A pilot study on the conjunctive use of surface water and groundwater resources during a drought period. The case of pumping groundwater in Calanda irrigation area (Aragon, Northeast of Spain)

by Javier Salomó^1,*, María Teresa Carceller¹, Alba Cervera², Rosana Navarro³, Antonio Sarasa³, Antonio Albarracín⁴, Agustín Blas⁴, Raúl Celador⁴, Gabriel Gallardo⁴, Andrés Maestre⁴, Carlota Oliván⁴, Laura Roy⁴, Javier Serrano⁴, Antonio Quintana⁵

¹ Oficina de Planificación Hidrológica, Confederación Hidrográfica del Ebro

² Comisaría de Aguas, Confederación Hidrográfica del Ebro

³ ESHYG S.L. (Estudios Hidrogeológicos y Geotécnicos, S.L.)

⁴ TRAGSATEC (Sociedad Estatal Tecnologías y Servicios Agrarios, S.A., S.M.E., M.P.)

⁵ TRAGSA (Empresa de Transformación Agraria, S.A.)

^* Corresponding author: jsalomo@chebro.es

Abstract

During hydrologic year 2023-2024, there was a severe drought event affecting the Guadalope River catchment. The Ebro River Basin Organization set a pilot study in the area, which consisted of pumping groundwater from an existing drilled well into the Calanda reservoir at a flow of 250 l·s^-1 for 17 days. Results showed that, during the drought period, there was hydraulic connection among nearby aquifers but not between the Guadalope River and the contiguous aquifers. It can be concluded that it would be necessary to complete this pilot study to obtain new and more accurate hydrogeological data. It is also considered that those who will be benefited from the pumping should be the promoters of new pumping tests in the future.

Keywords

groundwater, drought, pumping, conjunctive water use, Ebro River basin.

Note:

Papers published in this special issue of the European Geologist journal have undergone a thorough peer-review process but have not been copy-edited. Authors bear full responsibility for the linguistic accuracy of their contributions.

This work is licensed under a Creative Commons Attribution 4.0 International License.

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1. Introduction

Droughts are natural challenges for the economic, social and environmental development of whatever region or country in the Mediterranean basin. In addition, climate change effects can aggravate the impacts of droughts, adding pressure to already water-stressed areas. In order to face these events in the best possible way, Administrations usually elaborate and approve Drought Management Plans (DMPs). DMPs contain the basic technical rules and law procedures to officially declare drought situations. Besides, DMPs compile the list of measures to apply and the actions to be carried out by the competent Administrations. Therefore, it can be stated that DMPs represent strategic tools with positive results in drought impact adaptation.

One example of these DMPs is the 2018 Ebro River Watershed Drought Management Plan (2018 Ebro DMP), which is managed by the Ebro River Basin Organization (CHE). Among other measures, the 2018 Ebro DMP includes a group of actions focused on managing drought events in the Guadalope River catchment. One of these actions is to consider a conjunctive water use, abstracting surface water alongside groundwater from both the Guadalope River and its surrounding aquifers. This action is planned to be applied nearby the zone of natural water discharge of the springs called “Los Fontanales”, upstream the Calanda dam (Teruel province, northeast of Spain).

During hydrologic year 2023-2024, there was a severe drought event, which affected the Guadalope River basin. According to available data, before the beginning of the irrigation campaign, the total volume of water resources retained in the reservoirs within the limits of the Guadalope River basin was only 22.4 % of the maximum storage capacity. Following the provisions of the 2018 Ebro DMP, at 13^th June 2024, the Presidency of CHE officially declared the situation of “Exceptional Situation due to Extraordinary Drought” (SESE, acronym after the name in Spanish) in the Guadalope River basin. Thus, the above-mentioned action of conjunctive water use from different sources started to be applied.

1.1. Brief description of the study area

From an administrative point of view, the study area belongs to the Bajo Aragón region (within the Autonomous Community of Aragón). It extends from the southern Ebro River basin to the last foothills of the Iberian System.

The study area has a dry continental Mediterranean climate, with an average air temperature of 15.2 ºC. It has cold winters and hot, dry summers. Its average annual rainfall and reference evapotranspiration (Penman-Monteith method) are 367 mm and 1331 mm, respectively (2004-2024), according to data from the agrometeorological station of Calanda [1], located in the study area (UTM X: 734842; UTM Y: 4538190).

