茂县宗渠堰塞湖漫顶溃决洪水演进规律模型试验研究

5.12汶川大地震诱发了大量堰塞湖,这些堰塞湖一旦溃决,溃决洪水将对下游居民的生命财产造成很大的威胁,因此研究堰塞湖溃决洪水沿程水位变化规律对决策部门发布洪水预警,组织撤离与逃生,实施紧急救援等具有十分重要的意义。该文选取四川省茂县宗渠堰塞湖为原型进行野外模型试验,通过在堰塞湖库区及其下游建立一套高清晰DV摄影为主,辅以下游水位定点标记的模型试验方法,研究了堰塞湖库区水位变化过程,通过对时间差分推导出堰塞湖水量平衡方程,进一步得到溃口流量随时间变化规律;研究了下游水位变化过程揭示出堰塞湖漫顶溃决洪水的演进规律。溃口发展过程在纵向上主要以陡坎前进的方式推进,而横向上主要由土体坍滑失稳引起。此结果也可为今后堰塞湖的应急排险,溃决洪水的深入研究等具有参考价值。     

堰塞湖在灾害链演化中的控制作用及其断链防灾思路

堰塞湖是灾害链的重要环节,对灾害链的演化起着关键的控制作用。本文结合汶川地震典型堰塞湖灾害链实例,分析了堰塞湖在灾害链演化过程中四个关键控制作用:堰塞湖使灾害链加长、提供水源、降低演化条件、扩展时空影响,并针对性地提出了堰塞湖灾害链的断链防灾思路:评估、监测预报基础上的应急处置,防治稳定后的有效利用,最终达到灾害链综合防控与变害为利相结合的目标。     

川藏公路南线泥石流坝溃决洪水过程试验研究

川藏公路南线(西藏境内)由于区域地质地貌和气候环境条件的特殊性,近几十年来曾多次发生泥石流堵溃事件,坝体溃决所产生的洪水给下游造成了灾难性破坏.根据13组室内泥石流坝溃决模型试验对洪水流量过程进行研究发现,对流量影响最大的是堵塞坝的溃决形式,即重力再启动形式的溃决洪峰流量最大,水力再启动次之,冲刷型溃决最小;溃坝洪水洪峰流量与上游来水量流量成正比关系.溃决过程中的洪峰位置出现在库区水下泄30%～50%的时候;不论哪种形式溃决,洪峰在时间轴上的位置主要集中在整个洪水历时的1/3处.该研究可以为泥石流坝溃决洪水预测和下游综合避险减灾提供参考.     

冰碛湖溃决型泥石流演化过程试验研究

[目的]分析冰湖溃决型泥石流演化过程中运动参数的变化特征,为冰湖溃决型泥石流的防治提供理论依据。[方法]采用水槽试验,探讨冰碛湖溃决型泥石流形成和演化过程。[结果]冰碛湖溃决泥石流属于典型的水力类泥石流;根据水沙两相流容重的变化,冰碛湖溃决型洪水演化为泥石流的过程可以概括为挟沙水流—泥石流—挟沙水流的演变,相对应的泥石流的粒径从粉砂到砾石,再到粉沙的变化过程;泥石流容重越大,一次泥石流过程中颗粒粒径越粗。从不同组次的试验结果来看,冰碛湖溃决泥石流粒径与其容重也存在正相关关系。[结论]泥石流的运动和演化过程本质上取决于冰碛湖溃决型洪水功率和沟床堆积物的粒径特征。     

人工坝溃决洪水峰顶流量计算公式应用于滑坡堵江坝的可行性探讨

滑坡堵江事件在山区广泛发育,堵江形成的天然坝的稳定性一般不高,在暴雨、地震等诱发因素的作用下可能发生溃决,溃坝洪水对下游河道及沿江两岸的各种设施及居民生命造成巨大威胁,因此溃坝洪水计算意义重大,而峰顶流量和洪水演进过程中洪峰高度的变化直接决定了溃坝洪水的灾害程度。利用谢任之教授提出的人工坝溃决洪水计算方法,根据滑坡天然坝体溃决的实际情况,合理地分析溃口形态,调整了溃口宽度的取值方法,并将其应用于滑坡堵江天然坝瞬时溃决洪水峰顶流量计算中,经历史溃坝实例验证计算结果可靠,为天然坝溃决洪水峰顶流量计算提供了新的思路和方法,也为溃坝洪水灾害评价提供了重要依据。     

