Desarrollo turístico y mercado inmobiliario en la comarca del Bajo Segura (Alicante)

La presente comunicación se inscribe en el marco del proyecto de investigación “Planificación y gestión sostenible del turismo. Propuesta metodológica y aplicación de un sistema de información turística” (METASIG), con referencia 1FD97-0403, financiado por la Comisión Interministerial de Ciencia y Tecnología (CICYT) y la Comisión Europea (FEDER).

Seguimiento geométrico de terraplenes mediante líneas continuas de asiento en la Vega Baja del Segura, Alicante

La Vega Baja del Segura (Alicante) se caracteriza por la baja resistencia portante de los suelos y en consecuencia por las grandes deformaciones que sufren las construcciones que sobre ellos se levantan. La gran demanda turística de vías de comunicación con la costa sur de la provincia de Alicante ha obligado a construir diversas carreteras cuyos terraplenes alcanzan alturas superiores a los 8 m, así como deformaciones decimétricas y en algunos casos excepcionales de magnitud métrica. Las líneas continuas de asiento es una técnica innovadora que se lleva utilizando durante algunos años en la Vega Baja y que evita los laboriosos procedimientos de auscultación topográfica, sirviendo de instrumento de seguimiento geométrico de los mismos y permitiendo la representación gráfica del terraplén original y de su deformada. Esta técnica permite además a la Administración establecer los volúmenes de tierra necesarios para compensar el hundimiento de los terraplenes de forma exacta. Con el presente trabajo se pretende dar a conocer la metodología de las líneas continuas de asientos, así como mostrar algún ejemplo real de aplicación de las mismas, mostrando la evolución geométrica del terraplén en el tiempo y mostrando el procedimiento de cálculo de volúmenes.

Relationship between piezometric level and ground deformations measured by means of DInSAR in the Vega Media of the Segura River (Spain)

Differential SAR Interferometry (DInSAR) is a remote sensing method with the well demonstrated ability to monitor geological hazards like earthquakes, landslides and subsidence. Among all these hazards, subsidence involves the settlement of the ground surface affecting wide areas. Frequently, subsidence is induced by overexploitation of aquifers and constitutes a common problem that affects developed societies. The excessive pumping of underground water decreases the piezometric level in the subsoil and, as a consequence, increases the effective stresses with depth causing a consolidation of the soil column. This consolidation originates a settlement of ground surface that must be withstood by civil structures built on these areas. In this paper we make use of an advanced DInSAR approach - the Coherent Pixels Technique (CPT) [1] - to monitor subsidence induced by aquifer overexploitation in the Vega Media of the Segura River (SE Spain) from 1993 to the present. 28 ERS-1/2 scenes covering a time interval of about 10 years were used to study this phenomenon. The deformation map retrieved with CPT technique shows settlements of up to 80 mm at some points of the studied zone. These values agree with data obtained by means of borehole extensometers, but not with the distribution of damaged buildings, well points and basements, because the occurrence of damages also depends on the structural quality of the buildings and their foundations. The most interesting relationship observed is the one existing between piezometric changes, settlement evolution and local geology. Three main patterns of ground surface and piezometric level behaviour have been distinguished for the study zone during this period: 1) areas where deformation occurs while ground conditions remain altered (recent deformable sediments), 2) areas with no deformation (old and non-deformable materials), and 3) areas where ground deformation mimics piezometric level changes (expansive soils). The temporal relationship between deformation patterns and soil characteristics has been analysed in this work, showing a delay between them. Moreover, this technique has allowed the measurement of ground subsidence for a period (1993-1995) where no instrument information was available.

DInSAR monitoring of aquifer compaction due to water withdrawal: Vegas Baja and Media of the Segura river (SE, Spain) case study

This study was partially financed by the Spanish Ministry of Education and Science and EU FEDER under project TEC2005-06863, by the Valencia Regional Government under projects GV006/179 and ACOMP07/087, and by the University of Alicante under projects VIGROB2004102, VIGROB-053, and VIGROB-114.

Diseño de un modelo geológico-geotécnico 3D de la Vega Baja del Río Segura (Alicante, SE España)

Los modelos geológico-geotécnicos permiten al ingeniero comprender mejor las condiciones reinantes en un determinado lugar, además de identificar los principales problemas geotécnicos y hacer más realista la estimación de propiedades del suelo. En este trabajo se presenta la metodología empleada para el diseño de un modelo geológico-geotécnico tridimensional de la Vega Baja del Río Segura que consta de cuatro zonas caracterizadas por sus propiedades geotécnicas y su problemática asociada. El modelo resulta fundamentalmente de gran utilidad para la planificación de investigaciones preliminares de obras civiles.

Monitorización de la subsidencia del terreno en la Vega Media del río Segura mediante Interferometría SAR diferencial (DInSAR)

Ground subsidence caused by aquifer exploitation is a geotechnical hazard that affects wide areas, causing important economic damages. This phenomenon is due to soil consolidation produced by the increase of effective stress caused by piezometric depletion. In this work a Remote Sensing Technique called Coherent Pixel (CPT) is applied to monitor subsidence in the Vega Media of the Segura River during a period of eleven years.

