Characteristics,classification and ordination of riparian plant communities in the Three-Gorges areas

Sixteen different vegetation types of grassland and shrubland were selected to study the component and diversity of plant species of riparian plant communities along main channel in the Three-Gorges areas. Species richness (s), Simpson index (D), and Shannon-Weiner index (H) were used to study the biodiversity and the hierarchical classification was carried out by the methods of TWINSPAN and DCA ordination. The results showed that the components of flora were complex and dominated by the temperate type in the riparian plant communities. Species diversity was not different between the communities, but Shannon-Weiner indexes of different layers in some grassland were significantly different. TWINSPAN and DCA indicated that riparian plant communities distributed along the gradient of moisture.

Insights into the long-term stability of landslide dams on the eastern margin of the Tibetan Plateau, China——A case study of the Diexi area

Landslide dams,especially long-term stable landslide dams,have been recognized as important contributors to regional geomorphological evolution.Here,the Diexi area,a long-term stable dam-prone area located in upstream of the Minjiang River on the eastern Tibetan Plateau,was adopted to reveal reasons that landslide dams are concentrated in this area and maintain long-term stability via detailed field investigations,landslide dam sampling,unmanned aerial vehicle(UAV)images,and digital surface models(DSM).The results show the controlling factors that the slopes are prone to sliding and rock mass structure deterioration including lithological combination mode,slope structure,topographic conditions,a series of NNE-trending radial fissures and hydrological conditions.Fault activities,which have caused many earthquakes,are the main inducing factor.Landslide dams are prone to occurrence in the Diexi area owing to the combined effect of the narrow channels,the large landslide dam volume and the rock fragments.The river flow,and the landslide dam volume,material,structure,and parameters control the stability of landslide dams.The landslide dam consists of various sizes of boulders and all landslide dams exhibit an obvious inverse grading sequence,and this size combination could consume most of the flow energy,and consequently protect the dam from incision.Additionally,a total of seven knickpoints were formed by landslide dams,and the longitudinal gradient upstream of every landslide dam was found to decrease by the action of knickpoint.In the eastern margin of the Tibetan Plateau,there are numerous landslide dams existed for hundreds or thousands of years.Studies on the long-term stable landslide dams in the Diexi area could provide experience for studying similar kinds of landslide dams in this region.

Mapping of moraine dammed glacial lakes and assessment of their areal changes in the central and eastern Himalayas using satellite data

The relatively rapid recession of glaciers in the Himalayas and formation of moraine dammed glacial lakes(MDGLs) in the recent past have increased the risk of glacier lake outburst floods(GLOF) in the countries of Nepal and Bhutan and in the mountainous territory of Sikkim in India. As a product of climate change and global warming, such a risk has not only raised the level of threats to the habitation and infrastructure of the region, but has also contributed to the worsening of the balance of the unique ecosystem that exists in this domain that sustains several of the highest mountain peaks of the world. This study attempts to present an up to date mapping of the MDGLs in the central and eastern Himalayan regions using remote sensing data, with an objective to analyse their surface area variations with time from 1990 through 2015, disaggregated over six episodes. The study also includes the evaluation for susceptibility of MDGLs to GLOF with the least criteria decision analysis(LCDA). Forty two major MDGLs, each having a lake surface area greater than 0.2 km2, that were identified in the Himalayan ranges of Nepal, Bhutan, and Sikkim, have been categorized according to their surface area expansion rates in space and time. The lakes have been identified as located within the elevation range of 3800 m and6800 m above mean sea level(a msl). With a total surface area of 37.9 km2, these MDGLs as a whole were observed to have expanded by an astonishing 43.6% in area over the 25 year period of this study. A factor is introduced to numerically sort the lakes in terms of their relative yearly expansion rates, based on their interpretation of their surface area extents from satellite imageries. Verification of predicted GLOF events in the past using this factor with the limited field data as reported in literature indicates that the present analysis may be considered a sufficiently reliable and rapid technique for assessing the potential bursting susceptibility of the MDGLs. The analysis also indicates that, as of now, there are eight MDGLs in the region which appear to be in highly vulnerable states and have high chances in causing potential GLOF events anytime in the recent future.

Fission Track Method to Date Fault Activity—As Exemplified by the Three Gorges Dam Area of the Yangtze River Valley, China

The Xiannushan and Jiuwanxi are the two major fracture belts adjacent to the Three Gorges Dam Site. Apatites are selected from fracture clay and fracture\|cliff rock in the fracture belts and examined with the fission track dating method. Our study shows that the Xiannushan and Jiuwanxi fracture belts were tectonically active at 0.60±0.04Ma and 0.29±0.04Ma ago, respectively. Their ages are close to those obtained by the U\|series method.

