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541.
在河流排污引起的污染物扩散计算中,不同河流宽度类别对应不同的移流扩散解析解算式,但缺少具体的河流宽度分类判别准则,给实际应用带来很大困难。按照河流污染物扩散受边界反射影响程度的不同,从移流扩散解析解算式的简化条件出发,提出了宽阔、中宽、窄小的分类方法和定义;根据二维可忽略边界反射的条件和达到全断面均匀混合距离小于等于河流宽度的条件,分别求解了河流宽阔与中宽窄小的分区临界关系线和中宽与窄小的分区临界关系线,提出了相应判据的数学表达式;给出了河流宽阔、中宽、窄小的分类判别准则以及各类别河流移流扩散解析解算式的对应关系。最后指出基于环境扩散条件的河流宽阔、中宽、窄小分区是相对的,对于同一河流在不同水力要素、扩散系数、排污强度和允许浓度升高值等条件下,可以得到不同的分区结果。 相似文献
542.
提出了基于冰冻河流的一种水下测量方法,即GPS RTK无验潮测深方法。此方法可充分利用北方冬季时间,不需要验潮,也不需要使用测量船作业,极大地降低了作业成本。 相似文献
543.
Marina Tagliaferro María Laura Miserendino Ana Liberoff Analia Quiroga Miguel Pascual 《Limnologica》2013,43(6):500-509
Three large rivers have their headwaters in the Patagonian Ice Fields (PIFs) in the Andes Mountains, the largest mid-latitude ice masses on Earth: Santa Cruz, Baker and Pascua. They are the last large free flowing rivers in Patagonia, but plans are advanced for building dams for hydroelectric power generation. The three PIF rivers, with a discharge dominated by ice melt, share a common, unique hydrograph compared to that of the other eight large rivers in the region: a distinct seasonal cycle, and an extremely stable discharge, with much lower variability than other rivers. In this study we present the first extensive survey of habitats and benthic macroinvertebrates in the least studied system, the Santa Cruz River. We assess how much of the natural capital provided and sustained by benthic invertebrates are expected to be lost by flooding and discuss how dams would affect riverine habitat and biota. In the Santa Cruz River, we conducted an intensive field survey during September 2010; a total of 52 sites located at regular 6 km intervals were sampled along the 310 river-km for macroinvertebrates and seventeen habitat variables. Although some habitat structure is apparent at the local scale, the Santa Cruz River could be described as very homogeneous. Macroinvertebrate density and the richness (38 genera) found in the Santa Cruz River resulted to be one of the lowest in comparison with 42 other Patagonian rivers. Albeit weak, the structure of the macroinvertebrates assemblages was successfully described by a reduced set of variables. The reduced flow variation and the lack of bed scouring flows have a direct and negative effect on the heterogeneity of riverbeds and banks. The high turbidity of the Santa Cruz River may also contribute to shorter food webs, by affecting autotrophic production, general trophic structure, and overall macroinvertebrate productivity and diversity. Dams will obliterate 51% of the lotic environment, including the most productive sections of the river according to our macroinvertebrate data. Since Santa Cruz River has a naturally homogeneous flow cycle, dams may provide more variable flows and more diverse habitat. Our data provide critically valuable baseline information to understand the effects of dams on the unique set of glacial driven large rivers of Patagonia. 相似文献
544.
Optical remote sensing of submerged aquatic vegetation: Opportunities for shallow clearwater streams
Remote sensing has rarely been used as a tool to map and monitor submerged aquatic vegetation (SAV) in rivers, due to a combination of insufficient spatial resolution of available image data and strong attenuation of light in water through absorption and scattering. The latter process reduces the possibility to use spectral reflectance information to accurately classify submerged species. However, increasing availability of very high resolution (VHR) image data may enable the use of shape and texture features to help discriminate between species by taking an object based image analysis (OBIA) approach, and overcome some of the present limitations.This study aimed to investigate the possibility of using optical remote sensing for the detection and mapping of SAV. It firstly looked at the possibilities to discriminate submerged macrophyte species based on spectral information only. Reflectance spectra of three macrophyte species were measured in situ across a range of submergence depths. The results showed that water depth will be a limiting factor for the classification of species from remote sensing images. Only Spiked Water Milfoil (Myriophyllum spicatum) was indicated as spectrally distinct through ANOVA analysis, but subsequent Jeffries–Matusita distance analysis did not confirm this. In particular Water Crowfoot (Ranunculus fluitans) and Pondweed (Potamogeton pectinatus) could not be discriminated at 95% significance level. Spectral separability of these two species was also not possible without the effect of an overlying water column.Secondly, the possibility to improve species discrimination, using spatial and textural information was investigated for the same SAV species. VHR image data was acquired with a Near Infrared (NIR) sensitive DSLR camera from four different heights including a telescopic pole and a Helikite UAS. The results show that shape and texture information can improve the detection of the spectrally similar Pondweed and Water Crowfoot from VHR image data. The best performing feature ‘length/width ratio of sub-objects’ was obtained through expert knowledge. All of the shape and texture based features performed better at species differentiation than the spectrally based features.In conclusion this study has shown that there is considerable potential for the combination of VHR data and OBIA to map SAV in shallow stream environments, which can benefit species monitoring and management. 相似文献
545.
