Civil Engineering

Although the safety of horizontal curves has been researched, data availability and quality have been the Achilles’ heel of many studies. Furthermore, safety at horizontal curves has become more significant in view of the changes in the latest Manual on Uniform Traffic Control Devices with respect to traffic control devices at horizontal curves. The objective of this research was to evaluate the safety of horizontal curves through the use of curve geometric characteristics and sign data. The focus was on collecting a good-quality large data set to develop models and explore the relationship between safety at horizontal curves and sign types, specifically curve and turn signs. The data set included curves on different types of roads to determine the difference in safety  characteristics that had not been examined in the literature. The crash prediction models displayed highly significant variables, which showed a positive relationship with annual average daily traffic, posted speed, and curve length, and a negative relationship with curve radius. The results show that sharper curves (Classes B–F) on two-lane roads are less safe than curves on freeways and multilane and urban roads. However, further investigation is required into the safety characteristics of Class A curves on freeways and multilane roads, compared with two-lane roads. Moreover, sign usage was not found to be a significant factor for sharper curves, which suggests that, regardless of the presence of the curve or turn sign, other influencing factors take over. The crash prediction model results provided greater detail and identified variables with large significance.

An integrated framework that is comprised of field surveys of groundwater, surface water and soils, laboratory process experiments and hydrologic and geochemical modeling is used to identify the origin (anthropogenic versus geogenic sources), fate and transport of hexavalent Cr in Tertiary and Quaternary deposits of Oropos plain in Greece. Groundwater and soils were analyzed in May 2008 and exhibited considerable Cr concentrations. Mineralogical analysis and micro-XRF analysis of the heavy soil fractions (metallic components) showed Cr bearing phases like chromites, Cr-silicate phases with positive correlation between Si, Al, Fe and Cr soil concentrations. Column experiments showed the Cr(VI) desorption ability of soils, e.g. concentration of 20 lg L À1 was detected after the application of 50 mm of rain. The groundwater model simulated the variability of Cr concentrations emanating from both anthropogenic and geogenic sources, successfully using rate constants obtained from the laboratory experiments, e.g. 4.24 nM h À1 for serpentine soil and 0.77 nM h À1 for soil in alluvial deposits. The mineralogical and geochemical results support a geogenic origin for Cr in soils and groundwater of Oropos plain while modeling results suggest that contaminants transported by Asopos River have affected only the upper layers of the subsurface in the vicinity of the river. The framework can be used to establish background concentrations or clean up levels of Cr-contaminated soils and groundwater.

The greater area of the Asopos river, situated at the Region of Sterea Ellada, north of Athens is a unique case of combined anthropogenic and geogenic origin of chromium contamination. The high concentrations of chromium and hexavalent chromium found at the groundwater system of Asopos have resulted in an increased public concern, since part of the groundwater is used for water abstraction for human consumption and most of it for irrigation purposes. The objective of this work was to organize all available data pertinent to the groundwater flow and chromium transport modeling of the area into maps, using geographical information systems, geotechnical graphics software and geostatistical techniques. The data was collected from various sources such as field campaigns, existing reports, data logs etc. One of the most important parameters that affect chromium transport is the geology of the area, thus a digitized geological map of the main formations encountered in the upper layers of the subsurface of the region was generated. In addition, geological boring logs for a large number of wells were created (using a geotechnical graphics software) and then combined in order to create vertical cross-sections, at various locations in the greater area, that define the geological characteristics of the deeper layers. The combination of the above defines the 3-D representation of the geological stratification of the physical system. Another parameter of interest in the area is the groundwater level and flow direction. In order to create a hydraulic head map of the area, the locations of more than 1000 shallow and deep wells that have been documented in the greater area of the Asopos river basin were defined using GIS software. A kriging technique was then applied to the available data in order to produce hydraulic head contours and consequently define the general groundwater flow direction. The same technique was applied for the generation of chromium concentration contours that provide an indication of the most problematic locations as well as a general chromium background level in the greater area.

