an atypical distribution of flood discharge in the middle reach. In this area the river loss 30% of water discharge which are stored in the floodplain. Study of hydraulic geometry at a-station, suggests that width is almost constant as response to increasing discharge, but depth and velocity increase significantly.