Groundwater protection in Mediterranean countries after the European water framework directive     

C. Martínez Navarrete  J. Grima Olmedo  J. J. Durán Valsero  J. D. Gómez Gómez  J. A. Luque Espinar  J. A. de la Orden Gómez 《Environmental Geology》2008,54(3):537-549

The European Water Framework Directive (WFD) has driven the protection of groundwater and characterization of water bodies. Development of appropriate and efficient approaches which consider the special features of the hydrologic regime is essential. The results of different projects that have been carried out to integrate characterization and protection of water bodies are summarized herein. In the Les eaux de la Mediterranée (AQUAMED) Project, applicability to the Mediterranean Region of guidelines provided by the European Commission to facilitate the WFD implementation has been verified. The Background criteria for the identification of groundwater thresholds (BRIDGE) Project developed a methodology to establish threshold values of pollutants contributing to the chemical status of groundwater bodies. This method has been applied to pollutants used to classify groundwater bodies as at risk of not achieving objectives of the WFD. Selected features of protection areas for drinking water and safeguard zones are analyzed, as well as the possibility of using wellhead protection areas.  相似文献   

Field investigation of surface sand and dust movement over different sandy grasslands in the Otindag Sandy Land,China     

Shulin Liu  Tao Wang  Guangting Chen  Jian Guo  Xian Xue  Shaoxiu Ma 《Environmental Geology》2008,53(6):1225-1233

The characteristics of sand and dust movement over different sandy grasslands in China’s Otindag Sandy Land were explored based on field observations and laboratory analyses. Threshold wind speeds (the speed required to initiate sand movement) at a height of 2 m above the ground were estimated in the field for different surface types. Threshold wind speed above shifting dunes in the study area is about 4.6 m s⁻¹ at this height. This value was smaller than values observed above other surfaces, resulting in a greater risk of blowing sand above these dunes. Differences in sand transport rates (STR) as a function of the severity of desertification resulted primarily from differences in surface vegetation cover and secondarily from the soil’s grain-size distribution. STR increased exponentially with increasing near-bed wind velocity. Under the same wind conditions, STR increased with increasing severity of desertification: from 0.08 g cm⁻² min⁻¹ above semi-fixed dunes to 8 g cm⁻² min⁻¹ above semi-shifting dunes and 25 g cm⁻² min⁻¹ above shifting dunes. Vegetation’s affect on STR was clearly large. Different components of sand and dust were trapped over different lands: mostly sand grains but little dust were trapped above shifting dunes, but much dust was collected over semi-shifting and semi-fixed dunes. Human disturbance is likely to produce dust even from fixed dunes as a result of trampling by animals and vehicle travel. In addition, spring rainfall decreased the risk of sand and dust movement by accelerating germination of plants and the formation of a soil crust.  相似文献   

Critical phenomena in thermal conductivity: Implications for lower mantle dynamics     

Anne M. Hofmeister  David A. Yuen 《Journal of Geodynamics》2007,44(3-5):186-199

Microscopic mechanisms for heat transport in dense minerals (phonon scattering and photon attenuation) exhibit aspects of threshold behavior, discussed qualitatively here. For all minerals examined so-far using laser-flash analysis, the lattice component of the thermal conductivity of the mantle asymptotes to a constant above a critical temperature of 1500 K. Radiative transfer calculated from absorption spectra has thresholds in both grain-size and Fe content, and a rather complex dependence on temperature. These critical phenomena impact convection of the lower mantle, because the lattice contribution tends to destabilize the cold boundary layers, whereas radiative transfer mostly promotes stability in the lower mantle, unless the grains are large and Fe-rich, which makes convection chaotic and time-dependent. The specific behavior suggests that flow in the lower mantle is sluggish, whereas flow in the upper mantle-transition zone is time-dependent. The decrease in k_rad as Fe/(Fe + Mg) increases beyond 0.1 may be connected with formation of lower mantle, thermo-chemical plumes through positive feedback.  相似文献   

The effect of plastic fines on the pore pressure generation characteristics of saturated sands   总被引：2，自引：0，他引：2  

Mehdi Derakhshandi  Ellen M. Rathje  Kenan Hazirbaba  S.M. Mirhosseini 《Soil Dynamics and Earthquake Engineering》2008,28(5):376-386

Pore water pressure generation during earthquake shaking initiates liquefaction and affects the shear strength, shear stiffness, deformation, and settlement characteristics of soil deposits. The effect of plastic fines (kaolinite) on pore pressure generation in saturated sands was studied through strain-controlled cyclic triaxial tests. In addition to pore pressure generation, this experimental study also focused on evaluating the threshold shear strain for pore pressure generation and the volumetric compressibility of specimens during pore pressure dissipation. The results reveal that specimens having up to 20% plastic fines content generated larger values of pore water pressure than clean sand specimens. At 30% fines content, the excess pore water pressure decreased below that of clean sand. The threshold shear strain, which indicates the strain level above which pore pressures begin to generate, was assessed for different kaolinite–sand mixtures. The threshold shear strain was similar for 0–20% fines (γ_t0.006–0.008%), but increased to about 0.025% for 30% fines. The volumetric compressibility, measured after pore pressure generation, was similar for all specimens. The transition of behavior at fines contents between 20% and 30% can be attributed to a change in the soil structure from one dominated by sand grains to one dominated by fines.  相似文献   