The aquifer located on this study area pertains to the Aliaga-Calanda groundwater body (code ES091MSBT092, after Third Hydrological Plan of the Ebro River). Covering a total surface of 1,858 km² distributed among the provinces of Castellón, Teruel and Zaragoza, this groundwater body presents a significant structural complexity, since it is located on the interference zone between the Iberian and the Catalánides mountainous ranges, which is characterized by the existence of numerous fold-and-thrust belts that determine its hydrogeological functioning. The Jurassic carbonate formations act as a thick regional aquifer, recharged by permeable outcrops and by rivers seepage in the headwater areas, where piezometric levels are below the surface streams. Water discharges occur in the lowest areas of the watershed, where the natural streams and rivers intercept the piezometric levels of the regional aquifer, as is the case of “Los Fontanales” springs.

Guadalope and Bergantes Rivers cross the study area. The Guadalope River is a tributary of the Ebro River by its right bank. The Guadalope River is 160 km long and its basin has a total surface of 3870 km². This surface encompasses the provinces of Castellón, Zaragoza and Teruel, largely this last one. It rises in the Iberian System (“Puerto de Sollavientos”, province of Teruel), at an altitude of 1600 masl, and it flows into the Ebro River, at 110 masl, next to the village of Caspe (province of Zaragoza). The Bergantes River is the main tributary of the Guadalope River by its right bank. It is 64 km long and its basin has a total area of about 1201 km². The Bergantes River also rises in the Iberian System (“Els Ports”, province of Castellón), at an altitude of 1230 masl.

Like many other rivers in the Ebro River basin, the basin of the Guadalope River is regulated by several dams, whose reservoirs supply water to meet agricultural, urban and industrial demands, to generate hydroelectric power or for recreational uses. The big five current reservoirs along the course of the Guadalope River, from upstream to downstream, are Aliaga (0.9 hm³), Santolea (42.6 hm³), Calanda (54.3 hm³), Caspe (81.5 hm³) and Moros (0.5 hm³).

In the study area, the Guadalope River entries into the Calanda reservoir. In the same area, there can be found the mouth of the Bergantes River into the Guadalope River, just in the entrance (tail) of the mentioned reservoir (see Figure 1).

Downstream the Calanda dam, there is an important agricultural production area. Water supply through irrigation canals from Calanda reservoir is one of the key factors for farming production in this region. Particularly, this agricultural area is specialised in fruit tree production. Most of the cropland is devoted to peach production, which is mostly commercialised under the Protected Designation of Origin “Melocotón de Calanda” (an officially-protected status). It can also be underlined the production of quality extra virgin olive oil under the Protected Designation of Origin “Aceite del Bajo Aragón”.

1.2. Previous studies in the study area

Some hydrogeological studies have been already conducted in this area previously, from the end of eighties until nowadays, although in a discontinuous way. It can be stated that the elaboration of hydrogeological studies in this area has been always linked to the development of projects regarding irrigation or industrial water supply.

ENDESA (Empresa Nacional de Electricidad, S.A.) conducted a hydrogeological study in 1987 [2], whose aim was to elaborate a geological cartography that fits better to the reality on field. This study established the boundaries of the hydrogeological unit of “Los Bertolines-Cantera del Pinar”, which is made up of Triassic and Jurassic (Dogger-Malm) carbonate materials that, although disconnected in some areas, naturally respond as a single aquifer unit. Guadalope and Bergantes Rivers cross this hydrogeological unit and it was inferred that both streams could have an influent nature in this area. The annual total infiltration was quantified of about 11.27 hm³ and the estimated discharge through the springs of “Los Fontanales” was quantified of about 1000 l·s^-1.

In 1996, the MOPTMA (Ministerio de Obras Públicas, Transportes y Medio Ambiente), through its Geological Service [3], published the results of a pumping test which had been conducted in “Masía Nueva 1” well. A flow up to 92 l·s^-1 was pumped, with extremely high transmissivity values that were very difficult to estimate, given the rapidity with which static level was reached. There was a possible connection with the Guadalope River, located about 340 m away. In this study, it was also identified that the main discharge area was around “Los Fontanales” springs.

In 2007, ENDESA [4] conducted a 170-hour phased pumping test in “Masía Nueva 2” well. A maximum flow of 334 l·s^-1 was pumped for 2220 minutes. Residual drawdown was 0.38 m after 4 hours of recovery. The calculated values of transmissivity ranged between 12000 and 15500 m² per day, and the calculated values of storage coefficient ranged between 0.004 and 0.01. In order to estimate those hydraulic parameters of that pumping test, the EPHEBO computer programme was used.