Compound Planting of Bletilla striata under Forest in the Three Gorges Dam Area

[Objectives] The aim was to study the artificial cultivation of Bletilla striata to realize large scale and standardization planting. [Methods] The comparison tests were conducted on B. striata with different canopy densities of the Magnolia officinalis forests,different compound planting densities and different tending measures and management. [Results] When the stand canopy density was 0. 4-0. 6,the per unit yield of B. striata was 5. 4%,6. 8% higher than that at the canopy density of less than 0. 4 and more than 0. 6,respectively. When the planting density was 30 cm × 30 cm,the per unit yield increased by 16. 1%,12. 0%,13. 1% respectively compared with the planting density of 20 cm × 20 cm,25 cm × 25 cm,35 cm × 35 cm. When B. striata was planted from October to November,the per unit yield was 5. 6% higher than that planted from December to January of the following year,and 21. 3% higher than that from February to March of the second year. When farmyard manure was applied during the cultivation,the per unit yield was 31. 7% and 18. 4% higher than the application of chemical fertilizer and compound fertilizer. When weeding 4 times per year,the per unit yield increased by 240. 1%,137. 0% and 43. 9% respectively from that weeding 1 times,2 times,3 times per year. [Conclusions]When planting B. striata,the stand canopy density of 0. 4-0. 6 could make it receive absolutely shelters and the lighting conditions required for the growth,thereby bringing in high emergence rate,good growth potential and high yield. The best planting effect of B. striata could achieve by planting from October to November with the planting density of 30 cm × 30 cm,which can play the maximum benefit of individual plants. Moreover,weeding 4 times per year combined with the use of farmyard manure can promote the development and growth of tubers,which can greatly improve the yield of B. striata.

黄土高原径流侵蚀功率输沙模型的改进

水土流失对流域生态危害严重,输沙量模拟和预测可以为流域水土流失防治提供依据,因此精确的输沙模型是流域水土流失治理的重要工具。为了精确模拟变化环境下黄土高原年输沙量,该研究基于黄土高原19个水文站的径流和输沙数据,通过随机森林变量重要性度量方法评估年径流侵蚀功率、淤地坝指数、淤地坝相对指数、归一化植被指数、不透水地面积等因子对流域年输沙量的影响,使用非线性最小二乘法估算年输沙模型参数,对比分析不同因子组合的年输沙模型精度,提出适用性较强的黄土高原年输沙模型,据此开展年输沙量变化贡献率分析。结果表明:1)以幂函数形式构建的仅含径流侵蚀功率单因子输沙模型精度与流域面积有显著的负相关关系,相关系数为-0.505(P<0.05),模型精度随着流域面积增大而下降,在面积大于7000 km^(2)的流域适用性较差;2)年径流侵蚀功率、淤地坝指数及不透水地面积因子组合建立的多因子年输沙模型在黄土高原适用性最佳,模型在率定期纳什效率系数平均值为0.84,均方根误差平均值为0.21亿t,在验证期纳什系数平均值为0.79,均方根误差平均值为0.27亿t。3)影响研究流域年输沙量变化的因素依次是:年径流侵蚀功率、不透水地面积和淤地坝指数。研究可以为黄土高原不同区域水土流失防治和生态治理工作提供理论支撑。

基于HYDRUS-1D模型的水库近坝区土壤水分动态模拟

为探究五强溪水库近坝区土壤水分动态变化规律,以研究区内土壤墒情站为研究对象,利用实测逐日降雨与逐日蒸发数据驱动HYDRUS-1D模型反演土壤水力特性参数,分别在深度为10、20、40 cm观察点处进行土壤水分动态模拟,探讨研究区土壤水分动态变化规律及模型的应用效果。结果表明:不同观察点土壤水分模拟值与实测值的决定系数平均值为0.74,纳什效率系数平均值为0.71,均方根误差在0.011~0.035 cm^(3)/cm^(3)之间;0~10 cm深度的土壤水分对降雨和蒸发的响应最灵敏,波动最大;在水库主汛期(4—6月份)土壤水分变化平稳,且保持在较高的水平;研究期内7—12月份土壤水分在较大降雨情况下出现短暂饱和,土壤干湿变化明显,模拟值与实测值吻合度较高;整体上,HYDRUS-1D模型在研究区土壤水分动态模拟中具有较高的精度,可为研究区土壤水分估计及其动态变化规律研究提供有效方法。

