Sergio Martos-Rosillo

Groundwater recharge in semi-arid carbonate aquifers under intensive use: the Estepa Range aquifers (Seville, southern Spain)

Quantifying groundwater recharge in carbonate aquifers located in semi-arid regions and subjected to intensive groundwater use is no easy task. One reason is that there are very few available methods suitable for application under such climatic conditions, and moreover, some of the methods that might be applied were originally designed with reference to non-carbonate aquifers. In addition, it is necessary to take into account the fact that, in any given aquifer, groundwater recharge is modified by the groundwater exploitation. Here we focus on four methods selected to assess their suitability for estimating groundwater recharge in carbonate aquifers affected by intensive exploitation. The methods were applied to the Estepa Range aquifers of Seville, southern Spain, which are subjected to different degrees of exploitation. Two conventional methods were used: chloride mass balance and daily soil–water balance. These results were compared with the results obtained by means of two non-conventional methods, designed for application to the carbonate aquifers of southern Spain: the APLIS and ERAS methods. The results of the different methods are analogous, comparable to those obtained in nearby non-exploited carbonate aquifers, confirming their suitability for use with carbonate aquifers in either natural or exploited regimes in a semi-arid climate.

Comparison of Recharge Estimation Methods During a Wet Period in a Karst Aquifer

Management of water resources, implying their appropriate protection, calls for a sound evaluation of recharge. Such assessment is very complex in karst aquifers. Most methods are developed for application to detrital aquifers, without taking into account the extraordinary heterogeneity of porosity and permeability of karst systems. It is commonly recommended to estimate recharge using multiple methods; however, differences inherent to the diverse methods make it difficult to clarify the accuracy of each result. In this study, recharge was estimated in a karst aquifer working in a natural regime, in a Mediterranean-type climate, in the western part of the Sierra de las Nieves (southern Spain). Mediterranean climate regions are characterized by high inter-annual rainfall variability featuring long dry periods and short intense wet periods, the latter constituting the most important contribution to aquifer water input. This paper aims to identify the methods that provide the most plausible range of recharge rate during wet periods. Six methods were tested: the classical method of Thornthwaite-Mather, the Visual Balan code, the chloride balance method, and spatially distributed methods such as APLIS, a novel spatiotemporal estimation of recharge, and ZOODRM. The results help determine valid methods for application in the rest of the unit of study and in similar karst aquifers.

Karst massif susceptibility from rock matrix, fracture and conduit porosities: a case study of the Sierra de las Nieves (Málaga, Spain)

The potential contamination of a karst massif from surface sources can be evaluated and represented in a susceptibility map. In the case of a carbonate aquifer, the susceptibility assessment must take into account their very complex and heterogeneous nature. The complexity originates in the presence of three types of porosity: matrix rock, fracture and conduit porosity. This paper presents a method for karst susceptibility mapping by estimating the three porosity types and evaluates their integration in a single susceptibility index. Matrix rock porosity is measured in the laboratory from samples collected in the field and is well correlated with lithology. Fracture porosity is estimated from fracture mapping and field measurements of secondary fracture porosity. Geostatistical methods are used to obtain continuous fields of rock matrix porosity and fracture porosity. Conduit porosity is calculated from a power model fitted to speleological cave mapping data. However, because of the scarcity and sampling bias of conduit data, probabilistic models are conjectured. A fourth porosity factor evaluated is the detritic filling of karst depressions. The integration of the different porosities in a single susceptibility factor gives a quantitative map that is reclassified to provide a qualitative, easy to interpret susceptibility index map of the karst system. Porosity estimation may also be of interest in recharge estimation and mathematical modelling of flow and transport in karst systems. The case study used to illustrate this approach is the Sierra de las Nieves karstified rock mass, a high relief Mediterranean karst in the province of Málaga in southern Spain.

