Complexity research of regional groundwater depth series based on multiscale entropy: a case study of Jiangsanjiang Branch Bureau in China

To describe the complexity features of regional groundwater depth series, using Jiansanjiang Branch Bureau in China as an example, the complexity of monthly groundwater depth series were analyzed with the multiscale entropy (MSE) method and the complexity spatial distribution maps of 15 farms and their subarea were drawn by GIS technology. The results of this paper show that the complexities of monthly groundwater depth series have the following characteristics: southern area is the most complicated, middle area is the least complicated, northern area is in the middle of these two. Human production activities are the main driving factor causing complexity of regional groundwater depth series. The multi-dimensional variation of groundwater depth status can be reflected by the MSE method which is constant and accurate, and needs less data. The research achievements reveal the complexity and areal variation of local groundwater resources system, and provide the scientific basis for rationally utilizing and developing groundwater resources in Jiansanjiang Branch Bureau and even in the whole Sanjiang Plain in China.     

How water use of <Emphasis Type="Italic">Salix</Emphasis><Emphasis Type="Italic">psammophila</Emphasis> bush depends on groundwater depth in a semi-desert area

To investigate the groundwater levels changes effects on the transpiration of Salix psammophila (S. psammophila) bush, systemic measurements of meteorological conditions, sap flow of S. psammophila, soil water contents and groundwater levels were conducted in the Hailiutu River catchment, NW of China. Based on the collected field data, Hydrus-1D software package was used to calibrate water movement for root uptake in the saturated–unsaturated zone. The soil hydraulic parameters and root uptake function parameters were calibrated. The simulated results of soil water contents and sap flow fitted well with the observed ones. Based on the calibrated hydraulic parameters, different groundwater levels were imposed at the low boundary to simulate the groundwater levels changes effects on the transpiration. The relationship between ratio of actual transpiration and potential (T/T _p) and groundwater water table depth was established. The results shows that the ratio of actual transpiration and potential transpiration decreases with groundwater table depth increase as inverse ‘S’ shape. And the turn point is corresponding to the extinct depth, i.e., no groundwater contribution to S. psammophila transpiration. To further verify this phenomenon is universal, the soil hydraulic parameters were replaced with the other five groups in the calibrated forward model. The results confirmed the similar changes of T _a/T _p with the groundwater levels changed, i.e. inverse ‘S’ shape. However, the extinction depth is different corresponding to different soil hydraulic parameters. So, the research results indicated the relationship between transpiration and groundwater levels is non-linear function.     

A comparative study of shallow groundwater level simulation with WA–ANN and ITS model in a coastal island of south China

Accurate and reliable prediction of shallow groundwater level is a critical component in water resources management. Two nonlinear models, WA–ANN method based on discrete wavelet transform (WA) and artificial neural network (ANN) and integrated time series (ITS) model, were developed to predict groundwater level fluctuations of a shallow coastal aquifer (Fujian Province, China). The two models were testified with the monitored groundwater level from 2000 to 2011. Two representative wells are selected with different locations within the study area. The error criteria were estimated using the coefficient of determination (R ²), Nash–Sutcliffe model efficiency coefficient (E), and root-mean-square error (RMSE). The best model was determined based on the RMSE of prediction using independent test data set. The WA–ANN models were found to provide more accurate monthly average groundwater level forecasts compared to the ITS models. The results of the study indicate the potential of WA–ANN models in forecasting groundwater levels. It is recommended that additional studies explore this proposed method, which can be used in turn to facilitate the development and implementation of more effective and sustainable groundwater management strategies.     

Characteristics of deuterium excess parameters for geothermal water in Beijing

This study investigates the characteristics of geothermal water in 10 geothermal fields in Beijing. The relationships between the deuterium excess parameter (d) and temperature, depth, age of geothermal groundwater, groundwater flow field, and Eh were investigated using geothermal groundwater samples. Results showed that (1) the average d value of geothermal water is 5.4, whereas that of the groundwater in normal temperature is 6.04. The differences are induced by the oxygen isotope exchange during the water–rock interaction, which may be more easily completed in geothermal water than in cold groundwater. (2) The d value increases remarkably with the age of the geothermal groundwater. The d value increases from 11.2 to 14.6 when the age of the geothermal water is 12,760 ± 130 a and 38,960 ± 630 a, respectively. Moreover, the isotope heat exchange for composition of the hydrogen and oxygen isotopes in the geothermal groundwater proceeds sufficiently with time. (3) The d value decreases from 5.72 to 3.03 when the depth increases from 125.13 to 3221 m. Generally, in the same area, the d value decreases with depth because the temperature is increasing. (4) The d value of the groundwater gradually reduces from the northern recharge area to the southern discharge area. The average d value is 7.31 in the northern recharge area and 5.68 in the middle Beijing Depression, whereas the d value in the southern area of Fengheying is ?9.20. The larger difference in d values between the recharge and discharge areas is due to the slower velocity of underwater flow, which induces longer time for oxygen exchange. (5) The relationship between the d and Eh is complex. When Eh is <200 mV, the d value of the geothermal water decreases with the decrease in Eh. When Eh is higher than 200 mV, the d value increases slightly with the decrease in Eh. The study of the characteristics of deuterium excess parameters for geothermal water could provide a scientific isotopic evidence for assessment and exploitation measures in geothermal groundwater systems.     

