元谋干热河谷区冲沟横断面不对称性特征

发布时间：2018-08-16 12:08

【摘要】：冲沟是由暂时性表面流冲刷地表而形成的沟道,是联系过去、现在和未来沟蚀事件的桥梁。冲沟的形态包括平面、横断面和纵剖面,其中冲沟的横剖面形态不仅可用来估算冲沟侵蚀量和冲沟侵蚀速率,也可阐明由下切和侧蚀引起的发育演化过程。本研究使用Leica DistoTM D8激光测距仪于元谋干热河谷区,测量456条冲沟横断面,之后使用CASS 7.0与Excel 2003软件绘制并量算冲沟横断面形态参数。主要结论如下:(1)选取沟宽不对称率(al)、面积不对称率(aa)、侵蚀线不对称率(aw)、侵蚀面不对称率(ar)四个冲沟横断面不对称指标,衡量元谋干热河谷冲沟横断面不对称程度。结果表明:从不同区域角度分析,以沟宽不对称率、面积不对称率以及侵蚀线不对称率为参照指标,除茂易村以左倾型横断面为主外,其他四个区域冲沟横断面均以右倾型为主。然而,以侵蚀面不对称率为参照指标,除苴林村以右倾型横断面为主,其他四个区域均以左倾型横断面为主。从不同部位角度分析,沟身、沟口均以右倾型横断面为主,沟口在沟宽不对称率和面积不对称率为参照指标衡量时,以右倾型为主,在侵蚀线不对称率和侵蚀面不对称率为参照指标衡量时,以左倾型为主。元谋干热河谷区冲沟横断面以右倾型为主,其次为左倾型,准对称型最少。(2)左倾型、准对称型和右倾型横断面数量随横断面深度的增加,均呈现减少趋势,且三类冲沟横断面的深度都主要集中在0-8m之间。其中,深度在0-4m之间的左倾型、准对称型和右倾型的冲沟横断面,分别占各自总数的44.22%、43.36%和48.98%;在4-8m之间的三类冲沟横断面,分别占各自总数的41.50%、44.25%和37.24%。从不同类型横断面的宽度来看,三类冲沟横断面的数量均随其宽度的增加呈现先增加后减小的趋势:左倾型、准对称型和右倾型的横断面数量均在8-16m区间内增加到最大,分别占各自总数的54.42%、59.26%和47.45%,之后随着横断面宽度的增加,横断面数量逐渐减小。左倾型、准对称型和右倾型横断面数量随着面积的增加,均呈现减少趋势,且三类冲沟的横断面面积都主要集中在0-50m2之间,分别占各自总数的53.74%、50.44%和54.08%。从不同类型横断面的宽深比来看,左倾型、准对称型和右倾型横断面数量随着横断面宽深比的增加呈现显著增加后急剧减小的趋势:三类冲沟横断面数量均在2-4区间内增加到最大,分别占各自总数的70.07%、74.34%和58.16%,最后随着横断面宽深比的增加,横断面数量迅速减少。总之,以深度、宽度、面积和宽深比为参照指标时,左倾型、准对称型和右倾型横断面之间并没有比较明显的差异。(3)元谋干热河谷区独特的气候条件和土壤性质使该区冲沟侵蚀极其严重。研究发现冲沟横断面不对称形态受土壤性质、沟底汇流方向、植被条件以及潜蚀地貌等因素影响。该区土壤性质上下层差异明显,表层为土壤胶结性较好,干燥时异常坚硬的古红土层,下层为粉砂质沉积岩,土质多为壤质,较松软。冲沟两侧土体的抗侵蚀能力的不同是造成横断面呈不对称形态的关键因素。水流在经过弯道时,会在离心力的作用下对两侧产生差异侵蚀——“凸岸堆积,凹岸侵蚀”,也会影响横断面形态的实际表现。加之,植被条件——植物根系对沟区土体的撑托作用,会在局部范围内影响横断面形态特征。沟区的潜蚀地貌(陷穴、竖井、土桥、淘洞等)会加速沟壁、沟底的崩塌和塌陷,从而在很大程度上影响冲沟横断面形态的特征。
[Abstract]:A gully is a channel formed by a temporary surface flow that washes away the surface of the earth. It is a bridge connecting past, present and future gully erosion events. The gully morphology includes plane, cross-sectional and vertical profiles, in which the cross-sectional shape of the gully can be used not only to estimate gully erosion amount and rate, but also to illustrate the development caused by undercutting and lateral erosion. In this study, 456 gully cross-sections were measured by Leica DistoTM D8 laser rangefinder in Yuanmou dry-hot valley area, and then the shape parameters of gully cross-sections were plotted and calculated by CASS 7.0 and Excel 2003 software. The main conclusions are as follows: (1) The asymmetric rate of gully width (al), the asymmetric rate of area (aa), the asymmetric rate of erosion line (aw), and the invasion rate were selected. The results show that the asymmetry ratio of gully width, area and erosion line are taken as the reference indexes from different regional perspectives. Except Maoyi Village's left-leaning cross section, the other four areas are taken as the main index. However, with the asymmetry of erosion surface as the reference index, except for the right-inclined cross section in Chuilin village, the left-inclined cross section is the main one in the other four areas. The cross section of gullies in Yuanmou dry-hot valley is mainly right-dipping type, followed by left-dipping type, and the number of quasi-symmetrical type is the least. (2) Left-dipping type, quasi-symmetrical type and right-dipping type cross section increase with the depth of cross section. The depth of the three types of gullies is mainly between 0-8m. The left-dipping, quasi-symmetrical and right-dipping gullies account for 44.22%, 43.36% and 48.98% of the total respectively, and the three types of gullies between 4-8M account for 41.50%, 44.25% and 37.2% of the total respectively. 4%. The number of three types of gullies increases first and then decreases with the increase of their width. The number of left-leaning, quasi-symmetrical and right-leaning gullies increases to the maximum in the range of 8-16m, accounting for 54.42%, 59.26% and 47.45% of their total, respectively, and then increases with the increase of their width. In addition, the number of cross-sections decreased gradually. The number of left-dipping, quasi-symmetrical and right-dipping cross-sections decreased with the increase of the area. The cross-sectional areas of the three types of gullies were mainly concentrated in the range of 0-50m2, accounting for 53.74%, 50.44% and 54.08% of the total respectively. The number of the three types of gullies increased to the maximum in the 2-4 range, accounting for 70.07%, 74.34% and 58.16% of the total respectively. Finally, the number of the three types of gullies decreased rapidly with the increase of the ratio of width to depth. When the ratio of width, area and width to depth is the reference index, there is no obvious difference between left-dipping, quasi-symmetrical and right-dipping cross-sections. (3) The unique climatic conditions and soil properties in Yuanmou dry-hot valley make the gully erosion extremely serious. Influenced by the conditions and the buried erosion landforms, the soil properties in this area are obviously different between the upper and lower layers. The surface layer is the paleo-laterite layer with good soil cementation, which is abnormally hard when dry. The lower layer is silty sedimentary rock, and the soil is mostly loam and soft. Factors. When water flows through a bend, it will erode the two sides differently under the action of centrifugal force - "convex bank accumulation, concave bank erosion". It will also affect the actual performance of cross-sectional morphology. In addition, vegetation conditions - - the supporting effect of plant roots on the soil in the gully area will affect the cross-sectional morphological characteristics in a local scope. Geomorphology (caves, shafts, earth bridges, caves, etc.) can accelerate the collapse and subsidence of gully walls and the bottom of the gully, thus greatly affecting the characteristics of gully cross-sectional morphology.
【学位授予单位】：西华师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S157.1

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