ARTIFICIAL RECHARGE AS A TECHNIQUE TO ALLEVIATE THE
OVEREXPLOITATION OF SMALL AQUIFERS LOCATED ON THE
SPANISH MEDITERRANEAN COAST
J.L. Armayor Cachero1 , J.A. de la Orden Gomez1 , J.M. Murillo Díaz1 .
1
Spanish Mining and Geological Institute (IGME), Spain
INTRODUCTION
In south-eastern and eastern Iberia and in the Balearic Islands, there are a number of small
aquifers with limited resources (usually less than 4 hm3 /year) that comprise the sole source
of water for (generally intensive) agriculture and the demands of the tourist industry.
The high demands made on this type of aquifer have frequently resulted in overexploitation and severe levels of marine intrusion. Proposals have been made to alleviate
this problem, particularly since the 1990s, by the application of various techniques and
management strategies. Among such measures is the use of artificial recharge, in various
operational modes.
This article describes studies that have been made of small aquifers in the province of
Alicante, using as a recharge method the construction of retention and infiltration barriers
on the river beds. The examples in question correspond to the coastal aquifers of Jávea and
Vergel (Fig. 1).
BACKGROUND
The Jávea aquifer is in the north of the province of Alicante, lying between Sierra de
Benitachell, Castell de la Solana and Cabo San Martín to the south and Macizo del Montgó
and Cabo de San Antonio to the north. To the east it is in direct contact with the
Mediterranean Sea. This comprises a good example of a small detritic coastal aquifer, with
a surface area of 13 km2 and a mean thickness of 20 m, which has historically suffered
problems of over-exploitation associated with processes of marine intrusion (Pulido, 1976;
IGME-DPA,1982; DPA, 1992; Boluda et al., 1997 a and b) which to date have only been
partially resolved.
The final section of the Gorgos river (known as the Jalón river in the middle sector) is in
direct connection with the Jávea quaternary aquifer. Despite its discontinuous nature, the
river provides the aquifer with natural recharge by infiltration through the river bed when
water is flowing. The basin of the Jalón-Gorgos river is elongated in an E-W direction, with
a surface area of approximately 283 km2 and a total length of 53 km, at altitudes ranging
from sea level to 1,384 m a.s.l.
In the mid-1990s, as a result of the private initiative of local farmers, who are the main
users of groundwater, a number of engineering projects were carried out, consisting of eight
filtering trenches (Armayor et al., 2000) in the bed of the River Gorgos. The aim of these
was to increase the recharge of the Jávea aquifer when surface water flowed. The
infiltration capacity of these constructions, however, given the infrequent flooding of the
River Jalón-Gorgos, is insufficient to resolve the water supply problem in the area.
Figure 1. Location of the study area within Spain: River Jalón-Gorgos and River Girona
basins.
The coastal aquifer of Vergel is also located in the northern part of the province of
Alicante, lying between Sierra de Segaria and Sierra del Mediodía to the north and northwest, and Sierra de Castell de la Solana and Macizo del Montgó to the south and southwest. This aquiferous subunit, forming part of the Plana de Gandía-Denia aquifer, is
detritic, coastal, and has a small surface area of approximately 20 km2 , with a mean
thickness of 27-30 m. The water has suffered from marine intrusion and the contamination
associated with agricultural practices, particularly during the last few decades.
This aquifer presents a hydraulic connection with the River Girona, known as the Ebo at its
source, which provides a natural infiltration recharge through the river bed when water is
flowing. The basin of the River Girona has a surface area of some 118 km2 and it is
elongated in a W-E direction with a total length of 38 km.
Historically, the water resources of the River Girona basin have been exploited by different
methods: the central part of the basin features a dense network of drainage galleries,
horizontal perforations excavated in the soil to channel the alluvial groundwater of the
River Girona. Some of these galleries date back over 700 years, to the time of the Moors,
who used them as the main source of irrigation water. In the upper part of the river, the
Isbert reservoir acts as a system of artificial recharge for the aquifers located to either side,
due to the high permeability of its banks and bed, although it was originally built to store
water for irrigation. The presence of a mill dam in the lowermost sector of the River Girona
means that part of the water flow can be used, by gravity, in artificial recharge by its
conduction into two wells.
METHODOLOGY
To determine the water entering both the Gorgos and the Girona rivers it was necessary to
use a theoretical method, namely that proposed by the US Soil Conservation Service
(S.C.S.) (MOPU, 1987). It was impossible to compile direct data due to the lack of
hydrometric measuring points. The quantity of these water resources and their seasonal
variation determine the viability of the artificial recharge operation.
The initial data used to calculate surface runoff were those corresponding to the daily
precipitation measured over a series of 36 years (1962-1997) in the case of the River JalónGorgos and 11 years (1974-85) for the River Girona. These data, together with others
referring to soil and crop types and the steepness of the terrain, enable us to determine a
precipitation threshold above which runoff occurs, and the quantity of such runoff.