震裂山体滑坡一溃决型泥石流特征及防治措施研究

“5·12”大地震后形成较多震裂山体,震裂山体在暴雨、余震作用下一旦失稳,将会形成高势能滑坡,堵塞下部沟道,形成堰塞湖,在动静水压及掏蚀作用下导致堰塞湖的溃决,形成破坏力极强的溃决型泥石流。四川安县甘沟泥石流就是典型的溃决型泥石流,2009年8月24日,由于强降雨作用,甘沟支沟牛颈沟滑坡高速下滑,形成堰塞湖最终溃坝,暴发了溃决型泥石流,为震区典型的滑坡-泥石流地质灾害链。由于牛颈沟还残余大量物源,在暴雨情况下再次暴发溃决型泥石流的可能性很大,因此提出以下应对措施:护排为主,结合低坝消能;及时清淤,恢复植被;加强监测,及时警报。     

新疆叶尔羌河冰川突发性洪水成因调查与分析

1984年8月30日新疆叶尔羌河爆发特大洪水, 仅沿河水利工程损失50余万元, 抢修费达30万元。该河在解放以来, 曾先后有15次突发性洪水灾害。为此, 1985年4月至1987年, 新疆水利厅、中科院冰川所等单位组织了联合科考队伍, 首次赴该河的源头, 探索洪水的奥密。初步查明洪水来自源头时现代冰川区, 是由于冰川前进阻塞河道, 形成冰坝湖、堰塞湖, 其溃决酿成大洪水所致。     

不同条件下泥石流堰塞坝的溃决过程

[目的]对不同因素作用下的泥石流堰塞坝溃决过程进行试验研究,为泥石流堰塞坝的灾害防治和灾后重建等提供科学支撑。[方法]开展了不同来水流量、坝体形态、黏粒含量、坝高和初始含水量条件下的溃决试验。将漫顶溃决过程分为4个阶段:坡面侵蚀过程、陡坎侵蚀过程、下切和侧向侵蚀过程和衰退过程。此外,分析了泥石流堰塞坝坝体破坏机理,并给出下游坡面泥沙起动临界条件的计算式。[结果]溃决流量与来水流量之间呈非线性正相关;溃决洪峰流量随着背水坡坡度增加而增加;溃决洪峰流量随着坝高的增加而迅速增加,泥石流堰塞坝坝体黏粒含量与溃决洪峰流量之间整体呈现负相关;溃决洪峰流量随着土体初始含水量的增加而缓慢降低,但变化的范围不大。[结论]在泥石流堰塞坝溃决的不同因素中,坝高和黏粒含量影响最大,来水流量次之,背水坡度和初始含水量影响最小。     

基于HEC-HMS的青狮潭水库入库洪水预报研究

[目的]构建青狮潭水库入库洪水预报模型,为实际预报业务提供参考,也可以为桂林市上游地区无资料地区水文气象规律研究提供支撑。[方法]HEC-HMS是一个包含多个产汇流模型的水文模型系统,适用于不同地区的水文问题分析和计算,广泛运用于洪水预报、防灾减灾等方面。利用该模型对桂林市青狮潭水库上游流域进行水文建模,模拟流域发生暴雨时青狮潭水库的入库洪水过程,以此作为研究洪水预报依据。[结果]通过研究发现HEC-HMS模型模拟的结果平均确定性系数达到0.88,洪峰流量和峰现时间误差均达到乙级预报标准。[结论]HEC-HMS模型在青狮潭流域适用性较好,可以用于青狮潭水库入库洪水预报。     

辽宁省中小型水库洪水预报预警技术

中小型水库普遍存在基础资料缺乏、调度能力差的自身缺陷,决定了其预报预警工作不能借鉴大型水库经验成果,重点应从洪水估报、抗雨能力和风险评估等方面增强水库的预报预警能力。且由于中小型水库流域面积小,洪水入库时间短,应充分运用结合现代气象预报技术,通过假拟预警的方式掌握水库的风险情况和承受能力,为水库的排险避险争取更多的时间。因此,应重点从开发顶层中小型水库总体预报预警平台角度,研究构建流域或省市级预报预警系统,建议充分结合中小河流洪水预报预警,建立流域防洪减灾预报预警支持体系,服务于经济建设。     

