María Luisa Calvache

Differential features of alluvial fans controlled by tectonic or eustatic accommodation space. Examples from the Betic Cordillera, Spain

Abstract The creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area (along basin–margin faults) or to a rise in base level. Depending (amongst others) on the relative importance of these two factors, the margins of terrestrial sedimentary basins (where alluvial fans develop) produce aggradational, progradational or retrogradational stratigraphic architecture. We studied a total of 43 Quaternary alluvial fans in the Granada and Bajo Segura basins (Betic Cordillera, Spain). The analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns, which is the result of differences in eustasy and tectonics. The qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related, in each case, to the main mechanism operative in the creation of accommodation space. These patterns are described as follows. (1) Alluvial aggradation is the main result of high tectonic subsidence with the development of quite open, but small fans with a constant steep slope lacking incised channels and headward-eroding gullies. (2) In contrast, when the principal mechanism in creating accommodation space is low tectonic subsidence, progradation occurs and the fans are narrower and larger. Moreover, the slopes of such fans are less steep in relation to the drainage area than in the above case, being constant or even concave in longitudinal profile. They also have short, deep incised channels, culminating downfan in a depositional lobe. In inactive zones, long, deep headward-eroding gullies develop. (3) Areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin, although with a pronounced mountain embayment, which gives them a characteristic “mushroom” shape in plan view. In the latter case, retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas, usually showing a segmented longitudinal profile with a low gradient. The feeder channels do not surpass stream order 3, and various extremely long and shallow incised channels can appear. (4) Contrary to the case of fans developing under a regime of subsidence, when the accommodation is due to base level rise, the fan slopes bear no relation to the extent of the catchment basins. In such a case, the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet-flows over the alluvial surface.

Controls on fan development — evidence from fan morphometry and sedimentology; Sierra Nevada, SE Spain

Abstract We have studied the morphology and the morphometric relations between alluvial fans and drainage basins in a bajada system including more than 20 coalescent fans developed since the Late Pleistocene as a result of the recent uplift of the Sierra Nevada (Betic Cordillera, Spain). Three allocycles of tectonic origin were recognised across which there is a clear evolution from debris flow to sheet flow dominated fans, in connection with a decrease in the volume of fines available in the source areas. The larger volume of accommodation space created by higher tectonic subsidence in the northern sector favoured vertical accumulation of sediment, with the appearance of less elongated fans. In the rest of the system, where subsidence is less, more elongated fans appear, with the development of incised channels and irregular distribution of sediment in depositional lobes. This involves the appearance of markedly asymmetric transverse profiles, as well as lengthy recurrence between the sedimentation events on particular sectors of the fans, where headward-eroding gullies develop. The lithology of the source area, where intensely fractured rocks are found, is responsible for an important sediment supply and a significant degree of clast sorting from the source area. Consequently, a weak longitudinal trend in particle size can be recognised, which influences the predominance of longitudinal constant-slope profiles and anomalous relations between both fan area and fan slope and their drainage areas. Recent intense tectonic activity has caused the appearance of abnormally low slopes in upper sectors of some catchments, where mass flows are trapped, and the fans present a subsequently higher proportion of sheet flows. Recent piracy phenomena can be recognised in some of the drainage basins, which indicate rejuvenation of the source area, in which case the fan presents a rapid increase in the proportion of mass flows with the development of a segmented longitudinal profile. Due to the recent nature of the processes, the morphometric relations in the fan fed by the basin affected by capture do not coincide with the other fans in the area.

