Mudanças Topográficas e Sedimentológicas em uma Unidade Soleira- Depressão no Córrego Guavirá, Marechal Cândido Rondon, Paraná

Water depth and substrate grain size composition were measured in a riffle-pool unit in the Guavirá stream, municipal district of Marechal Cândido Rondon, western region of Paraná State, Brazil. The objective of the work was to describe the effects of the floods on stream bed topography and sedimentological characteristics of the bottom sediments. During the first survey (December 2000, dry period), the sediment of bottom corresponds to granule and the mean elevation of the bed was of 314,382 m. With the occurrence of the precipitations in January and February 2001, the floods caused oscillations in the bed surface heights (314,177 m in the 2th and 314,403 m in the 3th surveys respectively) and the mean size of the bottom sediments had a continuous decrease: very coarse sand to coarse sand. The oscillation of the bed topography during the rainy period demonstrates that the velocity reversal of the flow during the inundations constantly migrate, fact that can explain erosion and deposition in a same reach during consecutive floods. In spite of bed elevation and sedimentological changes were observed in the riffle-pool unit, any longitudinal migration of the features was not verified even with the occurrence of floods exceeding the bankfull level.