In this paper, we use carbon isotopes in the dissolved load of rivers from the Lesser Antilles volcanic arc (Guadeloupe, Martinique and Dominica islands) to constrain the source of the carbon dioxide (CO2) involved in the neutralization reactions during water–rock interactions. The δ13C data span a large range of variations, from –19‰ to –5 · 2‰ for DIC (dissolved inorganic carbon) concentrations ranging from 11 μM to 2000 μM. Coupled with major element concentrations, carbon isotopic ratios are interpreted as reflecting a mixture of magmatic CO2 (enriched in heavy carbon (δ13C ≈ –3 · 5‰) and biogenic CO2 produced in soils (enriched in light carbon (δ13C < –17‰)). Carbon isotopes show that, at the regional scale, 23 to 40% of CO2 consumed by weathering reactions is of magmatic origin and is transferred to the river system through aquifers under various thermal regimes. These numbers remain first‐order estimates as the major uncertainty in using carbon isotopes as a source tracer is that carbon isotopes can be fractionated by a number of processes, including soil and river degassing. Chemical weathering is clearly, at least, partly controlled by the input of magmatic CO2, either under hydrothermal (hot) or surficial (cold) weathering regimes. This study shows that the contribution of magmatic CO2 to chemical weathering is an additional parameter that could explain the high weathering rates of volcanic rocks. The study also shows that a significant part of the carbon degassed from the Earth's interior is not released as CO2 to the atmosphere, but as DIC to the ocean because it interacts with the groundwater system. This study calls for a better understanding of the contributions of deep carbon to the hydrosphere and its influence on the development of the Critical Zone. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
546.
ABSTRACTThe article discusses the range and course of changes in the thermal regime of 14 rivers in Poland over the period 1961–2010. Eleven rivers are located in the Central European Plain, and the others flow in the foothills of the Carpathians Mountains. Statistical analyses take into consideration the results of daily measurements of water temperature carried out at 16 hydrological stations by the Institute of Meteorology and Water Management—National Research Institute. In the first part of the analysed period (1961–1986) water temperature in most rivers declined in relation to its mean value for the entire study period (1961–2010). In 1987 there was a reverse trend: the temperature started rising. The fastest increase in water temperature was recorded in the western part of the study area, and it became slower towards the east. In the southern part of the study area (the foothills) changes of that kind were not observed. The mean yearly temperature of fluvial waters in the Central European Plain showed a positive trend, ranging from 0.17 to 0.27°C (10 years)-1, whereas it did not change in the rivers in the foothills of the Carpathians Mountains. Its fastest rise was recorded in spring, and it reached from 0.08 to 0.43°C (10 years)-1. The increase in water temperature correlated strongly with rising air temperature. The temperature of river waters in the lowlands is believed to be a good indicator of climatic changes.
Editor M.C. Acreman Associate editor T. Okruszko 相似文献
547.
ABSTRACTSomalia has frequently been affected by droughts, famines and water-related humanitarian crises. Water is scarce and the only perennial streams, the Juba and Shabelle rivers, are trans-boundary with river flows mainly originating from the Ethiopian highlands. In both riparian countries water demands are projected to increase. This paper reveals the impact of rising regional water abstractions on stream flows by illustrating sectoral demands and joining them into scenarios of medium and high population and economic growth. These scenarios are associated to the time horizons of 2035 and 2055, respectively. The scenarios disclose alarming trends especially for the Shabelle River: in the medium and high growth scenarios, water demands surpass the available river flows by 200 and 3500 hm3, respectively. The calculated deficits partly derive from conflicting assumptions about river flows by the two main riparian countries, an obstacle to any integrated planning efforts and sustained regional development.
