降雨类型对褐土横垄坡面土壤侵蚀过程的影响

Effects of rainfall patterns on hillslope soil erosion process of cinnamon soil in contour ridge system

雨型是影响土壤侵蚀过程的重要因子之一,而影响效应与耕作措施密切相关。目前,雨型对横垄坡面土壤侵蚀过程的影响机制尚不清楚。该文以褐土横垄坡面为研究对象,设计了平均雨强和降雨量相同的4种雨型(增加、减弱、增加-减弱和减弱-增加型),采用可同时调节垄向和坡面坡度的土槽进行模拟降雨,研究各个雨型下不同侵蚀阶段的产流产沙特征。结果表明:雨型间的径流量和侵蚀量在细沟间和细沟侵蚀阶段均差异显著,且差异在细沟阶段体现的更为明显。雨型间径流量的大小顺序为增加-减弱型>减弱型>减弱-增加型>增加型,侵蚀量则为增加-减弱型>减弱-增加型>减弱型>增加型。给定雨强下(30、60或90 mm/h),径流量、径流贡献率和侵蚀量贡献率均随降雨过程中雨强发生时序的延迟而增加,而单位径流侵蚀量呈相反趋势;雨型间给定雨强同一发生时序下的径流量和侵蚀量及其它们对总径流量和总侵蚀量的贡献率均差异显著。4种雨型下,幂函数均能很好的描述细沟间和细沟侵蚀阶段内产沙率与径流率间的关系,且方程中的指数均低于2,但雨型间幂函数方程中的指数存在明显差异。以上研究结果有助于深入理解褐土垄作系统下的土壤侵蚀机理,并为横坡垄作的合理利用提供科学指导。

Varying of rainfall intensity during rainfall events is a common phenomenon,and soil erosion processes are strongly affected by intra-storm variations in rainfall characteristics.In general,the combination of rainfall intensities in the rainfall process can be regarded as the storm pattern.In agricultural fields,the influence of storm patterns on erosion processes is largely related to tillage treatments.Contour ridging is an effective soil conservation practice and is used throughout the world.However,less information is available regarding the effect of storm pattern on soil erosion processes in a contour ridge system.In this study,the rainfall simulation experiment was conducted to determine the characteristics of runoff and sediment yielding during inter-rill and rill erosion stages under4storm patterns(the rising,falling,rising-falling,and falling-rising patterns)for cinnamon soil in a contour ridge system.And the ridge direction and field slope could be simultaneously changed in the experimental plot.Each storm pattern included3rainfall intensities,i.e.30,60and90mm/h,which respectively lasted for20min during rainfall and comprised the same total rainfall amount and kinetic energy.Results showed that not only the total runoff but also sediment yield exhibited significant differences among storm patterns during both inter-rill erosion and rill erosion stages.Runoff for varied storm patterns was ranked in the following order:falling-rising>falling>rising-falling>rising pattern,but the difference in sediment yield showed a sequence of falling-rising>rising-falling>falling>rising pattern.Runoff from the falling-rising,falling,and rising-falling patterns increased by1.49,1.41,and1.25times,respectively,compared to that from the rising pattern,while the corresponding increase ratio of sediment yield was43.03%,3.30%,and10.03%,respectively.However,the differences were more pronounced during the rill erosion stage.Compared with the rising pattern,runoff and sediment yield from the falling,falling-rising patterns and rising-falling during this stage increased by8.89%and-27.05%,77.60%and92.59%,193.62%and238.89%,respectively.For a given rainfall intensity,runoff,runoff contribution rate,and sediment yield contribution rate gradually increased with the delay of rainfall intensity occurring sequence during the rainfall,while sediment yield by unit runoff presented the opposite tendency.Even at the same occurring stage of a given rainfall intensity,runoff,sediment yield,and their contribution rates were significantly different among different storm patterns,while the influence of occurring sequence for a given rainfall intensity on soil erosion process was the most obvious under30mm/h rainfall intensity.Power function fitted the relationship between runoff rate and sediment yield rate for both inter-rill erosion and rill erosion stages,but the exponent was lower than2.However,there was obvious difference in the exponent of power function among storm patterns,especially in the rill erosion stage.The exponent of power function from the falling,rising-falling,and falling-rising patterns during the rill erosion stage increased by2.46,2.52and1.46times,respectively,compared to that from the rising pattern.This indicated that storm pattern greatly affected runoff and sediment yield,especially during the rill erosion stage.This is mainly because soil erodibility and sediment production process varied with the change of storm pattern.So,the effect of storm pattern should be considered when developing soil erosion models.These findings are helpful to deeply understand erosion mechanism in a contour ridge system and supply guidance for implementing contour ridge systems.