Long‐term Control Mechanisms of Stream Piracy Processes in Southeast Spain

The Guadix Basin developed as an endorheic depression during the Upper Miocene‐Upper Pleistocene. Its principal palaeogeographical characteristics are a large lake in the eastern sector, an axial fluvial system and two fluvial systems transverse to it in the western sector. The uplift of a central sector of the Betic Cordillera during the Upper Pleistocene affected the study area, causing northward tilting from the Internal Zone of the cordillera (Sierra Nevada and Sierra de Baza), step-faulting of the Plio-Pleistocene infill of the ancient basin (leaving more northern sectors in a lower topographical position), alteration of fluvial current profiles and displacement of the ancient Axial System to a position very close to the divide between the ancient endorheic Guadix Basin and the Guadalquivir Basin. This facilitated capture of the endorheic basin by the headward erosion of a tributary of the Guadalquivir River. The region then began to be rapidly eroded, as the new base level was now some 500 m lower than that of the ancient basin. The present drainage network is similar to that of the ancient endorheic basin as regards the location of the main streams and the distribution of drainage patterns and fluvial styles, although flow reversal is found in some stretches and a barbed drainage pattern appears locally. As a result of the inheritance of drainage from the ancient basin, fluvial superimposition is found in some stretches of the main streams.

Contribution of environmental isotopes to the understanding of complex hydrologic systems. A case study: Sierra de Gador, SE Spain

Determining the content of 18O and deuterium in the groundwater at the southern edge of the Sierra de Gador, between October 1991 and March 1993, has enabled identification of the flow system of the waters, the recharge and mixing processes and the possible mechanisms of salinization. Analysis of the precipitation indicates the dominant source and direction of the air masses. The local meteoric water line that is established indicates a primarily Mediterranean origin for the precipitation recharging the aquifers. The variation of 18O content with altitude (−0·35 per mille per 100 m) enables an estimation of the principal recharge area, which corresponds to a zone between 1200 and 1800 m a.s.l.

Conditioning factors in flooding of karstic poljes—the case of the Zafarraya polje (South Spain)

Abstract The Zafarraya polje undergoes periodical flooding, of which the last episode (1996–1997) was analysed in detail on this paper. On the basis of the retention curves of the two lakes that formed in the northwestern and southwestern sectors, we calculated the total infiltration capacity of the polje to have a maximum value of 3–3.5 m3/s and so we infer that when the flow of the Arroyo de la Madre exceeds this figure, there will be a risk of flooding in the polje. We also propose a model for the 1996 flood that can be extended to other similar occurrences in this and other poljes where we can establish the role played by groundwater and surface water during this flood. In response to the heavy precipitation, the flow of the Arroyo de la Madre rose abruptly, exceeding the infiltration capacity of the main swallow holes on the polje, causing first the northern lake and then the southern lake to form with only surface water supply. The water table of the karst aquifer rose sharply, reaching a situation of equilibrium between the level in the lakes and the water table in this sector of the karst aquifer that prevented infiltration through the swallow holes. In the case of the southern lake, there were even cases of swallow holes that began to operate as estavelles. During this phase of maximum flooding, one single lake was present, which was divided into two once more when the water table of the karst aquifer in the polje sector began to fall and surface supply also began to decrease.

Saltwater intrusion into a small coastal aquifer (Rio Verde, Almuñecar, southern Spain)

Abstract A mathematical simulation of the contact zone between fresh water and salt water in the Rio Verde aquifer via two models leads to a satisfactory understanding of the development over time of a saline wedge. One of the two models is a finite-element model, taking both fluids to be immiscible; the other is a finite-difference model, which considers the zone as being a single phase of variable density. Whereas the latter, mass-transport model, gives more accurate information about the composition of the mixing zone, the sharp interface model, although somewhat less precise, gives a 3-D picture of the freshwater-saltwater contact. The application of both models leads to the conclusion that the saline wedge is gradually encroaching inland.

