Hydrochemical processes in the quaternary glacis and dejection cones of the Low Almanzora region (Almeria, SE Spain)
Barragan-Alarcon, Guillermo
Department of Hydrogeology and Analytical Chemistry
Universidad de Almeria, La Cañada de San Urbano 04120 Almeria, Spain
Abstract—Quaternary glacis and dejection cones play a distributor role between basement aquifers and Neogene intramontaneous basins in Low Almanzora region. To study hydrochemical processes in the quaternary glacis a revision of geological cartography and georreferencing of aquifer points has been made using GIS. Analysis of water samples to determine mayoritary and minoritary components has permitted to apply estatistical techniques of ACP and Factorial Analyse and geoestatistical techniques of krigging.
Quaternary glacis; dejection cones; hydrochemical trends;ACP; sulphates.
I. Introduction
The lower Almanzora river hydrographic basin is located in the eastern area of the Internal Zone of the Betic Cordillera, in the Southeast of Spain. The landscape is sculpted over intramontaneous basins filled with mostly marine, and, in minor proportion, continental sediments, of Upper Miocene and Pliocene age. Mountain ranges of the Betic basement, essentially constituted by materials of the Alpujarride and Nevado Filabride complexes, separate the basins (fig.1).
The Almanzora river flows nowadays by the southern area of Huercal Overa basin, and crosses cutting the Almagro Sierra, where it scarce water is stored by the Cuevas Dam. Finally it flows into the Mediterranean Sea near Villaricos. The most eastern Estancias Sierra, the Enmedio Sierra, and part of the Almagro Sierra pour their waters by the Guazamara corridor. The alignment of Aguilon Sierra, Los Pinos Sierra and Almagrera Sierra pour their waters into the Canalejas Rambla, which collects the Guazamara Rambla, and it’s joined to the Almanzora River near Villaricos.
The Low Almanzora region has developed an agriculture of high economic productivity in the last years, but it is strongly limited by the scarceness of water. The high variability in different years, with more than the double of water in one wet year than in one dry year, and in some cases more than quadruple, aggravate the scarceness. The sum of the contributions of superficial run off, in Santa Barbara gauging station, and of the natural rainfall in the studied area is ranged between 42 and 13.8 Mm3.
In 2003 the irrigated area was 19286 has (32% of the surface of Pulpi, Cuevas and Huércal-Overa municipalities). The water deficit is partially compensated, by now, with remote contributions from the Tajo river and Negratin dam. The mean volume transvased is 45.4 Mm3, 32 Mm3 from Negratin and 14.4 Mm3 from Tajo-Segura-Sur. The total recharge with both natural recharge and transvased water ranges between 59.2 and 87.4 Mm3. Whatever the sum of urban demand and agriculture demand has been estimated in approximately 90 Mm3, between 30.8 Mm3 and 2.6 Mm3 remain without coverage by GALASA and by the basin administrative institutions. Here the owners of private boreholes and irrigators associations that use underground waters take part. Recently a desalation plant has begun to work.
In this paper I attempt to elucidate hydrochemical processes in the quaternary glacis and dejection cones, which play a distributor role between basement aquifers and sedimentary filling in Neogene intermountainous depressions. To do this I have modelled flow by the glacis and dejection cones in the basis of the observed piezometric levels. Sulphates and carbonates dissolve and precipitate in this quaternary sediments till equilibrium is reached. Minoritary components are analysed and related to basement aquifer water in a previous step to estimate underground entries by the alluvial fan.
II. Geological and hydrogeological frameworks
The Huercal-Overa basin has been basculated in recent times, so, the northern part of the basin has suffered upliftening. This process generated several levels of alluvial sediments with glacis morphology, from North to South and Southeast, which play an important role in the distribution of the water. Some of the glacis are still actives, specially those levels near Urcal and Santa Maria de Nieva, which pour towards Almajalejo Rambla, Guzmaina Rambla and towards El Saltador area. Guzmaina Rambla and Almajalejo Rambla join to the Almanzora River. Some glacis in the northern border of the Huercal-Overa Basin feed the Norias Rambla and the Guazamara corridor. The total extent of all these glacis in the studied area is 77.96 km2. Many of the springs or water collectors are in the lower topographic points of the glacis.
The Almagro Sierra generated glacis too, towards the South and East, to the Vera basin and the Guazamara Corridor, but they are hanged and strongly dissected by erosion. The role as distributor of the fans at East and South of Almagro Sierra, is minor because they are hanging and very dissected by the erosion.
In the Northern border of the Almagro Sierra faster and more energetic ascent of the basement rocks, determined dejection cones to be formed in quaternary age.
In the sedimentary rocks of the basins there are limited aquifer systems, which are generally separated from the basement by marls. The geometric shape of these aquifers is similar to little buckets, which is the case of El Saltador aquifer; there are quaternary materials of little thickness in Guazamara corridor. The low Almanzora River alluvial has very salt water that can only be used in some kinds of cultures. In miocene aquifers are important the silts and grey clays from tortoniense in Tallante hill and in Sierrecica, that experiment an underground discharge, by their northern contact with glacis.
