水动力条件下太湖透明度模拟研究

根据太湖实测资料分析得到了太湖悬浮物浓度和透明度之间呈现明显的反比关系, 归纳总结了以往研究成果中建立的太湖透明度与悬浮物浓度之间的关系, 说明可以通过模拟太湖悬浮物来反映太湖透明度的变化规律. 实测资料表明, 不同水深处的悬浮物浓度与风速的变化趋势大致相近, 风速越大, 悬浮物浓度越大. 太湖波浪、湖流与悬浮物浓度均呈现正相关关系, 悬浮物浓度随着波浪和湖流的增大而增大, 但波浪是影响底泥再悬浮的主要因素, 流速次之. 建立了太湖湖流、波浪和悬浮物耦合的数学模型, 在悬浮物模型中考虑了波浪和湖流的综合影响. 并将床面层附近底泥的起悬量和沉降量分开处理, 考虑了近底水流中湍流脉动的随机特性, 引入了底泥起悬条件. 模型清楚地反映出了悬浮物中的底泥颗粒与床面层内运动底泥及床面活动底泥发生相互交换过程中的两个方面. 模拟结果表明太湖悬浮物沿岸区域受湖流的影响较大, 湖心区域受波浪影响较大. 利用该模型, 模拟了太湖悬浮物和透明度的变化规律, 模拟结果被实测值较好验证, 说明所建立的模型是基本合理的, 可用来进行太湖透明度的模拟和预测.     

浅水湖泊沉积物磷释放的波浪水槽试验研究

为探索浅水湖泊水动力扰动作用对沉积物内源营养盐释放的规律,采用波浪水槽试验研究了波浪扰动对太湖和巢湖沉积物悬浮和磷释放的作用.试验结果显示在强波浪扰动下,底泥大规模悬浮,使得水体中悬浮固体(SS)、总磷(TP)和溶解性总磷(DTP)含量显著升高,太湖和巢湖底泥水槽试验中上覆水体TP含量分别升高了6倍和3倍,DTP分别升高了1倍和70％,太湖底泥试验中溶解性活性磷(SRP)含量亦升高了25％.掀沙过程中,不但表层底泥间隙水中的溶解性磷释放到上覆水体当中,沉积物颗粒所吸附的磷也大量转化为SRP而解吸释放.然而,强波浪掀沙一段时间后,溶解态磷的释放逐渐受到限制.随着波浪扰动作用的持续,悬浮物的中值粒径减小,细颗粒组分的百分含量明显增加,使得悬浮物对溶解态磷的吸附能力增强;波浪扰动显著提高了水体的溶解氧浓度,也会促进水体铁锰物质的氧化,增大其对磷酸根离子的吸附能力.这些变化可能是波浪掀沙后期限制水体SRP浓度进一步升高的主要原因.太湖底泥波浪水槽试验的结果与太湖梅梁湾中心区域常见风浪扰动下底泥的悬浮起动情况相吻合,底泥起动的临界切应力也基本相同,强波浪掀沙的切应力条件及水体SS,TP及SRP浓度变化的特点也一致,表明本实验的结果接近太湖的实际状况.本研究说明太湖的水动力扰动能显著提高水体TP及SRP浓度,大波掀沙初期对底泥磷释放的影响最大,后期的影响强度则有所下降.     

太湖底泥悬浮中营养盐释放的波浪水槽试验

波浪水槽中研究了小波掀沙(波高8.77cm,波周期0.8s)和大波掀沙(波高12.31cm和13.29cm,波周期1.0s)对太湖沉积物悬浮及N、P营养盐释放的作用规律.结果显示:小波掀沙时,底泥并未发生大量悬浮,SS浓度最高时仅13.6mg/L;大波掀沙时,底泥大规模悬浮,SS浓度最高达达245.2mg/L水体悬浮物、营养盐浓度变化滞后波高变化1h以上.当波高改变1h后,水体悬浮物、N、P营养盐浓度才改变到相应的平衡浓度.除总磷浓度显著提高外,小波掀沙对水体N、P浓度的影响很小,大波掀沙则显著提高了水体总氮、总溶解氮、总磷、总溶解磷、氨氮(NH4 -N)、溶解性活性磷(SRP),其中NH4 -N、SRP最大增幅达30％和20％.小波和大波掀沙过程中,水体溶解氧浓度均持续增加,掀沙2h后增高2mg/L,溶解性有机碳持续下降,2h后下降33％-51％.试验结果表明,掀沙过程中水体充氧及颗粒物的絮凝、吸附作用可能是限制NH4 -N、SRP浓度增高的重要因素之一.     