The EPHEBO software was developed by the Department of Soil Mechanics at the Polytechnic University of Catalonia. EPHEBO allows the interpretation of pumping tests through automatic calibration by using graphical methods (Theis, Hantush, Cooper-Jacob, Neuman superposition).

The data was interpreted based on pumping and level recovery in the pumping well (“Masía Nueva 2”), taking into account the hydraulic losses obtained through automatic calibration, as well as the observed drawdown in the “Masía Nueva 1” well.

The results of these previous studies may confirm the existence of a highly productive aquifer, with a regional flux and a very large water supply area available for exploitation. Nevertheless, it has been difficult to determine the precise extension of this regional aquifer. In fact, despite these preliminary conclusions, it is considered that one of the main lacks is a major knowledge of the hydrogeology in the study area. This is an important fact that constraints any hydrogeological study in this area. It is clear that to know the extension of the regional aquifer is pivotal in order to better estimate the available groundwater resources.

2. Objective

The objective of this pilot study was to determine the feasibility of the conjunctive water use from three different perspectives: economic, social and environmental. It should be underlined the designed working procedure: several public and private actors got involved in this project in a coordinated and cooperative way, establishing a team-working network.

3. Materials and methods

For this pilot study, three drilled wells (“Masía Nueva 2”, “Masía Nueva 1” and “Fontanales”) were operated and monitored. “Masía Nueva 1” and “Fontanales” acted as piezometers.

• “Masía Nueva 2” is 285.58 m deep and it penetrates into the Upper Jurassic calcareous materials (Malm). It was drilled in 2007, during a pumping test undertook by ENDESA (see 2. Previous studies in the study area). This well was drilled using direct rotary percussion and reverse rotation, tubed with blank and punched casing with a diameter of 550 mm up to 198.5 m and 400 mm up to 285.58 m, with the upper 19.5 m of the annular space being cemented.
• “Masía Nueva 1” is 264 m deep and it penetrates into the Middle and Upper Jurassic limestone materials, which are highly karstified (Dogger-Malm). It was drilled in 1992, during a pumping test undertook by the Geological Service of the MOPTMA (see 2. Previous studies in the study area).
• “Fontanales” is 190 m deep and it penetrates into the Lower Jurassic materials (Lias) and the Upper Triassic materials (Keuper). It was drilled in 2007, during a pumping test undertook by ENDESA (see 2. Previous studies in the study area). A total deep of 156.26 m was tubed, cementing until the end of the drilling.

“Masía Nueva 2”, “Masía Nueva 1” and “Fontanales” wells are located in the municipality of La Ginebrosa (province of Teruel), although the related aquifer also extends to the neighbouring municipalities (Mas de las Matas, Aguaviva and Foz-Calanda). The distance from “Masía Nueva 2” is 111 m to “Masía Nueva 1” and 1190 m to “Fontanales”.

Figure 1 shows the location of the three monitored wells in the study area.

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During the design of the pilot study, two main technical concerns arose:

• The radius of influence caused by the pumping from the “Masía Nueva 2” well.
• The possible influence of the pumping on the Guadalope River’s flow rate. The distance between the “Masía Nueva 2” well and the nearest point of the Guadalope riverbed was only 300 metres.
• The preparation of the pumping test involved a series of technical tasks at various locations:
• Video-monitoring inside the “Masía Nueva 2” well, to verify that there were no physical obstructions.
• Installation of automatic level measuring devices in the “Masía Nueva 2”, “Masía Nueva 1”, and “Fontanales” wells.
• Preparation of gauging points along the Guadalope River (6), “Los Fontanales” springs (1) and an irrigation canal (1) that supplies the irrigation tract of Mas de las Matas. These preparatory tasks also involved the topographical survey of all the designated points. In the study area, there are not official gauging stations in the Guadalope River nor in the Bergantes River.

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It must be considered that the location of the gauging points was based on hydrogeological criteria, but also on the initial conditions of the gauged sections, given the fact that the use of mechanical means for their adaptation was not feasible. Flow control was carried out using current-meter gauges directly in the designated sections along the riverbed. Having been prepared for the only purpose of this study, these places were not official monitoring gauging stations. This is why gauged sections included rocky riverbeds and vegetated banks, which generated “shadows” and “flow tubes,” as well as fluctuations in the water level and some turbulence in higher-velocity areas. As a result, measurement errors (10-15%) could be considerably greater than those existing in official gauged sections.

Next, control points shown in Figure 3 are described.

