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1.
The production of coarse sediment in mountain landscapes depends mainly on the type and activity of geomorphic processes and topographic and natural conditions (e.g. vegetation cover) of these catchments. The supply of sediment from these slopes to mountain streams and its subsequent transport lead to sediment connectivity, which describes the integrated coupled state of these systems. Studies from the Northern Calcareous Alps show that the size of the sediment contributing area (SCA), a subset of the drainage area that effectively delivers sediment to the channel network, can be used as a predictor of sediment delivery to mountain streams. The SCA concept is delineated on a digital elevation model (DEM) using a set of rules related to the steepness and length of slopes directly adjacent to the channel network, the gradient of the latter and the vegetation cover. The present study investigates the applicability of this concept to the Western Alps to identify geomorphologically active areas and to estimate mean annual sediment yield (SY) in mainly debris-flow-prone catchments. We use a statistical approach that shows a parameter optimisation and a linear regression of SY on SCA extent. We use a dataset of ~25 years of assessed coarse sediment accumulation in 35 sediment retention basins. In the investigated catchments, sediment transport is governed by several factors, mainly by the extent of vegetation-free areas with a minimum slope of 23° that is coupled to the channel network with a very low gradient of the latter. With our improved framework, we can show that the SCA approach can be applied to catchments that are widely distributed, in a large spatial scale (hectare area) and very heterogeneous in their properties. In general, the investigated catchments show high connectivity, resulting in significant correlations between long-term average yield and the size of the SCA.  相似文献   
2.
Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land-use changes and climatic variability are hindering the actions needed to future-proof Tanzanian land-use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20-fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land-use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land-use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality.  相似文献   
3.
基于海滩地形动力学、遥感影像的风险预识别以及现场排查等方法,对西涌滨海旅游区海滩裂流风险进行了初步评估。评估结果表明:地形动力分析结果显示,西涌滨海旅游区泳场逐月平均沙滩类型大部分是沿岸沙坝和裂流沟槽交替的沙坝型(B),风险等级高;影像特征判断该沙滩属于沿岸沙坝和裂流沟槽交替的沙坝型(B)或者低潮位附近伴有冲流沙坝及裂流沟槽的低潮沙坝裂流型(LTBR),裂流风险等级高;历史影像和现场调研均发现该海滩发生过裂流;综合判定该海滩裂流风险等级为高。但鉴于观测资料限制和评价方法自身局限性的影响,本次排查结论仅为初步结论,其合理性尚需更加深入的研究。  相似文献   
4.
Subsurface dams are rather effective and used for the prevention of saltwater intrusion in coastal regions around the world. We carried out the laboratory experiments to investigate the elevation of saltwater wedge after the construction of subsurface dams. The elevation of saltwater wedge refers to the upward movement of the downstream saltwater wedge because the subsurface dams obstruct the regional groundwater flow and reduce the freshwater discharge. Consequently, the saltwater wedge cannot further extend in the longitudinal direction but rises in the vertical profile resulting in significant downstream aquifer salinization. In order to quantitatively address this issue, field-scale numerical simulations were conducted to explore the influence of various dam heights, distances, and hydraulic gradients on the elevation of saltwater wedge. Our investigation shows that the upward movement of the saltwater wedge and its areal extension in the vertical domain of the downstream aquifer become more severe with a higher dam and performed a great dependence on the freshwater discharge. Furthermore, the increase of the hydraulic gradient and the dam distance from the sea boundary leads to a more pronounced wedge elevation. This phenomenon comes from the variation of the freshwater discharge due to the modification of dam height, location, and hydraulic gradient. Large freshwater discharge can generate greater repulsive force to restrain the elevation of saltwater wedge. These conclusions provide theoretical references for the behaviour of the freshwater–seawater interface after the construction of subsurface dams and help optimize the design strategy to better utilize the coastal groundwater resources.  相似文献   
5.
沈宇恒 《北京测绘》2020,(4):490-494
为了研究黄土山区地形对煤层群开采地表位移的影响,以榆林某矿为地质原型,利用数值软件模拟地表为近水平、正坡、负坡、凸面和凹面五种地形条件下煤层群开采。结果表明:黄土山区地形的变化,对煤层群开采顶板垂直应力影响不明显,对地表位移影响较大;单向坡开采,斜坡滑移引起的下沉量在坡顶与开采沉陷量形成“叠加”,在坡底形成“抵消”;在组合坡中,煤层群开采地表位移量相差很大,说明在变坡点附近地表位移较为复杂。  相似文献   
6.
Antarctic polynyas play an important role in regional atmosphere?ice?ocean interactions and are considered to help generate the global deep ocean conveyer belt.Polynyas therefore have a potential impact on the Earth’s climate in terms of the production of sea ice and high-salinity shelf water.In this study,we investigated the relationship between the area of the Terra Nova Bay polynya and the air temperature as well as the eastward and northward wind based on the ERA5 and ERAInterim reanalysis datasets and observations from automatic weather stations during the polar night.We examined the correlation between each factor and the polynya area under different temperature conditions.Previous studies have focused more on the effect of winds on the polynya,but the relationship between air temperature and the polynya area has not been fully investigated.Our study shows,eliminating the influence of winds,lower air temperature has a stronger positive correlation with the polynya area.The results show that the relationship between the polynya area and air temperature is more likely to be interactively influenced.As temperature drops,the relationship of the polynya area with air temperature becomes closer with increasing correlation coefficients.In the low temperature conditions,the correlation coefficients of the polynya area with air temperature are above 0.5,larger than that with the wind speed.  相似文献   
7.
土地景观形态能够反映土地利用空间行为特征。在对鄱阳湖地区1995年、2000年、2015年和2018年4个时间点的土地利用现状进行描述的基础上,通过分形维数、分形稳定性、斑块密度、斑块形状破碎度和景观隔离指数分析区域景观格局变化,并运用分形理论对土地利用空间行为进行分析。研究结果显示在1995年到2018年的20多年间,建设用地一直是分形维数最高的土地类型;但从时间尺度上,建设用地的分形维数呈下降趋势,表明建设用地空间形态在土地利用空间行为的作用下逐渐向有序方向发展。水田、旱地和有林地一直是分形维数最低的土地利用类型,且处于景观分形不稳定状态。斑块密度、斑块形状破碎化指数以及景观分离度指数的计算结果支持了分形维数分析的结论。从实现区域土地合理布局的角度,建议通过科学合理的规划,降低区域建设用地的分形维数,引导建设用地有序发展。对于诸如有林地、灌木林地、高覆盖度草地和水域等自然景观,应增加其分形维数以减少人为干扰,维护其稳定性。同时建议在国土空间规划中引入分形维数,将分形维数作为评价区域土地利用格局合理性的一项指标。  相似文献   
8.
沃溪矿床位于湘西雪峰隆起区的转折部位,是该区金锑钨矿床的典型代表。该矿床成矿元素及成矿期次较为复杂,各成矿阶段的形成时代长期存在争议。本次研究在对沃溪矿床详细野外调查及岩相学观察的基础上,对深部中段矿体中的白钨矿、磷灰石及浅部中段矿体中的黑钨矿开展了U-Pb同位素分析。依据本次所获年龄数据,结合观察到的矿脉交切关系、矿物共生组合等特征,本文认为沃溪矿床除了加里东期成矿作用之外,还存在燕山期成矿作用。其中,白钨矿形成相对较早,成矿年龄为149.0±12Ma、144.8±1.7Ma、139.8±6.1Ma;黑钨矿与白钨矿同时生成(或稍晚),成矿年龄为137.8±3.9Ma、134.8±5.1Ma;自然金、辉锑矿主要在白钨矿、黑钨矿形成以后通过沉淀而成,且自然金在晚阶段(125.8±5.6Ma、123.8±4.6Ma)石英-碳酸盐脉中仍有少量产出。综合已有年代学资料推测,沃溪矿床可能在经历了加里东期陆内造山成矿作用之后,还经受了燕山期伸展构造背景下深部流体不同程度的叠加改造作用。而该矿床发现的矿脉原地破裂后被后期矿物胶结等现象,则指示其矿脉的形成与液压致裂作用有关,这种作用导致矿脉反复裂开-愈合,有利于成矿元素(尤其是金)的活化迁移和再富集沉淀。  相似文献   
9.
张威涛  任利剑  运迎霞 《地理科学》2020,40(11):1899-1908
关注滨海城市竖向避难场所的选址可靠性问题,首先深化确立“竖向避难场所”概念;然后构建竖向避难场所选址可靠性评价模型,综合自然地理要素和建成环境要素,从与灾害直接作用相关的选址暴露性、与应急交通相关的选址敏感性、与应急服务相关的选址适应性3个维度展开,搭建3级评价指标体系;再以天津滨海新区为例、聚焦滨海城市潮洪灾害和人口安全矛盾的集核——临港城区展开实证研究,借助ArcGIS分类与可视化发现:高低可靠性选址之间具有明显的空间分异,可以分解为灾害暴露性的“近岸高?远岸低”分异、交通敏感性的“外围高?中心低”分异、服务适应性的“中心与沿河高?外围低”兼“近港高?远港低”分异。同时发现:商业设施用地选址价值较高,在高可靠性选址中占比第一;中小学和社会福利设施用地选址价值最高,在高可靠性选址中占比第二;文化科研和娱乐康体设施用地在高可靠性选址中占比最小。针对临港城区实证研究结果,提出滨海城市竖向避难场所选址及可靠性提升对策。  相似文献   
10.
经济密度是衡量区域经济发展水平和聚集程度的重要指标之一。以重庆市38个县(区)所辖范围为研究区,建立了人均和地均相结合的综合测度指标体系,采用主成分分析确定指标权重,将PCA TOPSIS评价法运用到经济密度综合测度中,依据测度对象与最优值的相对接近程度,综合测度1997年、2001年、2006年和2013年重庆市县域经济密度,获得各个时间断面经济密度综合指数及其排名。通过利用ArcGIS制图功能绘制重庆市经济密度等级分布图,揭示其空间分异演变规律,利用Moran’s I,LISA和热点分析分别探索了县域经济密度的全局和局部空间自相关及其时空演变规律,并讨论影响经济密度高低的主要因素。通过对县域经济密度的综合测度及时空演变的探究,为实现城市科学定位和制定中长期发展战略提供科学依据。  相似文献   
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