黄土丘陵区植被类型和降雨对坡面侵蚀产沙的影响

基于定西市安家沟流域2014―2016年连续3年侵蚀性降雨产流产沙资料,研究了植被类型和降雨对坡面侵蚀产沙的影响。结果表明,侵蚀性降雨可分为3类:A雨型(短历时、中高雨强)、B雨型(中雨量、小雨强)和C雨型(大雨量、小雨强),产流产沙频次为B雨型C雨型A雨型。径流系数油松林(6.915%～9.379%)、小麦地(5.838%～9.034%)和苜蓿地(6.610%～9.671%)分别是冰草地(2.724%～5.246%)的1.7～2.5倍,是沙棘林(2.296%～3.863%)的2～3倍。A雨型的径流系数大于B雨型和C雨型,B雨型和C雨型是产流的主要降雨类型。年均土壤流失量为小麦地(1.478～3.478 t/hm~2)苜蓿地(0.558～2.079 t/hm~2)油松林(0.459～0.887 t/hm~2)冰草地(0.097～0.253 t/hm~2)沙棘林(0.012～0.038 t/hm~2)。小麦地的土壤流失量分别是油松林的3～5倍,是冰草地的14倍,在坡度10°,15°,20°年均土壤流失量分别是沙棘林的123,130,92倍。C雨型对油松林产沙量的贡献率最大,B雨型次之,A雨型最小。A雨型对沙棘林产沙量的贡献率高达79%～86%,高强度、短历时降雨是沙棘林产沙的主要雨型。A雨型对小麦地和苜蓿地产沙量贡献率随着坡度的增大而增大,在坡度20°中、高雨强是小麦地和苜蓿地产沙量增加的主要雨型。小麦地、苜蓿地、油松林、冰草地的径流深与土壤流失量之间呈极显著线性正相关关系(P0.01),土壤流失量的增速为小麦地苜蓿地油松林冰草地,随着坡度的增大产沙速度加快。研究结果可为坡面侵蚀预报模型的建立提供重要的理论依据,同时对科学指导坡面水土保持措施配置有重要的实践意义。

Effects of Vegetation Types and Rainfall Regimes on Slope Erosion and Sediment Yield in Loess Hilly and Gully Region

Based on the observed data on runoff plots of Anjiagou watershed in 2014-2016 in Dingxi City, Gansu Province, the effects of vegetation types and rainfall regimes on slope erosion and sediment yield were studied. The results showed that:the erosive rainfall could be classified into three patterns:pattern A was an aggregation of rainfall events with short duration and medium to high intensity, pattern B with moderate rainfall and low intensity, and pattern C with heavy rainfall and low intensity. The rainfall frequency of runoff and sediment generation was pattern B > pattern C > pattern A. The runoff coefficients of pine forest (6.915%~9.379%), wheat field (5.838%~9.034%) and alfalfa land (6.610%~9.671%) were 1.7~2.5 times than that of ice grassland (2.724%~5.246%) and 2~3 times of seabuckthorn forest (2.296%~3.863%) respectively. The runoff coefficient of pattern A was greater than those of pattern B and C. Pattern B and C were the main rainfall patterns of runoff generation. Annual average amount of soil loss was as followed:wheat field (1.478~3.478 t/hm²)>alfalfa land (0.558~2.079 t/hm²)>pine forest (0.459~0.887 t/hm²)>ice grassland (0.097~0.253 t/hm²)>seabuckthorn forest (0.012~0.038 t/hm²). The amount of soil loss of wheat fields was 3~5 times than that of pine forest, and 14 times of ice grassland, reached 123, 130 and 92 times of that of seabuckthorn forest at the slope gradient of 10°, 15° and 20°, respectively. The contribution rate of pattern C to sediment yield of pine forest was the largest, pattern B was the second, and pattern A was the smallest. The contribution rates of pattern A to sediment yield of seabuckthorn forest reached 79%~86%. So high intensity and short duration rainfall was the main rainfall pattern causing soil loss in seabuckthorn forest. The contribution rates of pattern A to sediment yield increased with the increases of slope gradients in wheat field and alfalfa land. At the slope gradient of 20°, rainfall with medium to high rain intensities was the main rainfall pattern causing soil loss. There was a very significantly positive linear correlation (P<0.01) between the runoff depth and the amount of soil loss in wheat field, alfalfa land, pine forest and ice grassland, and the increment speed of soil loss was:wheat fields > alfalfa land > pine forest > ice grassland. At the same time, the increment speed of sediment yield was accelerated as the slope gradients increased. These findings could provide theoretical basis for building the soil erosion prediction model and important practical significance to scientifically guide the allocation of soil and water conservation measures on slope land.