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61.
Wu Shengguang Yang Dayuan Department of Geography Nanjing University Nanjing People''s Republic of ChinaWang Yunfei Nanjing Institute of Geography Limnology Academia Sini Nanjing People''s Republic of China 《地理学报(英文版)》1997,(2)
I.TheTerracesoftheUpperYellowRiverTheterracesoftheupperYellowRiveraremostlydispersedalongthewidercoursesinseveralMesozoicCenozoicbasins(Figure1).1.TerracesbetweenNgoringLakeandGyaringLakeThesurfacelayersofthesedimentinthewideandshallowbasinswheretheYell… 相似文献
62.
以天山北坡头屯河流域为例,在对山区不同海拔的降水特征、侵蚀产沙情势以及河流水沙运移特点分析的基础上,详尽就山区降水对河流水沙情势的年际变化、年内变化以及月变化的影响进行了分析研究,并就降水对不同海拔的河流水沙情势的影响强度及相互关系作了探讨. 相似文献
63.
Effects of geology and human activity on the dynamics of salt-water intrusion in three coastal aquifers in southern Spain 总被引:4,自引:0,他引:4
Mathematical modelling of salt-water intrusion processes in three aquifers on the southern coast of Spain (Río Verde, Río
Vélez and Castell de Ferro) reveals that, although all three systems are subject to the same climate and seasonal over-exploitation,
geological and human factors have very different effects on the dynamics of contamination. In the Río Verde aquifer, the most
important influence is the high volume of extractions occurring during the dry season; in Río Vélez, the intrusion is strongly
controlled by infiltration of water from the river to the aquifer, and, in the Castell de Ferro system, an intensely karstified
carbonate massif lying in contact with both the sea water and the detrital aquifer represents the main entrance point for
influx of sea water and subsequent washing of the aquifer. We have undertaken a mathematical simulation of various possible
measures to counteract intrusion, according to the specific characteristics of the process in each aquifer. These measures
include artificial recharge, use of natural recharge from the river as a hydraulic barrier, and the construction of a low-permeability
barrier.
Received: 5 December 1995 · Accepted: 12 April 1996 相似文献
64.
Thierry Rolland Stéphanie Fayolle Arlette Cazaubon Stéphane Pagnetti 《Aquatic Sciences - Research Across Boundaries》1997,59(1):57-73
In a sub-alpine river, the Asse, with an unpredictable discharge regime, chlorophyll, density and taxonomic diversity of both
drifting and periphytic communities were studied from a methodical approach. The investigations based on stamping two close
cross-sections to know their spatial distributions in a heterogeneous bed substrate showed a heterogeneous pattern of colonization
mainly influenced by hydrological variables as the current velocity, the size of the substrata (gravel-pebble-boulder). For
the drifting algae, mainly composed with benthic species temporarily unhooked to the substrata, the heterogeneity of the distribution
was reduced in fast flow which induced a mixing of the whole mass of water.
For the periphyton, some results indicated that the greatest diversity and the highest chlorophyll concentration were found
on pebble substratum where the current velocity was moderate. These results have also shown that the classical methods used
to day for investigations were inadequate for most Mediterranean rivers.
It was really difficult to estimate the water quality from classical index created for use in regular large plain rivers. 相似文献
65.
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67.
阐述了大汶河流域洪涝灾害的特点,并对洪涝灾害发生的原因进行了分析,提出了预防为主、综合治理、系统防治和重点防治相结合、标本兼治的防治思路及具体防治对策. 相似文献
68.
This paper introduces and evaluates a novel method for ascertaining the grain‐size distribution of subsurface sediments that involves profoundly less sampling effort than standard methods. It is based on hybrid sampling principles previously applied to the construction of synthetic surface grain‐size distributions. The method is developed from an empirical demonstration of the approximate similarity of surface and subsurface grain‐size distributions when compared over a common range of sizes. Subsurface hybrid models are found to provide good facsimiles of grain‐size distributions de?ned using standard criteria and to yield distribution percentiles with millimetre accuracy. The technique is presented as an expedient alternative to standard methods for large, perennial gravel‐bed rivers. As this is a new technique, prudent application is advised in lieu of further investigation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
69.
Jiongxin Xu 《地球表面变化过程与地形》2004,29(5):645-657
A comparison has been made between the hydraulic geometry of sand‐ and gravel‐bed rivers, based on data from alluvial rivers around the world. The results indicate a signi?cant difference in hydraulic geometry among sand‐ and gravel‐bed rivers with different channel patterns. On this basis, some diagrams for discrimination of meandering and braided channel patterns have been established. The relationships between channel width and water discharge, between channel depth and water discharge, between width–depth ratio and water discharge and between channel slope and water discharge can all be used for channel pattern discrimination. The relationship between channel width and channel depth can also be used for channel pattern discrimination. However, the accuracy of these relationships for channel pattern discrimination varies, and the depth–discharge relationship is a better discriminator of pattern type than the classic slope–discharge function. The cause for this difference has been explained qualitatively. To predict the development of channel patterns under different natural conditions, the pattern discriminator should be searched on the basis of independent or at least semi‐independent variables. The relationship between stream power and bed material grain size can be used to discriminate channel patterns, which shows a better result than the discriminator using the slope–discharge relationship. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
70.