Processes affecting groundwater temperature patterns in a coastal aquifer

The temperature depth profiles of six wells in the Motril-Salobren∼a aquifer were used as a basis for a comparative analysis involving various parameters to determine their relations and factors influencing the different trends. There is a clear influence of ambient temperature on all the profiles, with a lag time of two to five months. Nevertheless, there are clear differences in the temperature depth profile patterns that can be accounted for by other factors. First, there is a greater influence of localized recharge; Guadalfeo River as opposed to diffuse recharge; irrigation return flow and rainfall. Three of the wells located near the riverbed of the Guadalfeo River have extremely variable temperature-depth profiles and show clear river influence. In springtime, during the highest flood stages of the river due to cold melt water from the Sierra Nevada, the groundwater falls in temperature. During secondary peaks in river flow rates during the autumn due to rainfall, the warm water increases groundwater temperature. The effect of the river recharge decreases with distance from the course since there is less mixing with water from the Guadalfeo River. In addition, there are two temperature-depth profiles in which temperature variations remain shallow and follow a pattern that cannot be attributed to the influence of either of the above two parameters. Among these two cases, the most influential factor is the groundwater flow pattern typical of a discharge zone, characterized by vertical-flow components.

The Effects of Non-TIDAL Components, Depth of Measurement and the Use of Peak Delays in the Application of Tidal Response Methods

The efficacy and applicability of tidal response methods (TRMs) were assessed in terms of the techniques used, the, data used in the analysis, and the implementation of the methods under different conditions. The tidal efficiency (TE) and time lag (TL) methods were applied to directly measured groundwater head (GWH) values in the Motril-Salobreña coastal aquifer and compared with the same pre-filtered time series after eliminating the non-tidal signals through the continuous wavelet transform (CWT) procedure. The use of maximum and minimum groundwater peaks and sea-level peaks in combination to obtain different delay values and the effects of asymmetries in tidal fluctuations were assessed. Application of the TE method yields different D values when a complete groundwater head time series is considered, instead of the net induced tidal oscillation. Moreover, when the asymmetry of tidal oscillations is not taken into account, the application of TL may yield a higher uncertainty. In unconfined coastal aquifers, hydraulic diffusivity can be overestimated by the TE method if the non-tidal components are not removed from the measured time series of groundwater head. However, prior filtering provides better diffusivity results when the TE method is applied. The depth of the water head measurements leads to different D values when applying the TE method as a consequence of the changes in the specific storage with depth, which result from changes in pressure. The results of the application of the TL method depend on whether maximum or minimum peaks are used. Since the use of maximum peak delays can overestimate D, minimum peak delays are recommended, as they yield D values that are closer to the values obtained using the TE method.

Groundwater and Global Change in the Western Mediterranean Area

ed. This volume did not lead to long-term irreversible environmental effects, as evidenced by the recovery of the piezometric levels from 2007, reaching in 2010 a value similar to those before pumping (Fig. 4). Abstractions planned for the period 2017–2020 have been determined by the CHS taking into account the historical response of the aquifer in similar drought situations.

Assessing the Uncertainties of the Water Budget in the Torrevieja Aquifer (Southeast Spain)

The frequent scarcity of water in the coastal aquifers of the Mediterranean areas makes essential the adequate management of groundwater with a good knowledge of the inputs and the outputs of the aquifers. The establishment of the water budget of aquifers is often hindered by uncertainties in the connection with other aquifers and the sea, or the permeability of layers that can disconnect hydraulically parts of the system. In the study of these regions, a common challenge is the lack of information at deep locations or disperse data in time and space that do not allow to provide reliable answers. Under these circumstances, the construction of simplified numerical models simulating groundwater flow can be used to verify or deny different hypothesis. In this study, the characteristics of Torrevieja aquifer (South East of Spain) have been analyzed proposing alternative conceptual models to explain the annual deficit of 4.4 Mm3 between inputs and outputs. The effect of a semipermeable top layer and the differentiation of the aquifer in two parts with distinct recharge sources was tested and compared with the hydrochemical information of groundwater samples to provide new perspectives about the characteristics of this aquifer. This study also shows how to use common hydrogeological tools and information of databases to address the uncertainties in the study of coastal aquifers.