Modelling the behaviour of oil spills in ice‐infested waters

Abstract

This paper describes methodologies developed for predicting the drift and spread of oil spills in ice‐infested waters. Particular emphasis is placed on oil spills in medium and high ice concentrations. For ice concentrations greater than about 30%, the oil is found to drift with the ice. Empirical methods are used to determine the spread of oil in ice of different concentrations. The study showed that the equilibrium oil thickness in slush or brash (broken) ice is nearly 4 times that on cold water, which is itself very different from that on warm water. Comparisons with limited available data show good agreement.     

Detrital provenance of the Grenvillian Oaxacan Complex,southern Mexico: a zircon perspective

The Oaxacan Complex is the largest exposure of Grenvillian-age rocks in Mexico, constituting the backbone of the Oaxaquia microcontinent. Whereas the main rock-forming events were previously established at 1,150–1,200 Ma (charnockite–syenite–gabbros), 1,020 Ma (AMCG suite), 990 Ma (granulite-facies metamorphism), and ca. 970 Ma post-tectonic pegmatites, no data are yet available to establish provenance links with other Grenville-age terranes. In this work, we studied detrital zircons belonging to 12 samples, all metamorphosed under granulite facies but variably affected by retrogression. Laser ablation inductively coupled plasma mass spectrometry U–Pb geochronology was employed on selected zircons to determine their crystallization age and geochemistry. The results of the analysis of about 100 crystals per sample show that the studied zircons range between ca. 940 and 1,400 Ma, with only three samples having zircons between 1,400 and 1,600 Ma, and only one showing older zircons up to ca. 1,775 Ma. Whereas some of the slightly discordant (1–5 %) zircons in several samples show ages younger than the granulite metamorphism (probably as a result of Pb loss), and thus a disturbed geochemical pattern (abnormal enrichment in LREE, decreasing HREE), a few metamorphic zircons show flat and depleted HREE patterns, contrasting with the igneous pattern of older zircons (positive Ce anomaly, negative Eu anomaly, enriched HREE pattern). The main distributions observed using the kernel density estimator diagrams fall in the range 975–995 Ma (six samples), 1,100 Ma (four samples) and 1,120–1,170 Ma (six samples). Only the southernmost sample shows a marked peak at ca. 1,400 Ma. The application of the Kolmogorov–Smirnov (K–S) statistical test to the studied samples and particularly the comparison of obtained P values yield interesting similarities. Overall, two sample groups show internal similarities, i.e., they may belong to the same source area, whereas only one sample is dissimilar, failing to pass the K–S test. Comparison of these data with the timing of comparable events in the Sveconorwegian orogens, the Sunsas and Rondonia-San Ignacio belts of Amazonia, and some of the Precambrian massifs cropping out in the Andes help to constrain possible Mesoproterozoic conjugate margins of Oaxaquia.     

Fostering assumption-based stress-test thinking in managing groundwater systems: learning to avoid failures due to basic dynamics

Sustainable groundwater resource management can only be achieved if planning processes address the basic dynamics of the groundwater system. Conceptual and distributed groundwater models do not necessarily translate into an understanding of how a plan might operate in reality. Prompted by Australian experiences, ‘iterative closed-question modelling’ has been used to develop a process of iterative dialogue about management options, objectives and knowledge. Simple hypothetical models of basic system dynamics that satisfy agreed assumptions are used to stress-test the ability of a proposed management plan to achieve desired future conditions. Participants learn from models in which a plan succeeds and fails, updating their assumptions, expectations or plan. Their new understanding is tested against further hypothetical models. The models act as intellectual devices that confront users with new scenarios to discuss. This theoretical approach is illustrated using simple one and two-cell groundwater models that convey basic notions of capture and spatial impacts of pumping. Simple extensions can address uncertain climate, managed-aquifer recharge and alternate water sources. Having learnt to address the dynamics captured by these models, participants may be better placed to address local conditions and develop more effective arrangements to achieve management outcomes.     

Groundwater contamination assessment in Al-Quwy’yia area of central Saudi Arabia using transient electromagnetic and 2D electrical resistivity tomography

Groundwater contamination is one of the most significant problems in arid countries. Al-Quwiy’yia region is an example of an area where the groundwater is contaminated as a result of infiltration of waste water in low-lying areas adjacent to inhabited zones. Such contamination poses significant environmental threats for the surrounding environment and groundwater. Surface observations and spatial distribution of contamination observed in the shallow aquifer indicate that the main contamination sources were from sewage as well as from waste water dumping. However, the main source of water supply for the whole area is groundwater abstracted from the relatively shallow aquifer. Therefore, the transient electromagnetic method (TEM) and 2D electrical resistivity tomography (2D ERT) have been applied close to the waste water dump site to characterize the response of pollution plumes. Both of these geoelectrical techniques are sensitive to electrical conductivity as well as to other physical properties, which are greatly influenced by the polluted groundwater. Therefore, it is possible to profile the contamination plumes, both vertically and horizontally, in the vicinity of the measured stations. The ERT profiles gave detailed information about the lateral distribution of the contaminated groundwater, whereas the TEM demonstrated the vertical extensions.     

