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

在季风气候条件下，在泰国北部和东北部的坡耕地上设置了3个试验田，对产流条件和产流过程进行了定量研究。利用安装在小型田间地块（1m × 1m或25m × 2.5 m）的数据记录仪，每10分钟连续监测降雨量、土壤体积含水量和地表径流量。在此基础上，将水源稳定降雨的命运划分为土壤水分增加、地表径流和失水三个目的地。根据这些数据，确定了降雨强度、土壤初始含水量等对失水速率和地表径流量的影响及其产生的初始条件。研究结果表明：1)流域失水速率和地表径流量均与降雨强度密切相关；2)雨季前期，深埋的降水大部分通过蒸散散失，部分以毛细水的形式积累到土壤中；结果表明，在整个雨季，土壤水分呈逐渐增加的趋势，特别是在中、细粒土壤中。3)在雨季后期，土壤内部排水失水量增加。4)各试验区在雨季降雨强度和土壤水分状况上存在不同的分布规律。导致以下类型的产流风险：1)泰国东北部低海拔地区降雨强度依赖性风险；2)泰国北部中等海拔地区毛细饱和度增强风险；3)泰国北部高原雨季后期降雨强度增加风险

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