Potential leakage paths at the dams constructed on karst terrains in Iran

Water leakage has been reported from several dams constructed on karst terrains in Iran. In this study the main reasons for dam leakage were identified by studying ten examples, the Lar, Kowsar, Seymareh, Tangab, and Shah-Ghasem dams with considerable leakage, and the Karun I, Karun III, Karun IV, Salman-Farsi, and Marun dams with negligible leakage. The “Potential Leakage Passage (PLP)” is defined as those parts of a karst aquifer which transfer reservoir water to downstream. The most important control on leakage is in the narrowest part of the PLP, the “bottleneck” that depends mainly on the geological settings. At the dams with negligible leakage, sealing of the PLPs was found to be technologically and economically feasible by connecting all the edges of grout curtain to the natural impermeable barriers. In the cases of dams with considerable leakage, wider PLPs were not completely sealed and the installed grout curtain did not fully connect to the impermeable rock. To reduce the risk of leakage and inform effective design of grout curtains, the characteristics of the PLP should be determined during the initial stage of dam studies, and incorporate geological and hydrogeological information in the ground model. This study highlights the significant risk of engineering project failures that can occur if hydrogeological conditions are not properly assessed, understood and managed early in development of dam location, design and construction.

Estimación de zonas potenciales de aguas subterráneas en la cuenca del río Portoviejo mediante análisis jerárquico basado en SIG y teledetección

La utilización del agua subterránea en Ecuador se ha venido incrementando y cada día gana importancia debido al agotamiento, contaminación o inexistencia de fuentes superficiales. Sin embargo, la información hidrogeológica de la cual dispone el país es incompleta, desactualizada y dispersa, faltando implementar estrategias para la gestión del recurso hídrico subterráneo, iniciando con el proceso de legalización y regularización de los concesionarios formales e informales. El presente estudio tuvo como objetivo determinar las zonas potenciales de aguas subterráneas en la cuenca del río Portoviejo aplicando el método de análisis jerárquico (AHP, según sus siglas en inglés) basado en el sistema de información geográfica (SIG) y teledetección de acceso libre. A partir de este análisis se obtuvo el índice de potencial de aguas subterráneas (GWPI, según sus siglas en inglés), utilizado para la creación del mapa de zonas potenciales, el cual fue comparado con datos existentes en el inventario de puntos de agua. En la validación, se obtuvo una efectividad del 87 % para el mapa resultante, el cual ha sido influenciado en mayor grado por la permeabilidad de la roca, la precipitación y la densidad de drenajes, y en menor proporción por la pendiente del terreno y el índice de vegetación de diferencia normalizada (NDVI, según sus siglas en inglés). Palabra clave: agua subterránea, AHP, GWPI. Abstract The use of groundwater in Ecuador has been increasing and is gaining importance every day due to the depletion, contamination, or non-existence of surface sources. However, the hydrogeological information available in the country is incomplete, outdated, and dispersed, and there is a lack of strategies for managing subway water resources, starting with the process of legalization and regularization of formal and informal concessionaires. The objective of this study was to determine the potential groundwater areas in the Portoviejo River basin by applying the hierarchical analysis method (AHP) based on geographic information system (GIS) and remote sensing with free access. From this analysis, the groundwater potential index (GWPI) was obtained, used to create the map of potential areas, which was compared with existing data in the inventory of water points. In the validation, effectiveness of 87 % was obtained for the resulting map, which has been influenced in greater degree by the permeability of the rock, the precipitation and the density of drainages, and in smaller proportion by the slope of the land and the normalized difference vegetation index (NDVI). Keywords: AHP, groundwater, GWPI.

Geometric Model of a Coastal Aquifer to Promote the Sustainable Use of Water. Manglaralto, Ecuador

Modeling an aquifer provides significant advantages when evaluating and estimating the water resource for its sustainable use. This study focuses on the rural parish Manglaralto, a semi-arid area with a shortage of water, and without supply service by the public network. Still, it has a great demand for supply by the local and floating population (tourism). This has caused the coastal aquifer, which supplies the area’s water, to show signs of overexploitation, and its natural balance is compromised. The aim is to establish a geometric model of the aquifer through geological and geophysical analysis to set sustainable water-use guidelines. The methodology includes: (i) the processing of the current technical and hydrogeological information to know the aquifer’s data; (ii) geometric modeling of the aquifer through the correlation of technical information, using the GeoModeller software; (iii) proposals for the sustainable use of water in the framework of the United Nations’ Agenda 2030. The geometric model results reveal that the aquifer’s thickness varies from 4 m at the head of the river to 30 m at the sea’s mouth. The volume of water is estimated at 13.6 Hm3. The sustainable-use proposals ensure that more than half of the population receives the community company’s service. More than 40% of the territory is a protected area, and 64% of the population has sewerage service. This geometric model is a visual contribution that allows us to know the aquifer’s shape and establishes guidelines that help strengthen the water supply’s development and sustainability over time.