• This gauging point was located on the Guadalope River, upstream P3.1. This was the initial gauging point.
• This gauging point was located on the irrigation canal that supplies the irrigation tract of Mas de las Matas. This irrigation canal comes from the Guadalope River upstream P1 and it flows into the Guadalope River upstream P3.1.

In consequence, the sum of flows in P1 and P2 was considered as the total measured flow in the Guadalope River upstream P3.1.

• 1. This gauging point was located on the point of water discharge from the “Masía Nueva 2” well into the Guadalope River, downstream P1 and P2. The distance between “Masía Nueva 2” and this point of discharge was 400 metres.
• This gauging point was located on the Guadalope River, downstream P3.1 and upstream P4.
• This gauging point was located on the confluence of the Bergantes River into the Guadalope River, downstream P3.
• 1. This gauging point was located on the Guadalope River, downstream P4.
• This gauging point was located on the Guadalope River, downstream P5.1 and upstream P6 and P7. From a geological perspective, this gauging point was located on the transition between Jurassic and Triassic materials in the regional aquifer.
• This gauging point was located on the Guadalope River, downstream P7.
• This gauging point was located on the springs called “Los Fontanales”, between P5 and P6, over one specific surge water hole. It was located on the left bank of the river, at an elevation of approximately 2.5 m above the water level at the time of the study. Another surge was also monitored, but only visually, without any gauging operation, on the right bank of the river, just in the opposite side of P7, at a roughly similar elevation.

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The pumping test was carried out at the “Masía Nueva 2” well from 13 to 30 August 2024. Starting with a flow rate of 100 l·s^-1, this value was raised at a steady pace up to 175 l·s^-1 after 30 minutes and, from here, to 250 l·s^-1 after another 30 minutes, value that was kept constant for the rest of the pumping test, which lasted for an additional time of 17 days and 7 hours. The pumping test was carried out following a technical working procedure that was established before the start of the pumping test.

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Groundwater levels in the three wells and surface waters flow rate in the gauging points were monitored according to the above-mentioned technical working procedure.

Water samples were taken from both surface waters and groundwater for analytical determinations, having been conducted in situ more than 200 (pH, temperature and electrical conductivity). Apart from these in situ analytical determinations, other 52 were conducted in an accredited laboratory for the most common elements and parameters. Water samples were also taken from the “Masía Nueva 2” well to carry on potability tests.

Initially, a total volume of up to 0.45 hm³ had been foreseen to be abstracted, but, at the end of the pumping process, the final abstracted volume from the “Masía Nueva 2” well was 0.39 hm³ (87 %). This difference was due to a breakdown in the generator of the pumping equipment, which forced to stop the pumping test ahead of schedule.

Finally, obtained results have been analysed and discussed. It is expected that, in future drought events, water users in the study area would undertake the methodology followed in this pumping test, taking into account the practical recommendations derived from it.

4. Results

4.1. Hydrogeological functioning of the aquifer

Table 1 shows the registered values of the pumped flow and the piezometric drawdown per each pumping stage in the “Masía Nueva 2” well. Initially, before the start of the pumping test, the registered static level was 52.37 m in the “Masía Nueva 2” well.

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Table 1: Registered values of the pumped flow and the piezometric drawdown per each pumping stage in the “Masía Nueva 2” well.

Pumping stage	Flow (l·s-1)	Time (minutes)	Accumulated time (minutes)	Partial drawdown (m)	Accumulated drawdown (m)	Dynamic level (m) after each pumping stage
1	100	30	30	0.43	0.43	52.80
2	175	30	60	0.69	1.12	53.49
Long duration	250	24900	24960	2.16	3.28	55.65

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Table 2 shows the registered values of the partial increase and the final residual drawdown in the piezometric level in the “Masía Nueva 2” well after a recovery period of 39 days.

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Table 2: Registered values of the partial increase and the final residual drawdown in the piezometric level in the “Masía Nueva 2” well.

Time (days)	Partial increase (m)	Final residual drawdown (m)	Static level (m) after the recovery period
39	3.14	0.14	52.51

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In Table 2, the final residual drawdown has been calculated as the difference between the total accumulated drawdown (3.28 m) and the partial increase (3.14 m).

Table 3 shows the registered values of the piezometric drawdown in the “Masía Nueva 1” well during the pumping test. Initially, the registered static level was 49.30 m in the “Masía Nueva 1” well.

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Table 3: Registered values of the piezometric drawdown in the “Masía Nueva 1” well during the pumping test.

