黄土高塬沟壑区土地利用方式对沟头溯源侵蚀过程的影响

发布时间：2018-05-27 19:38

本文选题：沟头溯源侵蚀 + 土地利用　；参考：《西北农林科技大学》2017年硕士论文

【摘要】：黄土高塬沟壑区退耕还林还草措施实施以来,该区土地利用方式与植被覆盖发生了显著变化,部分小流域土壤侵蚀环境得到根本性改善,水土流失得到有效控制。但高塬沟壑区高强度暴雨径流对塬面的破坏蚕食作用依然强烈,土地利用方式的改变,对沟头溯源侵蚀过程的作用机制目前并不明确。本文以黄土高塬沟壑区农地弃耕后的典型自然恢复草地和灌草地为研究对象,建立“沟头-塬面”实体模型,以农地为对照,采用野外人工“模拟降雨+放水冲刷”试验方法,结合照片三维重建技术,对比分析了不同土地利用沟头土体土壤理化性质及根系分布特征,阐述了土地利用、塬面坡度和沟头高度对溯源侵蚀径流产沙及塬面泥沙贡献率、径流水动力特征、重力侵蚀及沟头形态演化过程的影响,揭示了土地利用方式对沟头溯源侵蚀过程的作用机制。为黄土高塬沟壑区“固沟保塬”及区域土壤侵蚀模型建立提供科学依据。获得以下主要结论:(1)农地沟头平均径流率和径流含沙量变化范围为14.060~14.750 L·h-1和0.054~0.077 g·mL-1,草地、灌草地上植被对沟头溯源侵蚀的蓄水和减沙效益分别为17.50%~21.91%、15.77%~27.38%和70.37%~71.93%、56.58%~62.96%。径流率及径流含沙量均随塬面坡度和沟头高度的增大而增大,农地、灌草地上,9°塬坡小区径流率和径流含沙量较3°塬坡小区分别增加了4.91%、21.67%和41.80%、45.81%,1.5m沟头高度小区径流率和径流含沙量较1.2 m分别增加了4.15%、14.86%和40.74%、65.00%。草地和灌草地沟头溯源侵蚀径流含沙量变异系数较农地分别增加了67.81%~95.31%和41.16%~155.93%。(2)阐明了塬面泥沙对沟头溯源侵蚀产沙贡献率特征。农地塬面泥沙贡献率为12.70%~26.31%,相同条件下,草地和灌草地小区塬面泥沙贡献率较农地分别降低24.76%~43.09%和52.25%~62.18%。塬面泥沙贡献率随坡度的增大而增大,随沟头高度的增大而降低,在农地和灌草地上,9°塬坡塬面泥沙贡献率是3°塬坡的1.36倍和1.19倍,1.5 m沟头小区塬面泥沙贡献率是1.2 m沟头小区的65.77%和71.82%。(3)不同处理沟头径流流型均为紊流,流态均呈急流。农地沟头径流剪切力、径流功率、单位径流功率、断面比能变化范围分别为5.70~9.77 N·m-2、2.45~5.48 W·m-2、0.0230~0.0920 m·s-1、0.0212~0.0299 m,相同条件下草地和灌草地上各参数分别较农地降低8.32%~52.35%、38.99%~68.56%、31.24%~37.02%、51.06%~53.18%和-5.11%~51.75%、27.92%~72.16%、22.75%~41.35%、37.40%~58.29%。农地沟头射流水平出射动能、沟头跌水剪切力变化范围0.570~1.005 J、356.88~434.61 N·m-2,相同条件下草地和灌草地各参数分别降低了63.30%~64.41%、7.00%~16.00%和47.33%~70.57%、6.17%~22.06%。不同土地利用条件下,溯源侵蚀产沙率与水力学参数相关性普遍不显著。(4)沟头溯源过程中重力侵蚀形式主要包括崩塌、滑塌、泥流、倾倒和冲落等,其中崩塌占据主导地位,各处理崩塌次数占重力侵蚀频次的61.90%~100%。农地、草地和灌草地沟头重力侵蚀频次分别为21~33次、14~17次和18~45次,不同处理下重力侵蚀事件集中时段均不相同,表现出一定的随机性。重力侵蚀发生的时间分布表现出阶段性规律,提出了“重力侵蚀时间速率”的概念,即同一阶段内相邻2次重力侵蚀事件所隔时间(min)”,0~180min内这一速率呈“增减”循环变化趋势。重力侵蚀主要发生在沟头上部,占重力侵蚀总事件数的52.38%~100%。根据崩塌位置及崩塌后的沟头形态变化,将崩塌事件划分为沟头、沟坡和沟壁崩塌3种类型,农地、草地和灌草地沟头崩塌频率分别为7.69%~35.00%、15.38%~27.27%和16.67%~35.71%,沟头高度为1.2m时,沟头崩塌频率以灌草地最大,农地最小。3种土地利用沟壁崩塌频率分别为55.00%~92.31%、23.08%~36.36%和38.89%~50%,相同条件下,沟壁崩塌频率以农地最大。(5)植被对沟头前进过程具有显著地抑制效应,试验条件下,农地沟头前进速率变化范围0.99~2.08 cm·min-1,相同条件下草地和灌草地沟头前进速率较农地分别降低了85.39%~88.58%和72.47%~81.47%。塬面坡度和沟头高度增大可促进沟头溯源前进,在农地和灌草地上,9°塬面沟头前进速率较3°塬面分别增加了110.67%和41.84%,1.5 m沟头前进速率分别是1.2 m沟头的1.60倍和1.37倍。不同土地利用沟头前进主导驱动力不同,农地沟头主要通过径流冲刷作用导致沟头前进,而草地和灌草地沟头前进过程与沟头崩塌密切相关。相比于农地,草地和灌草地沟头土体根系密集分布、土壤渗透系数增大、崩解速率减小、有机质含量增高和水稳性大团聚体含量增多等是其沟头前进速率远低于农地的主要原因,而草地细根(0.5 mm)根系密度及根长密度较大可能是其沟头前进速率低于灌草地沟头的主要原因。
[Abstract]:Since the implementation of the measures for returning farmland to forest and grassland in the Loess Plateau Gully Area, the land use mode and vegetation cover have changed significantly in this area. The soil erosion environment in some small basins has been fundamentally improved and the soil erosion has been effectively controlled. However, the high intensity rainstorm in the gully region of the highland gully area is still strong in the destruction of the tableland surface. The mechanism of the process of gully head retrogressive erosion is not clear at present. In this paper, the typical natural restoration grassland and irrigation grassland in the loess plateau gully area are studied. The model of "gully head - tableland surface" is established, and the