Acid neutralizing capacity of lakes in the North Cascades area of Washington State

Thirty three lakes were surveyed in 1983 in the North Cascades area of Washington State and 27 additional lakes were surveyed in 1984 to characterize lake chemistry in the area. Lakewater ANC was less than 100 ueq 1^?1 for 37% of the lakes and less than 200 ueq 1^?1 for 68% of the lakes. The North Cascades are very similar to unimpacted sensitive areas of North America and Northern Europe in mean alkalinity and (Ca + Mg). Bedrock geology appears to have a significant influence on surface water ANC with lakes on granitic and metamorphic bedrocks having the lowest ANC.     

帕隆藏布江上游冰湖分布及其变化

利用高分辨率遥感影像的判读,结合现场调查、校核和前人资料分析,研究了西藏自治区帕隆藏布江上游然乌—培龙段冰湖的分布变化规律。结果发现:(1)该区有大小冰湖131个,其中面积>0.01km2的有99个,最大冰湖面积达到0.976km2。(2)99个面积>0.01km2的冰湖中冰碛湖最多达68个,占68.7%;分布于海拔4 500～5 000m的冰湖有53个,占53.3%。(3)可对比的83个冰湖中,冰碛湖总面积2005年为7.21km2,较1988年的7.03km2仅增加2.56%。其中,面积减小的有45个,占54.2%,面积增加的38个,占45.8%。(4)近18a来,该冰湖区总面积变化很小,但部分冰湖面积增大异常,受海洋性冰川影响,在该区域内出现大范围冰湖溃决的可能性很小,但暴发零星冰湖溃决的可能性很大。     

Biomass-Size Distribution of the Aquatic Community in Limed, Circumneutral and Acidified Reference Lakes

Semi-quantitative biomass-size distributions (BSD's) along a joint axis of individual size provided an integrated illustration of aquatic communities sampled at different taxonomic and trophic levels. The approach was applied within the Swedish ISELAW-programme (integrated studies of the effects of liming acidified waters) to test the general hypothesis that aquatic communities in limed lakes are not systematically different from communities in comparable non-limed circumneutral lakes. Input data included pelagic phytoplankton and zooplankton, sublittoral/profundal macroinvertebrates, and benthic fish, within twelve Swedish lakes (six limed, two acidic and four circumneutral reference lakes). The four compartments were sampled on different spatial scales, but each designed for between-lakes comparisons. There were no clear-cut differences in overall size distribution between the three categories of lakes. The mean BSD of limed lakes was indeed more similar to the mean BSD of circumneutral lakes than to that of two acidic lakes. Due to high variation within categories, however, acifidication status alone can not be used for reliable prediction of BSD in a certain lake.     

An evaluation of New York state lake liming data and the application of models from Scandinavian lakes to Adirondack lakes

Limestone dissolution efficiencies and reacidification rates observed in ten small Adirondack Mountain lakes, treated in 1983 to 1984 as part of the Extensive Liming Study (ELS), were compared with Scandinavian model predictions of dissolution (Sverdrup and Bjerle, 1983), and reacidification (Wright, 1985). The standard deviation of predicted initial dissolution was 15.4% of the observed fraction of limestone dissolved. Model predictions of dissolution for the Scandinavian lakes were similarly within 8 to 14% of observed values. Further analysis of the ELS data indicated that of the dissolution model parameters, dose rate alone was the best predictor of initial dissolution efficiency. Dissolution rates declined exponentially with time to undetectable levels within 2 to 3 yr following treatment. Total limestone dissolution efficiencies were in the range of 17 to 59% for the ELS lakes, which are comparable to levels observed in Scandinavian treatments with similar limestone materials (26 to 64%). Analysis of data from other Adirondack lakes limed by private groups and the New York State Department of Environmental Conservation for fisheries management programs, yielded similar estimates of dissolution efficiency for calcite based materials (average 36%). However, some of these lakes which were treated with slaked lime [Ca(OH)₂], exhibited initial dissolution efficiencies approaching 100%. The simple two box dilution model of reacidification, satisfactorily predicted Ca loss rates in the ELS lakes, indicating the importance of hydrology (water retention time) as a factor controlling reacidification rates in these small, limed lakes. For the ELS lakes, the ratio of watershed area/lake volume satisfactorily predicted Ca loss rates (R² = 0.96) and this simplified empirical model was applied to other Adirondack lakes where inadequate water chemistry and hydrologic data were available to utilize the dilution model. Limed Adirondack lakes with mean water retention times less than 4 mo reacidified within 1 yr after treatment. Given the preponderance of acidified lakes in the Adirondack region with retention times less than this threshold value of 4 mo (approximately 80% of lakes <10 ha surface area), simple whole lake liming practices would not be adequate for maintaining water quality suitable for the support of viable fish populations in these lakes.     