The impact of subsurface geological structure on the groundwater occurrence using geophysical techniques in wadi El Kallabiyyah and wadi As Sabil,East Esna,Eastern Desert,Egypt

The present study aims to explain some hydrogeological problems that are related to geological setting in two wadis: El Kallabiyyah and As Sabil East Esna. For this purpose, land magnetic, vertical electrical soundings, and two-dimensional electrical resistivity imaging profiles were measured. The lithological succession comprises Upper Cretaceous to Quaternary deposits that rest on a Precambrian basement rock. The results of the interpretation of the land magnetic measurements in wadi El Kallabiyyah represent the depth to the basement rock which ranges from 260 to 660 m and increases towards the northeast trend, but in wadi As Sabil, there is a large basin at the center of the wadi with the recorded depth to the basement reaching 1,300 m due to the effect of two normal faults (F1 and F2). The results of the interpretation of the vertical electrical sounding and two-dimensional imaging confirmed the presence of these faults in wadi As Sabil. The results of the geoelectrical measurements in wadi El Kallabiyyah represented the water-bearing layer at the third unit that consists of sands, gravels, boulders, and clays. The presence of clay will affect the potentiality of a drilled well. For wadi As Sabil, the results of geoelectrical measurements led to the lower part of the second unit which acts as a water-bearing layer that consists of sands, boulders, gravels, and clays. It can be concluded that the best site for drilling wells in wadi El Kallabiyyah is at vertical electrical sounding no.5 with a total depth of not less than 230 m. In wadi As Sabil, the drilled wells must be concentrated at the center and the downstream.     

Hydrogeophysical investigations on the Pleistocene aquifer,Kom Hamada area,West Nile Delta,Egypt

Hydrogeophysical investigations of the Pleistocene aquifer at the Kom Hamada area, Egypt, have been conducted to determine the characteristics of groundwater. The main water-bearing formations in the study area are composed of Quaternary deposits. Water samples were taken and chemically analyzed at 29 sites. The constructed iso-salinity contour map of the study area showed an increase in salinity from 451.75 mg/l at eastern parts to 1,091.85 mg/l at western parts. The groundwater of the study area showed a hydrochemical evolution from Ca–HCO₃ at the eastern side to Na–Cl at the western side. Some of groundwater constituents have high concentration values exceeding the safe limit for drinking. Eighteen vertical electrical soundings (VES) were conducted in the study area. These soundings were conducted near existing wells to obtain layer parameters of the various penetrated layers and to calculate the petrophysical characteristics of the aquifers. The resistivity of the first water-bearing layer ranges between 34 and 47 Ω m. The thickness of this layer ranges between 26 and 79 m. This layer represents the first aquifer, where it is followed by another water-bearing layer with resistivity ranges between 29 and 62 Ω m and extends downward. The two aquifers are hydraulically connected. Variation of the resistivities of these two water-bearing layers is mainly due to the lithological variation. The resistivity values along with the TDS values of the two water-bearing layers indicate fresh to brackish water types.     

Application of spectral analysis technique on ground magnetic data to calculate the Curie depth point of the eastern shore of the Gulf of Suez,Egypt

The bottom of the magnetized crust determined from the spectral analysis of magnetic anomaly is interpreted as a level of the Curie point isotherm. A spectral analysis technique was used to estimate the depth of the magnetic anomalies sources (Curie point depth analysis) of the eastern shore of the Gulf of Suez, Egypt. The depth to the tops and centers of the magnetic anomalies are calculated by azimuthally averaged power spectrum method for the whole area. The results obtained suggests from this study showed that the average depth to the top of the crustal block ranges between 1.15 and 1.9 km, whereas the average depth to the center of the deepest crustal block ranges between 9.1 and 12.7 km. Curie point depths in the study area range between 14.5 km in the northwestern part of the study area and 26 km in the southeastern part of the study area. The results imply a high geothermal gradient (34.7 °C/km) and corresponding high heat flow value (72.87 mW/m²) in the northwestern part of the study area. The southeastern part of the study area displays a low geothermal gradient (24.26 °C/km) and low heat flow value (50.9 mW/m²). These results are consistent with the existence of the possible promising geothermal reservoir in the eastern shore of the Gulf of Suez especially at Hammam Faraun area.     