Streamflow drought time series forecasting   总被引：5，自引：2，他引：5  

Reza Modarres 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(3):223-233

Drought is considered to be an extreme climatic event causing significant damage both in the natural environment and in human lives. Due to the important role of drought forecasting in water resources planning and management and the stochastic behavior of drought, a multiplicative seasonal autoregressive integrated moving average (SARIMA) model is applied to the monthly streamflow forecasting of the Zayandehrud River in western Isfahan province, Iran. After forecasting 12 leading month streamflow, four drought thresholds including streamflow mean, monthly streamflow mean, 2-, 5-, 10- and 20-year return period monthly drought and standardized streamflow index were chosen. Both observed and forecasted streamflow showed a drought period with different severity in the lead-time. This study also demonstrates the usefulness of SARIMA models in forecasting, water resources planning and management.  相似文献   

EFFECTS OF FLOW INTENSITY, OBSTACLE ALIGNMENT AND CROSS-SECTION GEOMETRY ON SCOUR AT BRIDGE ABUTMENTS     

A. H. CARDOSO  J. S. SANTOS  M. ROCA EFFECTS OF FLOW INTENSITY  OBSTACLE ALIGNMENT  CROSS-SECTION GEOMETRY ON SCOUR AT BRIDGE ABUTMENTS A. H. CARDOSO  J. S. SANTOS  M. ROCA EFFECTS OF FLOW INTENSITY  OBSTACLE ALIGNMENT  CROSS-SECTIO 《国际泥沙研究》2002,17(2)

1 INTRODUCTION Local scour at bridge piers and abutments has long concerned engineers. Scour depth estimation has attracted considerable research interest and activity, and a number of prediction methods exist at present (see, e.g., comprehensive lists of predictors given by Melville and Colleman, 2000). Several studies have been completed since the 1950s for the particular case of scour at bridge abutments. Since the beginning of the 1980s, the University of Auckland, New Zealand, …  相似文献   

河型成因的各种理论及其间关系   总被引：14，自引：1，他引：14  

倪晋仁  张仁 《地理学报》1991,46(3):366-372

本文较为系统地将河型成因的各种研究方法按其所依据的理论分类,并指出了各种理论之间的内在联系。文中讨论了各种研究方法所具有的优缺点、各研究方法之间的互补作用以及各种研究方法在表面处理方式不同的背后所隐藏的使河流趋向某一极值状态(或稳定状态)的共同倾向,并据此指出了进一步研究河型成因问题时的侧重面。  相似文献   

Accounting seasonal nonstationarity in time series models for short-term ozone level forecast     

Sung Eun Kim  Ashok Kumar 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(4):241-248

Due to the nonlinear feature of a ozone process, regression based models such as the autoregressive models with an exogenous vector process (ARX) suffer from persistent diurnal behaviors in residuals that cause systematic over-predictions and under-predictions and fail to make accurate multi-step forecasts. In this article we present a simple class of the functional coefficient ARX (FARX) model which allows the regression coefficients to vary as a function of another variable. As a special case of the FARX model, we investigate the threshold ARX (TARX) model of Tong [Lecture notes in Statistics, Springer-Verlag, Berlin, 1983; Nonlinear time series: a dynamics system approach, Oxford University Press, Oxford, 1990] which separates the ARX model in terms of a variable called the threshold variable. In this study we use time of day as the threshold variable. The TARX model can be used directly for ozone forecasts; however, investigation of the estimated coefficients over the threshold regimes suggests polynomial coefficient functions in the FARX model. This provides a parsimonious model without deteriorating the forecast performance and successfully captures the diurnal nonstationarity in ozone data. A general linear F-test is used to test varying coefficients and the portmanteau tests, based on the autocorrelation and partial autocorrelation of fitted residuals, are used to test error autocorrelations. The proposed models were applied to a 2 year dataset of hourly ozone concentrations obtained in downtown Cincinnati, OH, USA. For the exogenous processes, outdoor temperature, wind speed, and wind direction were used. The results showed that both TARX and FARX models substantially improve one-day-ahead forecasts and remove the diurnal pattern in residuals for the cases considered.  相似文献   

气候多雨与强震发生的延时关系   总被引：7，自引：0，他引：7       下载免费PDF全文

刘德富 《地球物理学报》1987,30(5):487-493

本文通过建立门限回归模型,研究了华北地区气候变化与强震发生的关系,发现明显有大约12年的延时相关。该延时尺度对中国其它地区和日本、美国的地震活动也同样适合。认为气候多雨是长期地震预报中的一个可用重要因素。  相似文献   

Initiation conditions for debris flows generated by runoff at Chalk Cliffs, central Colorado   总被引：7，自引：1，他引：6  

Jeffrey A. Coe  David A. Kinner  Jonathan W. Godt 《Geomorphology》2008,96(3-4):270

We have monitored initiation conditions for six debris flows between May 2004 and July 2006 in a 0.3 km² drainage basin at Chalk Cliffs; a band of hydrothermally-altered quartz monzonite in central Colorado. Debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14° to 45°. The availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes. Rainfall exceeding I = 6.61(D)^− 0.77, where I is rainfall intensity (mm/h), and D is duration (h), was required for the initiation of debris flows in the drainage basin. The approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0.15 m³/s. Colluvium in the basin was unsaturated immediately prior to (antecedent) and during debris flows. Antecedent, volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4–9%, and 4–7%, respectively. During debris flows, peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10–20%, and 4–12%, respectively. Channel sediment at a depth of 45 cm was unsaturated before and during debris flows; antecedent moisture ranged from 20–22%, and peak moisture ranged from 24–38%. Although we have no measurements from shallow rill or channel sediment, we infer that it was unsaturated before debris flows, and saturated by surface-water runoff during debris flows.Our results allow us to make the following general statements with regard to debris flows generated by runoff in semi-arid to arid mountainous regions: 1) high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff, 2) locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows, and 3) rainfall and simulated surface-water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment.  相似文献