Non‐intrusive global/local analysis for the study of fine cracking     

Cécile Oliver‐Leblond  Arnaud Delaplace  Frédéric Ragueneau  Benjamin Richard 《国际地质力学数值与分析法杂志》2013,37(8):973-992

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Effects of different operational modes on the flood‐induced turbidity current of a canyon‐shaped reservoir: case study on Liuxihe Reservoir,South China     

Sheng Wang  Xin Qian  Bo‐Ping Han  Lian‐Cong Luo  Rui Ye  Wen Xiong 《水文研究》2013,27(26):4004-4016

Suspended matter is an important indicator of water quality in freshwater systems. The flood‐induced turbidity current plays a dominant role in the seasonal dynamic of suspended matter in the Liuxihe Reservoir (23°45′50″N; 113°46′52″E), a large, stratified reservoir at the Tropic of Cancer in southern China. Field measurements show that loading and distribution of suspended matter in the reservoir differ in typical wet, dry and medium years, as a result of different discharge volumes and water level variation patterns. Using historical data and the practical demand for water supply and flood control, we generalized two feasible reservoir operational modes: flood impounding mode (drawing down the reservoir to a low level before flood events to impound inflow during the flooding season) and moderate level change mode (drawing down the reservoir to a moderate level before flood events, then keeping the level within the flood control level during runoff events). To examine the effects of different operational modes and outlet depths on the reservoir's flood‐induced turbidity current, a numerical simulation model was applied in three types of hydrological conditions. The results show that the mode with moderate drawdown and recharge processes can decrease loading of suspended matter in spring and promote turbidity current release during flood events, and upper withdrawal can improve the effects of turbid water release. We suggest that more attention should be focused on water quality management in the reservoir operation stage, severe artificial water level fluctuation being avoided and selective withdrawal becoming an optional management measure. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Holocene migration of oceanic front systems over the Conrad Rise in the Indian Sector of the Southern Ocean     

Kota Katsuki  Minoru Ikehara  Yusuke Yokoyama  Masako Yamane  Boo‐Keun Khim 《第四纪科学杂志》2012,27(2):203-210

There has been limited previous research about Holocene climate variability in the Indian Sector of the Southern Ocean. Here we examine centennial‐scale changes in diatom assemblages and stable isotopic ratios since 10 000 cal a BP in a high‐accumulation‐rate sediment core from the Conrad Rise. Although abundances of dominant diatom taxa (Fragilariopsis kerguelensis and Thalassiothrix antarctica) are comparatively constant, relative abundances of secondary taxa fluctuate. Before c. 9900 cal a BP, winter sea‐ice and cold water covered the Conrad Rise. Following deglaciation the sea‐ice retreated from the Conrad Rise, lagging that of the Atlantic and eastern Indian Sectors by about 1500 a. The Polar Front moved southward during the early Holocene optimum and north Antarctic Zone waters covered the Conrad Rise for about 650 a. After 9300 cal a BP, solar insolation strongly influenced sea surface temperature and primary productivity in the Southern Ocean. In the high‐latitude Indian Sector, productivity increased 1500 a after the onset of late Holocene neoglaciation. Periodic δ¹⁸O and cold‐water diatom taxa spikes (at intervals of 200 and 300–500 a, respectively) occurred after 9300 cal a BP, probably associated with solar activity. Fluctuations in short‐term sea surface temperature and cold‐water taxa are synchronous with changes in δD observed in an east Antarctic ice core. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Assessment of future runoff trends under multiple climate change scenarios in the Willamette River Basin,Oregon, USA     