太湖梅梁湾湖区悬浮物动态沉降特征的野外观测

沉降运动是悬浮物主要运动形式之一,是影响营养盐内源释放的主要运动过程,研究悬浮物沉降速度对湖泊富营养化的研究具有重要意义.为了解浅水湖泊悬浮物的沉降特征,以太湖梅梁湾为例,采用声学多普勒流速仪,光学后向散射浊度仪以及风速风向仪在梅梁湾进行了连续9 d的野外观测.采用扩散沉降平衡的方法计算小风速情况下悬浮物的沉降速度,并对沉降速度与垂向流速、风速、悬浮物浓度的关系进行分析.结果表明悬浮物平均沉降速度为0.0785 mm/s,表层垂向流速和悬浮物浓度对悬浮物沉降速度变化起主要作用;而在底层,风速、垂向流速、悬浮物浓度都对悬浮物运动有重要影响,具体表现为风速1.5 m/s时,垂向流速紊动增大,悬浮物因起悬而浓度较大,并且沉降速度波动较大;风速1.5 m/s时,垂向流速基本向下且流速较小,沉降速度也较小.本文揭示了大型浅水湖泊悬浮物的动态沉降特征,为今后太湖污染物的输移、水环境数学模型和湖泊富营养化的深入研究奠定了必要的基础.     

风浪扰动下湖滨带悬浮物和营养盐响应特征

为研究风浪扰动下沉积物起悬过程中悬浮物浓度的分布特征和水体营养盐时空分布状况,以太湖西北湖滨带为例,选择代表4种不同生境的6个点位进行了连续12 d的野外观测.利用高精度分层同步采样装置,采用重量法计算悬浮量,并对悬浮过程中总磷(TP)、总氮(TN)、铵态氮(NH_4~+-N)和硝态氮(NO_3~--N)浓度进行分析.结果表明:风速是引起太湖西北湖滨带水体悬浮物增加的主要因素,沉积物悬浮的临界风速为3.6 m/s.各点位悬浮物浓度的均值差异明显,表现为:无植被区植被区河口区湖心区.太湖西北湖滨带水体氮、磷浓度日变化幅度较大,TN浓度为1.82~4.96 mg/L,TP浓度为0.10~1.47 mg/L.NH_4~+-N和NO_3~--N浓度分别在0.09~2.83和1.05~3.69 mg/L之间波动.近岸无植被区水柱的总悬浮量与风速的相关性最好,相关系数达到0.722;而远岸湖心区与风速的相关系数仅为0.039.悬浮物浓度除了受风情(风向和风速)的影响外,同样受水深、地形特征和水生植被的影响.     

太湖底泥垂向构成类型及底泥-水界面组成物质

针对太湖中底泥-水界面上物质的状态、性质及其对水质的影响问题,本文通过对太湖8个湖区39个采样点的现场调查取样和实验室检测,分析太湖底泥状态和垂向上的构成、不同区域底泥-水界面物质的差异及底泥与磷释放和湖泛之间的关系.结果表明:太湖底泥-水界面上存在3种物质:粉质硬黏土、淤泥质粉土和悬浊水层.粉质硬黏土(硬底板)是太湖...     

不同水动力扰动下太湖沉积物的悬浮特征

利用2002年7月及2003年4月分别在太湖乌龟山和梅梁湾的水动力观测资料,计算了波浪和湖流产生的湖底切应力,分析了二者对太湖沉积物悬浮的不同贡献.结果发现,在小扰动情况下,流切应力大于波切应力,但不能引起沉积物的悬浮;在强扰动情况下,底流对沉积物悬浮的影响可以忽略,且扰动越强,其作用越小,而波浪的影响却愈加突出;在中等扰动下,二者的相互作用产生沉积物的悬浮,但波浪的作用较为显著.该结论能为计算太湖水体悬浮物浓度和动态内源释放提供重要的参考依据.     