Marls contain sulphates and gypsum, and the salt concentration grows remarkably in the vicinity of them. It’s in quaternary and plioquaternary continental sediments where the most of the water is captured and maintains a salinity level that allows the agriculture and human supply.
In basement are remarkable the carbonate aquifers from Variegato Unit and Tres Pacos Unit in Almagro Sierra. Carbonates from Variegato unit has very low TDS. Carbonates from the lower Formation in Tres Pacos Unit (at the North of Almagro Sierra) store water, that has been extracted by boreholes, but in the natural regime it deeply discharges to the Saltador aquifer, like is deducible of piezometric levels in Geotehic (1983). Sometimes fractured quarcites can also store minor quantities of water, that is the case of the outcrop which feeds Fuente Alamo spring. In Upper Formation of Tres Pacos Unit carbonates are mixed with gypsum and breccia, so they doesn’t form an useful aquifer because of the high salinity. There is contact along a band of two kilometres between the Upper formation of Tres Pacos Unit with Gypsum brechas and the deyection cones that shed to bucket.
Other rocks with aquifer behaviour that could have some interest are the carbonates of La Jara Unit in Estancias Sierra. Underground communication between this carbonates and Saltador aquifers doesn’t seem probable, because recovering of marls and tortoniense cemented gravel, but can not be rejected at all.
This carbonates form confined aquifers under quarcites and phyllites first, tortoniense cemented gravel second, and under marls third. However discharge to glacis occurs in the North of the Huercal Overa basin, but not directly. That discharge works like a siphon depending on the reserves of water in the confined carbonate aquifer. The outgoing of the groundwater condition the formation of travertines, that evidence it ascending flow (Martin Vallejo, M. et al., 1994).
The release of CO2 by the decrease of pressure makes carbonates to precipitate forming the travertines. This travertines appear overlapping quarcites and phyllites, and tortoniense cemented gravel. Travertines changes gradually to marsh carbonates and to the glacis. So glacis collect the water that scape from confined aquifer and conduct it to plioquaternary aquifer.
CO2 release has been observed in wells near San Francisco and La Oñorica, in El Saltador aquifer. Ceron (1991) and Ceron and Pulido Bosch (1996a and b) refers CO2 release near Pulpi, and in Los Guiraos well, near Guazamara. Massive carbonate precipitation was the reason of the abandon of Agua Picante well, near Sierrecica de Nieva. These all are more evidences of the ascending flow of water, but in this case discharge doesn’t arrive to surface and it is not distributed by glacis. It arrives by the floor of the plioquaternary aquifer.
In Enmedio Sierra carbonates and fractured metabasites have some interest as aquifer systems too. In the Ranges alineated near to the coast line carbonates at the foot of Aguilon Sierra and that located in Palomas alineation store some water.
III. Methodology
I have done a revision of geological cartography using MAGNA 1:50000 digitized and updating it with recent published works of Garcia Tortosa et al. (2002) and Garcia Melendez et al. (2003), aereal photographs 1:5000 and field observations. I have considered too more ancient works like ENADIMSA (1982) and BRIEND (1981) that apply a specific treatment to glacis and quaternary materials. This spatial information has been transformed to vectorial data and processed in a geodatabase, built with ARCGIS 9.0.
Data from boreholes of the studied area has been collected from Andalusian Water Agency and irrigators associations. 523 aquifer points have been georreferenced (though some of them are now dried or present high salt contents), and 36 are located on the glacis coverage. In a buffer of 100 m around the glacis the number of aquifer points increases to 54, eight of the points are galleries or zimbras that collect the discharge of glacis.
In reports about the aquifers state writen for IGME and for Diputación of Almería and in other anonymous sources I have collected 454 chemical analysis from waters in low Almanzora region, dating after 1970.
During a year, I have collected samples every three months in a network of 58 aquifer points, with the already mentioned analysis, the data reach to 164 points, but this network has been designed for other purposes so I only have 107 analysis of 24 aquifer points fed with water from glacis.
Some measures were collected in field like E.C., pH, T, Eh O2 y bicarbonates. When pH was high enough carbonates were measured too. The procedure was the same that used in Vallejos Izquierdo (1991). Samples were filtered and store in cold. 185 samples of mayoritary chemical components have been analysed in the Almeria University with a chromatograph HPLG.
42 samples where analysed for minoritary elements analysis in the Canadian laboratory Acmelab. Samples were acidificated to preserve metals concentrations. Furthermore, analysis of silica, iron and manganese were made in the UAL laboratory. These analysis were contrated with previous analysis used by Martin Vallejo (1997) and by Collado Fernandez D. (2002)
IV. Results
Some plots like Stiff plot and Pipper plot permit to study change in the chemistry of mayoritary components. In Pipper plot we can see an increasing of sulphate relative concentrations towards the South near of the contact with Upper Formation of Tres Pacos Unit.
