Modeling approaches and strategies for data-scarce aquifers: example of the Dar es Salaam aquifer in Tanzania

Management of groundwater resources can be improved by using groundwater models to perform risk analyses and to improve development strategies, but a lack of extensive basic data often limits the implementation of sophisticated models. Dar es Salaam in Tanzania is an example of a city where increasing groundwater use in a Pleistocene aquifer is causing groundwater-related problems such as saline intrusion along the coastline, lowering of water-table levels, and contamination of pumping wells. The lack of a water-level monitoring network introduces a problem for basic data collection and model calibration and validation. As a replacement, local water-supply wells were used for measuring groundwater depth, and well-top heights were estimated from a regional digital elevation model to recalculate water depths to hydraulic heads. These were used to draw a regional piezometric map. Hydraulic parameters were estimated from short-time pumping tests in the local wells, but variation in hydraulic conductivity was attributed to uncertainty in well characteristics (information often unavailable) and not to aquifer heterogeneity. A MODFLOW model was calibrated with a homogeneous hydraulic conductivity field and a sensitivity analysis between the conductivity and aquifer recharge showed that average annual recharge will likely be in the range 80–100 mm/year.     

Convergence acceleration of iterative sequences for equilibrium chemistry computations

Computational Geosciences - The modeling of thermodynamic equilibria leads to complex nonlinear chemical systems which are often solved with the Newton-Raphson method. But this resolution can lead...     

A geomorphological approach to sustainable planning and management of the coastal zone of Kuwait

The coastal zone in Kuwait has been under a considerable pressure from conflicting land uses since the early 1960s, as well as from the destruction and oil pollution caused by the Gulf War. To avoid further damage and to protect the coastal heritage it is essential to adopt an environmentally sustainable management process. This paper shows how the study of coastal geomorphology can provide a sound basis for sustainable planning and management. Based on coastal landforms, sediments and processes, the coastline of Kuwait was divided into nine geomorphic zones. These zones were grouped into two main geomorphic provinces. The northern province is marked by extensive muddy intertidal flats and dominated by a depositional and low-energy environment. The southern geomorphic province is characterised by relatively steep beach profiles, rocky/sandy tidal flats and a moderate to high-energy environment. The study has demonstrated that pollution, benthic ecology and other environmental conditions of the coast are a function of coastline geomorphology, sedimentology and related processes. The geomorphological information was used to determine the coastal vulnerability and to assess the environmental impacts of development projects and other human activities. Several strategies were outlined to integrate the geomorphic approach into the management of the coastal resources.     

The microstructural properties and deformation environments of the Kugarchi folded complex,Southern Urals

The Kugarchi folded complex is located on the western slope of the Southern Urals; it is a region of complex disharmonic folding in the Lower Carboniferous limestones. We revealed and studied two systems of mineral veins and accompanying veinlets in limestones. The microstructural analysis was used to recognize several deformation stages and orientations of the principal strain directions. This folded complex is interpreted to have formed under conditions close to uniaxial compression accompanied by a progressive change in the extensional strain direction from vertical to horizontal.     

Impact of rock-water interactions and recharge on water resources quality of the Agadir-Essaouira basin,southwestern Morocco

The Agadir-Essaouira area in the occidental High Atlas Mountains of Morocco is characterized by a semi-arid climate. The scarcity and quality of water resources, exacerbated by long drought periods, constitute a major problem for a sustainable development of this region. Groundwater resources of carbonate units within Jurassic and Cretaceous aquifers are requested for drinking and irrigation purposes. In this study, we collected 84 samples from wells, boreholes, springs, and rivers. Hydrochemical and isotopic data were used to examine the mineralization and origin of water, which control groundwater quality. The chemical composition of water seems to be controlled by water-rock interactions, such as dissolution of carbonates (calcite and dolomite), weathering of gypsum, as well as ion exchange processes, which explain the observed variability. Stable isotopes results show that groundwater from the mainly marly Cretaceous aquifer are submitted to an evaporation effect, while samples from the chiefly calcareous Jurassic aquifer indicate a meteoric origin, due to a rapid infiltration of recharge runoff through the karstic outcrops. The low values of δ¹⁸O and δ²H suggest a local recharge from areas with elevations ranging from 400 to 1200 m for the Cretaceous aquifer and from 800 to 1500 m for the Jurassic units.     