Metal concentration in the gill,gastrointestinal tract,and carcass of white suckers (Catostomus commersoni) in relation to lake acidity

Adult white suckers were collected from four lakes in Maine that ranged in pH from 7.0 to 5.4. The gastrointestinal tract and remainder of the carcass of fishes of similar age and size from each lake, and gills from additional fishes of similar size, were analyzed for Al, Cd, Pb, and Zn. Carcasses were also analyzed for Hg. Concentrations of Al, Cd, and Pb were highest in the gastrointestinal tract and lowest in the carcass; Zn concentration was highest in the gill. For carcass, all metals except Al differed significantly among lakes, for gill tissue Cd and Pb differed, and for gastrointestinal tract, only Cd differed among lakes. Where differences were significant, patterns among lakes were similar in each tissue analyzed. Concentrations of Cd, Hg, and Pb were negatively correlated with lake water pH, acid neutralizing capacity (ANC), Ca, and lake:watershed area, and positively correlated with lake water SO₄, indicating that concentrations were higher in fish from more acidic lakes. Zinc concentrations in gills were unrelated to lake acidity, and carcass concentrations were higher in the less acidic lakes, which is the opposite of the pattern for the other metals studied. Zinc in gastrointestinal tract did not differ among lakes. Although the lakes we studied were located in undisturbed watersheds and did not receive any point source discharges, fish metal concentrations were comparable to or higher than those reported from waters receiving industrial discharges.     

Common loons (Gavia immer) nesting on low ph lakes in northern Wisconsin have elevated blood mercury content

The Wisconsin Department of Natural Resources conducted a pilot study during the summer of 1991 to determine the extent of mercury (Hg) exposure in common loons (Gavia immer) breeding in Wisconsin. Loons are at risk to elevated Hg exposure in Wisconsin because they often nest on acidified, low alkalinity lakes. Fish from these lakes bioaccumulate MeHg to a greater extent than biota from neutral pH lakes. Using nightlighting techniques, 35 adult loons were captured on 20 northern Wisconsin lakes (pH=5.0–8.7) in 1991. Blood and feather samples were collected for Hg analysis. The mean Hg content of blood cells collected from adult loons on low pH lakes (pH≤6.3) was significantly greater than the Hg content of adult loons collected on neutral/alkaline pH lakes (pH>-7.0) (F=19.87, P<0.001). There was a highly significant negative linear relationship between adult loon blood cell Hg concentrations and lake pH (r²=0.38, F=15.27, P>0.001); indicating loons nesting on low pH lakes receive greater Hg exposure than loons nesting on neutral pH lakes. The relationship was greater amongst adult males (r²=0.56) than amongst adult females (r²=0.36). Because of this documented exposure, an additional 330 loons were captured 1992-94 on 73 lakes in northern Wisconsin. The Hg exposure of adult and juvenile common loons is being quantified. Individual loons were fitted with unique color-coded leg bands, and the 1992–96 reproductive performance, apnual return rates, and nesting behavior of adult loons with the known Hg exposure is currently being assessed.     