Hydrogeochemistry and hydrogeology of a fractured urban aquifer in the metropolitan region of Florianópolis, Southern Brazil

This paper was carried out through database of hydrogeological information of tubular wells based on the Groundwater Information System (SIAGAS) from the Geological Survey of Brazil (CPRM). The geology of the study area shows two main domains, a complex Crystalline Precambrian Shield partially covered by Quaternary sediments. Two main regional directions of tectonic lineaments were defined using satellite images with NE-SW and NW-SE orientations. The average discharges and specific capacities of the wells show values of 13.1 m 3 /h and 0.59 m 3 /h/m respectively. NW-SE linear structures were more productive than NE-SW, however the highest discharge values and the highest average (15.6 m 3 /h) are related to abstractions influenced by both directions simultaneously. Serra do Tabuleiro Granite is the lithology with the greatest productive potential in the region, followed by São Pedro de Alcântara Granite and the Granite-Gneiss-Migmatitic Complex. Sodium bicarbonate and calcium bicarbonate waters are the two main hydrochemical groups that occur in the region. The dissolution of calcium carbonate filling the fractures of the rocks is the main source responsible for the alkalinity of the water. The cationic proportion is defined by Na + > Ca 2+ > Mg 2+ > K + . In some wells, the increasing of Total Dissolved Solids (TDS) is probably related to the contribution of adjacent Quaternary porous aquifers deposited under marine influence.

Proposal for a Method Predicting Suitable Areas for Installation of Ground-Source Heat Pump Systems Based on Response Surface Methodology

The installation potential of ground-source heat pump (GSHP) systems has been studied based on the spatial interpolation of numerical simulation results using ground heat exchanger (GHE) models. This study is the first to create an estimation formula for the heat exchange rate (HER) to obtain a solution equivalent to the numerical analysis results considering the average method when supplying three-dimensional (3D) hydrogeological information that affects the HER to a two-dimensional (2D) map. It was found that the main factors affecting the HER were groundwater flow velocity, subsurface temperature, and thermal conductivity. The response surface methodology was utilized to approximate the HER using the above-mentioned three parameters. The estimated HER showed very strong agreement with that calculated by the GHE models. The application of the estimation formula to the simulation of the 3D groundwater flow and heat transport model of the Sendai Plain (Japan) better reflects the hydrogeological information of the regional model than conventional maps. The proposed method improves the spatial resolution of maps and allows for the easy creation of the HER estimation formula.

Groundwater flow and fluid/groundwater geochemical characterization at Ischia Island: a new strategy for the mitigation of the volcanic risk

<p>The volcanic system of Ischia is characterized by an intense hydrothermal activity, documented since the early 16th century by the study of Iasolino (1588), which represents the first systematic analysis of the thermal springs of the island for therapeutic purposes. Later studies partially contributed to the enhancement of knowledge on the volcanic, hydrogeological and hydrothermal features of the island, highlighting the strong interaction between hydrothermal flowpaths and volcano-tectonic processes . The reconstruction of the hydrothermal system becomes, therefore, a fundamental element for territorial planning, not only in terms of management of the huge water and geothermal resource, but also and above all in a perspective of prevention and mitigation of volcanic risk. Thermal springs, fumaroles and clay deposits due to the hydrothermal alteration of volcanic products testifies for the existence of an active deep hydrothermal system. Commonly, the geochemical characterization of fluids and groundwater has been used for the definition of the origin and structure of hydrothermal systems, when hydrogeological information is incomplete. However, volcanic hydrothermal systems, such as that characterizes the island of Ischia, are particularly difficult to analyze and outline, as the groundwater resources are the result of an articulated and dynamic interaction among meteoric water, sea water and fluids of deep origin. In such cases, the need for an interdisciplinary approach is evident, involving knowledge and research methods ranging from geology to volcanology, geophysics, geochemistry and hydrogeology. With particular reference to the functional and structural representation of the geothermal system of the island of Ischia and the resulting correlations with the volcano-tectonic processes, the examination of previous information highlights the need to update and improve the knowledge on groundwater hydrodynamics and mineralization processes.</p><p>Therefore, this study represents the result of  a strong interdisciplinary action that, starting from the design and implementation of a database on the existing geological/volcanological and hydrogeological information, contributes to highlight the critical issues, defines an operating scheme of the hydro-geo-thermal system of the island of Ischia, and aims at upgrade its hydrogeological, geochemical and volcanic monitoring system, in order to contribute to the mitigation of natural risks.</p><p>Moreover, this study well fits into the framework of the ongoing researches on volcanic hazard at Ischia and is integrated with the actions planned by the Italian Department of Civil Defense. The knowledge of groundwater dynamics and pathways is of fundamental importance for understanding the water/magma interaction processes in case of re-alimentation of the shallow magmatic system, and the assessment of the possibility of phreatic explosions occurrence.</p><p> </p>

Electrical resistivity tomography contribution to the characterization of underground cavities in the region of Safi, Morocco

Natural underground cavities represent a major risk that compromises the durability of infrastructures and buildings and requires an urgent evaluation in order to be integrated in urban planning and decision-making. Nevertheless, the assessment of the hazard related to them requires a better understanding of the complexity of karst phenomena that may be well-developed in an area even without the presence of any surface indices. Actually, evolutions of karst underground features are controlled by a set of predisposing factors. The present study aims to contribute to the delineation and characterization of underground cavities in the coastal part between Safi and Oualidia. The choice of the study area was based on a preliminary analysis of site conditions and the main controlling factors of superficial karst especially those related to geology, hydrology and geomorphology. In this part of Safi region, The high salinity of seawater enhances the process of dissolution creating so an aggressive environment and favorable conditions for an accelerated extension of karst networks. In order to detect and estimate the approximate extensions of karst networks and features in this area, results of seven electrical profiles were interpreted in correlation with available geological and hydrogeological information.