Estimation of unrecorded groundwater abstractions in Jordan through regional groundwater modelling

Jordan suffers from water scarcity and groundwater covers the majority of Jordan’s water supply. Therefore, there is an urgent need to manage this resource conscientiously. A regional numerical groundwater flow model, developed as part of a decision support system for the country of Jordan, allows for quantification of the overexploitation of groundwater resources and enables determination of the extent of unrecorded agricultural groundwater abstraction. Groundwater in Jordan is abstracted from three main aquifers partly separated by aquitards. With updated geological, structural, and hydrogeological data available in the country, a regional numerical groundwater flow model for the whole of Jordan and the southernmost part of Syria was developed using MODFLOW. It was first calibrated for a steady-state condition using data from the 1960s, when groundwater abstraction was negligible. After transient calibration using groundwater level measurements from all aquifers, model results reproduce the large groundwater-level declines experienced in the last decades, which have led to the drying out of numerous springs. They show a reversal of groundwater flow directions in some regions, due to over-abstraction, and demonstrate that documented abstractions are not sufficient to cause the observed groundwater-level decline. Only after considering irrigation water demand derived from remote sensing data, the model is able to simulate these declines. Illegal abstractions can be quantified and predictive scenarios show the potential impact of different management strategies on future groundwater resources.

     

Models of the REE distribution in the black shale Bazhenov Formation of the West Siberian marine basin,Russia

Rare-earth elements abundance in black shales of the Upper Jurassic (Tithonian Stage)–Lower Cretaceous (Berriassian Stage) Bazhenov Formation is discussed. This formation is the principal oil source rocks of West Siberia. The deposits within the formation can be subdivided into two main marine groups: (a) moderately hemipelagic deposits (clayey-siliceous, including phosphatic and carbonate rocks) and low-density distal clayey turbidites (argillites), both are considered as normal and (b) silty argillites and clayey-silt rocks, which are channel deposits and considered as anomalous. The hemipelagic rocks of normal sections, which are enriched in the rare-earth elements (REE), accumulated under both slow rates of sedimentation (clayey-siliceous rocks) and faster rates of sedimentation (argillites). The channel deposits of anomalous sections, which are impoverished in the REE, accumulated exclusively under fast rates of sedimentation.Within the hemipelagic group the rate of sedimentation of the argillites was faster than of the clayey-siliceous rocks, but the REE concentration in the former rocks (140.4 ppm) is higher than in the latter group (97.4 ppm). The argillites are more than twice enriched in clayey material than clayey-siliceous rocks. It is likely that the clay fraction was the main carrier of REE in these rocks. In the channel group of rocks, the REE abundance in clayey-silt rocks (21.2 ppm) is lower than in the silty argillite (84.6 ppm), in which the clay content is elevated.With respect to redox potential the Bazhenov Formation rocks can be subdivided further into three groups, based on the degree of pyritization index (DOP): (1) the highly reducing clayey-siliceous rocks of normal sections, with high DOP; (2) the substantially reducing argillites and carbonate rocks of normal sections, with intermediate DOP; (3) the moderately reducing rocks of anomalous sections with low DOP. The rocks with the high DOP (group 1) are characterized by ΣLREE/Σ(M+H)REE ratios between 7.37 and 7.5, whereas the rocks with the lower DOP (group 2 and 3) are characterized by ΣLREE/Σ(M+H)REE ratios between 12.8 and 13.5. Negative Ce anomalies are either small or absent in all deposits, which is typical for reducing conditions.Thus, the Bazhenov Formation exemplifies the complex depositional conditions that influence the REE concentration in black shale. However, it is this very complexity that has contributed to the development of six separate depositional models (REE contents in ppm are given in brackets). (1) Phosphatic clayey-siliceous rocks of normal sections (367.95); (2) argillites of normal sections (130.73); (3) clayey-siliceous rocks of normal sections (85.97); (4) carbonate rocks, largely dolomites of normal sections (23.23); (5) silty argillites of anomalous sections (78.7) and (6) clayey-silt rocks of anomalous sections (19.66).     

