THE ONGOING AVULSION OF THE TAQUARI RIVER – AN EXAMPLE OF NODAL AVULSION ON A DISTRIBUTIVE FLUVIAL SYSTEM

The Taquari fluvial system in the Pantanal of Brazil provides an example of the dynamic avulsion processes of rivers on a distributive fluvial system (DFS). Because rivers on DFS have a high potential for preservation, as they are generally in sedimentary basins, a greater understanding of modern river avulsions provides insights into the processes that may be captured in the rock record. In order to document the changes that are occurring during the Taquari river avulsion, a time series of LANDSAT imagery from 1985 to present was compiled. As of July 2009, the avulsion is not yet complete and discharge is being routed to both the old channel and in a new crevasse channel. Over the 24 years of available data, many geomorphological changes have become apparent in and below the avulsion area. The avulsion area is marked by the growth of new splays and the formation of a new meander belt. The new channel appears to have formed gradually through the development and abandonment of splays at different locations along the old channel, with the position of this new channel stabilizing only since 1999. The old channel belt is experiencing a decrease in volume through time, likely associated with the higher volumes of water and sediment being captured by the new channel. The decreasing volume of water and sediment load occurring in the old channel causes some areas to decrease sinuosity as the stream is recaptured in old chutes while in other reaches the river continues to increase sinuosity through lateral channel migration and continued point bar development. Seasonal patterns of inundation of the floodbasins also occur below the site of avulsion. Because this avulsion is not yet complete, we expect more morphological changes to occur before the new meander belt is stabilized. Future research will include, continued monitoring of the real time changes occurring along this river as well as an analysis focusing on the ecological changes associated with this river avulsion using available Normalized Difference Vegetation Index (NDVI) and other vegetation indices.