Abstract:

There are few experimental studies on in-situ simulation of rainfall on Benggang colluvial slope. Clarifying the influence of different rainfall intensities, slopes and initial soil moisture content on the initial runoff production time of colluvial slope and their critical thresholds can improve the understanding of the runoff production and concentration in the Benggang catchment, and may provide guidelines for rational allocation of water and soil resources and improvement of Benggang erosion control. In this study, 8 Benggang colluvial slopes at Guanxu Town in Deqing County of Guangdong Province were taken as the experimental sites. Based on the previous measurement of physical and chemical properties of the colluvial soil mass, using a portable field simulated rainfall device, a wireless weather meter and a soil profile moisture meter, in the runoff field of the colluvial slope with an area of 1 m×2 m, 12 field simulated rainfall and runoff production on the colluvial slopes were carried out with different combinations of 9 rainfall intensities (0.8-3.8 mm·min^-1), 8 slopes (9°-38°) and 12 initial soil moistures (0.2%-20.5%) at 10 cm depth. The results show that the initial runoff production time gradually decreased with the continuous increase of rainfall intensity, and there was no obvious threshold phenomenon. When the slope was less than 26°, the initial runoff production time decreased as the slope increased; when the slope was more than 30°, the initial runoff production time slightly lengthened with the increase of the slope; it is preliminarily determined that the slope of 26°-30° was the critical slope affecting the initial runoff production time. When the initial soil moisture at 10 cm depth was less than 7.8%, the initial runoff production time had no obvious regularity with the change of initial soil moisture; when the initial soil moisture at 10 cm depth was more than 8.3%, the initial runoff production time decreased with the increase of the initial soil moisture; therefore, the initial soil moisture of 7.8%-8.3% at 10 cm depth may be a critical threshold affecting the initial runoff production time. Among the three main factors affecting the initial runoff production time of colluvial slope, the influence of rainfall intensity was the greatest, followed by the initial soil moisture, and the influence of slope was relatively minimal. Furthermore, soil condition is also one of the key factors affecting the runoff generation and concentration on colluvial slopes. Comparative analysis of the runoff generation and concentration process of the colluvial slopes under different regional soil textures, types and conditions is a research direction that needs to be strengthened, and the critical phenomenon of the slope and initial soil moisture at 10 cm depth need also to be demonstrated by more field experiments and empirical researches in the future.

Key words: Benggang, colluvial slope, initial runoff production time, simulated rainfall experiment, influential factor, critical threshold, response surface analysis

摘要：

崩岗崩积体坡面原位模拟降雨试验研究还不多见。明确不同雨强、坡度和土体初始含水率对崩积体坡面初始产流时间的影响及其临界阈值，可加深对崩岗产汇流的认识，为合理配置水土资源和完善崩岗治理提供指导。以广东德庆县8个崩积体为试验地点，基于前期对崩积体土体理化性质的测定，采用便携式野外模拟降雨装置、无线自计气象仪和土壤剖面水分测定仪，在面积1 m×2 m的崩积体坡面径流场内，通过9种雨强（0.8—3.8 mm·min^-1）、8种坡度（9°—38°）、12次10 cm深度土体初始含水率（0.2%—20.5%）的不同组合，进行了12场野外模拟降雨及崩积体坡面产流试验。结果表明，初始产流时间随降雨强度的持续增大而逐渐缩短，没有表现出明显的阈值现象。当坡度<26°—30°时，初始产流时间随坡度的增大而缩短；当坡度>26°—30°时，初始产流时间随坡度的增大而略有加长，初步判断26°—30°的坡度是影响初始产流时间的临界坡度。当10 cm深度土体初始含水率<7.8%—8.3%时，初始产流时间随10 cm深度土体初始含水率的变化没有明显的规律性；当10 cm深度土体初始含水率>7.8%—8.3%时，初始产流时间随10 cm深度土体初始含水率的升高而缩短，因而7.8%—8.3%的10 cm深度土体初始含水率可能是影响初始产流时间的临界阈值。在影响崩积体坡面初始产流时间的3个主要因素中，降雨强度对初始产流时间影响最大，土体初始含水率的影响次之，坡度的影响相对最小。土壤条件也是影响崩积体坡面产汇流的关键因素之一，开展不同区域土壤质地、土壤类型、土壤状况下崩积体坡面产汇流过程的对比分析，是今后需要加强的研究方向。该文初步发现的坡度和10 cm深度土体初始含水率的临界现象，也需要开展更多的试验和实证研究。

关键词: 崩岗, 崩积体坡面, 初始产流时间, 模拟降雨试验, 影响因素, 临界阈值, 响应曲面分析