长期野外监测红壤裸露坡地侵蚀性降雨分布及产沙分析

侵蚀性降雨及其侵蚀泥沙分布特征研究是掌握土壤侵蚀规律的基础,同时也可为水土保持综合治理提供理论依据。研究选择红壤裸地坡面径流小区为研究对象,利用实际观测法收集到2001-2016年的565次长序列侵蚀性降雨及其径流泥沙资料,运用数理统计方法分析侵蚀性降雨及其泥沙的发生频率和强度的分布特征,在此基础上分析降雨类型对侵蚀产沙的影响。研究结果表明,研究区侵蚀性降雨量占总降雨量的87.82%,主要分布在降雨量为25 mm以上和降雨强度5mm/h以下的降雨事件。次降雨侵蚀强度小于100t/km~2的侵蚀次数占总次数的76.81%,而其侵蚀总量只占总量的7.28%;侵蚀强度大于500t/km~2的降雨侵蚀次数只占总次数的6.36%,但其侵蚀泥沙量可占总量的60.96%,次降雨侵蚀产沙量分布极为不均。降雨量25～100mm且平均雨强小于20mm/h的降雨类型造成研究区土壤侵蚀量最大。次降雨量100 mm和降雨强度20 mm/h可作为红壤裸露坡地水土流失防御的设计暴雨特征值。研究结果有助于揭示红壤坡地次降雨侵蚀规律和水土保持措施布设。

Analysis of erosive rainfall distribution and sediment yield on long-term field monitoring sloping bare land of red soil

Red soil region in southern China is one of the regions where soil erosion and flood disasters are serious, and the erosive rainfall is the direct driving force. The distribution of erosive rainfall and its erosion characteristics are the basis for understanding the law of soil erosion, and can also provide a theoretical basis for comprehensive control of soil and water conservation. At present, most of the relevant research data series are collected relatively in short time frames and the conclusions from those studies need further verifications. At the same time, there is a lack of research on soil erodibility characteristics under erosive rainfall. In this study, data of rainfall and sediment of 565 individual erosive rainfalls from 2001 to 2016 in experimental plots on bare slopes of red soil in north part of Jiangxi Province were collected, and then the distribution characteristics of erosive rainfall and its erosivity were analyzed from the intensity and frequency of rainfall and their impacts on soil erosion. On this basis, the influence of rainfall pattern on erosion and sediment yield was analyzed. The results showed that the average annual erosive rainfall in the study area was 1 246.2 mm, accounting for 87.82% of the total annual average rainfall, mainly distributed in the rainfall amount greater than 25 mm and the rain intensity less than 5 mm/h. The durations of rainfall erosion events with erosion intensity less than 100 t/km2 accounted for 76.81% of the total rainfall times, while the total amount of erosion sediment accounted for only 7.28% of the total amount of sediment. Rainfall erosion duration with erosion intensity greater than 500 t/km2 accounted for only 6.36% of the total times, but the erosion sediment amount accounted for 60.96% of the total amount of sediment, which indicated that the distribution of sediment yield under rainfall erosion was extremely uneven. The amount of soil erosion mainly occurred in the slope land under 25-100 mm rainfall, and the number of soil erosion occurred under this rainfall accounted for 46.37% of the total number of rain events, resulting in 71.67% of the total amount of soil erosion. Among them, erosion intensity greater than 1 000 t/km2 was concentrated in 25-50 mm grade rainfall. High rainfall intensity greater than 20 mm/h had a low proportion of soil erosion, resulted in both occurrence frequency and in the total amount of soil erosion, but the probability of strong erosion caused by such event was high. Soil erosion of bare slopes in red soil was mainly affected by both rainfall intensity and rainfall. The rainfall of 25-50 mm and the average rainfall intensity of 5-10 mm/h resulted in the largest amount of soil erosion. Medium rainfall intensity and heavy rainfall or moderate rainfall and large rainfall intensity were the rainfall patterns that caused severe erosion. The rainfall amount of 100 mm and the rainfall intensity of 20 mm/h can be used as the reference value of rainfall standard for soil erosion prevention in red soil bare sloping land. The results will provide a useful reference for further revealing the law of soil erosion on red soil sloping land and constructing erosion prediction model.