Il‐Won Jung  Heejun Chang 《水文研究》2011,25(2):258-277

We investigated trends in future seasonal runoff components in the Willamette River Basin (WRB) of Oregon for the twenty‐first century. Statistically downscaled climate projections by Climate Impacts Group (CIG), eight different global climate model (GCM) simulations with two different greenhouse gas (GHG) emission scenarios, (A1B and B1), were used as inputs for the US Geological Survey's Precipitation Runoff Modelling System. Ensemble mean results show negative trends in spring (March, April and May) and summer (June, July and August) runoff and positive trends in fall (September, October and November) and winter (December, January and February) runoff for 2000–2099. This is a result of temperature controls on the snowpack and declining summer and increasing winter precipitation. With temperature increases throughout the basin, snow water equivalent (SWE) is projected to decline consistently for all seasons. The decreases in the centre of timing and 7‐day low flows and increases in the top 5% flow are caused by the earlier snowmelt in spring, decreases in summer runoff and increases in fall and winter runoff, respectively. Winter runoff changes are more pronounced in higher elevations than in low elevations in winter. Seasonal runoff trends are associated with the complex interactions of climatic and topographic variables. While SWE is the most important explanatory variable for spring and winter runoff trends, precipitation has the strongest influence on fall runoff. Spatial error regression models that incorporate spatial dependence better explain the variations of runoff trends than ordinary least‐squares (OLS) multiple regression models. Our results show that long‐term trends of water balance components in the WRB could be highly affected by anthropogenic climate change, but the direction and magnitude of such changes are highly dependent on the interactions between climate change and land surface hydrology. This suggests a need for spatially explicit adaptive water resource management within the WRB under climate change. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Prediction of depth‐integrated fluxes of suspended sediment in the Amazon River: particle aggregation as a complicating factor     

J. Bouchez  F. Métivier  M. Lupker  L. Maurice  M. Perez  J. Gaillardet  C. France‐Lanord 《水文研究》2011,25(5):778-794

Large rivers have been previously shown to be vertically heterogeneous in terms of suspended particulate matter (SPM) concentration, as a result of sorting of suspended solids. Therefore, the spatial distribution of suspended sediments within the river section has to be known to assess the riverine sedimentary flux. Numerous studies have focused on the vertical distribution of SPM in a river channel from a theoretical or experimental perspective, but only a few were conducted so far on very large rivers. Moreover, a technique for the prediction of depth‐integrated suspended sediment fluxes in very large rivers based on sediment transport dynamics has not yet been proposed. We sampled river water along depth following several vertical profiles, at four locations on the Amazon River and its main tributaries and at two distinct water stages. Depending on the vertical profile, a one‐ to fivefold increase in SPM concentration is observed from river channel surface to bottom, which has a significant impact on the ‘depth‐averaged’ SPM concentration. For each cross section, a so‐called Rouse profile quantitatively accounts for the trend of SPM concentration increase with depth, and a representative Rouse number can be measured for each cross section. However, the prediction of this Rouse number would require the knowledge of the settling velocity of particles, which is dependent on the state of aggregation affecting particles within the river. We demonstrate that in the Amazon River, particle aggregation significantly influences the Rouse number and renders its determination impossible from grain‐size distribution data obtained in the lab. However, in each cross section, the Rouse profile obtained from the fit of the data can serve as a basis to model, at first order, the SPM concentration at any position in the river cross section. This approach, combined with acoustic Doppler current profiler (ADCP) water velocity transects, allows us to accurately estimate the depth‐integrated instantaneous sediment flux. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Groundwater geochemistry of the Chihuahua City region in the Rio Conchos Basin (northern Mexico) and implications for water resources management     

Jürgen Mahlknecht  Axel Horst  Gabriela Hernández-Limón  Ramon Aravena 《水文研究》2008,22(24):4736-4751

The Chihuahua City region, located in the semiarid-arid northern highlands of Mexico, has experienced intensive groundwater abstraction during the last 40 years to meet water demands in the region. A geochemical survey was carried out to investigate the evolution from baseline to modern conditions of a 130-km flow path including the El Sauz–Chihuahua–Aldama–San Diego de Alcalá regions. The research approach included the use of major chemical elements, chlorofluorocarbons and environmental isotope (¹⁸O, ²H, ¹³C and ¹⁴C) tracers. Stable isotopes indicate that groundwater evolves from the evaporation of local rainfall and surface water. Groundwater located at the lower end of the flow section is up to 6000 years old and older groundwater in the order of 9000 years BP was found in a deep well located in the upper part of the flow system, implying contribution from a neighbour basin. The background groundwater chemistry upstream of Chihuahua City results from feldspar weathering. Beyond Chihuahua City the chemical conditions are strongly modified owing to disposal of sewage from public and industrial water supplies into the Rio Chuviscar, subsequent allocation of this water to agricultural irrigation areas and direct infiltration under the river bed. As a consequence, anions like chloride and sulphate are mainly related to surface sources. Nitrate is controlled in part by sewage from public supply and industry and in part by agricultural practices. Arsenic and fluoride are related to weathering of rock formations of local mineralized ranges and subsequent enrichment of the basin-fill by magmatic processes. The results of this study have implications for groundwater management in an arid region that depends entirely on groundwater for domestic, industrial and agricultural water consumption. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

