Process of Runoff Generation at Different Cultivated Sloping Sites in North and Northeast Thailand

Abstract

The conditions for surface runoff generation, which is usually strongly related to the process of soil erosion, were analyzed in three plots at different cultivated sloping sites in North and Northeast Thailand using a runoff gauge connected to a data logger. In most of the cases, the rainfall intensity and the surface soil moisture contributed significantly to surface runoff generation. The rainfall intensity in the Khon Kaen plot on sandy soils was higher than that in the other two plots with fine-textured soils in the northern region, and surface runoff occasionally occurred throughout the rainy season with no clear seasonal trend, unlike in the other two plots, where surface runoff occurred more often during the latter half of the rainy season due to the higher rainfall intensity and/or capillary saturation of surface soils. The proportion of the surface runoff generated in relation to the amount of rainfall increased with the increase of the slope gradient of the plots. The proportion of the amount of soil erosion in relation to the amount of surface runoff was, however, the largest in the sandy plot of Khon Kaen with the lowest slope gradient, indicating that the sandy soils were more easily eroded than the clayey soils presumably due to the weakly organized structure of the soil aggregates. Therefore, the conditions that enhance the risk of surface runoff and soil erosion were found to vary and should be taken into account for agricultural management in the respective regions.