Artificial recharge by means of careo channels versus natural aquifer recharge in a semi-arid, high-mountain watershed (Sierra Nevada, Spain)

Abstract

The acequias de careo are ancestral water channels excavated during the early Al-Andalus period (8th–10th centuries), which are used to recharge aquifers in the watersheds of the Sierra Nevada mountain range (Southeastern Spain). The water channels are maintained by local communities, and their main function is collecting snowmelt, but also runoff from rainfall from the headwaters of river basins and distributing it throughout the upper parts of the slopes. This method of aquifer artificial recharge extends the availability of water resources in the lowlands of the river basins during the dry season when there is almost no precipitation and water demand is higher. This study investigates the contribution of the careo channels in the watershed of Bérchules concerning the total aquifer recharge during the 2014–2015 hydrological year. Several channels were gauged, and the runoff data were compared with those obtained from a semi-distributed hydrological model applied to the same hydrological basin. The natural infiltration of meteoric waters accounted for 52% of the total recharge, while the remaining 48% corresponded to water transported and infiltrated by the careo channels. In other words, the careo recharge system enhances by 92% the natural recharge to the aquifer. Our results demonstrate the importance of this ancestral and efficient channel system for recharging slope aquifers developed in hard rocks. The acequias de careo are nature-based solutions for increasing water resources availability that have contributed to a prosperous life in the Sierra Nevada. Its long history (>1200 years) suggests that the system has remarkable resilience properties, which have allowed adaptation and permance for centuries in drastically changing climatic and socioeconomic conditions. This recharge system could also be applied to —or inspire similar adaptation measures in— semi-arid mountain areas around the world where it may help in mitigating climate change effects.

Full text

Artificial recharge by means of careo channels versus natural aquifer
recharge in a semi-arid, high-mountain watershed (Sierra Nevada, Spain)
J. Jódar
a,
⁎,T. Zakaluk
b
, A. González-Ramón
a
,A. Ruiz-Constán
a
, C. Marín Lechado
a
, J.M. Martín-Civantos
b
,
E. Custodio
c
, J. Urrutia
d
,C. Herrera
d
,L.J. Lambán
a
,J.J. Durán
a
,S. Martos-Rosillo
a
a
Centro Nacional Instituto Geológico y Minero de España, Consejo Superior de Investigaciones Científicas IGME-CSIC, Spain
b
MEMOLab Universidad de Granada, Spain
c
Groundwater Hydrology Group, Dept. Civil and Environmental Eng., TechnicalUniversity of Catalonia (UPC), Royal Academyof Sciences of Spain, iUNAT, Universidad de Las
Palmas de Gran Canaria, Spain
d
Center for Research and Development of Water Ecosystems, Universidad Bernardo O'Higgins, Santiago, Chile
HIGHLIGHTS
•Total aquifer recharge equals 28% of pre-
cipitation in the Bérchules watershed.
•Artificial- recharge from careo channels
represents 48% of total aquifer recharge.
•Careo channels rechargeis similar to natu-
ral rainfed diffuse recharge.
•Groundwater discharge controls the hy-
drological behavior of the Bérchules wa-
tershed.
•The recharge channels are nature-based
solutions for water management.
GRAPHICAL ABSTRACT
ABSTRACTARTICLE INFO
Article history:
Received 9 December 2021
Received inrevised form 30 January 2022
Accepted 13 February 2022
Available online 18 February 2022
Editor: Damia Barcelo
The acequias de careo are ancestral water channels excavated during the early Al-Andalus period (8th–10th centuries),
which are used to recharge aquifers in the watersheds of the Sierra Nevada mountain range (Southeastern Spain). The
water channels are maintained by local communities, and their main function is collecting snowmelt, but also runoff
from rainfall from the headwaters of river basins and distributing it throughout the upper parts of the slopes. This method
of aquifer artificial recharge extends the availability of water resources in the lowlands of the river basins during the dry
season when there is almost no precipitation and water demand is higher. This study investigates thecontribution of the
careo channels in the watershed of Bérchules concerning the total aquifer recharge during the 2014–2015 hydrological
year. Several channels were gauged, and the runoff data werecompared with those obtained from a semi-distributed hy-
drological model applied to the same hydrological basin. The natural infiltration of meteoric waters accounted for 52% of
the total recharge, while the remaining 48% corresponded to water transported and infiltrated by the careo channels. In
other words, the careo recharge system enhances by 92% the natural recharge to the aquifer. Our results demonstrate the
importance of this ancestral and efficient channel system for recharging slope aquifers developed in hard rocks. The ace-
quias de careo are nature-based solutions for increasing water resources availability that have contributed to a prosperous
life in the Sierra Nevada. Its long history (>1200 years) suggests that the system has remarkable resilience properties,
which have allowed adaptation and permance for centuries in drastically changing climatic and socioeconomic condi-
tions. This recharge system could also be applied to —or inspire similar adaptation measures in—semi-arid mountain
areas around the world where it may help in mitigating climate change effects.
