Keywords
semiarid, undisturbed plot, erosion, runoff
Start Date
1-7-2008 12:00 AM
Abstract
In the Brazilian semi arid region, a combination between human activities and climatic factors produces an increase in the ecosystem susceptibility to soil erosion. In this study, runoff and soil erosion processes due to natural rainstorm events on a 0.025 ha undisturbed experimental plot is analyzed. The site was instrumented to monitor rainfall, overland flow, runoff and erosion. Automatic devices were installed to monitor rainfall and the level of a 5 m3 tank at a 1-minute time step. The sediment transported by the flow was collected after each event. Plot average slope is 2.5%, vegetated of both permanent and annual plants, composed by a combination of xerophytes shrubs, brushes and grass species, whose patterns change with growing season as a result of its natural development dynamics. It was observed that runoff and soil erosion was controlled by rainfall pattern, antecedent soil moisture and vegetation. Also, vegetation height and density is influenced by soil structure and faunal activity, increasing both soil storage capacity and surface roughness. Wetting up period data (February 13 to April 25/2007) showed that runoff generation is the result of a non-linear interdependency of rainfall pattern, soil wetness condition and vegetation characteristics. Runoff coefficients less than 0.1 occurred at approximately 82 per cent of the observed events. Moreover, a positive feedback was observed involving vegetative species dynamics, soil properties and faunal activity producing annual plants regeneration. Also, annual plants distribution within the plot seemed to be controlled by permanent trees canopy, where density was higher. Finally, it was obtained an empirical relationship between short-term sediment production and rainstorm amount valid for 2006-2007 wetting up period individual rainstorm events. Hence, this approach has provided a continuous record of rainfall-runoff-sediment production field monitoring data which can be used to analyze hydrologic and vegetative dynamics at plot scale. Also, it highlights the role of vegetative cover as a controlling factor on erosion protection management.
Overland flow and soil erosion in an undisturbed Brazilian Northeastern Semiarid Experimental Plot
In the Brazilian semi arid region, a combination between human activities and climatic factors produces an increase in the ecosystem susceptibility to soil erosion. In this study, runoff and soil erosion processes due to natural rainstorm events on a 0.025 ha undisturbed experimental plot is analyzed. The site was instrumented to monitor rainfall, overland flow, runoff and erosion. Automatic devices were installed to monitor rainfall and the level of a 5 m3 tank at a 1-minute time step. The sediment transported by the flow was collected after each event. Plot average slope is 2.5%, vegetated of both permanent and annual plants, composed by a combination of xerophytes shrubs, brushes and grass species, whose patterns change with growing season as a result of its natural development dynamics. It was observed that runoff and soil erosion was controlled by rainfall pattern, antecedent soil moisture and vegetation. Also, vegetation height and density is influenced by soil structure and faunal activity, increasing both soil storage capacity and surface roughness. Wetting up period data (February 13 to April 25/2007) showed that runoff generation is the result of a non-linear interdependency of rainfall pattern, soil wetness condition and vegetation characteristics. Runoff coefficients less than 0.1 occurred at approximately 82 per cent of the observed events. Moreover, a positive feedback was observed involving vegetative species dynamics, soil properties and faunal activity producing annual plants regeneration. Also, annual plants distribution within the plot seemed to be controlled by permanent trees canopy, where density was higher. Finally, it was obtained an empirical relationship between short-term sediment production and rainstorm amount valid for 2006-2007 wetting up period individual rainstorm events. Hence, this approach has provided a continuous record of rainfall-runoff-sediment production field monitoring data which can be used to analyze hydrologic and vegetative dynamics at plot scale. Also, it highlights the role of vegetative cover as a controlling factor on erosion protection management.
