Study on initial process of soil erosion, on sloped, cropland in humid tropics using soil water-monitoring system

利用水动力监测系统对泰国北部和东北部坡耕地在季风气候条件下的产流条件和产流过程进行了定量研究。利用安装在小范围(1m×1m或25m×2.5m)田间小区的数据记录仪，每隔10分钟连续监测降雨量、土壤体积含水率和地表径流量。在此基础上，将水生强降雨的去向划分为土壤增湿、地表径流和水分流失三个归宿。在此基础上，确定了水分流失和地表径流的速率及其产生的初始条件为降雨强度、土壤初始含水率等的函数，得到的结果如下：1)水分流失速率和地表径流均强烈依赖于降雨强度；2)在雨季初期，坚硬的降水大部分通过蒸发蒸腾损失，并以毛管水的形式部分积累到土壤中：结果是整个雨季土壤水分逐渐增加，特别是在中到细质土壤中；3)在雨季后期，通过内部排水增加了水分损失；4)不同试验地的雨强和雨季土壤水分状况有不同的分布规律。导致以下类型的径流产生风险：i)泰国东北部低海拔地区降雨强度相关的风险泰国北部中等海拔地区毛管饱和增强风险泰国北部高地雨季后期降雨强度增加带来的风险

The condition and process of runoff generation were studied quantitatively by a water dynamics-monitoring system Three experimental plots were installed on sloped agricultural field in northern or northeastern Thailand under monsoon climate. The amount of rainfall, volumetric soil moisture content, and the amount of surface runoff were continuously monitored for every 10 minutes using a datalogger, which was installed in a small-scale field plot (1m × 1m or 25m × 2.5 m). Then the fate of water derived firm rainfall was divided into three destinations, i.e. increment of soil moisture, surface runoff and water loss. Based on these data, the rate of water loss and surface runoff and the initial conditions for their generation were determined as functions of rainfall intensity, initial soil moisture content, etc. The results obtained are summarized below :1) Both the rate of water loss and surface runoff were strongly dependent on rainfall intensity ; and also on initial moisture content of the surface soil to some degree2) In early stage of rainy season, water delved firm rainfall is largely lost through evapotranspiration, and partially accumulated into the soil as capillary water : As a result, gradual increment of soil water throughout rainy season is observed especially in medium to the fine textured soils3) In late rainy season, a water loss through internal drainage increased4) Different distribution patterns for rainfall intensity and soil moisture condition during rainy season were observed among the experimental plots, resulting in following types of runoff generation risks :i) rainfall intensity-dependent risk in low elevation area in northeastem Thailandii) capillary saturation-enhanced risk in medium elevation area in northern Thailandiii) risk by increased rainfall intensity in later rainy season in highland in northern Thailand