河道开挖效果预测方法初步研究          下载免费PDF全文

杨国录  吴虹娟  余明辉  李纪泽  王昌慈 《水科学进展》2002,13(3):345-350

针对河道开挖后挖河效果预测的重要性,初步提出了预测挖河效果的三个评判标准:挖沙减淤比、复原率和稳定坡.引用黄河山东河段“挖河固堤工程”资料,通过数学模型计算结果对挖河效果预测的三个评判标准进行了说明,并展示使用三个评判因子分析挖河效果的有效性和应用潜力.  相似文献   

Analysis of deposition and erosion of Dongting Lake by GIS     

Gao Jun-feng  Zhang Chen  Jiang Jia-hu  Huang Qun 《地理学报(英文版)》2001,11(4):402-410

The Dongting Lake is located in the south beach of the middle reaches of the Yangtze River. Its catchment, with an area of 262,823 km2 or about 12% of the total Yangtze River catchment, is situated between 28o43?29o32扤 and 112o54?113o8扙, and crosses Hubei and Hunan provinces in administrative division. The main tributaries include Xiangjiang, Zishui, Yuanjiang, Lishui rivers (4 Tributaries) and some local rivers, such as Miluo River, Xinqiang River and other little streams. In the nor…  相似文献   

Oxidation of Elemental Mercury in the Atmosphere; Constraints Imposed by Global Scale Modelling   总被引：1，自引：0，他引：1  

Torbjörn Bergan  Henning Rodhe 《Journal of Atmospheric Chemistry》2001,40(2):191-212

We use the global mercury model published by Bergan et al. (1999) to evaluate the potential role of ozone and the hydroxyl radical as gas phase oxidants for the oxidation of elemental mercury in the atmosphere. The magnitude of natural and man-made mercury emissions are taken from recent literature estimates. We consider only two mercury reservoirs, elemental mercury, Hg⁰, and the more soluble divalent form, HgII. Wet and dry deposition of HgII is explicitly treated.Applying monthly mean fields of ozone for the oxidation of gas phase Hg⁰ and using the reaction rate by Hall (1995) yields a global transformation of Hg⁰ to HgII which is too slow to keep the simulated concentration of Hg⁰ near observed values. This shows that there must be additional important removal processes for Hg⁰ or that the reaction rate proposed by Hall (1995) is too slow. A simulation in which the oxidation rate was artificially increased, so that the global turn-over time of Hg⁰ is one year and the simulated average concentration of Hg⁰ realistic, produces latitudinal and seasonal variations in Hg⁰ that do not support the hypothesis that gas phase reaction with O₃ is the major oxidation process for Hg⁰.Recent studies indicate that OH may be an important gas phase oxidant for Hg⁰ (Sommar et al., 2001). Using OH as the sole oxidantand applying the oxidation rate by Sommar et al., we calculate aconcentration of Hg⁰ well below (about a factor of three) the observations. By prescribing a slower rate, corresponding to a turn-over time of Hg⁰ of one year, we calculate concentrations of both Hg⁰ in surface air and HgII in precipitation which correspond reasonably well, both in magnitude and temporal variation, with seasonal observations in Europe and North America. This result supports the suggestion that the oxidation by OH is an important pathway for the removal of Hg⁰. In view of the uncertainties associated with our calculations, this conclusion should still be regarded as tentative.  相似文献   

下扬子地区海相盆地演化及油气勘探选区评价   总被引：2，自引：0，他引：2  

杨方之  闫吉柱  苏树桉  杨盛良  黄敏  郭念法  王武元 《江苏地质》2001,25(3):134-141

从晚震旦世开始至中三叠世,下扬子地区沉积了三套巨厚的海相烃源岩系(Z2-O3、C-P、T1).三套烃源岩热演化特点不同,下古生界烃源岩经历了加里东、印支-燕山期构造阶段的热演化(已达过成熟干气阶段);上古生界烃源岩基本处于生油阶段晚期;三叠系大部烃源岩处于成熟生油阶段,少数处于未成熟阶段.区内下古生界烃源岩经历了两次成油过程,即加里东运动前的盆地沉降阶段和加里东运动后晚古生代陆表海沉积阶段.海相油气储盖条件发育,配置有利,经多年油气勘探证实,下古生界油气勘探应立足于苏北地区;上古生界油气勘探除苏北地区外,尚有皖南与浙西地区.中生界海相油气勘探应集中在几个发育较好的中生代盆地,如常州、句容、无为、望江等盆地.  相似文献   

青藏东北部若尔盖高原全新世泥炭沉积年代学研究   总被引：13，自引：1，他引：13  

孙广友  罗新正  R.E.Turner 《沉积学报》2001,19(2):177-181,206

用泥炭纹泥计年与14C测年相结合的新方法,首次在青藏高原东北部的若尔盖高原建立了系列完整、可信度佳和年尺度的高分辨率更新世末及全新世泥炭沉积年代谱,时间跨度为 13 6 5 5年至现在;阐明了若尔盖高原不同类型全新世泥炭沉积的时序和空间分异规律;从沉积学上证实了各期仙女木事件的存在和发生时间;划定全新世大暖期为距今 95 0 0～ 2 0 0 0年,是泥炭沉积高速期;计算了泥炭沉积率。上述结果对青藏高原也有一定代表意义.  相似文献   