Keywords:
Careo channel
Slope aquifer
Nature-based solution
Managed aquifer recharge
Science of the Total Environment 825 (2022) 153937
⁎Corresponding author at: IGME CSIC, C/Manuel Lasala, 44.9°B, 50006 Zaragoza, Spain.
E-mail addresses: j.jodar@csic.es j.jodar@igme.es (J. Jódar).
http://dx.doi.org/10.1016/j.scitotenv.2022.153937
0048-9697/© 2022 The Authors. Published by Elsevier B.V. This is an open access articleunder the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Contents lists available at ScienceDirect
Science of the Total Environment
journal homepage: www.elsevier.com/locate/scitotenv

1. Introduction
Sierra Nevada is a high mountain range located in the southeastern Ibe-
rian Peninsula. It formed as a consequence of the convergence between the
Eurasian and African plates during the Alpine orogeny. Its most prominent
peaks are Mulhacén (3482 m a.s.l.) and Veleta (3398 m a.s.l.), the highest
elevations of the peninsula. Its glaciers retreated, almost disappearing,
from the massif 13–15 ka BP, largely due to the proximity of the African
continent, which imposes semi-arid climatic conditions on this massif and
its surroundings (Gómez-Ortiz et al., 2012, 2015).
The past and present hydro-climatic conditions of the Sierra Nevada
massif have never beenideal for the developmentof permanent communi-
ties because of the high average elevation and the prevailing semi-arid cli-
mate conditions. Although the first evidence of human occupation can be
traced to Late Neolithic times, around 3000 BCE (Calatrava and Sayadi,
2019), it was not until the Al-Andalus period —under Muslim rule, between
the 8th and 15th centuries—that human activity became evident. With the
construction of extensive terrace cultivations all around the mountain
range, early settlers began tochange the naturallandscape drastically, espe-
cially on and around the southern slopes, where both a warmer climate and
a gentler topography can be found. The oldest permanent human settle-
ments of the area (e.g., Lanjarón, Trevélez, Bérchules) (Fig. 1) still exist
today (Martín Civantos, 2007, 2008).
To solve the problem of growing water demand due to agricultural ac-
tivity and associated settlements, people began excavating vast networks
of water channels, locally known as acequias de careo. These channels gently
descend along the contour lines of the slopes, have no impermeable lining,
range in size from 0.5 to2.5 m in width, and can beseveral kilometers long
(Pulido-Bosch and Sbih, 1995). The snowmelt, which mostly flows through
the mountain streams in spring, is diverted into such channels withthe ob-
jectives of (1) transporting and distributing water towards irrigated areas,
(2) transferring surplus water among neighboring hydrological basins,
and (3) regulating basin resources through the recharge of slope aquifers
with snowmelt water (Martos-Rosillo et al., 2019a). This system of water
use and management, based on the principle of water sowing and harvest-
ing using acequias de careo, has been documented since the Early Middle
Ages (8th–10th centuries) (Martín Civantos, 2010), and is still in operation
today, exemplifying the new paradigm of Integrated Water Management
(Vivas et al., 2009). Acequias de careo are solutions inspired by and sup-
ported by nature that use or mimic natural processes to help improve
water management (WWAP, 2018) and can, thus, be regarded as nature-
based solutions for water management (Martos-Rosillo et al., 2020).