Estadistical techniques of ACP and factorial analisis have been applied to the collected analysis. Three independent components were separated in ACP. The first of them is related with Calcium sulphates, magnesium and strontium, that exist in neogene fill and in Tres Pacos Unit of the Alpujárride complex. The second appears to be related with bicarbonates and silica, that coexist in the floor of the aquifers of Variegato Unit and in the contact between Blanquizares-Oria Unit and the Jara Unit. The third component correlates with bicarbonate, nitrate and Na, and it can be related with a superficial contamination factor favoured by anthropic activity.
Techniques of ordinary krigging has been used to validate the ranges and variations of concentrations of some mayoritary elements and study their evolution. Variogram has been estimated like a previous step to Krigging. With minoritary elements ordinary krigging can’t be used but sometimes a regular trending is observed. Silica and Stromtium reaches values similar to the mayoritary components.
V. Conclusions
The contact of Upper Formation of Tres Pacos Unit with dejection cones has his hydrochemical trace in the nearly collected samples from some boreholes.
Strontium is a mayoritary component from waters, principally in SE area in Saltador bucket, where it quadruplies sometimes Potasium concentration. Furthermore it takes higher values than in the Almagro Sierra, and this could be a connexion index with the basement aquifers. Underground mineralizations of celestite are originated in Almagro Sierra.
Silica appears with a downward trending towards South as we go far from quarcites and filites from Tonosa Formation in Estancias Sierra.
The data of mineral supplies from the basement are interesting related to the metal concentrations in the water. The marls and the gypsum rocks of the alpujarride basement are the main source for the total salinity of the waters, whereas the sources of metals are mineralisations in the rocks of the Alpujarride basement. Iron is always over the limit values. Manganese can be over limit values, but just in one case was indicator of fecal contamination. Maximum values of Mn were got in boreholes located in center of the Saltador bucket. So that high concentrations can be related with hidrotermal effects originated around a branch of the fault in “horse tail”, that is mentioned in Melendez Garcia et al. (2004) and Soler et al. (2003).
Aknowledgements.- This paper was prepared with the funds of a grant of Universitary Profesoral Formation from M.E.C. ref. AP2003-0214, developed in the frame of the research group RNM-189 “Hydrical resorces and ambiental geology”from University of Almeria. Dr. Guillermo Barragan-Bazan is thanked by his contribution to the field investigations. Dr. Antonio Pulido Bosch is aknowledged by his critical review of the original manuscript.
References
Briend, M., 1981, Evolution morpho-tectonique du bassin de Huercal-Overa (Cordillères Bétiques Orientales-Espagne). Tesis doct. Institute Geologique Albert de Lapparent, 208 pp.
Ceron, J.C., 1991, Estudio hidrogeoquímico de la cubeta de Pulpí (Almería y Murcia). Tesis de Licenciatura. Universidad de Granada,195 pp.
Ceron, J.C. and Pulido Bosch, A., 1996 a, Características hidroquímicas de aguas carbogaseosas en los Guiraos (Sudeste de España). Geogaceta, 19, 124-126.
Ceron, J.C. and Pulido Bosch, A., 1996 b, Algunas consideraciones sobre aguas termominerales con CO2 en los Guiraos (Sudeste de España). Geogaceta, 19, 127-129.
Collado Fernandez, D.M., 2002, Movilización de contaminantes en el terreno a partir de suelos contaminados.Tesis doct. Univ. Almería, 205 pp. +Anexos
Garcia Tortosa, F.J., Lopez-Garrido, A.C. and Sanz de Galdeano, C., 2002, Estratigrafía y estructura de la unidad de los Tres Pacos: La controversia sobre el complejo “Almágride” en la Sierra de Almagro (Cordillera Bética, Almería, España). Rev. Soc. Geol. España, 15 (1-2), 15-25.
Garcia Melendez E, Goy, J.L. and Zazo, S., 2003, Neotectonics and Plio-Quaternary landscape development within the eastern Huércal-Overa Basin (Betic Cordilleras, SE Spain). Geomorphology, 50, 111-133.
Garcia Melendez, E., Goy, J.L. y Zazo, S., 2004, Actividad tectónica cuaternaria en la cuenca de Huércal-Overa (Almería, Sureste de España): deformaciones asociadas a la falla de Albox. Geogaceta, 36, 63-66.
Martín Vallejo, M., Garcia-Rossell, L. and Berrad, F., 1994, Impacto geomorfológico del hidrotermalismo Geomorfología en España. Eds: Arnaez, J.; García Ruiz, J.M. y Gómez Villar, A. Sociedad Española de Geomorfología, 149-158.
Martin Vallejo, M., 1997, El sistema hidrotermal de la cuenca del Río Almanzora (N de la provincia de Almería) Tesis Doct. Univ. Granada., 302 pp. + Anexos
Soler, R.; Masana, E. and Santanach, P., 2003, Evidencias geomorfológicas y estructurales del levantamiento tectónico reciente debido al movimiento de la falla de Alhama de Murcia (Cordillera bética oriental). Rev. Soc. Geol. España, 16 (3-4), 123-134.
Vallejos Izquierdo, A., 1991, Contribución al conocimiento hidrogeológico de la cuenca del Río Almanzora (N de la provincia de Almería). Tesis de Licenciatura Univ. Granada., 160 pp. + Anexos.
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