SUMMARY
The Pantanal trough is located at the border line of the "couverture tabulaire"at Mato Grosso Plateau, under control of faults and Precambrian metamorphic andcrystalline continental crust with Apalachian Eocambrian sedimentary landforms.Modern alluvial formations have been formed at least 200 m below present sealevel, having around 300 m thickness. Thus, the Pantanal is a tectonic trough,completely bordered by the 200 m contour line. Subsidence explains gentleslopes, which are lesser than 1%. At the sheet flood fan axe. River floods arerunning slowly from neighbor mountains areas, allowing a grassland support formore than 5.000.000 of cattle.Pantanal alluvial deposits have built enormous coalescent sheet flood fans.The largest one is Taquari, which cross over residual mountain chains at theright hand border of the Paraguay, covering "glacis" (bahadas) lying at its ground.On the contact between this sheet flood fans and the "glacis" there is aseries of receptacle lakes, which are by the Paraguay floods. Some lakesrestore water to the Paraguay River during its low level after floods.During recent Quatemary dry periods the high Paraguay basin was endorreic.So, a number of Pantanal sheet flood fans are digged by wind erosion, formingtroughs. These troughs are partly covered by lagoons and partly by amphibiousvegetation, thus increasing runoff deficit. Therefore, the Pantanal plays an importantrole on the Paraguay hidrology, emphasizing floods but increasing runoffdeficit.It has been suggested to build large dams to regulate water flow in the rivers,near their entrances into the Pantanal. However, this radical change inenvironmental management needs a lot of knowledge, specially on this very complexand feeble environment, where, as a consequence, investments are very expensive.