WATER EROSION IN UPPER ARAGUAIA RIVER BASIN: DISTRIBUTION, CONTROLS, ORIGIN AND ACTUAL DYNAMIC

Abstract

This article presents the results from two research programs focusing the water erosion, principally over gullying, developed on South Upper Araguaia River Basin, Central Plateau of Brazil, covered by fragments of savanna biome, one of the planet’s hotspots, related to the Northern Plateau from Paraná Sedimentary Basin, located in Goiás and Mato Grosso States, where an intensive and inadequate deforestation of savanna and faults in management practices in the last three decades are done. These studies based on environmental studies in a multi-scale approach, are initiated by general analyze about the distribution of gullies and its relationships with natural controls and land use and management in order to select the most critical areas and develop detailed studies to subside the control planning. The small to big gullies mostly concentrated on hillslopes, predominantly on large catchments areas, frequently following the hollow of heads, or perpendicularly to the bottom of valleys principally in medium and upper basins from tributaries of Araguaia River, are placed in the lower surface related to smoothed interfluves with gentle slopes and fine regolith sandy soils derived from the eolic sandstone of Botucatu Formation, witch involves the high regional surface known as Chapada. Two selected critical areas to pedological and hydrological studies are focused. Detailed observations in toposequence of soils and laboratory analyses of soil samples accomplished by monitoring of rain by pluviometer and rain gauge and water table level monitoring through piezometric and geophysical methods in order to identify the relationships between soils, slope forms, land use and actual physic-hydrological behavior of soils and slopes are done. The conclusions emphasize one hydropedological unbalance related to the natural variables and land use, mainly on the footslopes. The hydrological unbalance is characterized by high hydraulic gradient and a link between the superficial and sub-superficial overflows converging to the saturated zone, principally during the rainy season, which favors the gully process, in a regressive pathway development related to piping land controlled by structural directions. Finally, one example for rehabilitation based on environmental laws, conservational practices and recuperation of legal reserves and permanent preservation of degraded areas is presented.