EDITOR Z.W. Kundzewicz; ASSOCIATE EDITOR F. Hattermann 相似文献
548.
John A. Matthews Lindsey J. McEwen 《Geografiska Annaler: Series A, Physical Geography》2013,95(2):185-195
Schmidt‐hammer exposure‐age dating (SHD) was applied to three flood berms in upper Vetlestølsdalen, southern Norway, using a local, high‐precision calibration curve that takes account of the colluvial origin of fluvial boulders in the youngest berm, which was deposited during the August 1979 flood. Precision of SHD dating for this berm was estimated as ±210 years, whereas predicted ages of the two older berms were 3195 ± 435 and 3405 ± 340 years, and subsections of the oldest berm yielded age ranges of ~900 years. The results demonstrate the feasibility of high‐precision SHD in the context of boulder landforms deposited by high‐magnitude floods, the requirement of a large sample of R values in the face of high natural variability, the necessity of an appropriate calibration curve to ensure accuracy, the usefulness of floods of known age for testing and improving calibration curves, and the potential effects of boulders of colluvial origin on R values (especially the susceptibility of young surfaces to roughness variations). The dated berms indicate a return period of ~1000–1500 years for floods of the magnitude of the 1979 flood event in the upper catchment. Thus, the long‐term persistence of flood boulder berms in the landscape has potential for reconstructing Holocene flood history and palaeohydrology from the geomorphic legacy of the most extreme Holocene floods. 相似文献
549.
Aggregation processes of fine sediments have rarely been integrated in numerical simulations of cohesive sediment transport in riverine systems. These processes, however, can significantly alter the hydrodynamic characteristics of suspended particulate matter (SPM), modifying the particle settling velocity, which is one of the most important parameters in modelling suspended sediment dynamics. The present paper presents data from field measurements and an approach to integrate particle aggregation in a hydrodynamic sediment transport model. The aggregation term used represents the interaction of multiple sediment classes (fractions) with corresponding multiple deposition behaviour. The k–ε–turbulence model was used to calculate the coefficient of vertical turbulent mixing needed for the two‐dimensional vertical‐plane simulations. The model has been applied to transport and deposition of tracer particles and natural SPM in a lake‐outlet lowland river (Spree River, Germany). The results of simulations were evaluated by comparison with field data obtained for two levels of river discharge. Experimental data for both discharge levels showed that under the prevailing uniform hydraulic conditions along the river reach, the settling velocity distribution did not change significantly downstream, whereas the amount of SPM declined. It was also shown that higher flow velocities (higher fluid shear) resulted in higher proportions of fast settling SPM fractions. We conclude that in accordance with the respective prevailing turbulence structures, typical aggregation mechanisms occur that continuously generate similar distribution patterns, including particles that settle toward the river bed and thus mainly contribute to the observed decline in the total SPM concentration. In order to determine time‐scales of aggregation and related mass fluxes between the settling velocity fractions, results of model simulations were fitted to experimental data for total SPM concentration and of settling velocity frequency distributions. The comparison with simulations for the case of non‐interacting fractions clearly demonstrated the practical significance of particle interaction for a more realistic modelling of cohesive sediment and contaminant transport. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
550.
Despite the presence of numerous dams in Québec, no study has yet been devoted to their impacts on flood levels. To compensate for this deficiency, we have compared the impacts of dams on the five characteristics (magnitude and its interannual variability, timing and its interannual variability, and asymmetry) of the maximum annual flows between natural rivers and regulated rivers by means of several statistical approaches (analysis of variance, chi‐square test, nonparametric tests, etc.). In the course of this study, we analysed 88 stations on pristine rivers and 60 stations on regulated rivers. The latter group was subdivided into three regulated hydrologic regimes, i.e. inversed flow regimes (25 stations), homogenization flow regimes (15 stations) and natural‐type flow regimes (20 stations). The following observations emerge from this study. (1) In inversed and homogenization flow regimes, generally associated with reservoirs, all the flow characteristics are modified. These modifications notably entrain a decrease in magnitude, a significant reduction in the frequency of the maximum annual spring flows when the snow is melting and an increase in skewness of the distribution and interannual variability of the magnitude and dates of occurrence of the annual maximum flows. We also observed the disappearance of most flows with a recurrence of over 10 years. All these changes particularly affect watersheds larger than 10 000 km2. (2) In natural‐type flow regimes, often associated with run‐of‐river dams, very few changes were observed compared with pristine rivers. These changes primarily affected watersheds smaller than 1000 km2. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献