Abstract
This study was undertaken in a 1566 ha drainage basin situated in an area with cuesta relief in the state of Sao Paulo, Brazil. The objectives were: 1) to map the maximum potential soil water retention capacity, and 2) simulate the depth of surface runoff in each geographical position of the area based on a typical rainfall event. The database required for the development of this research was generated in the environment of the geographical information system ArcInfo v.10.1. Undeformed soil samples were collected at 69 points. The ordinary kriging method was used in the interpolation of the values of soil density and maximum potential soil water retention capacity. The spherical model allowed for better adjustment of the semivariograms corresponding to the two soil attributes for the depth of 0 to 20 cm, while the Gaussian model enabled a better fit of the spatial behavior of the two variables for the depth of 20 to 40 cm. The simulation of the spatial distribution revealed a gradual increase in the depth of surface runoff for the rainfall event taken as example (25 mm) from the reverse to the peripheral depression of the cuesta (from west to east). There is a positive aspect observed in the gradient, since the sites of highest declivity, especially those at the front of the cuesta, are closer to the western boundary of the watershed where the lowest depths of runoff occur. This behavior, in conjunction with certain values of erodibility and depending on the land use and cover, can help mitigate the soil erosion processes in these areas.
Highlights
Among the descriptive and interpretative aspects of an environmental diagnosis, it is important to include an understanding of how the land and natural resources are used, considering degradations, threats, and an estimate of the fragility or vulnerability for the development of human activities [1].Water erosion assessment, which is part of the diagnosis of environmental problems, is highly relevant since inadequate land use can accelerate naturally occurring erosion and deposition processes, leading to modifications in soil conservation, water production and quality, and environmental changes in certain locations of a drainage basin [2]
The two-parameter Weibull distribution (b and c, involving scale and shape, respectively) was used to describe the frequency distributions (Table 1 and Figure 3) of the variables subjected to geostatistical analysis
The following conclusions were reached based on the results of this study: 1) The maximum potential soil water retention capacity showed a strong negative correlation with soil density, which strengthens the argument that, due to their structure, less dense soils are more porous and show a greater potential for water retention in macro- and micropores
Summary
Among the descriptive and interpretative aspects of an environmental diagnosis, it is important to include an understanding of how the land and natural resources are used, considering degradations, threats, and an estimate of the fragility or vulnerability for the development of human activities [1].Water erosion assessment, which is part of the diagnosis of environmental problems, is highly relevant since inadequate land use can accelerate naturally occurring erosion and deposition processes, leading to modifications in soil conservation, water production and quality, and environmental changes in certain locations of a drainage basin [2]. Various approaches and equations for risk assessment or predictive evaluation of soil erosion by water are available in the literature. The environment associated with cuesta relief areas in the state of São Paulo, Brazil, is extremely fragile and subject to different forms of negative impacts, including soil erosion [2]. Under these conditions, in studies developed in drainage basins, it is important to estimate sediment yield from a rainfall event or set of events.
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