Ancestral water management systems based on indigenous people's
wisdom exist in various other places in the world. In South America, partic-
ularly in Andean arid and semiarid regions (Yapa, 2013;Ochoa-Tocachi
et al., 2019;Martos-Rosillo et al., 2020), there is a variety of ancient
water sowing/harvesting systems (WSHS) to regulate aquifer recharge
(Martos-Rosillo et al., 2020). They include the pre-Hispanic amunas of
Peru (Ochoa-Tocachi et al., 2019), which developed independently on a
different continent but resemble careochannels of Sierra Nevada in design
and operation (Martos-Rosillo et al., 2019a, 2019b). In Perú, hundreds of
kilometers of abandoned amunas are currently being restored (Cárdenas-
Panduro, 2020), all of them in river basins that provide water to Lima. An-
other good example of WSHS is the cocha or albarrada in Ecuador, Peru and
Bolivia. These are ponds of low crest heights built for water infiltration,
which is enhanced by using earth construction materials (MINAGRI,
2016;Martos-Rosillo et al., 2020;Albarra cín et al., 2021). Similar to cochas,
but smaller, are Peru's cuchacuchas,infiltrating ponds with diameters rang-
ing between2 and 15 m (Yapa, 2016). The tape, another type of WSHS that
can be found in Ecuador, consists of tiny walls set up along the main chan-
nels of intermittent streams and rivers with the aim to collect water during
the rainy months. The infiltrated water can then be tapped via wells or
drainage galleries (Carrión et al., 2018;Martos-Rosillo et al., 2020). Sur-
prisingly, this WSHS can be also found in Kenya (Lasage et al., 2008).
Apart from these WSHS, numerous Andean high-altitude wetlands known
as bofedales are watered and expanded by constructing ditch networks to ir-
rigate pastures and infiltrate water (Martos-Rosillo et al., 2020). Down-
stream of all these WSHS, biodiversity is boosted; even species suited for
more humid conditions flourish through the operation of these systems,
allowing a diverse range of floral species with widely varying water re-
quirements to coexist (Yapa, 2013;Martos-Rosillo et al., 2020;Albarracín
et al., 2021).
All the aforementioned ancient WSHS approaches can be thought of
being Managed Aquifer Recharge systems combining “blue”and “green in-
frastructure”and/or being a generator of them (Benedict and McMahon,
2012). All of them are clear examples of Nature Based Solution for Water
Managemenet (NbSWM), representing an antagonistic concept to water
management with grey infrastructure (i.e., large concrete hydraulic
works) on which current water management models rely. Dams or reser-
voirs are a good example of such grey infrastructure. They are believed to
Fig. 1. (A) General location of the Sierra Nevada. (B) Thematic map with physical and geographic and geological attributes of the SierraNevada National and Natural Parks,
including the most important irrigation channel systems.(C) Map of the Bérchulesriver basin, markedin white dashed line, representingthe drainage network, the locationof
the Narila gauging station at the outlet of the basin, and the most relevant water channels, including the Acequia del Espino (AE).
J. Jódar et al. Science of the Total Environment 825 (2022) 153937
2

mitigate natural calamities such as floods, landslides, and debris flows
while facilitating groundwater recharge. Nevertheless, the option of build-
ing more reservoirs is socially, environmentally, and economically contro-
versial (Ribeiro, 2021). In this line, Spain is one of the countries in the
Mediterranean zone with the largest number of big dams per inhabitant.
Despite of that, Spain is suffering increasing intensity of long-lasting
droughts, which are challenging the capacity of such “grey infrastructures”,
alone, for satisfying human water demands without serious threats to
water-dependent ecosystems. The ancient WSHS as NbSWMs are more effi-
cient and ecosystem-friendly forms of water storage as groundwater re-
charge than grey infrastructures, which in turn are less sustainable and
cost-effective than NbSWMs (WWAP, 2018).
This study focuses on the Bérchules river basin, located in the central
sector of the southern slopes of the Sierra Nevada (Fig. 1), where a WSHS
system of acequias de careo still operates. The study area has a great demand
for water resources for two reasons: (1) the environmental policy of affores-
tation with monoculture of coniferous forest, which began in the mid 20th
century and continues today (Jiménez-Olivenza et al., 2015), and (2) the
transformation of agricultural land from traditionally rainfed to intensively
irrigated land for horticultural production (Carpintero et al., 2018). Al-
though the hydrological balance of the basin has been documented
(Martos-Rosillo et al., 2015, 2017;Jódar et al., 2017, 2018), the contribu-
tion of the careo channels to the total water resources has notyet been quan-
tified at the hydrological basin scale, and the contribution of the careo
channels to the total aquifer recharge is still unknown.