Flow in “Masía Nueva 2” well (l·s-1)	Time (minutes)	Drawdown (m)	Accumulated drawdown (m)	Dynamic level (m)
100-175	60	0.27	0.27	49.57
250	24900	0.99	1.26	50.56

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Table 4 shows the registered values of the partial increase and the final residual drawdown in the piezometric level in the “Masía Nueva 1” well after a recovery period of 39 days.

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Table 4: Registered values of the partial increase and the residual drawdown in piezometric level in the “Masía Nueva 1” well.

Time (days)	Partial increase (m)	Final residual drawdown (m)	Static level (m) after the recovery period
39	1.16	0.10	49.40

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In Table 4, the final residual drawdown has been calculated as the difference between the total accumulated drawdown (1.26 m) and the partial increase (1.16 m).

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Table 5 shows the registered values regarding the “Fontanales” well.

Piezometric level at 13 August 2024 (m)	32.73
Piezometric level at 30 August 2024 (m)	33.37
Piezometric level at 2 September 2024 (m)	33.20
Accumulated drawdown during the pumping test (m)	0.64 m
Partial increase from 30 August to 2 September 2024 (m)	0.17 m
Final residual drawdown (m)	0.47 m

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In Table 5, the final residual drawdown has been calculated as the difference between the total accumulated drawdown (0.64 m) and the partial increase (0.17 m). Unlike the other two wells, in the “Fontanales” well a monitored recovery period of 39 days could not be attained because of a failure in the automatic-measuring device, installed in this well, on 2 September 2024.

Figure 5 shows the evolution of the piezometric levels before, during and after the pumping test in the three monitored wells: “Masía Nueva 2”, “Masía Nueva 1” and “Fontanales”.

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Continuous pumping for almost 18 days resulted in a slight drawdown of approximately 3.28 m in the “Masía Nueva 2” well, 1.26 m in the “Masía Nueva 1” well and 0.64 m in the “Fontanales” well. It can be affirmed that the pumping well (“Masía Nueva 2”) showed an immediate recovery.

4.2. Hydrogeological functioning of the river

As it has been mentioned in the heading 3. Materials and methods, six gauging points were set up along the course of the Guadalope River: P1, P3, P4, P5.1, P5 and P6.

Figure 6 shows the evolution of the flow rate in the Guadalope River along the studied period.

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Eventually, the variation of flow in the Guadalope River along its course in the study area was estimated. This variation has been calculated as the difference in flow values between different control points, before, during and after the pumping test.

Figure 7 compares two analysed scenarios. On the one hand, the scenario 1 (blue continuous line), which consists of the registered flow variation in the Guadalope River between the final control point (P6) and the initial control points (P1+P2). Therefore, scenario 1 is not an estimation but it is based on real data. On the other hand, scenario 2 (orange discontinuous line) shows the estimated Guadalope River discharge under the assumption of no abstraction from the aquifer during the same period.

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4.3. Hydrogeological functioning of the springs

As it has been mentioned in the heading 3. Materials and methods, one gauging point was set up in one fountainhead in the zone of water discharge of “Los Fontanales” springs: P7.

Figure 8 shows the evolution of water discharge in the “Los Fontanales” springs before, during and after the pumping test. This discharge has been estimated as the difference between the values of flow in P5 and P6 control points in the river.

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4.4. Hydrochemical parameters

As it has been explained in the heading 3. Materials and methods, some hydrochemical parameters were determined both in situ and in laboratory along the studied period.

Figure 9 shows the results for the Piper diagram.

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Next, as another example of the conducted analysis, Figure 10 shows the graphic representation of the concentration of sulphate and bicarbonate, for all the conducted 52 analytical determinations:

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A first valuation about the sulphate-bicarbonate graphic brings there is no intersection groups between the surface waters and the groundwater.

4.5. Hydraulic parameters

The estimated hydraulic parameters of the aquifer were the permeability (K), the transmissivity (T) and the storage coefficient (S). These hydraulic parameters could be calculated thanks to the monitoring of groundwater piezometric levels before and during the pumping test, and also after the pumping test, that is, during the recovery period. The applied methodology to calculate the mentioned hydraulic parameters were both Theis and Jacob methods.

Table 6 shows the calculated values of these hydraulic parameters in the “Masía Nueva 2” and “Masía Nueva 1” wells comparing Jacob and Theis method.

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Table 6: Calculated values of hydraulic parameters using both Jacob and Theis method in the “Masía Nueva 2” and “Masía Nueva 1” wells.

