黄土丘陵沟壑区退耕后淤地坝拦沙特征

发布时间：2018-04-21 00:39

本文选题：退耕还林 + 淤地坝　；参考：《西北农林科技大学》2017年硕士论文

【摘要】：淤地坝是黄土高原有效拦截沟道泥沙的水土保持工程措施。随着大规模退耕还林还草的进行与植被不断的恢复演替,黄土高原的侵蚀环境发生了很大变化,淤地坝在新的下垫面变化条件下的拦沙作用尚不明确。为此,本研究借助3S技术,通过测量黄土丘陵沟壑区安塞县马家沟流域17座典型淤地坝在2004-2015年间的淤积量,分析其坝控流域土地利用与植被覆盖的分布与变化特征,探讨了退耕还林工程后不同下垫面特征及其变化对淤地坝拦沙量的影响,为今后淤地坝建设规划及其减沙效益评价提供依据。主要研究结果如下:1)黄土丘陵沟壑区退耕还林工程前各时段淤地坝控制流域以极强度侵蚀及剧烈侵蚀为主,1968年前、1968-1983年、1983-1999年的年均拦沙量分别为19342.23 t/km~2、11554.46 t/km~2、14946.32 t/km~2,且差异不显著;退耕还林工程实施后淤地坝的拦沙量2765.28 t/km~2,与此前各时段的差异显著。在2013年暴雨条件下淤地坝的拦沙量(10000-15000t/km~2)大幅增加,占建坝至2015年间总拦沙量的28.5-75.5%。2)17座淤地坝的控制流域的海拔分布在1095-1489m之间,坡度分布集中在25-45°之间。2004年时,各流域主要土地利用类型为灌木林地与草地,植被盖度为12.2-30.1%,其中灌木林地的植被盖度最大(40.6%);2015年时多数流域林地面积大幅增加,成为主要的土地利用类型;各流域的平均植被盖度在33.2-76.1%之间,平均达到44.7%。各坝控流域综合土地利用动态度在1.29-7.50%之间。3)淤地坝拦沙量与林地、未利用地、灌木林地的面积变化显著相关,其中林地面积的增加对控制流域侵蚀产沙的作用最为明显。由于各流域植被盖度普遍增加,植被盖度变化不是引起退耕后淤地坝拦沙量差异的主要原因。4)退耕还林工程后,2004与2015年各坝控流域的土地利用分布均有利于减轻土壤侵蚀,但2004-2015年间梯田面积的增加使流域内景观分布对土壤侵蚀的控制能力有所减弱。轻度侵蚀流域内的植被以林地为主,草地、灌木交错分布,在不同地形因子等级的分布优势没有明显变化,且未利用地、耕地占比少;重度侵蚀流域的植被分布优势有明显变化,低处主要为林地,高处各植被类型没有明显分布优势,且坡耕地、梯田比例与在距离淤地坝近处的分布优势增加。增加植被覆盖面积以及梯田等“源”距流域出口的距离,有助于控制流域的侵蚀产沙。
[Abstract]:Silt dam is an effective soil and water conservation engineering measure to intercept channel sediment in the Loess Plateau. With the large-scale conversion of farmland to forest and grassland and the continuous restoration of vegetation, the erosion environment of the Loess Plateau has changed greatly. Therefore, with the help of 3s technology, the distribution and change characteristics of land use and vegetation cover of 17 typical silt dams in Majiagou Valley, Ansai County, loess hilly and gully region from 2004 to 2015 were analyzed. The characteristics of different underlying surfaces and their effects on sediment retention of silt dams after returning farmland to forests are discussed, which provides a basis for the planning of silt dam construction and the evaluation of sediment reduction benefits in the future. The main results are as follows: before returning cropland to forest in Loess Hilly and Gully region, the silt dam control basin was dominated by extreme intensity erosion and severe erosion in each period, and the average annual sediment interception volume from 1968-1983 to 1983-1999 was 19342.23 t / km-1 / kg / kg / kg ~ 214946.32 t / km / m ~ (2), respectively, and the difference was not significant. The silt retention capacity of silt dam is 2765.28 t / km ~ (-2) after the implementation of returning farmland to forest project, and the difference is significant compared with previous periods. During the rainstorm period of 2013, the sediment amount of silt dam increased significantly from 1000 to 15000t / km ~ 2), and the control basin of 17 silt dams accounted for 28.5-75.55.50.17 silt dams in the period from construction to 2015 was distributed in the range of 1095-1489m above sea level, and the slope was concentrated between 25-45 掳. In 2004, The main types of land use in each watershed are shrub land and grassland with vegetation coverage of 12.2-30.1in which the vegetation coverage of shrubbery land is the largest 40.60.The forest land area of most watersheds increased significantly in 2015 and became the main land use type. The average vegetation coverage of each watershed ranged from 33.2-76.1%, with an average of 44.7%. The dynamic degree of comprehensive land use in each dam control basin was between 1.29-7.50%. 3) the amount of silt retention by silt dam was significantly related to the area of forestland, unused land and shrub land, and the increase of woodland area had the most obvious effect on controlling the erosion and sediment yield of watershed. Because the vegetation coverage of each watershed is increasing generally, the change of vegetation coverage is not the main reason that causes the difference of sediment retention amount of silt dam after returning farmland to forest. 4) the land use distribution of each dam control basin in 2004 and 2015 is beneficial to the mitigation of soil erosion. However, the increase of terrace area in 2004-2015 weakened the ability of landscape distribution to control soil erosion. The vegetation in the mildly eroded watershed was dominated by woodland, grassland and shrubs were interlaced, and there was no obvious change in the distribution superiority of different topographic factor grades, and the unutilized land was not used, and the proportion of cultivated land was less. The vegetation distribution advantage of the heavily eroded watershed has obvious change, the low part is mainly woodland, the vegetation type of height has no obvious distribution advantage, and the proportion of sloping farmland, terraced field and the distribution advantage near the silt dam increase. Increasing the vegetation coverage area and the distance between the "source" and the outlet of the basin is helpful to control the erosion and sediment yield of the basin.
【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

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