The Social Sustainable Aquifer Yield: An Indicator for the Analysis and Assessment of the Integrated Aquifers Management

Integrated Aquifers Management (IAM) demands innovative tools and methods that are able to consider as much perspectives as possible. This research is aimed to design, apply and provide an indicator named Social Sustainable Aquifer Yield (SSAY), expressed in units of time that includes pure hydrological variables as well as social ones. The indicator is defined as the relation between the Residence Time, which is the relation between aquifer Storage (S) and Recharge (R) (S/R), and the relation between the aquifer Pumping (P) and the new variable named Aquifer Social Yield (ASY). The whole indicator is defined by this formula: (S/R)/(P/ASY). The assessment of the residence time is essential in aquifers with at least one of the following features: i) high hydraulic diffusivity, and ii) small volume of reserves. Finally, the variable ASY is defined as the average perception from the stakeholders about the maximum acceptable aquifer exploitation. This indicator has been successfully applied in the aquifers located in southern Jaen province (South Spain) belonging to the Water System SE4-Jaén Water Supply. The results probe the high utility of the indicator, especially in regards to the public participation processes.

Correlation of the seasonal isotopic amplitude of precipitation with annual evaporation and altitude in alpine regions.

The time series of stable water isotope composition relative to IAEA-GNIP meteorological stations located in alpine zones are analyzed in order to study how the amplitude of the seasonal isotopic composition of precipitation (Aδ) varies along a vertical transect. A clear relationship between Aδ and local evaporation is obtained, with slopes of -0.87 ‰/100mm/yr and -7.3 ‰/100mm/yr for Aδ(18)O and Aδ(2)H, respectively. When all sampling points of the vertical transect receive the same moisture sources, then a linear relationship between Aδ and elevation is obtained, with vertical gradients of 0.16 ‰/100mm/yr and 1.46 ‰/100mm/yr forAδ(18)O and Aδ(2)H, respectively.

Factors determining subsidence in urbanized floodplains: evidence from MT-InSAR in Seville (southern Spain): FACTORS DETERMINING SUBSIDENCE IN URBANIZED FLOODPLAINS

Major rivers have traditionally been linked with important human settlements throughout history. The growth of cities over recent river deposits makes necessary the use of multidisciplinary approaches to characterize the evolution of drainage networks in urbanized areas. Since under-consolidated fluvial sediments are especially sensitive to compaction, their spatial distribution, thickness, and mechanical behavior must be studied. Here, we report on subsidence in the city of Seville (Southern Spain) between 2003 and 2010, through the analysis of the results obtained with the Multi-Temporal InSAR (MT-InSAR) technique. In addition, the temporal evolution of the subsidence is correlated with the rainfall, the river water column and the piezometric level. Finally, we characterize the geotechnical parameters of the fluvial sediments and calculate the theoretical settlement in the most representative sectors. Deformation maps clearly indicate that the spatial extent of subsidence is controlled by the distribution of under-consolidated fine-grained fluvial sediments at heights comprised in the range of river level variation. This is clearly evident at the western margin of the river and the surroundings of its tributaries, and differs from rainfall results as consequence of the anthropic regulation of the river. On the other hand, this influence is not detected at the eastern margin due to the shallow presence of coarse-grain consolidated sediments of different terrace levels. The derived results prove valuable for implementing urban planning strategies, and the InSAR technique can therefore be considered as a complementary tool to help unravel the subsidence tendency of cities located over under-consolidated fluvial deposits.

A Method for Automatic Detection and Delineation of Karst Depressions and Hills

Karst depressions of decametric scale (dolines, uvalas, poljes, and other endorheic basins) play an important role in the hydrogeology of karst aquifers. They are traps of sediment and when their detritic filling has an important thickness they can retain a large amount of water delaying their percolation towards the water table or towards the networks of conduits. Many times the delineation of the depressions may be difficult because the study area may be very large, or inaccessible or hidden by vegetation. In those circumstances, it is of great help to have an automatic method of depression detection and delineation. The proposed procedure uses the digital elevation model, a geographical information system, an algorithm of pit removal and basic operations of map algebra. The method provides the depth of each detected depression measured from its rim. This fact can be used to detect the center of maximum depth as well as for calculating morphometric parameters using depth. The final map of depressions can be characterized by altitude in order to have morphometric parameters related with elevation. The algorithm has been extended for detection and delineation of karst hills. The methodology is illustrated with the Sierra de las Nieves karst aquifer in the province of Malaga, Southern Spain, where the depressions and hills show a strong structural control.