近50年中国干湿气候界线波动及其成因初探   总被引：24，自引：2，他引：24  

杨建平  丁永建  陈仁升  刘连友 《气象学报》2003,61(3):364-373

文中在 10a际尺度上详细分析了中国干湿气候界线波动与气候的干湿变化 ,得出 :过去 5 0a中国干湿气候界线波动显著 ,区域差异大 ,呈现出整体移动和东西、南北相异波动的特征。 2 0世纪 6 0～ 70年代中国干湿气候存在一次突变 ,由较湿润变为干旱 ,但各地干旱程度不同。干湿气候界线波动与气候的干湿变化具有显著的年代际特征。在此基础上分析了气候界线波动的可能原因 ,中国干湿气候界线的波动与气候的干湿变化是西太平洋副热带高压强度位置导致的东南季风、孟加拉湾暖流所导致的西南季风以及高原季风、中纬度西风环流等综合作用的结果。中国各地区干湿位相变化不一致 ,区域差异大 ,是不同环流以及环流的不同强弱组合所致。东南季风、西南季风、高原季风、中纬度西风环流、西太平洋副热带高压的年代际变化是过去 5 0a中国干湿气候界线波动与气候干湿变化年代际变化的根本原因。 2 0世纪 6 0～ 70年代的干湿突变 ,是整个北半球大气环流异常的结果  相似文献   

The dynamics and characteristics of aeolian dust in dryland Central Asia: possible impacts on human exposure and respiratory health in the Aral Sea basin   总被引：6，自引：0，他引：6  

Giles F S Wiggs  Sarah L O'hara†  Johannah Wegerdt‡  Joost Van Der Meer§  Ian Small‡  Richard Hubbard¶ 《The Geographical journal》2003,169(2):142-157

The drying up of the Aral Sea has been described as one of the most staggering environmental disasters of the twentieth century. Over the last 40 years over 36 000 km² of the former seabed have been exposed, creating a potentially significant aeolian dust source. It is widely believed, but little researched, that increased dust storm activity in the region has had a major impact on human health. In this paper we report the findings of a study into the link between dust exposure and respiratory health amongst children in the Autonomous Republic of Karakalpakstan, Uzbekistan located on the southern shore of the Aral Sea. The findings indicate that dust deposition rates across the region are high, with sites located near the former shore of the sea being the worst affected. For these northerly regions the former bed of the Aral Sea is the most likely source of dust. The situation for the rest of the country appears to be far more complex. In these regions it appears that local sources and more distant sources to the south and south-west represent significant sediment providers, particularly in the early summer. Provisional analysis of the respiratory health data suggests that children living in the north of the country, where aeolian dust deposition rates are greater, show a lower frequency of respiratory problems. This inverse relationship requires further investigation, but highlights the complexities of environmental and human health inter-relationships.  相似文献   

鄂尔多斯盆地中部延安地区中侏罗统延安组高分辨率层序地层研究   总被引：19，自引：4，他引：19  

赵俊兴  陈洪德  向芳 《沉积学报》2003,21(2):307-312

利用高分辨率层序地层学方法,以延水河剖面研究为重点,详细剖析了中侏罗统延安组不同级次基准面旋回划分,建立了鄂尔多斯盆地延安地区延安组高分辨率层序地层格架。共识别出了36个短期、8个中期和3个长期基准面旋回。讨论了不同级次基准面旋回叠加式样与沉积相、沉积作用和构造作用等的响应关系,进一步通过基准面旋回层序研究了盆地的充填演化史。  相似文献   

甘孜绒坝岔古冰川演化与黄土古土壤对比研究   总被引：6，自引：3，他引：6  

许刘兵  周尚哲  李昌爱  崔建新  赵井东  业渝光 《冰川冻土》2003,25(5):504-509

横断山脉绒坝岔，保留有从倒数第二次冰期到新冰期的较完整的冰川沉积序列。对冰碛物进行了ESR测年，其分别形成于5．6kaBP、新冰期与末次冰期之间、16．3kaBP、18．7kaBP、43．7kaBP以及倒数第二次冰期。TL测年结果显示，甘孜雅砻江江畔阶地黄土从末次冰期之初开始堆积，结合甘孜黄土-古土壤序列代用指标的综合分析，发现绒坝岔冰碛物形成年代与甘孜剖面黄土、古土壤沉积年代有较好的对应关系。末次冰盛期(LGM)，绒坝岔冰碛垄走向有一次接近90。的改变；末次冰期间冰段，对应于MIS3b，其冰川规模甚至超过了LGM时期。  相似文献   

陕南柞水石瓮子上泥盆统滑塌沉积及其地质意义     

崔海峰 《高校地质学报》2003,9(1):63-71

泥盆纪是秦岭构造与古地理格局发生重大变革的时期。秦岭的泥盆系主要分布在南秦岭。资料表明，南秦岭泥盆系不是在统一的盆地中形成的，而是被古陆分隔的几个裂陷盆地的沉积产物。柞水石瓮子地处镇安盆地北缘，该处滑塌块体和斜坡砾岩广泛发育，物源为沿山阳－凤镇断裂向南作大规模逆冲推覆而被掩盖消失的小磨岭古陆，其形成受早古生代南秦岭区域抬升、全球海平面下降以及区内山阳－凤镇断裂和镇安－板岩镇断裂强烈活动的控制。区域性同造山陆块隆升与全球海平面下降造成了南秦岭晚古生代与早古生代地层之间区域性的不整合，一南秦岭在继续向北俯冲的同时，又沿南缘的勉略－巴山断裂带发生扩张，其内部也因拉张作用形成裂陷与块断隆起相间的古地理格局。南秦岭区域性隆起和裂陷可能与加里东运动和勉略有限洋盆的打开相关联。  相似文献