A combined hydrologic and hydraulic modeling approach for testing efficiency of structural flood control measures

The necessity of estimating the degree and spatial extent of positive impacts with regard to protecting communities and properties through potential flood control projects can be considered one of the main reasons for performing flood modeling. This paper presents an overall systematic approach based on the simulation of some extreme event conditions, using a hydrological model to generate the resulting river flows and then using a hydraulic modeling exercise to decide upon floodplain evolution in the case-study area, Bostanli river basin, which has been under the threat of flooding for many years. The potential serviceability of the planned Bostanli Dam in the study area was examined by using the HEC-HMS and HEC-RAS modeling tools, both integrated with GIS functions for spatial operations. The results indicate that the dam construction as planned would have a somewhat positive impact as a potential flood control measure, since it seems to decrease the flood peaks of 68.9 and 158.7 m³/s (that would potentially be generated by 100- and 500-year storm events under current conditions) to 65.5 and 150.7 m³/s (when the dam is in operation), respectively. However, this seems to contribute little to the overall flood mitigation performance in the basin.     

Extension at the coast of the Makran subduction zone (Iran)

In the Makran subduction zone, earthquake focal mechanisms and geodetic data indicate that the deforming prism currently experiences N–S compression. However, palaeostress inversions performed on normal faults observed along the coast reveal local stress components consistent with N‐S extension. Previously proposed mechanisms such as gravitational collapse are not favoured by N–S compression and surface uplift. We propose that the observed kinematics result from transient stress reversals following large earthquakes. During the interseismic period (now), the region experiences N–S compression. However, following a large reverse rupture on the subduction interface, stresses in the inner wedge relax, enabling a brief period of extensional faulting before a compressive stress state is re‐established. This mechanism, also observed in other subduction zones, requires low overall stresses in the upper plate and that the margin ruptures in large megathrust earthquakes that result in nearly complete stress drops.     

An Overview of Thunderstorm-Related Research on the Atmospheric Electric Field, Schumann Resonances, Sprites, and the Ionosphere at Sopron, Hungary

This paper gives a resume of the papers written in English which (a) describe some of the recording instruments in use at the Nagycenk Observatory (NCK) since the International Geophysical Year (IGY 1957–1958) and up to the present time, (b) summarise the most important and different types of observations associated with thunderstorms which have been made there, and (c) discuss their various geophysical interpretations. The paper describes the main results which have been obtained in four areas of thunderstorm associated atmospheric and geospace science within the context of Earth system science. These relate to the following parameters of atmospheric electricity: the vertical electric potential gradient just above the Earth’s surface and the air–Earth current as well as the point discharge current, Schumann resonance (SR) signals of the Earth-ionosphere cavity at 8, 14 and 20 Hz, transient luminous events (TLEs), and some aspects of the behaviour of the ionosphere. Deductions from these data sets are concerned with the global lightning activity and the conductivity of the air, with diurnal, seasonal, annual and long-term variations of the SR amplitudes and resonant frequencies in terms of migrating thunderstorm centres, with transient SR excitations and with sprites and other TLEs, and with ionospheric disturbances. The paper closes with some thoughts on future research directions based on the observations at NCK and Sopron and the results achieved since the IGY.     

Influence of Temporal Variations in River Discharge, pH, Alkalinity and Ca on the Speciation and Concentration of Heavy Metals in Some Mining Polluted Rivers

Dissolved (dialysis in situ) and total concentrations ofCu, Zn, Cd and Al in eight mining polluted rivers in the Røros area, central Norway, were determinedby atomic absorption spectrometry (flame and graphite furnace) and compared to pH, Caconcentration and alkalinity through seasonal variations in river discharge. Totalconcentrations of the metals were highest during early spring flood and during summer andautumn rain episodes. Dissolved concentrations also increased as the spring floodproceeded, but small discharge peaks within this 2 month period as well as a considerableautumn flood episode appeared to lower rather than to raise the dissolved metal concentrations.Consequently the dissolved fractions of Zn, Cd and Al showed a significant negative correlationwith river discharge, and were low at the discharge peaks. Possibly high sediment concentrationsoccurring at high flood conditions more than counteracted desorption induced by pHdecrease, and led to decreased dissolved fractions through adsorption. Cu speciationon the other hand seemed to be more closely linked to pH. Alkalinity and Ca concentration,both assumed to protect aquatic life from metal pollution, were significantly lowerduring episodes with high Cu and Al total concentrations.     

Ranking of Placer Gold Prospects in Chile Through Analytic Hierarchy Process

Chile has a rich, but poorly known history of placer gold mining. At present, this sector is almost nonexistent and there are some restrictions for its revival: disperse and partial information on existing resources and limited technical expertise to assess the potential of placer gold mine sites. This paper presents the background, methodology and results of the prioritization process of known prospects of this kind in Chile. This research was part of a publicly funded project aimed to incentivize the development of this industry. The ranking was carried out using the analytic hierarchy process, which allowed to include different quantitative and qualitative variables related to the economic potential, technical aspects, contextual viability and socioeconomic factors in the analysis. The results show that, despite the increasing relevance of environmental and community issues in mining development, the business potential and the economic/technical aspects are the main factors in the early selection of a site to advance in exploration and development activities. Both variables represented around 40% and 37% of weights in the final selection, respectively. In contrast, contextual viability and local socioeconomic impacts only accounted for the remaining 23%. This study also shows that the inclusion of experts with different backgrounds in the process enriches the analysis and does not significantly distort the final outcome of the prioritization. Finally, the relevance of using MCDM tools when assessing the attractiveness of mine sites for their development is highlighted, particularly when public funds for subsequent exploration activities are committed.