For the River Girona, additionally, an evaluation was made of the subterranean discharge of
various springs that flow into the river and of the flow volumes drained by horizontal
galleries located below the river bed.
At the same time as the study of surface and subterranean water flows, we carried out a
detailed analysis of the lithology of the beds of the Rivers Gorgos and Girona, to determine
the most favourable zones in which to site artificial recharge installations. These would
consist of small dams constructed on the river bed. By identifying the infiltration rate at the
zone considered most suitable for artificial recharge, the installations were optimally sized.
Their effectiveness was evaluated by means of a mathematical flow simulation program,
Flowpath 5 (Franz and Guider, 1995) for the Jávea aquifer and Processing Modflow 4.1
(Chiang and Kinzelbach, 1996) for the Vergel aquifer.
RESULTS
The results obtained are presented separately for the two study areas.
a) Artificial recharge operation in the Jávea aquifer
Statistical analysis of the climatic data reveals a mean annual precipitation of 795 mm, with
a maximum of 1601 mm/year and a minimum of 377 mm/year. In 'wet' years, precipitation
was over 872 mm/year, in normal years it was 642-872 mm/year, while in 'dry' years it was
below 642 mm/year. The mean maximum precipitation in 24 hours was 122 mm, with a
maximum of 230 mm and a minimum of 38 mm. The return period for the maximum 24hour precipitation is 25 years.
The months of maximum precipitation are October to January, while the driest months are
June, July and August. It should be noted that these periods of rainfall are usually
concentrated into a very few days. Thus, 62% of the rainfall over the 36 years analyzed fell
during periods of no more than 24 hours, a datum which is indicative of isolated periods of
intense rainfall (Fig. 2).
12
DAILY SURFACE RUNOFF (1986-1997) River Gorgos
(municipality of Jávea)
3
Daily surface runoff (hm /d)
11
10
9
8
7
6
5
4
3
2
0
01/01/86
01/04/86
01/07/86
01/10/86
01/01/87
01/04/87
01/07/87
01/10/87
01/01/88
01/04/88
01/07/88
01/10/88
01/01/89
01/04/89
01/07/89
01/10/89
01/01/90
01/04/90
01/07/90
01/10/90
01/01/91
01/04/91
01/07/91
01/10/91
01/01/92
01/04/92
01/07/92
01/10/92
01/01/93
01/04/93
01/07/93
01/10/93
01/01/94
01/04/94
01/07/94
01/10/94
01/01/95
01/04/95
01/07/95
01/10/95
01/01/96
01/04/96
01/07/96
01/10/96
01/01/97
01/04/97
01/07/97
01/10/97
1
Dates
Figure 2. Supply of surface water (1986-1997)
The mean concentration period for water proceeding from intense precipitation is 5.2 hours,
with a maximum waterflow after intense 24-hour precipitation of 851 m3 /s. After a 10-hour
intense precipitation, the corresponding figure was 1,579 m3 /s, and after a 4-hour downpour
it was 2,495 m3 /s.
The mean supply of surface water at the altitude of the two sites chosen for artificial
recharge installations is 5.2 hm3 /year, with a maximum of 20.4 hm3 /year in 1986 and a
minimum of 0.1 hm3 /year in 1982. The months of greatest water supply are November,
December and January, concentrated into an average 4 days per year in which water flows
over the river bed, although in some years up to 9 days' flow have been recorded. The mean
flow volume in the river bed for each episode of water supply varies from a minimum of
0.11 hm3 /day to a maximum of 4.1 hm3 /day. The great quantity of these flow volumes
makes it very difficult to design and construct artificial recharge installations, especially
concerning the control of flood waters. Therefore it was decided to propose artificial
recharge systems located actually on the river bed, rather than alternatives such as the
construction of canals or dams (Pulido, 1976). Furthermore, the high density of crops, and
particularly of citrus trees, and the correspondingly high values of land, made it inadvisable
to consider installations that would occupy a significant proportion of such cultivated land.
The two sites selected for the artificial recharge operations (Fig. 3) lie in the zone where
processes of natural recharge of the aquifer are most active, where the river course widens
and then narrows, which facilitates the siting of barriers and where soil infiltration rates, if
the river were dammed, would be around 12 mm/hour. Furthermore, this rate could be
improved to 372 mm/hour by scarification of the soil.
The height of the containing walls at such installations would be limited to a maximum of
2.5 m for safety reasons, in case of flash floods, and a minimum of 1.5 m to optimize the
volume of water available for recharge. The recharge volume could be increased by
dredging and levelling the river bed to increase storage capacity. Taking the two possible
sites into joint consideration, the maximum available volume of water stored for artificial
recharge in the most favourable case would be 117,862 m3 , while in the least favourable
case it would be 62,652 m3 .