Integrated studies of the effects of liming acidified waters (ISELAW-programme)

To assess the long-term (>15 years) effects of liming, an integrated programme for studies of the effects of liming in acidified waters (ISELAW) was initiated in 1989. At present, 14 lakes and 14 streams are included in the programme. Although on average of 14 years have passed since the first lime treatment, and the chemical goal of liming have been achieved in all lakes, i.e. to raise pH over 6.0 and alkalinity over 0.1 meq 1–1, changes in biota could still be observed in several of the lakes. Species richness and species diversity was in general not different in the limed lakes as compared to circumneutral reference lakes, although the composition of the fauna did not resembled that of neutral lakes. Among zooplankton, rotifers were still more abundant than expected in limed lakes. The fish communities appeared unstable and the species proportions as well as population structures are changing, partly as a result of re-colonisation of acid-sensitive species after liming. The results indicate that the long-term changes may persist for more than 15 years after liming and emphasise the importance of comparable time series in non-limed lakes.     

Phytoplankton community of an acidified,heavy metal—Contaminated lake near Sudbury,Ontario: 1973–1977

Phytoplankton data for 1973 to 1977 from Clearwater Lake, an acid- and heavy metal—contaminated lake near Sudbury, Ontario are presented.Peridinium inconspicuum (Lemmermann) comprised between 30 and 55% of the average, ice-free period biomass of 0.33 to 0.73 mg l^?1 and is considered indicative of acidic lakes if it forms a substantial portion of the total biomass. The data were compared with those from three other contaminated and ten uncontaminated lakes in Ontario. The phytoplankton communities of all contaminated lakes were dominated byP. inconspicuum while chrysophytes dominated the uncontaminated lakes. Community biomass was better correlated with phosphorus concentration than with hydrogen ion concentration. There was some evidence of reductions of biomass in lakes with the highest heavy metal concentrations. Limitations of phytoplankton data collected in synoptic surveys are discussed.     

Biotic Effects in Planktonic Crustacean Communities in Acifified Swedish Forest Lakes after Liming

In Sweden, approximately 16 000 of a total of about 85 000 lakes have been acidified due to acidic deposition. Of these about 8000 have been treated with limestone powder in order to detoxify the acidified waters and protect sensitive fauna. The present study was performed in ten lakes in the southern part of the country. The lakes belong to four different catchments and were in different stages of acidification at the time of lime treatment. The composition of the zooplankton and fish communities also differed and three lakes were empty of fish at the beginning of the studies. Quantitative sampling of planktonic crustaceans was performed during the ice free season between 1976–87 in five of the lakes and between 1977–87 in the other five. After treatment the pH increased significantly in all lakes except one. The average number of crustacean taxa found per sampling occasion increased in all lakes. Increases were statistically significant in four of the lakes. In the lakes empty of fish, increased abundances of chaoborids inhibited, by predation, the increase of species richness. Species richness increased after the introduction of fish and the subsequent reduction of the chaoborids. At the end of the study, more taxa were found in the limed study lakes than in non-treated west coast lakes with an alkalinity of 0.04–0.10 meq L^-1. Most species normally occurring in oligotrophic forest lakes were found. It was shown that the water quality after liming made the occurrence of sensitive species possible and that predation from fish and interactions within the zooplankton assemblage were of great importance to the species composition and structure of the zooplankton community.     

Mercury concentrations in northern pike,Esox lucius L., in small lakes of Evo area,southern Finland

We measured Hg concentrations in northern pike (Esox lucius) from 17 small lakes in Evo forest area, Lammi, southern Finland. The mean Hg concentration in muscle tissue of a 1 kg pike ranged from 0.15 to 1.36 μg g⁻¹ (ww) in the lakes. There was a trend towards higher concentrations in acidic and humic lakes than in circumneutral and clear-water lakes. The Hg content of pike from successive lakes of a lake chain was similar, whereas there were clear differences in the Hg concentrations among seepage lakes and the uppermost lakes of other lake chains. The latter was probably due to special characteristics of the lakes: in one lake pike was the only fish species, two of the lakes were regulated by beaver, and one lake was a groundwater or spring lake. Our observations indicate that Hg concentrations in pike can vary considerably from lake to lake in a small geographical area and that the variation among lakes in the accumulation of Hg in fish largely depends on lake characteristics and on the diet of pike.