尾矿库中U、Th和226Ra在亚粘土层的垂向迁移

在某铀尾矿库运行了31年后,取库底下方的亚粘土样,测量了从库底迁移的U、Th和226Ra的比活度分布.为研究其迁移规律,还测量了尾矿的颗粒分布、不同颗粒尾矿中核素的比活度和浸出因子、核素在亚粘土层的分配系数等参数,并采用一维对流弥散模式拟合得到核素在亚粘土层中比活度分布曲线.结果表明,矿泥是尾矿中的主要成分,其中的核素比活度高于矿砂;而浸出因子则低于矿砂.库底下方天然的和建库时人工铺垫的亚粘土层对三种核素具有较强的吸附滞留能力,从而有效地减少了核素的垂向迁移;U、Th和226Ra在亚粘土中的分配系数分别为62、1.3×103和9.8×102 mL/g,在库底下方核素比活度降到本底水平的距离,U为1.2 m,Th和226Ra为0.2 m.     

Prediction of regulation effects on natural biological rhythms in south-central African freshwater fish

Fish in south-central African freshwaters are governed by biological rhythms. First, these are associated with the markedly seasonal summer annual rainfall when breeding takes place with an initially high mortality among newspawned juveniles. Second, a longer term rhythm of annual rainfall variability occurs in cycles up to or more than a decade. These cause water levels to vary from exceptionally high levels to near desiccation in endorheic systems. Studies of the shallow endorheic lakes Mweru Wa'Ntipa (Zambia), Ngami (Botswana), and Chilwa (Malawi) are cited showing that species diversity rapidly increases by colonization from adjacent ‘inocula’ (relict communities surviving in more permanent nearby water bodies, e.g. deep pools in perennial streams) when filling starts. During the drydown phase of the cycle, diversity decreases through lack of annual breeding environment and diminution of water quantity and quality. A few, usually three, species remain longer which, being physiologically hardy or showing phenotypic plasticity, are tolerant of higher salinity, temperature, etc., conditions associated with dry-out. Despite the lakes' wide geographical separation these taxa in every case are a single species of the tilapia, genus Oreochromis, the catfish Clarias gariepinus, and the minnow Barbus paludinosus, which build up large populations valuable to local fisheries. Evidence from the Pongolo River, Zululand, regulated by a large dam, shows that fish of downstream endorheic lakes react similarly to artificial water deprivation, with mainly the same taxa persisting. Managed water releases timed to coincide with breeding rhythms largely restore the conditions which previously prevailed. Data from Zambezi impoundments indicate conversely that reaction of previously riverine fish to large man-made lakes is for previously sparse lentic taxa like Oreochromis to proliferate greatly while lotic forms like Labeo are reduced in number. Since fish stocks are a valuable natural resource, such basic scientific results may be applied with great advantage. The collaboration between engineer, biologist, and management authority can minimize adverse environmental effects and predict better opportunity cost assessments of a projected river manipulation.     

The impact of river regulation on invertebrate communities in the U.K.

The impact of river regulation on invertebrates has received comparatively little attention in the U.K., with most studies concentrating on the effects of impoundment. During dam construction invertebrate diversity and abundance decreases. Longer term alterations in community structure (which usually extend for a relatively short distance downstream) reflect changes in flow, substrate, temperature, and water quality. In particular adverse effects on invertebrates have been attributed to a reduction in substrate heterogeneity together with an accumulation of sediment. Responses to impoundment within and between taxonomic groups are highly variable. In general Ephemeroptera and Coleoptera are reduced. Of the Plecoptera the Perlodidae and Chloroperlidae are more likely to be adversely affected than the Nemouridae or Leuctridae. The impact of impoundment on net-spinning Trichoptera varies with reductions in some populations and enhancement in others. Simuliids are usually restricted, probably because of a lack of suitable oviposition or attachment sites. Freshets released from reservoirs increase the level of invertebrate drift. However, the full consequences of impoundment on drift, recolonization, and upstream migration have yet to be assessed. There is some evidence that modified temperature regimes cause extended egg hatching periods and alter larval growth rates but further studies are needed. Little is known of the effects of inter-river transfers on invertebrates, but it has been suggested that changes in flow velocity, water chemistry, suspended solids, and temperature together with translocation of organisms are all likely to be important. The limited information available for groundwater schemes indicates that they are not detrimental to invertebrates. Their impact, however, is dependent upon factors such as the extent and timing of flow augmentation. It is suggested that there is scope for positive management of invertebrate communities through river regulation, although at present attitudes and practices do not encourage this. Many gaps in our knowledge still remain and these are discussed in relation to future research needs.     

