Structural and depositional controls on Plio‐Pleistocene submarine channel geometry (Taranaki Basin,New Zealand)

High‐quality 3D seismic data are used to investigate the effect of the Parihaka Fault on the geometry of submarine channels in Northern Graben of the Taranaki Basin, New Zealand. The Parihaka Fault comprises of four segments (S1–S4) with variable displacements. As part of the Plio‐Pleistocene Giant Foresets Formation, the older Channel Complex Systems 1 and 2 reveal a two‐stage evolution: (a) a syn‐tectonic depositional stage with channels incising the slope during early fault growth (ca. 4.5 Ma) and (b) a stage of sediment bypass (ca. 3 Ma) leading to the infill of hanging‐wall depocentres. The Channel Complex System 3 is syn‐tectonic relative to segment S3 and was formed at ca. 2.5 Ma. We show that the successive generation of new fault segments towards the north controlled the formation of depocentres in the study area. This occurred in association to rotation and uplift of the footwall block of the Parihaka Fault and subsidence of its hanging‐wall block, with fault activity controlling the orientation of channel systems. As a result, we observe three drainage types in the study area: oblique, transverse and parallel to the Parihaka Fault. This work is important as it shows that relay zones separating the Parihaka Fault segments had limited influence on the geometry and location of channel systems. Submarine channels were diverted from their original courses close to the Parihaka Fault and flowed transversally to fault segments instead of running through relay ramps, contrasting to what is often recorded in the literature. A plausible explanation for such a discrepancy relates to rapid progradation of the Giant Foresets Formation during the Plio‐Pleistocene, with channel complexes becoming less confined, favouring footwall incision and basinward deposition of submarine fans.     

Overwash vulnerability assessment based on long-term washover evolution

An integrated methodology for evaluation of overwash vulnerability is developed with respect to the historical washover evolution of a barrier island system. Three different aspects of overwash are addressed in the vulnerability indices developed: overwashed shoreline ratio, maximum overwash intrusion recurrence, and complete barrier overwash. The indices were applied to the barriers in the Ria Formosa system in Southern Portugal using an aerial photography catalogue covering the period 1947–2001. Historical trends of washover evolution were observed to be different between the barriers analysed, but generally, there was a decrease in washover number and dimensions throughout the analysed period. The final overwash diagnostic obtained allowed an integrated overwash vulnerability rating to be defined for each barrier, with vulnerabilities ranging from low to extreme. The methodology has produced results that may assist coastal managers with information concerning barrier island system overwash hazard, define the temporal and geographical distributions of overwash, and provide indications as to where overwash is most likely to occur in the future.     

Geographic information technology usage in developing countries – A case study in Mozambique

ABSTRACT

Geographic information technologies (GIT) have matured, have become pervasive throughout many types of organizations over recent decades and gained a wide range of attention in diverse sectors of society. The goal of this paper is to identify the main drivers and uses of GIT in organizations and to give an overview of GIT uses in developing countries with a focus on a case study developed for Mozambique by analyzing the results of a survey of 123 Mozambican organizations that are current GIT users. The results show that the main drivers behind are compatibility, complexity, competitive pressure, donor pressure, government policy, intention to adopt, innovation, relative advantage, security, and technology competence. Organizations of the public and private sectors use GIT for customer/resource/risk management, decision support, education, research, monitoring, prediction, simulation, suitability analysis, sustainability, use and access.     

Seismic vulnerability assessment of historical urban centres: case study of the old city centre in Seixal, Portugal

The seismic vulnerability assessment of old masonry buildings is essential not only to buildings with recognised historical and heritage value but also to ordinary residential masonry buildings. This paper approaches the seismic vulnerability assessment of masonry buildings by applying a simplified methodology to the old city centre of Seixal in Portugal. The methodology adopted in this study was based on a vulnerability index used for the evaluation of damage and the study of loss scenarios on a large scale. Over 500 buildings were assessed using this methodology, and the results were analysed using an integrated Geographical Information System tool. The integration of the vulnerability and loss results could allow city councils or regional authorities to plan interventions based on a global view of the site under analysis, leading to more accurate and comprehensive risk mitigation strategies that support the requirements of safety and emergency planning.     