The objective of this work is twofold: 1) to present a methodological ap-
proach for estimating the infiltration capacity of the careo channels, and
2) to evaluate the careo channels' contribution to total groundwater re-
charge in the Bérchules basin. This will help understand the resilience of
such ancestral water management systems to past drastic social (Martín
Civantos, 2007, 2010) and climate changes (García-Alix et al., 2020;
Ramos-Román et al., 2016) that occurred in Sierra Nevada (Spain) from
the Middle Ages to date, while giving sound arguments to maintain these
aquifer recharge channel systems as adaptation measures to minimize the
impact of the forecasted climate change.
2. Study area
The study area lies on the southern face of Sierra Nevada,in southeast-
ern Spain (Fig. 1). The altitude of the Bérchules basin varies between 2913
m a.s.l. at Cerro del Gallo peak and 979 m a.s.l. in the Narila gauging sta-
tion, located at the outlet of the basin, where the average discharge flow
for the period 1970–2015 was 12.6 hm
3
/year. This basin has a surface
area of 68 km
2
. Its main drainage network is formed by the Grande de
Bérchules River, with a total length of 17.3 km from the headwaters of
the basin (to the NE), at 2600 m a.s.l., to Narila's gauging station. The
Chico River is the largest tributary of the Bérchules River. It originates,
over 2900 m a.s.l., to the northwest of the basin's headwaters.This tributary
joins the Grande de Bérchules River in the central part of the basin.
From a meteorological point of view, following the classification of
Köppen-Geiger (Peel et al., 2007), the area has a cold climate, with mild
and cool dry summers, together with significant altitudinal and thermal
variations (Rigueiro-Rodríguez et al., 2008;Gómez-Zotano et al., 2015).
The mean temperature (T) at the meteorological station of Bérchules
(1319 m a.s.l.) (Fig. 1D) is 13.3 °C. Mean precipitation (P) and potential
evapotranspiration (PET) are 677 and 1012 mm/year, respectively. P and
T show a clear altitudinal dependence on the southern slope of Sierra Ne-
vada (Fig. 2). In the basin, the presence andpersistence of snow isrestricted
to elevations higher than 2400 m a.s.l. and to a period between November
and May. Scrubs cover >50% of the total basin area, and conifers, which
have been introduced for reforestation purposes, especially during the sec-
ond half of the20th century, cover 15% of the basin. In the lower part of the
watershed, the climate is temperate Mediterranean. Irrigated horticultural
cropland extends over 1.3% of the total basin surface, up to heights above
2200 m a.s.l. (Jódar et al., 2018).
The Bérchules watershed is situated over poorly permeable rocks,
mostly schists, of the Nevado-Filábride Complex (Fig. 1). Weathering pro-
cesses have contributed to the development of a relatively permeable
layer over most of its surface, with a fissured and fractured zone topping
the unaltered rock (Fig. 3). Quaternary formations containing glacial and
periglacial sediments, including colluvium and slope debris, are mainly
found at heights above 2000 m a.s.l., overlying and complementing the al-
teration zone. From the hydrogeological point of view, the altered schists
and Quaternary materials together constitute a 30to 40 m thick formation
that holds a shallow unconfined aquifer with transmissivity ranging be-
tween 0.05 and 0.5 m
2
/s (IGME, 2015), with the most transmissive zone lo-
cated between 20 and 30 m depth. The permeable outcrops cover 59 km
2
of
the total 69 km
2
basin area.Unaltered hard rocks canbe found throughout
the rest of the watershed. The boundaries of this upper aquifer coincide
with those of the surface watershed.
In the Sierra Nevada and surrounding areas, a long-term shortage of
water supplies has been a major impediment to the establishment of perma-
nent communities. It was not until the Al-Andalus period in the 8th century
that people of Arabic-Berber origin started to tackle this problem effi-
ciently. They developed a water management system that makes use of an
extensive network of water infiltration channels (Delaigue, 1995;Martos-
Rosillo et al., 2019b). These hydraulic structures, locally known as acequias
de careo (Fig. 1C), are relatively shallow and narrow channels dug with
Fig. 2. (A)SeasonaldistributionofP,T,PET,averageflow discharge measured at the Narila gauging station (Q
Obs
)—represented with a variation interval associated to the
20% and 80% percentiles (Q
Int
)—and total basin runoff from the HBV model (Q
Calc
). (B) Altitudinal distribution of annual mean values of P, T, and PET on the southern face
of the Sierra Nevada (modified from Jódar et al., 2017, 2018).