Integral Porosity Estimation of the Sierra de Las Nieves Karst Aquifer (Málaga, Spain)

Karst aquifers are very complex and heterogeneous systems because of the presence of three kinds of porosity (matrix rock porosity, fracture porosity, and conduit porosity) that generally have a large spatial variability. In order to have realistic karst models the three kinds of porosity and their spatial variability must be taken into account. A quantitative model of a karst aquifer is proposed by integration of the three kinds of porosity in a three dimensional numeric model. Nevertheless, the main task of this work is restricted to the proposal of methods for their evaluation. Matrix rock porosity has been measured in the laboratory from samples collected in the field. Matrix rock porosity is well correlated with the lithology and with the structural position of the rock. Fracture porosity has been estimated from fracture mapping and field measurements. A geostatistical method is used to obtain a continuous field of fracture porosity. Conduit porosity has been calculated from a power model fitted to speleologic cave mapping data. However, because of the scarcity of conduit data, probabilistic models must be conjectured. The integration of the three kinds of porosity gives a three dimensional numerical model that can be used in vulnerability mapping, recharge estimation, and mathematical modeling of flow and transport in karst systems. The approach is illustrated with the Sierra de las Nieves karst aquifer in the province of Malaga in Southern Spain.

SAR interferometry monitoring of subsidence in a detritic basin related to water depletion in the underlying confined carbonate aquifer (Torremolinos, southern Spain)

This research underlines the need to improve water management policies for areas linked to confined karstic aquifers subjected to intensive exploitation, and to develop additional efforts towards monitoring their subsidence evolution. We analyze subsidence related to intensive use of groundwater in a confined karstic aquifer, through the use of the InSAR technique, by the southern coast of Spain (Costa del Sol). Carbonates are overlain by an unconfined detritic aquifer with interlayered high transmissivity rocks, in connection with the Mediterranean Sea, where the water level is rather stable. Despite this, an accumulated deformation in the line-of-sight (LOS) direction greater than -100 mm was observed by means of the ERS-1/2 (1992-2000) and Envisat (2003-2009) satellite SAR sensors. During this period, the Costa del Sol experienced a major population increase due to the expansion of the tourism industry, with the consequent increase in groundwater exploitation. The maximum LOS displacement rates recorded during both time spans are respectively -6 mm/yr and -11 mm/yr, respectively. During the entire period, there was an accumulated descent of the confined water level of 140 m, and several fluctuations of more than 80 m correlating with the subsidence trend observed for the whole area. Main sedimentary depocenters (up to 800 m), revealed by gravity prospecting, partly coincide with areas of subsidence maxima; yet ground deformation is also influenced by other factors, the main ones being the fine-grained facies distribution and rapid urbanization due to high touristic pressure.

Groundwater dynamics in a hydrologically-modified alpine watershed from an ancient managed recharge system (Sierra Nevada National Park, Southern Spain): Insights from hydrogeochemical and isotopic information

In many of the alpine watersheds of Sierra Nevada (Southern Spain) exists an ancient network of dug canals that collect, transport and facilitate the recharge the snowmelt in the underlying aquifer during the spring season. This practice, known as careos, in the lower part of the watersheds supply drinking water as spring discharge during the dry season. To study how this managed recharge technique modifies the natural response of these basins this work focuses on characterizing the hydrological behavior of one of the sites, the Berchules watershed. The mechanisms for mineralization of groundwater are based on geochemical processes such as evapo-concentration in the soil layer and silicate mineral weathering due to dissolved CO2 originated from both soil biogenic processes and the atmosphere. Groundwater presents a main hydrogeochemical calcium‑magnesium-bicarbonate type facies, which is associated to groundwater flowing through the upper weathered silicates and quickly drained through springs located in the uplands and in the intermediate altitude catchment zone. Additionally, in the lower part of the basin some springs discharge mineralized groundwater with a sodium-calcium-bicarbonate composition associated to regional groundwater flow. In natural conditions, this hydrogeological system behaves as a sloping aquifer, occurring recharge between 1400 and 2500 m a.s.l. The springs discharge groundwater with an isotopic content and temperature in coherence with the local rainfall isotopic and thermal atmospheric altitudinal lines. Nevertheless, once the careo recharge begins the affected springs reveal the fingerprint of the concentrated recharge system by blurring the fingerprint of both the isotopic and thermal altitudinal dependence in the springs discharge. This validates the previous conceptual model and supports average recharge values of 141 ± 140 mm/yr and total average water resources of 181 ± 111 mm/yr which include a 40% increase in the study period due to the effect of the acequias de careo.