	“Masía Nueva 2” well		“Masía Nueva 1” well		S	Radius of influence (m)
Method	T (m2 per day)	K (m per day)	T (m2 per day)	K (m per day)
Theis (1)	8600	27	17200	80	0.014	2860
Theis (2)	9200	29	10400	48	0.031
Jacob	7600	23	9000	42	0.043
Recovery test	6400	20	8800	41
Average values	7950	24.75	11350	48	0.03

⁽¹⁾ Use of graphic methods and formulas.

⁽²⁾ Use of software ‘PIBE’.

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These hydraulic parameters were not calculated for the “Fontanales” well. As it has been explained in the heading 4.1. Hydrogeological functioning of the aquifer, after the end of the pumping test, the automatic-measuring device and the data-logger installed in this well stopped working due to technical problems, having not being possible to take the measurements manually.

4.6. Economic costs of the pumping test

It is expected that this course of action of conjunctive water use be applied and monitored by the interested users, mainly irrigators’ communities. Therefore, it would be necessary to replicate this pilot study multiple times to obtain more accurate new hydrogeological data in the study area. Thus, the calculation of the economical costs of the pumping test is a key issue, in order to striking a balance between the abstraction costs and the profitability of getting groundwater from the natural system to ensure crop yields during other possible drought periods in the future.

Table 7 shows the economic costs. The final costs of contracting the technical works have been taken into account.

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Table 7: Economic costs for the pumping test.

Concept	Value
Total cost of technical assistance (a)	179.831,86 €
Total abstracted water volume from “Masía Nueva 2” well (b)	390.000 m3
Unitary cost of pumping groundwater (c) [c = a / b]	0,46 €·m-3

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5. Discussion

5.1. Hydrogeological functioning of the aquifer

It can be stated that the hydrogeological nature of the regional aquifer is only known in detail at its northeast sector, thanks to the previous conducted studies. As it has been mentioned in the heading 1.2. Previous studies in the study area, the hydrogeological boundaries of the aquifer are completely undefined, which poses a serious obstacle to assess the available groundwater resources. This lack of knowledge constraints the definition of any project viability.

In terms of piezometric level, regarding the heading 4.1. Hydrogeological functioning of the aquifer, it should be underlined the comparison among the relative minor accumulated drawdown (3.28 m), the partial increase (3.14 m), the final residual drawdown (0.14 m) and the slow recovery period (39 days). The hydrogeological definition of this sector of the aquifer indicates a trend towards total stabilisation.

The recovery of the water levels in the pumping well can be considered complete. During the period of measurements following the pumping test, the water level experienced rises and falls due to natural evolution in the aquifer. From 29 October 2024 (coinciding with the meteorological event of “cold drop”) until the end of December, the piezometric level even rose above the initial level before pumping.

5.2. Hydrogeological functioning of the river

The possible effluent (gaining) or influent (losing) nature of the Guadalope River with respect to the regional aquifer has been analysed across all control points. It has been observed that the effluent or influent nature of the Guadalope River has varied depending on the chosen control section.

• P1-P3. The hydraulic nature of the Guadalope River in this stretch was described as influent during the analysed period, but it did not influence the piezometric levels in the aquifer.

There was a loss of flow due to infiltration from the riverbed and banks. Under the natural conditions of the pumping test, water infiltration from the river does not depend on the aquifer’s piezometric level because the river “is hanging” over the aquifer. Thus, one of the main conclusions derived from the pumping test is that, in a hydrological state in which the level in the aquifer is below the level of the Guadalope River, the exploitation of the Jurassic aquifer has no impact on the river flow rate in the studied stretch.

In this section P1-P3, during the development of the pumping test, the piezometric level in the aquifer continued falling, but this issue did not have an influence on the hydraulic response of the river in this section: the drop in level did not cause an increase in the amount of water transferred from the river, since, for the aforementioned, infiltrated flow in the river only depends on the hydraulic parameters of the river stream (depth of water and conductance of the riverbed).

In this section P1-P3, there was only one day (06/09/2024) when the river revealed a gaining nature, but this fact was likely influenced by a water release from the Santolea reservoir (upstream the study area). The release of water from the Santolea reservoir serves to supply water both for consumptive uses and to ensuring the river’s established ecological flow regime. This flow rate is around 450 l·s^-1.

• P3-P5. The hydraulic nature of the Guadalope River in this stretch was variable during the analysed period. Before the start of the pumping, this section could had been described as an influent stream, but throughout the pumping test, it tended to become a gaining stream, probably due to the added flow during pumping, although there were times when it also revealed a “losing” nature.