澜沧江流域某水电站危险区域识别及溃决过程模拟

保证坝体稳定是水利水电工程的关键,在洪水及地质运动的作用下,大坝溃坝风险将会增加,一旦发生溃坝将会造成严重的经济、社会损失。以澜沧江某混凝土重力坝为例,开展坝体危险区域识别及溃决过程分析。利用有限元方法对坝体在洪水作用下的应力、应变进行研究,发现当水位漫顶时坝顶中心点位置位移最大,当伴有近场强震时,该区域极有可能发生破坏导致溃坝;利用HEC-RAS软件对该种工况的洪水演进情况进行了分析。

贵州省五千亩以上耕地坝区人口时空演变分析

运用GIS空间统计工具,将贵州省内五千亩以上耕地坝区2000—2020年共计21期WorldPop人口数据进行分析,定量揭示了贵州省五千亩以上耕地坝区21年来的人口分布时空格局及其变化特征。结果表明,贵州省耕地坝区人口呈先增后减的趋势,按人口增长曲线特征可以划分为稳定增长期(2000—2006年)、快速波动增长期(2006—2010年)、快速负增长期(2010—2015年)以及缓慢下降期(2015—2020年)4个阶段,总体下降了0.99万人,其中五千亩耕地坝区上升了0.94万人,万亩耕地坝区下降了1.93万人;五千亩以上耕地坝区人口分布以较低密度聚集区与低密度聚集区为主,人口分布差异较明显;人口密度的空间相关性总体上表现为无明显差异,在局部表现为HH集聚、LL集聚和HL集聚;坝区人口重心迁移幅度较小,经向变化和纬向变化均呈往复移动的趋势。

信江八字嘴航电枢纽工程坝址方案选择

在信江下游鄱阳湖区,地形水系复杂,河流分汊较多,坝址选择的河段范围大,枢纽坝址的方案选择较复杂。以信江八字嘴航电枢纽工程为例,在确保各坝址枢纽满足通航要求且与上下游梯级衔接的基础上,采用对各坝址枢纽功能、河道及两岸地形、建筑物布置合理、减少库区淹没等条件进行分析利弊的方法,提出坝址选择的思路,从地形地质条件、枢纽布置、工程量、通航条件、航道衔接条件、施工条件、库区淹没、工程总投资等方面进行坝址综合比选,得出八字嘴航电枢纽工程的推荐坝址。通过方案论证梳理坝址选择和枢纽布置的思路,成功解决了河口湖区复杂水系地形条件下的坝址选择难题。

漳河分洪口门分洪壅水措施研究

漳河遇50年一遇标准洪水时,分洪口门升斗铺村所在河道滩地较宽,地形较高,为保证分洪规模,需布置分洪壅水设施。文中拟定双堰(主槽堰加滩地堰)、主槽节制闸及双束堤(加主槽堰)3个方案,并从分洪可靠度、调度灵活性、对河道设计洪水位影响、占地及工程投资、管护费用等方面进行了综合分析比较及研究,最终推荐主槽节制闸方案。此次研究成果对类似分洪口门方案的分析具有借鉴意义。

复杂岩溶地区火成岩对建坝成库的影响——以张家寨水库为例

张家寨水库地处岩溶发育区,火成岩的存在形成了新的构造界面并切割了原有的地层分布,进而改变了地下水文地质条件。因此,查明该水库的地质构造特征、不同岩性的差异风化及火成岩分布对岩溶发育的影响,成为工程建设成功的关键。以张家寨水库工程区为研究对象,综合分析了该区域岩溶与火成岩复合物质条件下的建库难题,并提出了针对性措施。研究发现:该地区玄武岩分布区风化深度普遍较深,这直接影响了坝址的选择;辉绿岩侵入体与薄层灰岩的接触带差异风化明显,部分接触带闭合完整,可作为坝基持力层和地下水位低槽区帷幕灌浆下限;而局部接触带形成风化深槽,降低了岩体工程地质参数,不能满足建坝地基要求,需采取专门工程措施进行处理;此外,辉绿岩侵入灰岩料场中部,导致料场储量大为减少,对水库建设材料供应造成不利影响。研究成果可供类似工程借鉴。

大型水电站智慧坝区管理平台开发与应用

在信息化时代背景下,传统水电站坝区管理向可视化、智慧化管理转变。结合实际情况,就大型水电站智慧坝区管理平台的开发与应用进行探讨,归纳其建设原则、总体框架及其应用模块与应用成果,提出了一种高效、便捷且可靠的管理方案,为水电站坝区的现代化管理提供新的路径参考。