Community vulnerability to hazards: introducing local expert knowledge into the equation

The accuracies of three different evolutionary artificial neural network (ANN) approaches, ANN with genetic algorithm (ANN-GA), ANN with particle swarm optimization (ANN-PSO) and ANN with imperialist competitive algorithm (ANN-ICA), were compared in estimating groundwater levels (GWL) based on precipitation, evaporation and previous GWL data. The input combinations determined using auto-, partial auto- and cross-correlation analyses and tried for each model are: (i) GWL _t?1 and GWL _t?2; (ii) GWL _t?1, GWL _t?2 and P _t ; (iii) GWL _t?1, GWL _t?2 and E _t ; (iv) GWL _t?1, GWL _t?2, P _t and E _t ; (v) GWL _t?1, GWL _t?2 and P _t?1 where GWL _t , P _t and E _t indicate the GWL, precipitation and evaporation at time t, individually. The optimal ANN-GA, ANN-PSO and ANN-ICA models were obtained by trying various control parameters. The best accuracies of the ANN-GA, ANN-PSO and ANN-ICA models were obtained from input combination (i). The mean square error accuracies of the ANN-GA and ANN-ICA models were increased by 165 and 124% using ANN-PSO model. The results indicated that the ANN-PSO model performed better than the other models in modeling monthly groundwater levels.     

Toward reliable calibration of aquifer hydrodynamic parameters: characterizing and optimization of arid groundwater system using swarm intelligence optimization algorithm

Despite advanced development in computational techniques, the issue of how to adequately calibrate and minimize misfit between system properties and corresponding measurements remains a challenging task in groundwater modeling. Two important features of the groundwater regime, hydraulic conductivity (k) and specific yield (S _y), that control aquifer dynamic vary spatially within an aquifer system due to geologic heterogeneity. This paper provides the first attempt in using an advanced swarm-intelligence-based optimization algorithm (cuckoo optimization algorithm, COA) coupled with a distributed hydrogeology model (i.e., MODFLOW) to calibrate aquifer hydrodynamic parameters (S _y and k) over an arid groundwater system in east Iran. Our optimization approach was posed in a single-objective manner by the trade-off between sum of absolute error and the adherent swarm optimization approach. The COA optimization algorithm further yielded both hydraulic conductivity and specific yield parameters with high performance and the least error. Estimation of depth to water table revealed skillful prediction for a set of cells located at the middle of the aquifer system whereas showed unskillful prediction at the headwater due to frequent water storage changes at the inflow boundary. Groundwater depth reduced from east toward west and southwest parts of the aquifer because of extensive pumping activities that caused a smoothening influence on the shape of the simulated head curve. The results demonstrated a clear need to optimize arid aquifer parameters and to compute groundwater response across an arid region.     

Evolution of lacustrine basin in relation to variation in palaeowater depth and delta development: Neogene Bohai Bay Basin,Huanghekou area,northern China

This paper presents revision of the Neogene chronostratigraphic framework of the Huanghekou area in the Bohai Bay Basin, northern China, on the basis of integration of palaeomagnetic data and Neogene seismic stratigraphy. The modern Lake Dongting was selected for analyses of bottom sediments, water depth and elemental composition. Four elements, namely Al, V, Ni and Ga with R ² value larger than 0.7, were chosen to establish a quantitative relationship (F _P) between elemental composition and water depth of bottom sediments. A water depth of ~2.4 m was identified as an accumulation depth of Candoniella albicans, which is used to derive environmental variable (Φ) of formula F _P. Candoniella albicans is also found within the Neogene well W10 in the Huanghekou area. Considering 2.4 m as D value in formula F _p and measured element values at different depths of W10, Φ values were obtained at different depths. The quantitative palaeowater depths of each drilling well were estimated for the first time in this area by considering elemental composition of chip samples of four drilling wells in the Huanghekou area, which are directly iterated to the F _F. Palaeowater depth reconstruction of the Neogene in the Huanghekou area indicates an initial deepening trend and a later shallowing trend during the evolution, with average and deepest bathymetry at ~2.3 and ~4.8 m, respectively. Frequent fluctuations of palaeowater depth control the sand dispersal pattern in a shallow delta during the lower part of the Lower Member of Minghuazhen Formation.     