A simulated data series was used to create hypothetical recharge episodes for the chosen
sites. The results for the most favourable simulation were a mean annual recharge of 0.48
hm3 , with annual maxima of over 1 hm3 and minima of 0.11 hm3 . For the simulation
performed with walls of minimal height, the corresponding mean annual value was 0.28
hm3 . These results mean that for a water deficit situation in the aquifer, historically
considered to be 1 hm3 or less, the effect of artificial recharge would be to provide an
additional supply representing 10-50% of such a deficit, and reaching 100% in
exceptionally favourable years. The repercussion of this artificial recharge on renewable
aquifer resources calculated at 3 hm3 /year would represent 15% of the mean annual
volume, with maxima of up to 35%.
Finally, by applying the mathematical model and using the data provided by the
simulations of the proposed installations for artificial recharge, a comparative analysis was
made of different hydrodynamic functioning situations, both with and without artificial
recharge. The positive effect of the artificial recharge is shown by the increase recorded in
the piezometric levels of the aquifer
b) Artificial recharge operation in the Vergel aquifer
The mean surface runoff value in the basin of the River Girona was found to be 4.28
hm3 /year. Analysis of the data series shows that the maximum rate of surface runoff was
9.41 hm3 /year, while the minimum rate was just 0.24 hm3 /year.
Analysis of climatic typology revealed that years classified as 'dry' featured a mean surface
supply of 1.62 hm3 /year, while 'moderate' and 'wet' years provided 4.5 and 6.83 hm3 /year,
respectively.
It is interesting to note that, of the entire data series analyzed, over a total of 132 months,
there were 45 months (i.e. 34%) with zero surface runoff. In the series, the maximum
number of days per month in which water flowed over the river bed was five,
corresponding to the month of January 1977.
The months in which artificial recharge would be viable from the quantitative point of view
of an available surplus correspond, on the one hand, to December to May, when there is the
strongest guarantee of water supply to the installations, and on the other hand, to the
months of June and November in which there would be a "failure" risk of around 50% of
the days. The remaining months do not present a water surplus available for artificial
recharge operations, except in very sporadic flooding situations.
2º.SITE. 2ª SIMULATION
Wall height: 2,5 m. Altitude of wall a.s.l.: 19 m.
Volume of water retained: 97405,3 m 3.
Surface area inundated: 77183,9 m 2.
BLOCK DIAGRAM
Water retained
NORTH
PLA D'EN ROCA
PD. LA RIBA
RELIEF PLAN OF THE INUNDATED AREA
30 0m
20 0m
PLA D'EN ROCA
10 0m
19 m
0m
N
-10 0m
PD. LA RIBA
0m
100m
200m
300m
400m
500m
600m
700m
Figure 3. Simulation of the volume and surface area inundated at one of the selected
sites.
The proposed recharge installation is based on the infiltration of water through the bed of
the River Girona, by means of retention structures sited on the bed itself. These would
consist, basically, of dikes, with a height of one to two metres and a width equal to that of
the river bed. These would be constructed either of concrete or of inflatable rubber, or
alternatively by amassing the materials comprising the river bed.
To determine the number of dikes required, a topographic study of the profile of the river
was carried out, and the permeability of the river bed determined. In total, 13 dikes could
be constructed downriver from the Isbert Dam, with a distribution as shown in Fig. 4.
Figure 4. Scheme of the distribution, along the river course, of various retention and
infiltration barriers, as proposed for the basin of the River Girona.
The proposed installation would have a water retention capacity of somewhat over 70,000
m3 , with the volume retained by each dike being 1,100 to 7,700 m3 . Our analysis shows that
the installation could infiltrate, over a period of ten years, slightly over 18 hm3 of water
(with a mean of 1.82 hm3 /year), which would represent 21% of the total water surplus
available. This figure would increase the aquifer's groundwater resources of 11.1 hm3 /year
(Murillo et al., 1998) by 16%.
CONCLUSIONS
The utilization of the intermittent water flow of the Rivers Jalón-Gorgos and Girona to
obtain an artificial recharge of the coastal aquifers of Jávea and Vergel (Alicante), which
have long suffered problems of over-exploitation and marine intrusion, could be a highly
beneficial hydrogeological project.
The artificial recharge structures along the course of the River Gorgos would consist of
small concrete dams backed up by levelling and scarification work within the area to be
transformed.
The proposed artificial recharge programme requires, before any further action is taken,
complementary studies to be made of flash-flood phenomena to identify and control the
effects of possible inundations in the region of the installations.