耕地保护背景下坝区村庄的管控与发展——以石林县路美邑村为例

坝区村庄是具有云南地缘特征的一类农村聚落,广泛分布在各个坝区之中。坝区村庄承载着众多乡村人口的生产、生活功能,具有地势平、人口密、良田多三个特质。在坝区耕地保护政策趋紧的背景下,坝区村庄面临着耕地保护和村庄发展的困境。路美邑村是典型的坝区村庄,文章通过研究坝区相关政策要求和坝区村庄的特征,结合路美邑村的现状及资源优势,分析村庄面临的主要矛盾,以“一优先四融合”的规划措施进行内涵式发展,寻求耕地保护与村庄发展的平衡,力求为坝区空间管控提供有益探索。

三峡船闸上游待闸锚地抵坡丁靠锚位结构设计方案

针对传统抵坡丁靠锚位结构受三峡库区水位周期变化影响,出现周边土体淘刷流失导致结构设计受力条件严重恶化,暴露出的高强度混凝土结构易导致船舶底部损坏等问题,依托实际工程,按三峡坝区50 a一遇水流流速1.0 m∕s、风速22.0 m∕s环境条件,以靠泊5000吨级干散货船为代表船型,进行适用于坝区待闸锚地大型船舶抵坡丁靠锚位结构设计研究,重点对抵坡丁靠锚位尺度、船舶停泊方式、系缆力计算、护坡结构、施工工艺等进行系统论述。采用系缆桩两侧设置防护带,并将系缆设施布置为内嵌结构形式,系船柱顶部不超出坡面的设计方法。结果表明:该抵坡丁靠锚位结构形式既能满足锚泊结构稳定的要求,又能有效防止结构周围水土流失,可在水位落差大、水流流速小的库区船舶锚泊设施建设工程中进行复制推广。

高海拔地区高面板堆石坝智能建设关键技术及应用

高海拔地区高面板堆石坝建设规模大、施工环境恶劣,尽管智慧工程已经为高面板堆石坝建设管理提供重要基础,然而当前仍旧面临着众多考验,难以确保工程建设全方位受控。针对该问题,项目基于智慧工程理念,以拉哇水电站高面板堆石坝为主要研究对象,构建了高海拔地区高面板堆石坝智能建设关键技术体系。通过建立施工场区全覆盖通讯网络,并针对边坡与围堰安全、大坝填筑与基础处理质量进行全过程监控,有效确保了工程建设安全与质量,提升了施工过程管控水平。

砂泥岩地区软岩筑面板堆石坝设计

抽水蓄能电站设计遵循“以料定坝、土石平衡”的原则,需研究尽可能多地利用工程区开挖料筑坝。某抽水蓄能电站位于砂泥岩地区,工程开挖产生有较多的强风化岩体或强度较低的粉砂质泥岩夹层等软岩,笔者研究利用软岩作为筑坝材料的面板堆石坝设计,根据分区原则对坝体进行分区并对各分区筑坝材料进行试验研究,以及对大坝坝坡稳定和坝体应力变形进行三维有限元计算分析。结果表明,通过合理的坝体分区,在采用较多软岩作为筑坝材料的条件下大坝坝体排水、坝坡稳定和坝体变形等均满足规范要求。面板堆石坝采用软岩筑坝时,通过采用合理的坝体分区并控制相关设计指标,是可以确保工程安全的。

基于ANSYS的软岩堆石混凝土重力坝优化设计分析

为解决四川红层地区筑坝时软岩难以充分利用的工程问题,提出将软岩用于制作堆石混凝土并用于筑坝的方案,并采用有限元软件ANSYS对坝体变形和应力进行计算。在高压力区使用较高弹性模量混凝土、低压力区使用低弹性模量软岩堆石混凝土,并根据不同坝体分区来优化软岩堆石混凝土重力坝设计方案,结果表明:靠近下坝面的高弹性模量区能限制低弹性模量区混凝土的水平变形,区域内应力分布发生改变,使得坝体受力分布均匀,整体位移减小;利用软岩作为骨料的堆石混凝土的强度,既能满足坝体应力要求,又能减少征地和工程投资,说明软岩筑坝是合理可行的。

寒区面坝板止水结构防冻措施探析

寒区面板坝止水结构因低温易产生冰冻破坏,严重影响大坝的稳定性与安全性。本文通过对寒区面坝板止水结构冻害机理和破坏的分析,总结了目前解决止水结构受冻害的防冻措施和方法。同时,基于电伴热良好的防冻能力,对电伴热技术在寒区混凝土面板坝止水结构抗冻中的应用进行了可行性分析,同步结合传热过程的分析,提出电伴热系统的功率选用和布置设计的方法,为寒区混凝土面板坝止水结构的抗冻设计提供新的思路和参考。