     

SMOS reveals the signature of Indian Ocean Dipole events

The tropical Indian Ocean experiences an interannual mode of climatic variability, known as the Indian Ocean Dipole (IOD). The signature of this variability in ocean salinity is hypothesized based on modeling and assimilation studies, on account of scanty observations. Soil Moisture and Ocean Salinity (SMOS) satellite has been designed to take up the challenge of sea surface salinity remote sensing. We show that SMOS data can be used to infer the pattern of salinity variability linked with the IOD events. The core of maximum variability is located in the central tropical basin, south of the equator. This region is anomalously salty during the 2010 negative IOD event, and anomalously fresh during the 2011 positive IOD event. The peak-to-peak anomaly exceeds one salinity unit, between late 2010 and late 2011. In conjunction with other observational datasets, SMOS data allow us to draw the salt budget of the area. It turns out that the horizontal advection is the main driver of salinity anomalies. This finding is confirmed by the analysis of the outputs of a numerical model. This study shows that the advent of SMOS makes it feasible the quantitative assessment of the mechanisms of ocean surface salinity variability in the tropical basins, at interannual timescales.

     

External controls on the distribution,fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon,Cayo Coco (Cuba)

Active, carbonate‐mineralizing microbial mats flourish in a tropical, highly evaporative, marine‐fed lagoonal network to the south of Cayo Coco Island (Cuba). Hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies, a variable intensity of mineralization and a potential for preservation. In this study, the role of intrinsic (i.e. microbial) and extrinsic (i.e. physicochemical) controls on microbial mat development, mineralization and preservation was investigated. The network consists of lagoons, forming in the interdune depressions of a Pleistocene aeolian substratum; they developed due to a progressive increase in sea‐level since the Holocene. The hydrological budget in the Cayo Coco lagoonal network changes from west to east, increasing the salinity. This change progressively excludes grazers and increases the saturation index of carbonate minerals, favouring the development and mineralization of microbial mats in the easternmost lagoons. Detailed mapping of the easternmost lagoon shows four zones with different flooding regimes. The microbial activity in the mats was recorded using light–dark shifts in conjunction with microelectrode O₂ and HS^? profiles. High rates of O₂ production and consumption, in addition to substantial amounts of exopolymeric substances, are indicative of a potentially strong intrinsic control on mineralization. Seasonal, climate‐driven water fluctuations are key for mat development, mineralization, morphology and distribution. Microbial mats show no mineralization in the permanently submersed zone, and moderate mineralization in zones with alternating immersion and exposure. It is suggested that mineralization is also driven by water‐level fluctuations and evaporation. Mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation. The macrofabrics of the mats evolve from early colonizing Flat mats to complex Cerebroid or Terrace structures. The macrofabrics are influenced by the hydrodynamic regime: wind‐driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon. Other external drivers include: (i) storm events that either promote (for example, by bioclasts covering) or prevent (for example, by causing erosion) microbial mat preservation; and (ii) subsurface degassing, through mangrove roots and desiccation cracks covered by Flat mats (i.e. forming Hemispheroids and Cerebroidal structures). These findings provide in‐depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings.     

Salinisation de l’aquifère libre de la Chaouia côtière (Azemmour-Tnine Chtouka), Maroc

L’aquifère libre de la Chaouia côtière constitue un exemple des aquifères les plus exploités au Maroc. Ce travail est consacré à l’étude des processus de la salinisation des eaux souterraines par l’analyse physico-chimique de 39 puits répartis dans la zone. Deux types de faciès ont été révélés, l’un est chloruré-sodique dans la frange côtière ; l’autre faciès est de type chloruré bicarbonaté-calcique caractérisant les eaux exploitées dans les calcaires marneux du Crétacé. L’influence marine (aérosols et intrusion marine), la dissolution/précipitation de la roche aquifère et l’infiltration des eaux d’irrigation, sont parmi les causes de l’augmentation de la salinité des eaux souterraines, en plus de l’exploitation excessive de l’eau souterraine.     

Sediment transport pattern at the Barra Nova inlet, south Portugal: a conceptual model

The Barra Nova inlet, in south Portugal, is known to migrate progressively southeastwards under wave action. The morphodynamics of this system during a representative year suggests that this long-term evolution is dependent on a seasonal behavior of the tidal inlet which can be described through a three-stage model of post-storm, transition and extended fair-weather conditions. Processes involved in this evolution indicate that the historical migration of the Barra Nova is not dependent on the longshore drift forcing constricting the channel on the updrift coast, but rather on the adjustment of the system to a major erosion of the downdrift coast during short storm events.     

Slow and Fast Rotating Coronal Holes from Geomagnetic Indices

The evolution of the 27-day recurrence in the series of two solar indices (Wolf number WN and 10.7 cm radio flux F) and two geomagnetic indices (Dst and ζ, variance of the geomagnetic field recorded at a magnetic observatory) have been studied over the 1957 – 2007 time span. Spectral energies contained in two period domains (25 – 27.3 and 27.3 – 31 days), designated as E ₁ and E ₂, have been computed. Whereas the evolution of E ₁ is the same for the four indices, that of E ₂ is essentially different for WN and F on the one hand, Dst and ζ on the other hand. Some general conclusions on the dynamics of the solar outer layers are inferred from these results. First the solar activity, as measured by WN, and when averaged over a few years, evolves in the same way whatever the latitude. Second, two families of coronal holes (CHs) are identified; the rapidly and the slowly rotating CHs evolve quite differently.