基于改进Sarma法的倾倒变形体蓄水稳定性评价

库区强倾倒变形体常在蓄水期以特定模式发生失稳破坏。根据现场强倾倒变形体蓄水失稳特征,分析其破坏模式为"上拉下剪"式破坏,破坏面具有明显分段性。在传统Sarma法基础上,考虑饱和岩体强度降低及所受静水压力,通过调整岩层面强度折减系数改进了Sarma法。以Fortran为平台编写强倾倒变形体稳定性分析程序,通过苗尾水电站工程实例边坡对所提力学模型和分析方法进行验证,并与离散元模拟结果进行对比验证其准确性。最后进行参数分析,研究结果表明边坡自然坡角对倾倒变形体稳定性影响比较大,坡角越陡稳定性越低,同时软岩较多的边坡蓄水后稳定性将大大降低,得出的结论和规律符合工程实际。     

Application of CFD (Fluent) to LNG spills into geometrically complex environments

Recent discussions on the fate of LNG spills into impoundments have suggested that the commonly used combination of SOURCE5 and DEGADIS to predict the flammable vapor dispersion distances is not accurate, as it does not account for vapor entrainment by wind. SOURCE5 assumes the vapor layer to grow upward uniformly in the form of a quiescent saturated gas cloud that ultimately spills over impoundment walls. The rate of spillage is then used as the source term for DEGADIS. A more rigorous approach to predict the flammable vapor dispersion distance is to use a computational fluid dynamics (CFD) model. CFD codes can take into account the physical phenomena that govern the fate of LNG spills into impoundments, such as the mixing between air and the evaporated gas. Before a CFD code can be proposed as an alternate method for the prediction of flammable vapor cloud distances, it has to be validated with proper experimental data. This paper describes the use of Fluent, a widely-used commercial CFD code, to simulate one of the tests in the "Falcon" series of LNG spill tests. The "Falcon" test series was the only series that specifically addressed the effects of impoundment walls and construction obstructions on the behavior and dispersion of the vapor cloud. Most other tests, such as the Coyote and the Burro series, involved spills onto water and relatively flat ground. The paper discusses the critical parameters necessary for a CFD model to accurately predict the behavior of a cryogenic spill in a geometrically complex domain, and presents comparisons between the gas concentrations measured during the Falcon-1 test and those predicted using Fluent. Finally, the paper discusses the effect vapor barriers have in containing part of the spill thereby shortening the ignitable vapor cloud and therefore the required hazard area. This issue was addressed by comparing the Falcon-1 simulation (spill into the impoundment) with the simulation of an identical spill without any impoundment walls, or obstacles within the impoundment area.     

核工业某厂铀尾矿库补救行动剂量评价

本文分析评价了某厂铀尾矿库补救行动计划中工作人员与公众所受照射的剂量。补救行动中工作人员的照射途径主要是吸入氡及其子体、吸入空气中悬浮的尾矿尘和直接γ外照射。考虑可能的最大照射景象是，在工作时间内施工人员一直处于未覆盖的尾矿上，不考虑施工机械和设备对施工人员的防护作用，也不考虑其它防护措施的作用。剂量估算结果表明，工作工作所受的有效剂量为６．０ｍＳｖ／ａ。补救行动完成后，公众的照射分别考虑了正常和     

Changes in the benthic invertebrate communities of the thomson river,southeastern Australia,after dam construction

Benthic macroinvertebrates were quantitatively sampled at four sites, one above (T6) and three (T14A, T16, T21A) downstream of the Thomson Dam, Victoria, Australia, for three summers after completion of dam construction in 1983. Community composition was compared with that recorded previously during dam construction to determine the effects of the main environmental consequences of the dam, viz the input of fine sediment (< 2mm grain size), the temporary release of cold hypolimnetic water during summer, and altered levels of discharge. Unnaturally low summer water temperatures were only recorded at the two sites immediately downstream of the dam (in order downstream T14A and T16). After water temperatures returned to normal summer levels, species richness increased at these sites. Levels of fine sediment increased in the surface layers of the riverbed at T16 but not at T14A. By the time this study began levels at T16 had been reduced almost to pre-dam levels. At T21A levels approximately tripled after completion of construction. At T14A and T16 marked increases in species richness occurred during this study whereas at T21A species richness did not change, and was lower than that recorded during dam construction. Ordination and classification of samples clearly displayed these changes in the benthic communities downstream of the dam and the lack of change at T6 above the dam. Altered discharge resulted in some loss of habitable area and thus total standing stock at T14A only.     

