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自然降雨特征和作物覆盖对三峡库区紫色土坡耕地产流产沙影响

Effects of natural rainfall characteristics and crop coverage on runoff and sediment yield in purple soil slope cultivated land in the Three Gorges Reservoir areas

  • 摘要: 为探索解决三峡库区紫色土坡耕地侵蚀效应,该研究基于三峡库区腹地重庆万州付沟小流域6个标准径流小区(5个不同坡度作物覆盖小区,1个裸坡作对照)2021—2023年观测的108场自然降雨和径流小区产流产沙数据,利用K-mean聚类、Pearson相关分析等方法开展研究区降雨特征和坡面产流产沙对降雨和坡度的响应。结果表明:1)根据降雨量、降雨历时、降雨强度和最大30 min降雨强度4个特征指标,观测期内研究区降雨可划分为3种主要类型,A雨型(低频率、长历时、大雨量、小雨强)、B雨型(中频率、中历时、中雨量、中雨强)和C雨型(高频率、短历时、小雨量、大雨强),其中C雨型是研究区侵蚀性降雨的主要类型,诱发坡面侵蚀发生的临界降雨量、降雨强度和最大30 min降雨强度分别为6~21 mm、1.1~3.6 mm/h和1.2~7.6 mm/h;2)降雨量、降雨强度和最大30 min降雨强度对裸坡和作物覆盖试验小区产流均有显著影响(P<0.05),但坡面产沙仅与产流呈极显著相关(P<0.01),相同产流下,C雨型产沙量达到A雨型和B雨型的1.06~20.18倍;3)不同雨型对裸坡和作物覆盖试验小区产流产沙的贡献均呈现为C雨型>B雨型>A雨型,C雨型对坡面产流和产沙的贡献均值分别为48.19%和81.82%,作物覆盖试验小区相较于裸坡的产流量和产沙量分别减少61.67%和77.15%,降雨强度越大,坡度对产流产沙影响越小,且坡面侵蚀随坡度增大可能存在临界坡度在15°~25°之间。方差贡献率分析表明雨型对作物覆盖坡面产流产沙贡献均超过60%,其贡献达到坡度的2.60~5.05倍。试验结果表明在该研究区开展农业耕作过程中尤其要注重短历时、高强度降雨导致的侵蚀问题,结论可为研究区坡耕地水土流失综合治理提供参考。

     

    Abstract: Slope farmland has been the predominant land use type in the Three Gorges Reservoir area. There are the significant impacts of slop farmland on the regional ecological environment, due primarily to the soil erosion resulting from agricultural practices. Soil erosion patterns on sloping farmland can depend mainly on the climates and terrains. Additionally, the soil and water conservation can vary greatly in different regions and seasons. Crop coverage can be expected as the key measure for the soil erosion control. This study aims to investigate the relationship between slope sediment and runoff under different rainfall and terrain conditions. The dataset was taken from the 108 natural rainfall observations from 2021 to 2023. Rainfall events were then classified into the patterns using four indicators: rainfall amount, duration, intensity, and the maximum 30-minute intensity. K-means clustering analysis was also employed on the dataset. Data on runoff and sediment yield was collected from five experimental plots with different slope crop coverages, taking the bare slopes as the control. A systematic investigation was implemented on the effects of various rainfall characteristics (type, intensity, and maximum 30-minute intensity) and five slope gradients (5°, 10°, 15°, 20°, 25°) on the runoff and sediment yield. The sediment and runoff reduction benefits of crop coverage also assessed to quantify the contribution rates of rainfall type and slope gradient to sediment and runoff yield on crop-covered slopes. Additionally, Pearson correlation analysis was used to explore the relationship between runoff and sediment yield of different surfaces with rainfall characteristics and slope. The findings indicate that: 1) According to four rainfall characteristic indicators (rainfall amount, duration, intensity, and maximum 30-minute intensity), the 108 rainfall events were categorized into three patterns: A-type (low frequency, long duration, heavy rainfall, and low intensity), B-type (medium frequency, medium duration, moderate rainfall, and moderate intensity), and C-type (high frequency, short duration, light rainfall, and high intensity). C-type rainfall was dominated as the erosive type in the study area. Critical thresholds of rainfall amount, intensity, and maximum 30-minute intensity on the slope erosion were 6-21 mm, 1.1-3.6 mm/h, and 1.2-7.6 mm/h, respectively. 2) Rainfall amount, intensity, and maximum 30-minute intensity were also dominated the runoff generation on both bare and crop-covered slopes (P<0.05). However, the slope sediment yield was correlated with the runoff generation (P<0.01). Furthermore, the sediment yield from C-type rainfall was 4.77 to 17.69 times greater than that from A-type and B-type rainfall under the same runoff. The fitting coefficient of the linear relationship between sediment and water coverage of various crops increased by 1.33 to 5.06 times, as the slope increased. 3) The impact of various rainfall types on the runoff and sediment generation on the bare slopes and crop-covered slopes followed the descending order: C-type > B-type > A-type. The average contributions of C-type rainfall to runoff and sediment production on slopes were 48.19% and 81.82%, respectively. Crop coverage was significantly mitigated the soil erosion on slopes, in order to reduce the runoff and sediment of 61.67% and 77.15%, respectively. The slope erosion shared the critical slope between 15° and 25°, as the slope increased. The stronger the rainfall was, the less the impact of the slope on runoff and sediment production on the slope surface was. The contribution rate of rainfall pattern to runoff and sediment yield on the crop-covered slopes surpassed 60%, where the influence was 2.60 to 5.05 times greater than that of slope gradient. The findings can offer the scientific guidance for the comprehensive management of the soil erosion in sloping farmland in the study area. Furthermore, the scientific basis and practical direction can provide for the standards for erosion control measures on sloping farmland.

     

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