三峡水库汛期分期的变点分析方法研究

介绍了变点分析理论，结合三峡水库汛期的分期，阐述了均值变点、概率变点的理论与分析方法。采用宜昌站1882-2001年实测日流量资料，用均值变点分析方法对汛期每日最大洪峰构成的时间序列进行分期；同时选择一定的阈值，在假定发生概率服从二项分布的条件下，应用概率变点分析方法进行分期，最后给出了三峡水库汛期的分期方式。经比较表明，变点分析理论应用于汛期分期中，能反映来水的基本规律，具有一定的应用价值；但从理论上以及防洪的角度来讲，概率变点分析方法较均值变点方法更适于水库汛期的分期计算。     

西江下游高要水文站洪水预报方法的改进研究

西江下游河床逐年下切，使高要水文站洪水预报方案的预报误差增大。本文对有关情况进行了分析，并对如何改进高要水文站洪水预报方法进行了改进研究，取得了比较满意的成果。     

长江上游暴雨对1998年长江洪峰影响的分析

通过对１９９８ 年长江上游四川境内暴雨、雨量水文资料、卫星云图等分析,归纳出了１９９８ 年长江上游暴雨的基本特点,认识到长江上游暴雨、高原天气系统与四川云团的活动对１９９８ 年长江洪峰的形成有直接影响。     

三明市汛期中尺度降水的若干特征

利用 1980～ 1998年三明市 11个站 5～ 6月 16 2个暴雨日的逐时降水资料 ,分析了汛期暴雨日雨团和强雨团的时空分布、移动规律、降水过程与影响系统以及地形的作用等 ,揭示出该市汛期中尺度降水的若干特征和活动规律     

El Nio和La Nia冬季增强型和减弱型及其对中国夏季旱涝的影响

根据 El Nino和 La Nina发生以后冬季赤道东太平洋海温距平的月际差定义了 El Nino和 La Nina冬季增强型和冬季减弱型 ,讨论了 El Nino和 La Nina冬季增强型和减弱型冬、春、夏季大气环流、东亚季风及我国夏季降水和旱涝分布的特征 .我国夏季降水和旱涝有明显差异的四种不同分布型可能与冬季所处 ENSO循环的不同阶段以及大气环流和东亚季风对它的不同响应有关 .提出了从 El Nino和 La Nina冬季不同型→大气环流和东亚季风→我国夏季降水和旱涝分布型的物理统计概念模型 .     

黑龙江省洪水灾害等级评估模型--模糊综合评价法

用模糊综合评价法来评定洪水灾害等级是科学的,具有客观定量等优点。它将洪水灾害分为５个等级,即重、大、中、轻和微灾。其方法是：用灾害因素划定灾害等级,进行量级简化;转换隶属函数;求转换函数;求权重系数;建立灾害等级评估模型;确定模糊灾害等级。从模型计算结果来看,黑龙江省的洪水灾害是严重的,中灾平均２年发生一次,大灾平均５年发生一次,重灾平均１５￣１６年发生一次。     

广西前汛期暴雨天气过程的特征分析

通过对1959-1999年4～6月发生在广西的暴雨天气过程特征作一较系统的分析,得出4～6月广西出现暴雨天气过程的年平均次数分别为0.98、2.39、2.78次;4～6月不出现暴雨天气过程的机率分别为0.34、0.07和0.07;4～6月出现的暴雨过程的年平均日数为1.02、2.73和4.05d。     

Mitigation of asphaltics deposition during CO2 flood by enhancing CO2 solvency with chemical modifiers

CO₂ injected in the reservoir of McElroy Field, TX, for a CO₂ flood was in the supercritical state. Supercritical CO₂ fluid is capable of extracting light and intermediate hydrocarbons from rocks but is unable to extract heavy hydrocarbons and asphaltics. Therefore, plugging of asphaltics in reservoir rocks and a consequent reduction in injectivity and recovery may result when CO₂ only is used in enhanced oil recovery. By adding common solvents as chemical modifiers, the flooding fluid shows marked improvement in solvency for heavy components of crudes due to its increased density and polarity. Numerous supercritical CO₂ fluid extractions of dolomite rock from the Grayburg Formation containing known amount of spiked McElroy crude oil have been carried out to evaluate extraction efficiencies of CO₂ and CO₂ with chemical modifiers at various temperatures and pressures. All experiments show that extraction efficiency increases with increasing CO₂ pressure but decreases with increasing temperature. Addition of chemical modifiers to CO₂ also shows improved extraction efficiency and reduced asphaltic deposits. Under the pressure and temperature similar to McElroy reservoir conditions; chemically modified CO₂ yielded almost 3 times as much oil extracts as those in extractions with CO₂ only. It also reduced the asphaltics content in extracted rocks to nearly one half; indicating its potential for mitigating asphaltics plugging of formation rocks     

The 1998 Flood on the Yangtze, China

This paper examines the main causes ofthe 1998 flood on the Yangtze and addresses a numberof issues related to the exploitation of naturalresources and counter-measures to the flood hazard.The records show that both the amount of precipitationover the catchment and the floodwater discharge fromthe upper basin did not exceed the historical maximum,but water levels in the middle basin were recordedmuch higher than the historical maximum. Humanactivities have greatly increased the risk of theflood hazard. Extensive reclamation of the lakes andfluvial islands in the middle basin has considerablyreduced the floodwater storage and drainage capacityof these natural landscapes of the Yangtze Basin.Deforestation in the catchment area has induced soilerosion, resulting in a large amount of sedimentdeposited in reservoirs whose storage capacity is thusreduced. Strengthening the flood defence to protectpeople living on the floodplain has raised the waterlevel during the flood. An integrated approach isneeded to produce a balanced management plan that canmeet the financial needs of local people in thecatchment area as well as reduce flood risk to theindustries and urban residents in the middle basin ofthe Yangtze.     

Analysis of a Long Record of Annual Maximum Rainfall in Athens,Greece, and Design Rainfall Inferences

An annual series of maximum dailyrainfall extending through 1860–1995, i.e., 136 years,was extracted from the archives of a meteorologicalstation in Athens. This is the longest rainfall recordavailable in Greece and its analysis is required forthe prediction of intense rainfall in Athens, wherecurrently major flood protection works are under way.Moreover, the statistical analysis of this long recordcan be useful for investigating more generalisedissues regarding the adequacy of extreme valuedistributions for extreme rainfall analysis and theeffect of sample size on design rainfall inferences.Statistical exploration and tests based on this longrecord indicate no statistically significant climaticchanges in extreme rainfall during the last 136 years.Furthermore, statistical analysis shows that theconventionally employed Extreme Value Type I (EV1 orGumbel) distribution is inappropriate for the examinedrecord (especially in its upper tail), whereas thisdistribution would seem as an appropriate model iffewer years of measurements were available (i.e., partof this sample were used). On the contrary, theGeneral Extreme Value (GEV) distribution appears to besuitable for the examined series and its predictionsfor large return periods agree with the probablemaximum precipitation estimated by the statistical(Hershfield's) method, when the latter is consideredfrom a probabilistic point of view. Thus, the resultsof the analysis of this record agree with a recently(and internationally) expressed scepticism about theEV1 distribution which tends to underestimate thelargest extreme rainfall amounts. It is demonstratedthat the underestimation is quite substantial (e.g.,1 : 2) for large return periods and this fact must beconsidered as a warning against the widespread use ofthe EV1 distribution for rainfall extremes.