artificial "simulated rainfall + water scouring" test method is adopted in the field. The physical and chemical properties of soil soil and root distribution characteristics of soil soil in different land use were compared and analyzed. The effects of land use, the slope and the height of the gully on the sediment and the sediment contribution rate of the traceable erosion path, the hydrodynamic characteristics, the gravity erosion and the evolution of the groove head morphology were expounded. The mechanism of the effect of land use on gully head traceability erosion process provides scientific basis for the establishment of "Gu Gou Bao Yuan" and the establishment of regional soil erosion model in the loess plateau gully area. The following main conclusions are obtained: (1) the change range of average runoff rate and runoff sediment content of the farmland gully head is 14.060~ 14.750 L H-1 and 0.054~0.077 G. ML-1, grassland and irrigation grassland. The benefits of water storage and sediment reduction of the upper vegetation on the gully head retrogressive erosion are 17.50%~21.91%, 15.77%~27.38% and 70.37%~71.93% respectively. The 56.58%~62.96%. flow rate and runoff sediment concentration increase with the increase of the slope and the height of the gully head. On the farmland and in the grassland, the runoff rate and runoff content in the 9 degree slope of the tableland are increased by 4.91 respectively. %, 21.67% and 41.80%, 41.80%, 45.81%, 1.5m head height cell flow rate and runoff sediment concentration increased by 4.15%, 14.86% and 40.74% respectively, respectively, and the variation coefficient of sediment concentration in 65.00%. grassland and grasses was increased by 67.81%~95.31% and 41.16%~155.93%. (2), respectively. In the same condition, the contribution rate of the sediment contribution rate of the grassland and the grassland area to the 24.76%~43.09% and the 52.25%~62.18%. tableland increased with the increase of the slope, and decreased with the increase of the height of the gully head. On the farmland and the irrigated grassland, the sediment of the tableland was 9 degrees on the tableland of 9 degrees. The contribution rate is 1.36 times and 1.19 times of the 3 degree slope, and the sediment contribution rate of the 1.5 m gully head district is the 65.77% and the 71.82%. (3) of the 1.2 m trench area. The flow patterns of the runoff are all turbulent and the flow patterns are all jet flow. The shear force, the power of runoff, the power of the unit runoff, and the range of cross section ratio are 5.70~9.77 N. M-2,2.45~, respectively. 5.48 W. M-2,0.0230~0.0920 m. S-1,0.0212~0.0299 m, under the same conditions, the parameters of grassland and grassland were lower than that of farmland 8.32%~52.35%, 38.99%~68.56%, 31.24%~37.02%, 51.06%~53.18% and -5.11%~51.75%, 27.92%~72.16%, and 22.75%~41.35%. .570~1.005 J, 356.88~434.61 N. M-2, under the same conditions, the parameters of grassland and grassland were reduced by 63.30%~64.41%, 7.00%~16.00% and 47.33%~70.57%, and the correlation of sediment yield to source erosion and hydraulics