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931.
932.
黄河口近期环境演变与河口治理 总被引:4,自引:0,他引:4
本文分析了近几年来尾闾河道及河口滨海区实测资料,认为尾闾河道河相关系趋向于转好,河口变化造成的溯源冲淤作用影响范围仅有20几km,并且只有在汛期水流强度较大时,才发生溯源调整作用,非汛期淤积严重。由于河口砂咀向海凸出,三角洲前缘形成强流带,加上波浪作用及异重流发育,河口砂咀延伸速度明显减缓。最后,作者对目前河口治理中存在问题的解决提出了建议,尤其指出不应轻易放弃目前良好的河口行水环境。 相似文献
933.
934.
Karl-Heinz Schmidt 《地球表面变化过程与地形》1989,14(2):93-105
Since the beginning of the Cenozoic period several hundreds of metres of the sedimentary cover have been removed from the Colorado Plateau. Palaeoclimatic considerations show that the Colorado Plateau has been dominated by dry climates throughout the Cenozoic with the possible exception of the early Palaeocene. Today in the still prevailing arid climate, which strongly accentuates differences in rock resistance, the relief shows a structurally controlled cuesta scarp topography in the slightly deformed strata of alternating resistance. In examining whether the denudational efficiency of scarp retreat was sufficient to account for the wide erosional gaps in the sedimentary cover, rates of scarp retreat were determined by using the information of dated volcanic material and by applying a new method, which calculates the amount of retreat from the width of beheaded valleys of known age. Rates of retreat range from 0·5 to 6·7 km my?1. The results show that the rates of retreat are controlled by the thickness and resistance of the caprocks. A model of Cenozoic scarp retreat demonstrates that the rates of recession calculated for the scarps in Upper Cretaceous rocks were sufficient to bring them into their present positions from the centre of the Monument Uplift on the central Colorado Plateau. The late Eocene positions of the cliffs in the Early Tertiary formations give an indication of their maximal extent. After the Upper Cretaceous sediments had been removed from the uplifts, erosion cut through successively older rocks, and activated scarps in stratigraphically lower positions. Scarp retreat can operate simultaneously and independently at different levels, which enabled this erosional mechanism to remove great proportions of the sedimentary cover of the Colorado Plateau during the Cenozoic. 相似文献
935.
杨裕利 《武汉大学学报(信息科学版)》1986,(2)
运用地貌学方法,对河流阶地的研究,是探索平原区隐伏活动断裂的有效方法之一。依据实测河流阶地(御河,十里河,鹅毛口河,大峪河)的数据作横剖面图,阶地位相图和通过钻探资料的分析,证实有两条NE向隐伏断裂的存在,并在其控制下形成地垒,地垒构造至今还在活动。 相似文献
936.
甘肃冰沟门异常区在晚二叠世晚期肃南组(P_2~s)时发育了两种类型古河流。以大磁窑河为代表的网状支流河,蚀源区铀源丰度低,河床坡降大,流程短,水流急,不利于铀矿化的形成。古梨园河发育的中-晚期为低-高弯蛇曲河,边滩发育,规模适中(河宽<300m),铀源丰富,河水中富含植物碎屑等有机质,铀在沉积一成岩阶段于河流转弯处和主、支流交汇处形成聚集,为后生阶段的工业富集提供了良好的前提。 相似文献
937.
Yang Yuyun 《地球科学》1986,(2)
碳酸盐岩区悬托河谷的水文地质结构比较复杂。当修建水库时,渗漏常是最主要的工程地质问题。作者对悬托河谷的水文地质结构进行了划分,并对悬托河的形成条件进行了探讨,这对选择良好的库坝位置,指导工程地质勘察,评价水库渗漏,合理制定开发方案、工程规模及防渗措施,都具重要意义。 相似文献
938.
Karl-Heinz Schmidt 《地球表面变化过程与地形》1985,10(5):497-508
The variation of mechanical and chemical denudation is investigated using discharge and sediment yield data from the Upper Colorado River System. Annual precipitation ranges from approximately 150 mm to 1500 mm. Mean specific yield ranges from 0-2 1/s km2 ( = 6 mm p a) to 151/s km2 ( = 475 mm p a). The hydrological-geomorphological system adjusts itself to these varying climatic conditions; in some areas, however, the effects of lithology or land use seem to override the climatic controls. It is demonstrated that the increase in the absolute and particularly the relative amount of suspended sediment is closely related to a decrease in annual runoff and to an increase in the importance of high magnitude/low frequency events. This indicates that in areas of low annual runoff and high runoff variability, soluble rocks are more resistant than in more humid areas. During high magnitude/low frequency events, suspended sediment concentrations and loads are very high in semiarid areas due to sparse vegetation cover and dominance of direct runoff. Events of moderate magnitude and frequency, which in more humid areas transport most of the dissolved load, seldom occur. The trend towards increasing mechanical denudation is even observed in areas of very low runoff (0-221/s km2 = 7 mm p a). The peak of sediment yield in dry areas seems to approximate the point of no runoff very closely. Mechanical and chemical denudation are of equal importance at a runoff of about 300 mm per year. 相似文献
939.
The exponential downstream decline in particle size predicted by Sternberg (1875) is examined within a highly active alpine fluvial environment, the gravel-bed Squamish River in southwestern British Columbia. Transect survey procedures for sampling within the coarse alluvial gravels are described in detail. Downstream trends for various particle size statistics, plotted with distance from a major sediment source, are considered according to two scenarios. Evaluation of overall trends indicates that the downstream expression derived by Sternberg (1875) is not the most appropriate; rather, curves are better described by power functions. This reflects a very rapid decline in particle size immediately downstream of the major sediment source. Secondly, evaluation of downstream trends in relation to channel planform determines that exponential functions with different coefficients describe adequately relations within individual planform reaches. There is insufficient evidence to suggest which of these two scenarios may be appropriate. Several lines of evidence suggest that the trends found are more the result of selective sediment transport phenomena than of abrasion, a condition attributed to channel competence within a system dominated by sediment-supply conditions. 相似文献
940.