in a karstified coastal system using density-dependent modelling and comparison with the sharp-interface approach. Hydrological Sciences Journal, 57 , 985-999. Abstract Saltwater intrusion is a naturally occurring phenomenon that is exacerbated significantly by excessive groundwater exploitation in coastal aquifers. In order to determine the extent of saltwater intrusion in a karstified coastal aquifer in Crete, Greece, a three-dimensional, density-dependent groundwater flow and transport model was developed and compared to the more traditional sharp-interface approach. The karstified medium was modelled using a combination of the equivalent porous medium approach (for lower-order fractures) and a discrete fracture approach (for the main fractures/faults). The model takes into consideration the geomorphologic characteristics of the karstic system, such as the depth and orientation of the fault network, and the diffusion phenomena associated with the variable densities of freshwater and saltwater-parameters that create a complex system, inducing uncertainty in the model. The model results showed that the orientation of the fractures, the pumping activity and the fluid density effects drive the seawater intrusion front asymmetrically inland.

The purpose of this study was to create a modeling management tool for the simulation of extreme flow events under current and future climatic conditions. This tool is a combination of different components and can be applied in complex hydrogeological river basins, where frequent flood and drought phenomena occur. The first component is the statistical analysis of the available hydro-meteorological data. Specifically, principal components analysis was performed in order to quantify the importance of the hydro-meteorological parameters that affect the generation of extreme events. The second component is a prediction-forecasting artificial neural network (ANN) model that simulates, accurately and efficiently, river flow on an hourly basis. This model is based on a methodology that attempts to resolve a very difficult problem related to the accurate estimation of extreme flows. For this purpose, the available measurements (5 years of hourly data) were divided in two subsets: one for t...

The overall goal of the research presented here is to develop, test and evaluate a computer assisted analysis algorithm that defines how to achieve an acceptable level of DNAPL source-location accuracy using the least possible number of water quality samples. The search strategy includes a stochastic groundwater flow and transport model that is used to calculate the concentration random field and its associated uncertainty. The model assumes a finite number of potential source locations. Each potential source location is associated with a weight determined using a discrete Choquet Integral that reflects our confidence that it is the true source location.

An integrated approach for monitoring the vertical transport of a solute into the subsurface by using a geophysical method and a simulation model is proposed and evaluated. A medium-scale (1m 3 ) laboratory tank experiment was constructed to represent a real subsurface system, where an olive-oil mill wastewater (OOMW) spill might occur. High-resolution cross-hole electrical resistivity tomography (ERT) was performed to monitor the OOMW transport. Time-lapse ERT images defined the spatial geometry of the interface between the contaminated and uncontaminated soil into the unsaturated and saturated zones. Knowing the subsurface characteristics, the finite element flow and transport model FEFLOW was used for simulating the contaminant movement, utilizing the ERT results as a surrogate for concentration measurements for the calibration process. A statistical analysis of the ERT measurements and the corresponding transport model results for various time steps showed a good agreement between them. In addition, a sensitivity analysis of the most important parameters of the simulation model (unsaturated flow, saturated flow and transport) was performed. This laboratory-scale study emphasizes that the combined use of geophysical and transportmodeling approaches can be useful for small-scale field applications where contaminant concentration measurements are scarce, provided that its transferability from laboratory to field conditions is investigated thoroughly.

Managed Aquifer Recharge (MAR) is becoming an increasingly attractive water management option, especially in semi-arid areas. Nevertheless, field studies on the fate and transport of priority substances, heavy metals and pharmaceutical products within the recharged aquifer are rare. Based on the above, the objective of this project is to study the hydrological conditions of the coastal aquifer of Ezousa (Cyprus) and its ability to attenuate pollutants. The Ezousa riverbed is a locally important aquifer used for a MAR project where treated effluent from the Paphos Waste Water Treatment Plant is recharged into the aquifer through a number of artificial ponds along the riverbed. Additionally, groundwater is pumped for irrigation purposes from wells located nearby. The hydrological conditions of the area are unique due to the construction of the Kannaviou dam in 2005 that reduced natural recharge of the Ezousa aquifer significantly, inducing the saltwater intrusion phenomenon. A three-dimensional finite element model of the area was constructed using the FEFLOW software to simulate the groundwater flow conditions and transport of Phosphorous and cooper in the subsurface from the recharge process. The model was calibrated using hydraulic head and chemical data for the time period of 2002-2011. The groundwater model was coupled with a geochemical model PHREEQC attempting to evaluate nitrate and Copper processes. Inverse modeling calculation was used to determine sets of moles transfers of phases that are attributed to the water composition change in groundwater between the mixture of natural groundwater and reclaimed wastewater and the final water composition.