Spatio-temporal analysis of temperature variability,trend, and magnitude in the Hindu Kush region using Monte Carlo and Sen’s slope approaches

The present study explores the spatial and temporal deviations in temperature using Monte Carlo (MC) and Sen’s slope (SS) approaches in the Hindu Kush (HK) region. Climate change holds sturdy association against the temperature trend that has generated adverse impacts in the form of floods. In this attempt, for trend analysis, temperature has been selected as a meteorological parameter. This study mainly focuses on exploring the tendency in average temperature with respect to time and the consequential flood recurrences in the region. For the current study, data regarding temperature were typically collected from Pakistan Meteorological Department. In the study region, there are a total of seven meteorological station falls namely Dir, Chitral, Drosh, Saidu, Malam Jabba, Kalam, and Timergara. The temperature time series data was calculated and analyzed using MC and SS approaches for trend detection in order to demonstrate the kind of fluctuation in the Hindu Kush region. The resultant analysis further revealed that in the meteorological station of Dir, a more significant positive trend (α?=?0.0001) was found in mean monthly maximum, minimum, and monthly normal temperature. Likewise, at Drosh, a positive trend is detected in mean monthly maximum (α?=?0.04), monthly minimum (α?=?0.003), and monthly average (α?=?0.0005). Moreover, at Saidu met station, there is also a trend detected in temperature sub-variables such as monthly maximum (α?=?0.0001) and monthly minimum (α?=?0.001). In addition to these, at Kalam, there is a temperature trend noted for monthly minimum (α?=?0.01) and monthly average (α?=?0.02). Furthermore, the analysis demonstrates that there is no trend detected in the remaining stations, i.e., Chitral, Malam Jabba, Drosh, and Timergara. The overall analysis discovered that there is a sturdy relationship between climate change phenomenon and temperature variability. After using SS test to the temperature data of mean monthly maximum (TMMMax), the results explored that Kalam station grips the highest magnitude, i.e., Q?=?0.76; however, Timergara shows the lowermost, i.e., Q?=???0.34. For the monthly minimum temperature (TMMMin), at Kalam again, the highest value (Q?=?0.005) was detected; however, other stations revealed a negative trend, except Drosh which express no change in terms of magnitude. Similarly, in terms of monthly normal temperature (TMNor), Timergara station (Q?=???0.4) verified a negative trend magnitude and Malam Jabba station again trendless. Among all, the met station of Malam Jabba which holds an altitude of 2591 m is a hilly station just followed by Kalam having 2103 m height; however, Dir holds 1375 m height and the rest of the met stations show low elevation. The main reason for the temperature difference is the altitude of the study region.     

Temporal analysis of groundwater nitrate concentrations from wells in Prince Edward Island,Canada: application of a linear mixed effects model

Changes in nitrate concentration in groundwater from wells in Prince Edward Island, Canada were investigated over time using two datasets. Temporal trends in groundwater nitrate concentrations were assessed annually during 1981–1996 (1,299 observations), and both seasonally and monthly during 1988–1991 (1,868 observations). Data were analysed using linear mixed models with random effects and correlation structures. The average nitrate concentration in the monthly dataset was 3.99 mg/L as NO₃–N, with January, May, and November concentrations being higher (p?=?0.018). A seasonal effect was present when season was combined with land use type in an interaction term (p?=?0.004). Wells located in agricultural areas had greater nitrate concentrations than urban areas, which in turn, had greater values than low human-impact areas. Row-cropped areas had higher groundwater nitrate concentrations in the summer, whereas manure storage areas were higher in the spring and autumn. Nitrate in groundwater in areas with low human impact and with centralized sewage disposal infrastructure remained relatively low and stable throughout the seasons. There was no significant annual trend (p?=?0.954), but for individual sites, 9.6% significantly increased in nitrate concentration over time, and 6.6% significantly decreased over time.     