Surface soil assessment in the Ubhur area,north of Jeddah,western Saudi Arabia,using a multichannel analysis of surface waves method

Ten boreholes drilled in Ubhur area up to the depth of bedrock indicted the shallow depth of bedrock where the average depth ranges between 10 and 15 m. The standard penetration test N-values of these boreholes were measured and averaged. Based on N-values to the depth of bedrock, Ubhur area can be classified as site class C and D. Multichannel analysis of surface waves technique has been applied along seventy six profiles using 24-channel geophone array and 4.5Hz vertical geophones with 1m geophone spacing and sledgehammer and/or weight drop as seismic energy sources. Values of shear wave velocity to 30 m are calculated and then averaged (Vs30) where it ranges between 310.08 m/s and 1139.8 m/s. Therefore, Ubhur area can be classified into site class B, C and D based on site classification of the national earthquake hazards reduction program (NEHRP) recommendations. Accordingly, the greatest part of the study area falls in site class C while class B and D covered limited areas in the western and the eastern parts respectively. Depending on the shallow depth of bedrock in the study area, the Vs30 parameter is not applicable in the study area so the average values of Vs for the soil thickness, excluding the bedrock, have been calculated and mapped for site class C and D only. So Vs30 approach is not applicable for areas with shallow depth of bedrock which gives higher classification.     

Earthquake imprints on a lacustrine deltaic system: The Kürk Delta along the East Anatolian Fault (Turkey)

Deltas contain sedimentary records that are not only indicative of water‐level changes, but also particularly sensitive to earthquake shaking typically resulting in soft‐sediment‐deformation structures. The Kürk lacustrine delta lies at the south‐western extremity of Lake Hazar in eastern Turkey and is adjacent to the seismogenic East Anatolian Fault, which has generated earthquakes of magnitude 7. This study re‐evaluates water‐level changes and earthquake shaking that have affected the Kürk Delta, combining geophysical data (seismic‐reflection profiles and side‐scan sonar), remote sensing images, historical data, onland outcrops and offshore coring. The history of water‐level changes provides a temporal framework for the depositional record. In addition to the common soft‐sediment deformation documented previously, onland outcrops reveal a record of deformation (fracturing, tilt and clastic dykes) linked to large earthquake‐induced liquefactions and lateral spreading. The recurrent liquefaction structures can be used to obtain a palaeoseismological record. Five event horizons were identified that could be linked to historical earthquakes occurring in the last 1000 years along the East Anatolian Fault. Sedimentary cores sampling the most recent subaqueous sedimentation revealed the occurrence of another type of earthquake indicator. Based on radionuclide dating (¹³⁷Cs and ²¹⁰Pb), two major sedimentary events were attributed to the ad 1874 to 1875 East Anatolian Fault earthquake sequence. Their sedimentological characteristics were determined by X‐ray imagery, X‐ray diffraction, loss‐on‐ignition, grain‐size distribution and geophysical measurements. The events are interpreted to be hyperpycnal deposits linked to post‐seismic sediment reworking of earthquake‐triggered landslides.     

Extraction and accuracy assessment of high-resolution DEM and derived orthoimages from ALOS-PRISM data over Sahel-Doukkala (Morocco)

In Sahel-Doukkala, which is characterized by lands of a relatively low relief, global DEMs and DEMs generated from digitizing topographic maps, have been the primary source of several multidisciplinary researches. Although these products present a great value of the conducted research, the level of the given accuracy is not sufficient enough for detailed geospatial analysis. These requirements led us to generate a high-resolution DEM as an alternative of available global DEMs or/and DEMs generated from digitizing topographic maps. In this study, we present a workflow to extract high-resolution DEM at 5 m resolution and derived orthoimages from ALOS-PRISM data over Sahel-Doukkala, through photogrammetric techniques, using a variation of GCPs obtained from topographic maps at scale 1:25,000. The accuracy of the generated products is reported according to NSSDA standards. Using ten GCPs, a PRISM-DEM with 3.88 m vertical accuracy and 11.60 m horizontal accuracy, both at 95% confidence level is obtained. This DEM will serve as base dataset for further detailed geospatial analysis and mapping applications in order to identify the relationship between surface parameters and groundwater, and also to assess and understand all factors influencing the development of karst landscapes and consequently subsurface stability in the investigated area.