It is likely that these occasional and temporary changes in the hydraulic trend be normal in this section because it is an equilibrium section, near the entrance into the Calanda reservoir.

• P5-P6. This section was affected by the water discharge from the “Los Fontanales” springs that drained through the Liassic aquifer. The hydraulic nature of the Guadalope River in this stretch was described as effluent (gaining stream) during the analysed period.

In conclusion, it can be said that the flow in the Guadalope River, between P1 and P3, usually decreases, whereas it usually increases between P5 and P6, being it possible a shift between P3 and P5. For instance, it could happen that, during hydrological favorable circumstances, the Guadalope River show a net flow gaining in P3-P5 stretch.

On the whole, there is a net flow gain in the Guadalope River, within a range from 500 to 700 l·s^-1. At the beginning of the study section, gross water losses occur; at the end of the study section, gross water gains occur in the “Los Fontanales” discharge zone; and, in the intermediate zone, there are specific and temporary variations in the hydrogeological functioning of the river with respect to the aquifer.

If there had been no pumping, it is estimated that the circulating flow would probably have been by the order of magnitude of the abstracted water flow from the well (250 l·s^-1), although the flow can be highly variable (Figure 7).

In the study zone, the Bergantes River is characterized by not providing surface water resources except during periods of heavy rainfall at its headwaters.

5.3. Hydrogeological functioning of the springs

In this study, an average discharge of around 695 l·s^-1 has been estimated in “Los Fontanales” springs zone. The springs flow rate tended to decline during the pumping test, although measurements taken after the pumping test showed a similar downward trend, without the influence of pumping and with all piezometric levels in the aquifer recovered (Figure 8). In conclusion, the observed total decrease in the springs flow rate might be due to the sum of the decrease caused both by pumping and by the natural evolution of the aquifer under these dry weather conditions.

5.4. Hydrochemical parameters

Hereinafter, a very brief preliminary evaluation of the hydrochemics results is done.

In general, the different hydrochemical facies are mainly due to the underlying geological materials both in the aquifer and in the river basin.

By one hand, the facies of the water from the “Masía Nueva 2” and “Masía Nueva 1” wells can be characterized as bicarbonate. By other hand, water from the “Los Fontanales” springs also presents important values of concentration of bicarbonate, but also calcium and sulphate, mainly due to the lithology (“Carniolas” formation, which contains anhydrite mineral, so, the geology is rich in gypsum). It can also be pointed out the hydrochemical characterization of the control point P6, which is clearly influenced by the water discharge from the “Los Fontanales” springs upstream.

It is worth noting that the values of electrical conductivity ranged between 700 and 900 µS.cm^-1 both in the wells (groundwater) and control points (Guadalope River).

Finally, according to the potability analysis, the water in the pumping well has a very low concentration of metals, pesticides, and other contaminants, which have been, in any case, always below the established limits for human consumption according to water quality regulations. No microbiological load was detected.

6. Conclusions

Especially regarding the viability of exploiting the aquifer and the possible effects that the exploitation may arise, the derived conclusions from the pumping test carried out from 13 to 30 August 2024 are as it follows:

• The volume that was finally abstracted from the “Masía Nueva 2” well was 0.39 hm³, at a cost per unit rising up to 0.46 €·m^-3.
• Along the end of the summer and the beginning and medium autumn, the rainfall in the Guadalope River basin was an ideal complement to pumping produced water for recovering the levels of the water stored in the Calanda reservoir. In fact, the percentage of stored water with respect to the maximum storage capacity of the reservoir was raised from 21 % up to 76 %, comparing the situation between the mid-June and the beginning of November.
• No potential impact on the river due to this pumping test could be established; that is to say, no recirculation of flows was observed during the studied period.
• The Guadalope River may exhibit a losing (influent) or gaining (effluent) hydrogeological function. Where the river presents an influent hydrogeological function, this is independent of the drawdown caused in the aquifer by pumping. Therefore, the river is hydraulically disconnected from the aquifer.
• It should be noted that the absolute values ​​obtained in this pumping test should be taken with caution due to the multiple anthropogenic factors that influenced the differential gauging. These anthropogenic factors include both the release of water from the Santolea reservoir and the diversion of water to the Mas de las Matas irrigation tract (upstream the study area).
• It should also be noted that, during the pumping test, the established Guadalope River’s ecological flow regime was ensured.
• Pumping has not significantly affected the overall water discharge at the “Los Fontanales” springs zone. However, decreases in flow were observed at the higher elevation discharge points. This might be due to specific impacts from the pumping, and likely as well to the natural evolution of the aquifer.
• For the preparation of any pumping test, it is important to request in advance the corresponding administrative permit. For example, in the case of this pumping test, it was necessary to request authorization from the competent environmental authority in the area.
• It is also important taking into account the possible external negative effects in the environment. For instance, it should be considered the distance of the pumping test from the nearest villages, houses or farms. A constant background noise could cause discomfort to both people and animals, as an uncontrollable stress factor. In the case of people, this could have consequences in terms of health and, in the case of livestock, in terms of well-being, alongside their productivity.
• The results of this pumping test indicate that groundwater resources from the aquifer are significant. The excellent performance of the pumping confirms the existence of a very large water supply area available for exploitation. However, to quantify the existing groundwater resources in the aquifer requires additional studies, given that, currently, there are significant uncertainties regarding the aquifer’s limits and its piezometry, in particular. Special emphasis should be placed on the extent of the Jurassic aquifer along the right bank of the Guadalope River.
• In the context of an investigation project, it would be recommendable to apply isotopic techniques as a complement to the conducted analytical determinations. Isotopic techniques would deepen in the analysis of these water samples, especially regarding a better knowledge about the origin and the traceability of the ions between surface waters and groundwater, in other words, a better knowledge about the hydrogeological relation between the river and the aquifer.