A novel geographical information system-based Ant Miner algorithm model for delineating groundwater flowing artesian well boundary: a case study from Iraqi southern and western deserts

The Ant Miner algorithm was compared with the bivariate frequency ratio (FR) and boosted regression trees (BRT) algorithms in terms of its capacity to assess groundwater potential. A geospatial dataset was prepared that contains two components: a flowing well inventory map and eleven factors relevant to groundwater conditions. Average nearest neighbor technique was used to investigate the spatial pattern of flowing wells and to find the appropriate distance between flowing and nonflowing points in the study area. A wrapper approach known as random forest classifier and a filtering approach known as information gain ratio were used to identify the most relevant groundwater factors. The developed models were validated via the area under the operating characteristic curve. Results revealed that the Ant Miner model performed better in terms of both success (0.944) and prediction (0.92) rates compared to FR and BRT. Furthermore, the Ant Miner algorithm derived five simple, easily interpreted rules for predicting groundwater potential that can be used by hydrogeologists for identifying potential groundwater well locations with minimal effort and cost.     

Rogue events in spatiotemporal numerical simulations of unidirectional waves in basins of different depth

The evolution of unidirectional nonlinear sea surface waves is calculated numerically by means of solution of the Euler equations. The wave dynamics corresponds to quasi-equilibrium states characterized by JONSWAP spectra. The spatiotemporal data are collected and processed providing information about the wave height probability and typical appearance of abnormally high waves (rogue waves). The waves are considered at different water depths ranging from deep to relatively shallow cases (k _p h > 0.8, where k _p is the peak wavenumber, and h is the local depth). The asymmetry between front and rear rogue wave slopes is identified; it becomes apparent for sufficiently high waves in rough sea states at all considered depths k _p h ≥ 1.2. The lifetimes of rogue events may reach up to 30–60 wave periods depending on the water depth. The maximum observed wave has a height of about three significant wave heights. A few randomly chosen in situ time series from the Baltic Sea are in agreement with the general picture of the numerical simulations.     

Upscaling of transmissivity,derived from specific capacity: a hydrogeomorphological approach applied to the Doon Valley aquifer system in India

Transmissivity (T) is one of the most important parameters in groundwater studies, and is generally estimated from pumping tests. T can also be deduced from abundantly available specific-capacity (Q/s) data by using analytical and/or empirical approaches, further upscaled by geostatistical methods. A different, remote sensing based, hydrogeomorphological approach is proposed, to upscale T from point- or well-scale to aquifer-scale, and it is applied to the piedmont alluvial aquifer system of Doon Valley in India. In the first step, Q/s and T data-pairs available from aquifer tests were used to establish an empirical, logarithmic relation. Subsequently, satellite imagery along with available data from published and unpublished maps, literature sources and ground surveys were used to divide the aquifer system into major hydrogeomorphological domains that control the groundwater occurrence and flow. Then, the T data derived from Q/s (using the empirical relation) and that available from pumping tests at well-scale were upscaled to aquifer-scale by averaging the T values within each hydrogeomorphological domain. Such a stratification approach is especially useful in areas where availability of only a few data-pairs of known Q/s and T limit the use of geostatistical techniques. A comparative study of the published empirical relations between Q/s and T in various hydrogeologic settings revealed that the relation obtained for Doon Valley aquifer system is close to that found for a similar alluvial aquifer system in Morocco.     

Dynamic soil properties for microzonation of Delhi,India

Delhi, the capital of India, has experienced mild seismic shaking during several earthquakes in the past. The large variations of depth to bedrock and ground water table coupled with different soil types at different locations of Delhi necessitate a seismic microzonation study. Dynamic soil properties such as shear wave velocity, modulus reduction and damping characteristics of local soils are the basic and essential input parameters for conducting even a preliminary ground response analysis which is an essential input in microzonation studies. Shear wave velocity is not measured routinely due to its high cost and lack of the required expertise. Several researchers in the past developed correlations between shear wave velocity (V _s ) and routinely measured N values. In the present study, shear wave velocity profiles measured in the field at more than 80 borehole locations to a depth of about 20 to 32m using Spectral Analysis of Surface Waves (SASW) are presented and correlations between shear wave velocity and N values are also presented for use by engineers and designers. Results of strain and stress controlled cyclic triaxial tests on remoulded samples of sand-silt mixtures in the high strain range are used for generating the modulus reduction and damping curves and are compared with the well-known curves in the literature. The results presented in this article can be used for microzonation studies as well as site specific ground response analyses at Delhi.     