Asociaciones de foraminíferos del Messiniense y Plioceno del sector norte de la Cuenca del Bajo Segura

The Messinian and Pliocene stratigraphic record of the northern sector of the Bajo Segura Basin has been separated into three main allostratigraphic units (MI, MII and P). These units are composed of continental to marine depositional systems. The aim of this paper is study the foraminiferal assemblages belonging to lagoonal and marine systems. The distribution of these foraminiferal assemblages show two significantly paleoenvironmental changes: 1) an abrupt change from marine to lagoonal foraminifer assemblages at the MI/MII boundary, related with the beginning of the Lago Mare and Terminal Complex deposition; and 2) a significant marine foraminiferal repopulation at the beginning of the Pliocene as a consequence of the marine reflooding of the Mediterranean.

Pistas fósiles asociadas a la discontinuidad fini-Messiniense en el margen norte de la Cuenca del Bajo Segura (SE España)

A detailed analysis of the Upper Messinian-Lower Pliocene at the northern border of the Bajo Segura Basin (BSB) has been carried out. Trace fossils of firm- and rockground were collected, aiding in the recognition of three ichnofacies: Glossifungites (types A and B), Entobia and Gnathichnus. The ichnological data provide evidence that the Pliocene flooding of the BSB, after the Messinian Salinity Crisis, was developed in two pulses. In the first one, the ingression penetrated only along the paleovalleys and produced a coastal trasgressive lag (P0). In the second one, the ingression overflowed the margins of the paleovalleys and extended throughout the entire northern margin, also producing a coastal transgressive lag in the base of the P2 system. The record of the Entobia and Gnathichnus ichnofacies in the clasts of both lags evidences a relatively fast deepening-upward trend in both the transgressions.

La sección de San Miguel de Salinas (Cuenca del Bajo Segura): significado paleoambiental de las asociaciones de foraminíferos en relación con la Crisis de Salinidad del Messiniense

In the composite section of San Miguel de Salinas the following synthems are represented: MI (preevaporitic Messinan), MII (syn-evaporitic Messinian) and P (post-evaporitic Pliocene). The foraminiferal assemblages of these synthems have been studied in order to reveal the palaeoenvironmental changes related to the Mediterranean Salinity Crisis. The change between MI and MII synthems is characterized by the reduction of the foraminiferal biodiversity. Synthem MII records palaeoenvironmental stress related to the evaporitic deposition during the Salinity Crisis. Synthem P marks an abrupt increase of the foraminiferal biodiversity in coincidence with the Pliocene reflooding of the Mediterranean Sea.

Bioestratigrafía basada en foraminíferos planctónicos para el Mioceno superior y Plioceno de la Cuenca del Bajo Segura (Cordillera Bética oriental)

The planktonic foraminifers biostratigraphy is crucial in order to precise the timing of the main tectonosedimentary and palaeogeographic events through the evolution of the Bajo Segura Basin. Our results indicates that the marine stratigraphic record of the basin spans from the earliest late Miocene to the early Pliocene. For this temporal interval, all the recent, astronomically calibrated, planktonic foraminifers biozones had been documented. The oldest depositional stage in the basin is marked by a regional-scale transgression in coincidence with the MMi9 biozone (early Tortonian). The youngest basin-wide marine episode occurs at the MPl4a biozone (Zanclean). The Messinian Salinity Crisis, as a specially noticeable event in the Mediterranean domain, is bracketed between the last Messinian biozone (MMi13c) and the first Pliocene biozone (MPl1).

Applicazione dell’Indice di Funzionalità Fluviale (I.F.F.) al fiume Segura nella provincia di Alicante

L’obiettivo di questo studio è la valultazione della funzionalità ecologica del fiume Segura nella provincia di Alicante (Spagna) mediante l’applicazione dell’IFF (Indice di Funzionalità Fluviale). La motivazione di questa scelta è stata la volontà di partecipare all’introduzione di questo indice in Spagna, paese in cui non è abitualmente utilizzato. Sono stati valutati 24006 m di corso d’acqua suddivisi in 24 tratti di varie lunghezze, partendo dall’uscita del centro urbano di Orihuela fi no al centro abitato di Guardamar del Segura. Il giudizio della funzionalità del fiume complessivamente rientra nell’intervallo dei livelli da V a III-IV, con una percentuale maggiore dell’80% di livello IV sia per la sponda destra che per la sinistra. L’applicazione dell’Indice ha permesso non solo di valutare la funzionalità dei 24 tratti, ma anche di individuare i parametri più degradati del corso d’acqua e i parametri più «forti», dall’osservazione dei quali è possibile far partire un lavoro di ripristino ambientale e rinaturalizzazione del fiume.

Avenidas fluviales e inundaciones de los ríos Vinalopó y Segura en época islámica y sus consecuencias en el poblamiento

Son escasas las noticias de época andalusí sobre inundaciones fluviales en el sur de la provincia de Alicante. En la descripción de Elche del Mugrib de Ibn Sa’īd se nos informa indirectamente de una inundación del Vinalopó en el segundo cuarto del s. XIII; como consecuencia, la ciudad musulmana se anegó y bastante población la abandonó. Respecto al vecino río Segura, el geógrafo al-‘Udrī (m. 1085) al describimos el curso del río nos informa que su sistema de riegos es como el del Nilo; este paralelo se debe al uso inteligente que hacían los egipcios y los habitantes de la Vega Baja de las aguas de la inundación fluvial como abono periódico de sus tierras y como elemento para luchar contra los marjales. También se analizan otras noticias sobre la torre de Embergoñes, la cual, situada a la entrada del curso fluvial en Orihuela, consideramos que era un promontorio de señales y de vigilancia de la inundación. Finalmente se recuerda la existencia de acanaladuras en las puertas de la catedral de Orihuela para proteger el interior del templo de las aguas de avenida.