J. Jódar et al. Science of the Total Environment 825 (2022) 153937
3

simple tools and strengthened with local materials, but not sealed (Espín
et al., 2010). The channels' main function is to collect water and facilitate
its infiltration. The study area features three types of infiltration channels
(Fig. 3):
1. Careo channels: Channels that are solely used for aquifer recharge, a
practice known locally as careo. Their main function is to collect runoff
from the headwaters of the rivers and to infiltrate it along its way and
into pre-determined infiltration spots, locally called simas, where the
soil infiltration capacity is known to be high. They usually operate
from the beginning of autumn (October) until the end of the snowmelt
season (June), with some variation depending on the meteorological
characteristics of each hydrological year.
2. Recharge and irrigation channels: Channels that are used for both
groundwater recharge (i.e., careo; October–June) and crop irrigation
of agricultural areas situated below the channels (July–September).
Land that is irrigated with the traditional flooding method, or more re-
cently using localized irrigation methods, comprises approximately
0.88 km
2
of the area (~1.3% of the surface area of the Bérchules water-
shed; Carpintero et al., 2018).
3. Recharge and water transfer channels: Channels that are used for
groundwater recharge in a watershed while simultaneously transporting
water into a neighboring one. The water resources are shared equally
between both neighboring basins during autumn and winter. From
April until the end of the snowmelt season (June), the distribution of
such water resources changes: the total channel flowrate is divided be-
tween the original (i.e., where the snowmelt is generated) and neighbor-
ing basins, 3/7 and 4/7 respectively. From June onwards, usually
starting at the summer solstice (June 21st), the water is kept entirely
within the original watershed.
The Bérchules watershed's channel system consists of 19 major channels
with a total length of 57.45 km (Fig. 1D).Around21kmofthesechannels
are exclusively dedicated to aquifer recharge. The most important careo
channel of the area, the Acequia del Espino, originates in the upper part
of the watershed, where a small dyke is located at 1998 m a.s.l. diverts
part of the Chico de Bérchules River flow into the recharge channel
(Fig. 3A). This very simple hydraulic intervention, known locally as toma,
is maintained, and periodically controlled by local irrigation communities
(Fig. 3B), who not only ensure that enough water is entering the channel
but also have to guarantee the ecological flow of the river (CIS, 2015).
This channel has a length of around 7 km, an average width of 1.5 m, and
an average slope of 6.8%. Along its path, the channels cross several infiltra-
tion zones or simas, characterized by a high infiltration capacity, where
water is partially released from the channels for watering the topsoil and
recharging the aquifer. At an altitude of 1820 m a.s.l., the channel water
reaches its main destination,entering the sima de Bérchules, which consists
of a gently sloping, grassy, and highly permeable surface covering an area
of 32,300 m
2
(Fig. 3C). All the water that reaches this zone ends up infiltrat-
ing entirely into the sima, including peak flows that may reach 390 L/s,
which implies infiltration rates of over 1 m/day, as measured during the hy-
drological year 2014–2015.
Aquifer discharge plays a noteworthy role in the hydrodynamic re-
sponse of the basin. Groundwater amounts to 95% of the total discharge
of the basin (Jódar et al., 2017, 2018), which is reflected by the flat
shape of the average hydrograph (Fig. 2A). An inventory of the existing
springs in the Bérchules watershed listed 609 springs (9 springs/km
2
),
95% of them discharging <0.2 L/s, and most drying up in the dry period
(June to August) of the year (Martos-Rosillo et al., 2015). Close to 30% of
the total basin springs are found in the higher parts of the watershed, atel-
evations between 2165 and 2790 m a.s.l. (Fig. 4A; González-Ramón et al.,
2015). They are associated with changes in the terrain's slope or decreasing
thickness of the periglacial deposits (Fig. 4B). For the rest of the springs,
there is a clear relationship between their position and that of the careo
channels (González-Ramón et al., 2015), as they regulate both the spatial
distribution and the amount of discharge of the springs in the watershed.