Leaching of viruses and other microorganisms naturally occurring in pig slurry to tile drains on a well-structured loamy field in Denmark

The amount of animal manure used in modern agriculture is increasing due to the increase in global animal production. Pig slurry is known to contain zoonotic bacteria such as E. coli, Salmonella spp. and Campylobacter spp., and viruses such as hepatitis E virus and group A rotavirus. Coliform bacteria, present in manure, have previously been shown to leach into tile drains. This poses a potential threat to aquatic environments and may also influence the quality of drinking water. As knowledge is especially scarce about the fate of viruses when applied to fields in natural settings, this project sets out to investigate the leaching potential of six different microorganisms: E. coli and Enterococcus spp. (detected by colony assay), somatic coliphages (using plaque assays), and hepatitis E virus, porcine circovirus type 2, and group A rotavirus (by real-time polymerase chain reaction). All six microorganisms leached through the soil entering the tile drains situated at 1-m depth the first day following pig slurry application. The leaching pattern of group A rotavirus differed substantially from the pattern for somatic coliphages, which are otherwise used as indicators for virus contamination. Furthermore, group A rotavirus was detected in monitoring wells at 3.5-m depth up to 2 months after pig slurry application. The detection of viral genomic material in drainage water and shallow groundwater signifies a potential hazard to human health that needs to be investigated further, as water reservoirs used for recreational use and drinking water are potentially contaminated with zoonotic pathogens.     

Stable water isotopes of precipitation in China simulated by SWING2 models

The stable water isotope ratio in precipitation is a useful tracer of atmospheric circulation. Such observations, however, are very limited in space and time. To solve this problem, many isotope-enabled general circulation models (GCMs) are used to help the interpretation of isotope proxies. In this paper, several isotope-enabled GCMs released by the second Stable Water Isotope Intercomparison Group (SWING2) were selected to assess the spatial pattern of deuterium (δD) and the deuterium excess (d) of precipitation in China. The isotopic data of the Global Network of Isotopes in Precipitation (GNIP) and the Chinese Network of Isotopes in Precipitation (CHNIP) were also applied to verify the simulations. The results indicate that these models accurately simulate the spatial characteristics of δD and d of precipitation in China. The correlation between the observations and simulations for LMDZ is the highest among these models, while the root-mean-square (RMS) and standard deviation are not perfect. In addition, LMDZ is worse than other models in capturing the low signal in certain regions, such as CAM, GISS_E, and MIROC. For the monthly variation, most SWING2 models underestimate δD of the precipitation but overestimate the value of d, except for isoGSM. The simulated monthly variation of the water isotopes from SWING2 models is in general similar to the observations, and the trend corresponds to the monthly variation in the Northern Hemisphere. Moreover, all models are good at illustrating the temperature and precipitation amount effects, while they exhibit varying skills in interpreting the altitude and continental effects.     

Horizontal magnetic fields in the solar photosphere

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI λ1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of 192 G at the solar surface. According to the magnetic-field distribution obtained, the most probable absolute strength of the horizontal magnetic field at an optical depth of τ ₅ = 1(τ ₅ denotes τ at λ = 500 nm) is 50 G, while the mean value is 244 G. On average, the horizontal magnetic fields are stronger than the vertical fields to heights of about 400 km in the photosphere due to their higher density and the larger area they occupy. The maximum factor by which the horizontal fields are greater is 1.5. Strong horizontal magnetic flux tubes emerge at the surface as spots with field strengths of more than 500 G. These are smaller than granules in size, and have lifetimes of 3–6 min. They form in the photosphere due to the expulsion of magnetic fields by convective flows coming from deep subphotospheric layers. The data obtained qualitatively agree with observations with the Hinode space observatory.     

Coda <Emphasis Type="Italic">Q</Emphasis> in Qeshm Island,south of Iran,using aftershocks of the Qeshm earthquake of November 27, 2005