It is estimated that, although more specific details are still necessary concerning certain
aspects of the construction project, the water re-infiltrated into the Jávea aquifer might bear
a cost of around 10 pts/m3 . Nevertheless, if it became necessary to create special structures
in the vicinity of the infiltration installations in order to prevent flash-flood damage, then
the cost of the recharged water would be considerably increased and the project would
cease to be economically viable.
With respect to the artificial recharge operations considered for the basin of the River
Girona, studies have revealed the existence of water surpluses, both from surface runoff
and as groundwater, in sufficient quantity to justify planning artificial recharge
installations. Of the multiple options presented by this technique concerning the type of
infiltration installation that could be used, only one is analyzed in this communication,
namely retention and infiltration dikes. However, this option is not the only one considered
in the overall study of the river basin, as other types of recharge installation exist, such as
wells with deep-level horizontal galleries, the development and viability of which are
testified to by over 15 years' successful functioning (Murillo et al., 2000).
Although further studies are needed to obtain a more precise calculation of the investment
required to construct a recharge system such as the one proposed, it is estimated that the
cost of recharged water might vary between 2 and 3 pts/m3 .
Acknowledgements
This study is based on research carried out as part of project HID 96-1326, financed by
Comisión Interministerial de Ciencia y Tecnología (CICYT).
References
•
Armayor Cachero J.L. N., Murillo Díaz J.M.. and Rodríguez Hernández L., “Recarga
Artificial en el Acuífero de Jávea mediante aprovechamiento de los excedentes hídricos
procedentes del río Jalón-Gorgos(Alicante)”. V Congreso Español de Geología.
Geotemas 1(2)., 13-17, Alicante., 2000.
•
Boluda Botella N., Sempere Pérez C. and Ruíz Beviá F., “Evolución de la intrusión
marina en el acuífero cuaternario de Jávea (Alicante)”. I Congreso Ibérico de
Geoquímica. VII Congreso de geoquímica de España, 458-465, Soria., 1997a.
•
Boluda Botella N., Sempere Pérez C., Ruíz Beviá F., Gomis Yagüe V., “Aplicación de
un modelo hidrogeoquímico a la intrusión marina del acuífero cuaternario de Jávea”. I
Congreso Ibérico de Geoquímica. VII Congreso de geoquímica de España, 472-479,
Soria., 1997 b.
•
Chiang W., Kinzelbach W, Processing Modflow (a simulation system for modeling
groundwater flow and pollution). Scientific Software Group, Washington, 204pp, 1996
•
Diputación Provincial de Alicante (DPA)., Mapa del Agua. Memoria y plano, Alicante,
42 p. 1 plano. 1992.
•
Franz, T. and Guider,N., Flowpath. Groundwater Flow and Pathlines Simulation
Model. Edt. Waterloo hydrogeologic. User’s Manual. Columbia, Canadá, 190 pp, 1995.
•
IGME., Estudio hidrogeológico para el abastecimiento de agua a las localidades de
Jávea y Gata de Gorgos (Alicante). Informe, Valencia, 45pp,1plano, 1983.
•
IGME-DPA ., “Las aguas subterráneas de la Provincia de Alicante”. Capítulo II, 693706, Alicante., 1982.
•
ITGE-DPA ., Análisis previo de los resultados de las operaciones de recarga artificial
en Orba, Jijona y Cuenca del Gorgos. Recarga artificial mediante actuaciones en el
cauce del río Gorgos. Acuífero detrítico de Jávea (Alicante)., Madrid, 102 pp, 2
Anexos, 1999.
•
MOPU., Cálculo hidrometeorológico de caudales máximos en pequeñas cuencas
naturales. Tecnología carreteras MOPU.nº12, 25-31,76-84, Madrid., 1987.
•
Murillo Díaz J.M.., De La Orden-Gómez J.M. and Rodríguez Hernández L., “Recarga
Artificial mediante pozos con galerías horizontales en el acuífero de Gandái-Denía.
Términos municipales de Vergel y Els Poblets. Antecedentes históricos e investigación
hidrogeológica previa”. X Congreso Internacional de Minería y Metalurgia. Tomo 1,
61-82, Valencia., 1998.
•
Murillo Díaz J.M.., De La Orden-Gómez J.M., Armayor Cachero J.L. and Castaño
Castaño S., Recarga Artificial de Acuíferos. Síntesis metodológica. Estudios y
actuaciones realizadas en la provincia de Alicante. Diputación Provincial de Alicante,.
Alicante, 158 pp, 2000.
•
Pulido Bosch, A., “Salinización y recarga artificial en el acuífero de Jávea (Alicante)”.
Simposio Nacional de Hidrogeología. Tomo II, 772-787, Valencia., 1976.
Corresponding author: José Luis Armayor Cachero, Dirección de Hidrogeología y Aguas
Subterráneas, Instituto Geológico y Minero de España, C/Ríos Rosas, 23, 28003 Madrid,
España.
Email: [email protected]