Embankments on Soft Soil Reinforced with Stone Columns: Numerical Analysis and Proposal of a New Design Method

A parametric study of an embankment on soft soils reinforced with stone columns is performed using a computer program based on the finite element method. The cylindrical unit cell formulation is used by modeling one column and its surrounding soft soil with confined axisymmetric behaviour. The computer program incorporates the Biot consolidation theory (coupled formulation of the flow and equilibrium equations) with constitutive relations simulated by the p–q–θ critical state model. The following parameters are analysed: the replacement area ratio, the deformability of the column material, the thickness of the soft soil, the deformability of the fill and the friction angle of the column material. Based on the results of this study, a new design method is proposed, relating the settlement improvement factor to the two factors that revealed major influence: the replacement area ratio and the ratio between the deformability of the soft soil and the deformability of the column material.     

Semantic Expansion of Geographic Web Queries Based on Natural Language Positioning Expressions

The need for better Web search tools is getting increasing attention nowadays. About 20% of the queries currently submitted to search engines include geographic references. Thus, it is particularly important to work with the semantics of such queries, both by understanding the terminology and by recognizing geographic references in natural language text. In this paper, we explore the use of natural language expressions, which we call positioning expressions, to perform geographic searches on the Web, without resorting to geocoded data or gazetteers. Such positioning expressions denote the location of a subject of interest with respect to a landmark. Our approach leads to a query expansion technique that can be explored by virtually any keyword‐based search engine. Results obtained in our experiments show an expressive improvement over the traditional keyword‐based search and a potential path for tackling many kinds of common geographic queries.     

Integrated modelling for water quality management in a eutrophic reservoir in south-eastern Portugal

The Enxoé Reservoir was built in 1998. Since 2000, it has exhibited frequent high chlorophyll-a concentrations, reaching a geometric mean three times higher than the national limit for eutrophication, presenting the reservoir with the highest eutrophic state in Portugal. Toxic algal blooms have also often been observed, which pose serious challenges to water managers, as the reservoir is used for potable water production (25,000 inhabitants). The objective of this study was to implement a reservoir model (CE-QUAL-W2), with inputs from a watershed model (SWAT), in order to represent the actual reservoir state and to test management measures to reduce its trophic level and algal bloom concentration peaks. The integrated model was used to depict the origin of its trophic status. Simulations were also compared to measured data at the reservoir surface (water level, nitrate, orthophosphate, suspended solids, and oxygen) and in water profiles (temperature, oxygen). The model was able to represent stratification and thermocline depths, as well as the actual chlorophyll-a and dissolved oxygen concentrations. The model results showed that internal phosphorus load from deposited sediments was an important factor in fuelling the algal blooms. This process occurs predominantly in summer, when stratification takes place and aeration is reduced, promoting anoxic conditions in the bottom waters. Since the reservoir is relatively shallow (average 5 m), released phosphorus is then easily able to reach the photic zone in most parts of the reservoir, where it is consumed. Different management scenarios were tested, suggesting that a mesotrophic level could barely be reached and maintained simply by reducing the nutrient loads (both external and internal). It is suggested that only an increase in the reservoir dam height could produce a mesotrophic level, averting anoxia by blocking the release of phosphorus from sediments to the photic zone. Future work should focus on a cost–benefit analysis to test the feasibility of each of the proposed scenarios, taking advantage of the integration strategy to assess where in the watershed load reductions would be most effective.     

Free-Phase Gas Detection in Groundwater Wells via Water Pressure and Continuous Field Parameters

Detection of free-phase gas (FPG) in groundwater wells is critical for accurate assessment of dissolved gas concentrations and the occurrence of FPG in the subsurface, with consequent implications for understanding groundwater contamination and greenhouse gas emissions. However, identifying FPG is challenging during routine groundwater monitoring and there is poor agreement on the best approach to detect the occurrence of FPG in groundwater. In this study, laboratory experiments in a water column were designed to mimic nonflowing and flowing conditions in a groundwater well to evaluate how the presence of FPG affects water pressure and commonly used continuous field parameters. The laboratory results were extrapolated to interpret field data at an abandoned exploration well with episodic release of free-gas CO₂. The FPG effect on water pressure varied between flowing and nonflowing wells, and depending on whether the FPG was above or below the sensor. Electrical conductivity values were decreased and/or behaved erratically when FPG was present in the water column. Findings from this study have shown that the combined measurement of water pressure, electrical conductivity, and total dissolved gas pressure can provide information about the occurrence of FPG in groundwater wells. Measurement of these parameters at different depths can also provide information about relative depths and amounts of FPG within the well water column. This approach can be used for long-term monitoring of groundwater gases, managing gas-locking in production wells with gassy groundwater, and measuring fugitive greenhouse gas emissions from groundwater wells.