Coda wave attenuation is estimated for Qeshm Island which is located in the southeastern part of Zagros. For this purpose, the aftershocks of Qeshm earthquake in November 27, 2005, recorded within an epicentral distance less than 100 km, have been used. More than 829 earthquakes were recorded by a local temporary network consisting of 16 short period stations installed after a week after the main shock for ～10 weeks. The coda quality factor, Q _c, was estimated using the single-backscattering model in frequency bands of 0.5–24 Hz. In this research, lateral and vertical variations of coda Q in Qeshm Island are explored. In Qeshm Island, absence of significant lateral variation of coda Q is observed. To investigate the attenuation variation with depth, the coda Q value was calculated for coda time windows with different lengths (5, 10, 15, 20, 25, and 30 s). It is observed that coda Q increases with depth. However, in our study area, the rate of increase of coda Q with depth is not uniform. Beneath Qeshm Island, the rate of increase of coda Q is greater at depths less than ～40 km compared with those of larger depths. This is indicating the existence of a low attenuation anomalous structure under the ～40-km depth which may be correlated with the Moho depth in this region. The average frequency relation for this region is Q _c = 36 ± 1.2f ^{0.94 ± 0.039} at a 5 s-lapse time window length and Q _c = 110 ± 1.8f ^{0.88 ± 0.09} at a 30-s lapse time window length.     

Aquifer porosity in the Pan-African semi-arid context

Water scarcity is one of the major concerns that people are facing worldwide. Although the liquid is absolutely abundant through the globe, its availability poses too much problems specifically to each region. Those problems can result in one or a combination of three basic situations: declining water (drought), overabundance of surface water (floods) or degradation of the quality of water (pollution). All these situations are reflected in the scarcity of good quality water. Arid regions are particularly concerned. In such areas where groundwater contained in aquifers is usually perceived as providence, any project of groundwater exploration and exploitation must be preceded by prior careful and meticulous investigation, in order to avoid early and premature drying. This investigation is likely to predict the future behaviour of aquifers and to improve the groundwater resources management. Beside fundamental properties as hydraulic conductivity, the present paper that addresses the water sector in the semi-arid region of northern Cameroon emphasizes the importance of porosity on aquifer productivity and consequently on the groundwater resources management. The porosity of the local aquifer has then been determined using the Waxman and Smits model which establishes a reliable relationship between the apparent and corrected formation factors, F _a and F _c , taking the clay effects into consideration. This approach can be applied in other similar semi-arid regions through the world.     

Local site effect of a clay site in Shiraz based on seismic hazard of Shiraz Plain

Propagation of seismic waves through soil layers would drastically change the frequency content and amplitude-based features of ground motions at the surface. These alterations are known as seismic site effects. Computation of site effects of high-populated areas such as large cities is of great importance (e.g., it is used in development of seismic microzonation of a region). Shiraz is one of the most populous cities of Iran and is located in a high seismic hazardous region. A representative clay site in this city is selected to assess local site effects. The time series and random vibration theory procedure in the frequency domain are implemented to analyze the aforementioned site. Furthermore, the nonlinear dynamic soil behavior is simulated by the equivalent linear method and the nonlinear method via DEEPSOIL program. Three types of soil column uncertainties such as shear wave velocity, modulus reduction, and damping ratio of soil layers as well as depth of underlying rock half-space (D _bed) are considered herein. The mean amplification and standard deviation of natural logarithm of amplification factors are computed for a variety of analysis types. The results of the current study show that the computed mean and standard deviation of amplification factor in ln units by considering only V _S uncertainty are in good agreement with the corresponding ones by considering V _S and modulus reduction and damping ratio variabilities simultaneously for the studied site. Furthermore, it seems that the effect of bedrock depth in definition of spectral shapes of the Iranian seismic building code should be taken into account.     

Nonlinear consolidation in randomly heterogeneous highly compressible aquitards

Severe land subsidence due to groundwater extraction may occur in multiaquifer systems where highly compressible aquitards are present. The highly compressible nature of the aquitards leads to nonlinear consolidation where the groundwater flow parameters are stress-dependent. The case is further complicated by the heterogeneity of the hydrogeologic and geotechnical properties of the aquitards. The effect of realistic vertical heterogeneity of hydrogeologic and geotechnical parameters on the consolidation of highly compressible aquitards is investigated by means of one-dimensional Monte Carlo numerical simulations where the lower boundary represents the effect of an instant drop in hydraulic head due to groundwater pumping. Two thousand realizations are generated for each of the following parameters: hydraulic conductivity (K), compression index (C _c), void ratio (e) and m (an empirical parameter relating hydraulic conductivity and void ratio). The correlation structure, the mean and the variance for each parameter were obtained from a literature review about field studies in the lacustrine sediments of Mexico City. The results indicate that among the parameters considered, random K has the largest effect on the ensemble average behavior of the system when compared to a nonlinear consolidation model with deterministic initial parameters. The deterministic solution underestimates the ensemble average of total settlement when initial K is random. In addition, random K leads to the largest variance (and therefore largest uncertainty) of total settlement, groundwater flux and time to reach steady-state conditions.