parameters was generally not significant under different land use conditions. (4) the form of gravity erosion in the process of trench head traceability mainly included collapse. The collapse, mudflow, dumping and flushing, among which the collapse occupies the dominant position, the frequency of gravity erosion in the 61.90%~100%. farming land, which deals with the frequency of gravity erosion, is 21~33 times, 14~17 times and 18~45 times respectively, and the concentration period of gravity erosion under different treatments is different, which shows a certain randomness. The time distribution of the occurrence of force erosion shows a phase law, and the concept of "time rate of gravity erosion" is put forward, that is, the time of 2 adjacent gravity erosion events in the same stage (min), and this rate in 0~180min shows a "increase or decrease" cycle trend. The main weight of gravity erosion occurs at the top of the trench, accounting for 5 of the total number of gravity erosion events. According to the change of the collapse position and the shape of the trench after the collapse, 2.38%~100%. divides the collapse events into 3 types: the trench head, the gully slope and the ditch wall collapse. The frequency of the head collapse of the farmland, the grassland and the grasses is 7.69%~35.00%, 15.38%~27.27% and 16.67%~35.71%, and the height of the gully head is 1.2m. The frequency of the trench head collapse is the largest in the grassland and the smallest.3 species in the farm land. The frequency of the land-use ditch wall collapse is 55.00%~92.31%, 23.08%~36.36% and 38.89%~50% respectively. Under the same conditions, the frequency of the collapse of the ditch wall is the largest in the farmland. (5) the vegetation has a significant inhibition effect on the process of the trench head advance. Under the experimental conditions, the change range of the advance rate of the farm land trench is 0.99~2.08 cm. Min-1. The grassland and the gully head under the same condition are the same conditions. The advance rate of the 85.39%~88.58% and 72.47%~81.47%. Tableland and the height of the trench can promote the trench head to advance, respectively. On the farmland and the irrigation grassland, the speed of the 9 degrees gully head is 110.67% and 41.84% higher than that of the 3 degree plateau respectively, and the 1.5 m trench head forward rate is 1.60 times and 1.37 times that of the 1.2 m ditch. With the difference of leading driving force in the trench head, the head of the farmland gully is mainly caused by the effect of runoff scouring, while the process of grass and grass irrigation is closely related to the collapse of the ditch. The increase of the large aggregate content of the water stability is the main reason for the advance rate of its trench head far below the farmland, but the root density and the root length density of the fine root (0.5 mm) may be the main reason for the advance rate of its trench head lower than that of the grasses.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S157.1

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