Artificial Neural Networks (ANNs) have been lately used to predict the hydraulic head in well locations. In the present work, Particle Swarm Optimization (PSO) algorithm is used to train a feed-forward multi-layer ANN for the simulation of hydraulic head change at an observation well at the region of Agia, Chania, Greece. Three variants of the particle swarm optimization algorithm are considered, the classic one with the inertia weight improvement, PSO-TVAC and GLBest-PSO. The best performance was achieved by GLBest-PSO when implemented using field data from the region of interest, providing improved training results compared to the back propagation training algorithm. The trained ANN was subsequently used for midterm prediction of the hydraulic head as well as for the study of three climate change scenarios. Data time series were created using a stochastic weather generator, and the scenarios were examined for the period 2010-2020.

The simulation of the contaminant transport to determine the penetration of seawater front is extremely complex due to the uncertainty related to the depth and orientation of the fault network and also due to the diffusion phenomenon associated with the variable density between fresh and salt water. Furthermore, the pumping activity which takes place in the aquifer is variable upon demand and affects significantly the hydraulic characteristics of the aquifer during the simulation period. In this paper, using the FEFLOW numerical simulator a subsurface flow and contaminant transport model that estimates the penetration of seawater intrusion front for a karstified coastal aquifer in Crete, Greece was developed. The model takes into consideration the geomorphologic characteristics of the karstic system and the density-dependent groundwater flow. The model results showed that the connectivity of the fractures and the fluid density effects are important factors that drive the seawater intrusion front asymmetrically inland.

The contamination of the subsurface by organic compounds in the form of non-aqueous phase liquids (NAPLs) is among the most challenging environmental problems. Field investigations have shown that due to their low solubility and high interfacial tension, many NAPLs can persist in porous media for decades and even centuries. Among the more promising technologies for NAPL source zone remediation is in-situ cosolvent flushing which involves the injection of chemical agents for the enhanced solubilization and/or mobilization of the NAPL. In this study, we examined the significance of the cosolvent (ethanol) contact time on the DNAPL (Trichloroethylene-TCE) recovery from contaminated groundwater. Batch tests were first conducted to evaluate the operational parameters such as solubility, interfacial tension, and miscibility as a function of cosolvent content. Flushing experiments were performed using a two-dimensional tank (in the vertical plane with L= 80 cm, H=40 cm, and W=5 cm). The ef...

The accidental release of organic contaminants in the form of non-aqueous phase liquids (NAPLs) is a widespread and challenging environmental problem. Successful remediation of sites contaminated with NAPLs is essential for the protection of human health. An effective remediation method is the injection of chemical additives (cosolvents) together with water upgradient of the NAPL-contaminated area (flushing). The additives alter the physio-chemical properties of NAPLs, such as interfacial tension, and enhance their solubilities. Solubilized contaminants are carried downgradient and collected through recovery wells. The goal of the work presented here was the development of a numerical model that simulates accurately the experimental results of a DNAPL (TCE) flushing process using ethanol as a cosolvent. The effect of different ethanol contents (0%, 20% and 50%) on the remediation process were tested and evaluated. Experiments were conducted using a two-dimensional sand box, to allow for the impact of density variations on DNAPL mobility. The experimental results were used to calibrate a multiphase flow model based on a modified version of the UTCHEM simulator that includes an interfacial tension calculation. This IFT method enables UTCHEM to accurately simulate the process of ethanol concentration-dependent interfacial tension lowering.