To summarize, it can be established the general following conclusion.

This pilot study can be considered as a successful put into practice of the 2018 Ebro Drought Management Plan (DMP) for the study area. Under the hydrological situation during the pumping test, the viability of the exploitation of the aquifer around the tail of the Calanda reservoir is technically possible, without recirculation of flows between the aquifer and the Guadalope River.

In the future, and, if possible, under different hydrological conditions, it would be necessary to complete this pilot study in order to obtain more accurate new hydrogeological data in the analysed area. It should be noticed that this pilot study is not anymore included in the draft of the following Ebro DMP, so this measure shall be applied and monitored by its stakeholders, consisting of direct users’ communities, in future drought events. In this line, it is also foreseen that the operational pumping costs will decrease in an ordinary exploitation scenario.

7. Patents

There are not patents resulting from the work reported in this manuscript.

Author Contributions: Conceptualization, T.C., R.N. and A.S.; methodology, T.C., A.C., R.N. and A.S.; software, T.C., A.C. and R.N.; validation, T.C. and A.C.; formal analysis, T.C., R.N. and A.S.; investigation, J.SA., T.C., A.C., R.N., A.S., A.A., A.B., R.C., G.G., A.M., C.O., L.R., J.SE. and A.Q.; resources, T.C., A.C., R.N., A.S., A.A., A.B., R.C., G.G., A.M., C.O., L.R., J.SE. and A.Q.; data curation, T.C., A.C., R.N., A.S., A.A., A.B., R.C., G.G., A.M., C.O., L.R., J.SE. and A.Q.; writing-original draft preparation, R.N.; writing, review and editing, J.SA., T.C. and R.N.; visualization, T.C. and R.N.; supervision, T.C. and R.N.; project administration, T.C.; funding acquisition, T.C.

Javier Salomó: J.SA. María Teresa Carceller: T.C. Alba Cervera: A.C. Rosana Navarro: R.N. Antonio Sarasa: A.S. Antonio Albarracín: A.A. Agustín Blas: A.B. Raúl Celador: R.C. Gabriel Gallardo: G.G. Andrés Maestre: A.M. Carlota Oliván: C.O. Laura Roy: L.R. Javier Serrano: J.SE. Antonio Quintana: A.Q.

All authors have read and agreed to the published version of the manuscript.

Funding: this research was funded by the budget of the CHE.

Acknowledgments: the authors are grateful to the town council of La Ginebrosa and to the farmers and irrigators of the Mas de las Matas irrigation tract for their collaboration with this pilot study. The authors thank the hydrogeologists Miguel Ángel García Vera, Felipe Delgado Mangas and José María Gracia Aibar and the geological engineer Yasmina San Juan Juan José for their support in the preparation and interpretation of the figures about the hydrochemical parameters. The authors thank Daniel Merchán Elena for their cooperation during the gauging operations too. Finally, the authors also want to thank the civil engineer Gonzalo Rabasa Pérez for his review of the text.

Conflicts of Interest: the authors declare no conflict of interest.

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There are nor supplementary information nor materials.

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This article has been published in European Geologist journal 61 – 5th IPGC Special Edition 2