‘Unionising’ the new spaces of the new economy? Alternative labour organising in India’s IT Enabled Services-Business Process Outsourcing industry

This paper explores the lived experiences and aspirational social constructions of call centre work and employment in India’s high profile IT Enabled Services-Business Process Outsourcing (ITES-BPO) industry; the ways in which they differ from those previously documented amongst call centre workers in the Global North (specifically the UK); and the consequences of that geographical reconfiguration of offshored call centre work for the replicability in India of workplace collective bargaining strategies successfully developed in some UK call centres. These issues are analysed using new empirical evidence from a regional survey of 511 non-unionised ITES-BPO workers and 42 in-depth interviews in India’s National Capital Region. Based on this analysis, the paper then discusses the operation, outcomes and ongoing challenges faced by the newly formed ‘Union for ITES Professionals’ (UNITES Pro) in developing an alternative occupational organising model better suited to the particular needs, motivations and preferences of India’s young, mobile, call centre workers. The empirical analysis presented in the paper is located, therefore, within wider debates on the role of geographical context in shaping possibilities for organising white-collar service workers at different ends of global service chains in the new economy.     

Effects of rainfall on soil–structure system frequency: Examples based on poroelasticity and a comparison with full-scale measurements

In this paper, a simple two-dimensional soil–structure interaction model, based on Biot's theory of wave propagation in fluid saturated porous media, is used to explain the observed increase of the apparent frequencies of Millikan library in Pasadena, California, during heavy rainfall and recovery within days after the rain. These variations have been measured for small amplitude response (to microtremors and wind excitation), for which Biot's linear theory is valid. The postulated hypothesis is that the observed increases in frequency are due to the water saturation of the soil. The theoretical model used to explore this hypothesis consists of a shear wall supported by a circular foundation embedded in a poroelastic half-space. This rigid foundation model may be appropriate only for the NS response of Millikan library. This paper presents results for the foundation stiffness, and for the system response for model parameters similar to those for Millikan library (located on alluvium with shear wave velocity of about 300 m/s). The foundation impedance matrix, foundation input motion and system response are compared for dry and fully saturated half-space, with permeable and impermeable foundation. The results show that for embedded foundations, the effects of saturation on the horizontal foundation stiffness are as significant as for the vertical stiffness, contrary to what has been known for surface foundations investigated by other authors. Further, the results suggest a 1–2% increase in system frequency of the first two modes of vibration, depending on the drainage condition along the foundation–soil interface. Such increases agree qualitatively with the observations.     

Everyday effects, practices and causal mechanisms of ‘cultural embeddedness’: Learning from Utah’s high tech regional economy

In recent years, economic geographers have drawn extensively upon notions of ‘cultural embeddedness’ to explore how spatially variable sets of cultural conventions, norms, values and beliefs shape firms’ innovative performance in dynamic regional economies. However, our understanding of these causal links remains partial, reinforced by an ‘over-territorialised’ conception of cultural embeddedness which sidelines the role of institutional actors operating outside and across the boundaries of ‘the local’. So motivated, this paper offers a theoretically-informed - and theoretically informing - empirical analysis of the high tech regional economy in Salt Lake City, Utah to explore the everyday causal mechanisms, practices and processes - both local and extra-local - through which firms’ cultural embedding within the region is manifested, performed and (un)intentionally (re)produced. In so doing, this paper aims to further our understanding of the constitutive entanglement and complex interweaving of cultural/economic practices, and to contribute to the development of an in-depth empirical corpus of work which compliments the exciting conceptual developments that have largely dominated cultural economic geography over the last decade.