Effects of an upland impoundment on structural and functional properties of a small stream in a basaltic plateau (golan heights,Israel)

The aim of the study was to evaluate the impact of an upland storage reservoir, typical of the series of reservoirs in the Golan Heights basaltic plateau, on structural and functional properties of the downstream ecosystem, in the vicinity of the reservoir, shortly after damming. The effect of impoundment on water quality conditions may be divided into winter-spring, and summer periods. In the former, the impoundment seems to lengthen the period of flow of runoff quality water. This is evident by the elevated winter and spring turbidities and the higher concentrations of suspended solids below the reservoir. In summer, water quality below the reservoir is controlled by the consequences of stratification in the reservoir. The hypolimnial release results in depression of the maximal temperature and narrowing of the daily and seasonal temperature variations. It supplies water enriched in nutrients and low in oxygen, suspended solids and turbidity. The macroinvertebrate community responds to impoundment in density changes and shifting of dominance. We hypothesize that the thermal effect of hypolimnial release from warm monomictic reservoirs on the invertebrate community of warm streams will differ from an equivalent thermal change caused by cold dimictic reservoirs in cold, temperate zone, streams. The effect of impoundment on functional properties of the ecosystem are most pronounced. The rate of production of benthic algae biomass below the reservoir increased by more than two orders of magnitude, but the effect diminished downstream. The rate of processing of plant material below the reservoir was lower than above the reservoir. Further investigation is needed to clarify this effect. Changes in reservoir operation are recommended to diminish the effects of impoundment.     

Recovery of aquatic macroinvertebrate assemblages downstream of the Canning Dam,Western Australia

Macroinvertebrate assemblages downstream from the Canning Dam, on the Canning River, Western Australia, were sampled to assess the impact of long-term impoundment and the role of a major tributary in community recovery. Kick samples and associated physical measurements were taken from riffle zones in three reaches in March and July 1989. The lower reach was located immediately downstream of the confluence with Stinton Creek, the first major tributary below the dam, with the middle and upper reaches positioned between the tributary and the dam. Reduced concentrations of dissolved oxygen in the upper and middle reaches in March, compared to the lower reach were attributed to significantly higher levels of organics, high summer water temperatures, and a proposed increase in microbial activity. The build-up of organics was probably related to reduced flushing, as a result of impoundment. Stinton Creek increased the discharge of the Canning River below the confluence, particularly in winter, which presumably prevented the build-up of organics in the lower reach. Significant differences in the aquatic macroinvertebrate fauna between reaches were detected. A total of 68 taxa was recorded from the lower reach, 88 per cent of which were also present in the middle and upper reaches. However, the middle and upper reaches contained a greater number of taxa (112 and 90 respectively), approximately 50 per cent of which were not recorded from the lower reach. The additional taxa were more typical of lowland rivers or lentic (standing water) systems, suggesting that physical conditions in the middle and upper reaches were more like a lowland river than an upland stream. More collectors and shredders occurred in the upper and middle reaches, associated with the accumulation of particulate organic matter. Ordination and classification procedures based on macroinvertebrate assemblages clearly separated samples from the upper and middle reaches from the lower reach. There was also a distinct seasonal separation. These observations support a hypothesis that while the reduced flow below Canning Dam had an impact on the macroinvertebrate fauna, confluence with a major tributary (Stinton Creek) allowed recovery of the macroinvertebrate community, through the tributary acting as a source of increased discharge. The implications for the management of impounded rivers in southwestern Australia are discussed.     

Effect of impoundment on the growth and fishery of Bagrus docmac in lake Nasser

Changes of faunistic composition in impounded reaches of regulated rivers have been related to changes in environment from lotic to lentic. Rarely has this assumption been tested, however, Bagrus docmac is a long-lived freshwater catfish and was once a commercially valuable species in Lake Nasser. Its production declined abruptly following the early years of impoundment of the lake. This decline is significantly correlated to the increase of Tilapia catch. A modified model for the surplus production is introduced and estimated the potential yield as 195·7 metric tonnes. Relative growth rate of weight over length interval showed that the fish ranging between 20 to 40 cm in standard length have had the highest rate of weight gain which is attributed to gear selective mortality. Fish (18-83 cm in standard length) vertebrae (N = 105) are used for growth analysis, after their annuli are validated. Age-groups ranged between I to VI with an average age of 3·14. Age-groups II suffered high selective mortality which caused a fishing-up effect that took about four years to appear in the catch. Thus, the problem of Bagrus may be safely attributed to the effect of fishing gears which are mainly used to catch the relatively smaller Tilapia.