波浪影响下半无限含水层中隧道渗流场分析

根据线性波浪引起水下土体残余孔压增长理论,采用Laplace变换得到衬砌在受波浪荷载下的外水压力及渗流量,并得到水底带衬砌隧道渗流量和衬砌周边水头解答。计算结果表明：（1）波陡H/L>0.09后衬砌将要承担比静水压力引起的更大的外水压力,土体渗透系数减小波浪对隧道外水压力和渗流量的影响反而逐渐升高,当kL=1×10-7 m/s时,无论是波浪还是静水压力作用下隧道的渗流量都得到有效控制;（2）5~10 s周期的波浪及水深d相似文献   

大型表面流人工湿地长期运行下底泥污染特性及氧化层甄别

研究湿地底泥污染特性及水-土界面边界层性质是明确大型人工湿地长期运行下底泥内源污染问题的关键.本文以典型人工湿地为例,通过综合布点垂向分层监测湿地底泥理化性质,明确底泥污染特性,分析水-土界面边界氧化层现象、性质及形成机理,探讨其性质成因.结果表明：与湖泊类似,长期运行人工湿地底泥也会产生氧化层,垂向由上到下分为氧化层、污染层、过渡层和健康层;运行6年的湿地底泥可形成厚约1 cm、无明显臭味、棕黄色可塑状的氧化层;与污染层相比,氧化层色味变淡、流动性减弱,含水率、d（0.9）、亚铁、总有机碳和总氮含量分别降低7.20%、54.04%、54.59%、17.89%和7.00%,氧化还原电位和总磷含量分别升高150.41%和18.17%;氧化层是由氧化、沉降协同作用下形成的底泥表层氧化态微环境,其中上覆水溶解氧水平越高越有利于提高氧化层致密程度,降低氧化层有机质、总氮含量,上覆水悬浮物浓度越高、水深越深越有利于增加氧化层厚度.     

蓄水初期三峡水库草堂河水-气界面CO2和CH4通量日变化特征及其影响因素

为查明三峡水库蓄水初期典型支流水-气界面CO_2和CH_4通量的日变化特征,采用LGR在线分析仪-通量箱法,于2015年9月初在库腹一级支流草堂河回水区开展连续24 h的定位观测.结果表明,24 h监测期内,支流库湾水-气界面CO_2通量变幅为-81.642~180.991 mg/(m~2·h),呈"昼吸夜放"特征,均值为17.346 mg/(m~2·h),总体为释放特征;CH_4全天均表现为释放状态,释放通量均值为0.064 mg/(m~2·h),呈"昼弱夜强"变化.相关分析结果表明,CH_4和CO_2释放通量与风速呈正相关,与表层水温、溶解氧浓度、叶绿素a浓度呈负相关,说明风速物理扰动、浮游植物光合作用是控制草堂河水-气界面气体通量最重要的环境因素.同时,干-支流相互作用形成的特殊水环境(如异重流、水温分层)也与水-气界面温室气体通量过程密切相关,但是其作用机制更为复杂,应开展进一步系统观测和深入研究.     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Earthquake Engineering and Engineering Vibration Aims And Scope

正This journal is established by the Institute of Engineering Mechanics(IEM),China Earthquake Administration,to promote scientific exchange between Chinese and foreign scientists and engineers so as to improve the theory and practice of earthquake hazards mitigation,preparedness,and recovery.To accomplish this purpose,the journal aims to attract a balanced number of papers between Chinese and     

Foreword

Destructive earthquakes have caused great damage in China and the United States and collapsing buildings havecaused many deaths and injuries. The field of earthquake engineering studies earthquake hazards, the occurrence ofearthquakes of various magnitudes, the nature of the ground shaking during an earthquake, the vibration of structuresduring earthquakes, the strengthening of existing structures and the design of new structures to be earthquake resistant,and finally, how to cope with earthquake damage and restore a city to normal functioning. Such efforts are in progressin both countries, but unfortunately, the language barrier interferes with the free flow of information between China andthe Untied States. It would be mutually beneficial if some means could be developed to promote the exchangeof information across the Pacific Ocean. This new journal has been established for this purpose and its success willbe an important step in promoting earthquake engineering in China and the United States.     

WORLD ASSOCIATION FOR SEDIMENTATION AND EROSION RESEARCH(WASER)

正President:Giampaolo Di Silvio,Italy Vice Presidents:Ulrich C.E.Zanke,Germany Zhao-yin Wang,China The World Association for Sedimentation and Erosion Research(WASER),inaugurated on Oct.19,2004,is an independent non-governmental,non-profit organization.The mission of WASER is to promote international co-operation on the study     

Enhancing remote sensing research on global change to improve our understanding on Earth system processes

正Global Change includes climate change and other environmental changes caused by the joint interaction among various layers of Earth. From the positive side, global change provides new opportunities to human and other living forms on Earth. In the meantime, it creates tremendous challenges and negative impact. At present, the negative impacts have reached all primary processes of the global ecosystem and every aspect of human society, especially causing degradation of the ecosystem. For instance, intensive deforestation causes decline of biodiversity; global warming causes sea level rise and increases     

Solute concentrations in the lower niger river and the source rock contribution

Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO₃ > SO₄ > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1^?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals.