Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River,eastern Free State,South Africa     

S. Tooth  T. S. McCarthy  D. Brandt  P. J. Hancox  R. Morris 《地球表面变化过程与地形》2002,27(8):797-815

Floodplain wetlands are common features of rivers in southern Africa, but they have been little studied from a geological or geomorphological perspective. Study of the upper Klip River, eastern Free State, South Africa, indicates strong geological controls on the formation of alluvial meanders and associated floodplain wetlands. Along this river, pronounced and abrupt changes in valley width are strongly linked to lithological variations. Where weakly cemented sandstone crops out, the Klip has laterally eroded bedrock and carved valleys up to 1500 m wide. In these valleys, the river meanders (sinuosity up to ～1·75) on moderate gradients (<0·001) within extensive floodplains marked by numerous oxbow lakes, backswamps and abandoned channels, many of which host substantial wetlands. In contrast, where highly resistant dolerite crops out, lateral erosion of bedrock is restricted, with the Klip tending instead to erode vertically along joints or fractures. Here, valleys are narrower (<200 m), channel‐bed gradients are steeper (>0·003), the river follows a much straighter course (sinuosity ～1·10–1·34), and floodplains are restricted in width. Long‐term landscape development in the Klip and numerous similar catchments depends on the interaction between fluvial processes in the sandstone and dolerite valleys. In the sandstone valleys, vertical erosion rates are controlled by erosion rates of the more resistant dolerites downstream. Hence, in the short‐ to medium‐term (decades to tens of thousands of years), lateral erosion dominates over vertical erosion, with the river concomitantly planing sandstone in the channel floor and reworking floodplain sediments. The thickness of alluvial fill in the sandstone valleys is limited (<4 m), but the resultant meanders are naturally dynamic, with processes such as point bar deposition, cutoff formation and channel avulsion resulting in an assemblage of fluvial landforms. In the longer term (greater than tens of thousands of years), however, vertical erosion will occur in the sandstone valleys as the downstream dolerites are lowered by erosion, resulting in channel incision, floodplain abandonment, and desiccation of the wetlands. Identification of the geological controls on meander and wetland formation provides information vital for the design of effective management guidelines for these ecologically rich habitats, and also contributes to a better understanding of rivers that are intermediate between fully alluvial and fully bedrock. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

受限自然语言查询在GIS中的应用   总被引：9，自引：0，他引：9  

张连蓬  刘国林等 《测绘学院学报》2002,19(4):283-286,289

简单论述了空间信息系统的自然语言查询问题；在应用范围受限的条件下，提出了主要以自然语言中的关键词构造模式库来反映射查询语句的思想方法；建立了系统的体系结构，并对空间操作算子、空间查询语句、模式库的结构等关键问题进行了讨论。  相似文献   

沈阳市石佛寺地区水资源管理信息系统的开发与研制     

王秀杰  费守明  李同斌 《世界地质》2002,21(1):45-49

沈阳市石佛寺水源地自80年代投产运用以来，积累了大量的水文地质资料，为了进一步加强对该区地下水资源的科学管理，通过对可视化工具软件Delphi5.0的开发，进而研制了以计算机为载体的操作简便、界面友好、功能齐全的沈阳市石佛寺地区水资源管理信息系统。  相似文献   

应用MAPGIS处理地质、物化探图件   总被引：2，自引：0，他引：2  

姜建利  阴曼宁 《内蒙古地质》2002,(2)

目前MAPGIS地理信息系统软件已在地质行业中广泛应用。本文叙述的是作者在使用该系统进行物化探图件编制过程中的一点体会和经验。  相似文献   

浅谈成果地质资料目录数据库建立及利用   总被引：1，自引：0，他引：1  

冯锰 《内蒙古地质》2002,(3)

地质档案资料是国家重要的信息资源,成果地质资料目录数据库的建立及利用,提高了地质资料管理的效率和水平,实现了地质资料目录信息资源的共享,并将在国家经济建设中发挥它的重要作用。  相似文献   

地图数学基础计算软件的开发     

姚亭友  巩志伟  陈广泉 《测绘与空间地理信息》2002,25(3):33-34

地图依据特殊的数学法则这一特性使其具有严密的数学基础 ,计算机在地图数学基础计算中展现了前所未有的高效率 ,地图数学基础计算相关软件的开发、集成在生产实践中具有重要意义。  相似文献   

利用普通水准仪高精度监测建筑基础沉降   总被引：1，自引：0，他引：1  

姜晨光 《四川测绘》2002,25(1):35-37

介绍了利用普通水准仪高精度监测建筑基础沉降的特制器具和设备 ,叙述了相关的观测要领、方法及精度指标  相似文献   

河北省城镇基准地价结构比率变动分析     

马仁会  田凤雅  李强 《地理与地理信息科学》2002,18(3):61-65

该文分析河北省典型县 (市 )基准地价更新结果 ,计算了现行城镇土地基准地价内部结构比率关系 ,并与更新前基准地价内部结构比率进行比较 ,总结出比率变动的一般趋势。  相似文献   

Mineral Paragenesis of the Lepanto Copper and Gold and the Victoria Gold Deposits, Mankayan Mineral District, Philippines   总被引：5，自引：0，他引：5  

Rene Juna R. CLAVERIA 《Resource Geology》2001,51(2):97-106

Abstract: Mineral paragenesis of the alteration, ore and gangue minerals of the Lepanto epithermal copper‐gold deposit and the Victoria gold deposit, Mankayan Mineral District, Northern Luzon, Philippines, is discussed. The principal ore minerals of the Lepanto copper‐gold deposit are enargite and luzonite, with significant presence of tennantite‐tetrahedrite, chalcopyrite, sphalerite, galena, native gold/electrum and gold‐silver tellurides. Pervasive alteration zonations are commonly observed from silicification outward to advanced argillic then to propylitic zone. The ore mineralogy of the Lepanto copper‐gold deposit suggests high f_S2 in the early stages of mineralization corresponding to the deposition of the enargite‐luzonite‐pyrite assemblage. Subsequent decrease in the f_S2 formed the chalcopyrite‐tennantite‐pyrite assemblage. An increase in the f_S2 of the fluids with the formation of the covellite‐digenite‐telluride assemblage caused the deposition of native gold/electrum and gold‐silver tellurides. The principal ore minerals of the Victoria gold deposit are sphalerite, galena, chalcopyrite, tetrahedrite and native gold/electrum. The alteration halos are relatively narrow and in an outward sequence from the ore, silica alteration grades to illitic‐argillic alteration, which in turn grades to propylitic alteration. The Victoria gold mineralization has undergone early stages of silica supersaturation leading to quartz deposition. Vigorous boiling increased the pH of the fluids that led to the deposition of sulfides and carbonates. The consequent decrease in H₂S precipitated the gold. Gypsum and anhydrite mainly occur as overprints that cut the carbonate‐silica stages. The crosscutting and overprinting relationships of the Victoria quartz‐gold‐base metal veins on the Lepanto copper‐gold veins manifest the late introduction of near neutral pH hydrothermal fluids.  相似文献   

专题制图符号库的设计与实现     

李伟  周勇前 《武汉大学学报(信息科学版)》1997,(3)

介绍用面向对象方法实现专题图符号库设计，对符号库的组织方式、符号的分类及如何实现用户自行设计符号库进行详细的分析和论述，最后对本文所提出的符号设计思想进行总结。  相似文献