A generalized additive model for the spatial distribution of snowpack in the Spanish Pyrenees     

J. I. Lpez‐Moreno  D. Nogus‐Bravo 《水文研究》2005,19(16):3167-3176

A generalized additive model (GAM) was used to model the spatial distribution of snow depth in the central Spanish Pyrenees. Statistically significant non‐linear relationships were found between distinct location and topographical variables and the average depth of the April snowpack at 76 snow poles from 1985 to 2000. The joint effect of the predictor variables explained more than 73% of the variance of the dependent variable. The performance of the model was assessed by applying a number of quantitative approaches to the residuals from a cross‐validation test. The relatively low estimated errors and the possibility of understanding the processes that control snow accumulation, through the response curves of each independent variable, indicate that GAMs may be a useful tool for interpolating local snow depth or other climate parameters. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Effect of growing watershed imperviousness on hydrograph parameters and peak discharge     

Huang‐jia Huang  Shin‐jen Cheng  Jet‐chau Wen  Ju‐huang Lee 《水文研究》2008,22(13):2075-2085

An increasing impervious area is quickly extending over the Wu‐Tu watershed due to the endless demands of the people. Generally, impervious paving is a major result of urbanization and more recently has had the potential to produce more enormous flood disasters than those of the past. In this study, 40 available rainfall–runoff events were chosen to calibrate the applicable parameters of the models and to determine the relationships between the impervious surfaces and the calibrated parameters. Model inputs came from the outcomes of the block kriging method and the non‐linear programming method. In the optimal process, the shuffled complex evolution method and three criteria were applied to compare the observed and simulated hydrographs. The tendencies of the variations of the parameters with their corresponding imperviousness were established through regression analysis. Ten cases were used to examine the established equations of the parameters and impervious covers. Finally, the design flood routines of various return periods were furnished through use of approaches containing a design storm, block kriging, the SCS model, and a rainfall‐runoff model with established functional relationships. These simulated flood hydrographs were used to compare and understand the past, present, and future hydrological conditions of the watershed studied. In the research results, the time to peak of flood hydrographs for various storms was diminished approximately from 11 h to 6 h in different decrements, whereas peak flow increased respectively from 127 m³ s^?1 to 629 m³ s^?1 for different storm intensities. In addition, this study provides a design diagram for the peak flow ratio to help engineers and designers to construct hydraulic structures efficiently and prevent possible damage to human life and property. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

On bandwidth selection for nonparametric estimation in flood frequency analysis     

A. Quintela‐del‐Río 《水文研究》2011,25(5):671-678

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Stage‐discharge uncertainty derived with a non‐stationary rating curve in the Choluteca River,Honduras     

I. Westerberg  J.‐L. Guerrero  J. Seibert  K. J. Beven  S. Halldin 《水文研究》2011,25(4):603-613

Uncertainty in discharge data must be critically assessed before data can be used in, e.g. water resources estimation or hydrological modelling. In the alluvial Choluteca River in Honduras, the river‐bed characteristics change over time as fill, scour and other processes occur in the channel, leading to a non‐stationary stage‐discharge relationship and difficulties in deriving consistent rating curves. Few studies have investigated the uncertainties related to non‐stationarity in the stage‐discharge relationship. We calculated discharge and the associated uncertainty with a weighted fuzzy regression of rating curves applied within a moving time window, based on estimated uncertainties in the observed rating data. An 18‐year‐long dataset with unusually frequent ratings (1268 in total) was the basis of this study. A large temporal variability in the stage‐discharge relationship was found especially for low flows. The time‐variable rating curve resulted in discharge estimate differences of ? 60 to + 90% for low flows and ± 20% for medium to high flows when compared to a constant rating curve. The final estimated uncertainty in discharge was substantial and the uncertainty limits varied between ? 43 to + 73% of the best discharge estimate. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献