Consequently, their use affects the whole system's hydrogeological func-
tioning. Recharging the aquifer using these channels modifies the distribu-
tion of discharge zones (e.g., springs), increasing both the inertia of the
hydrogeological system and the number of springs, which in turn increases
discharge flow on the slopes of the watershed.
3. Methods and materials
3.1. Hydrometeorological data
The Narila gauging station, located at the exit of the Bérchules water-
shed (Fig. 1), provides a daily series of the basin outflow for the period
Fig. 3. (A) Sketch of the Bérchules watershed with existing types of channels. The starting point (toma) and ending point (Sima de Bérchules) of the El Espino channel are
indicated by labels “α”and “β”, respectively. The label “δ”indicates the origin of the Mecina interbasin transfer channel.
J. Jódar et al. Science of the Total Environment 825 (2022) 153937
4

1970–2015. For the same period, daily precipitation (P) and temperature
(T) time series were measured in the meteorological station located in the
village of Bérchules. These time series are used to estimate the potential
evapotranspiration (PET) time series by applying Hargreaves's method
(Hargreaves and Samani, 1982).
3.2. Evaluation of the total aquifer recharge by application of the HBV model
The HBV model (Bergström, 1976;Seibert and Bergström, 2021)isa
conceptual rainfall-runoff model used for watershed modeling. It is based
on the following water balance:
P−E−Qcalc ¼d
dt SP þSM þUZ þLZ
ðÞ ð1Þ
where P [LT
−1
] is precipitation in the form of rain and snow, E [LT
−1
]is
evapotranspiration, Q
calc
[LT
−1
] is the basin total runoff, SP [L] is water
storage as snow, SM [L] is the volume of water stored as soil moisture,
and UZ [L] and LZ [L] represent water storage in the upper and lower aqui-
fer layers, respectively. The upper aquifer layer generates theinterflow dis-
charge, whereas the lower aquifer layer produces the groundwater
discharge of the system (Fig. 5).
The HBV model provides the daily discharge of a hydrological basin,
basedondailyprecipitationandtemperature time series, and calculates the
recharge to the saturated zone. Precipitation enters as rain or snow depend-
ing on a predetermined threshold temperature. The first processing unit is
the snow routine, which simulates the snow accretion and melting processes.
It works as intermittent hydrological storage, accumulating snow and letting
it enter the system as snowmelt when daily temperatures exceed the freezing
point. Rain and snowmelt together enter the soil moisture routine, which dis-
tinguishes between soil recharge by direct infiltration (RT) and the contribu-
tion to soil moisture potential (Seibert, 2005). Furthermore, the soil moisture
routine computes the direct superficial runoff Q
S
[LT
−1
]andthepotential
evapotranspiration PET [LT
−1
] as a linear function of the soil moisture
(Seibert, 2005). If water flow exceeds the soil moisture capacity, a third pro-
cessing unit —the groundwater response routine—starts to distribute it be-
tween two interconnected reservoirs. The upper one acts like a saturated
subsurface layer generating surface and subsurface runoff, Q
0
[LT
−1
]and
Q
1
[LT
−1
], respectively (Fig. 5). The lower reservoir imitates an aquifer
that is generating groundwater runoff Q
2
[LT
−1
](Fig. 5). A predefined and
constant percolation rate, which coincides in steady-state with the value of
Q
2
, limits the amount of water that recharges the aquifer by entering the
lower reservoir. Finally, the runoff estimation routine calculates the total run-
off at the outflow point of the catchment (Q
calc
) by summing up all the runoff
components (i.e., Q
S
,Q
0
,Q
1,
and Q
2
).
Fig. 4. (A) Spring density map with the location of the main careo channels. (B) Geomorphological map of the Bérchules watershed.
J. Jódar et al. Science of the Total Environment 825 (2022) 153937
5

This work uses the HBV model adapted by Jódar et al. (2018) to simu-
late the hydrodynamic response of the Bérchules watershed. To this end,
the availability of the meteorological data (i.e., P, T, and PET) and the
Berchules River runoff time series is required. All the time series of the ap-
plied model cover the period 1970–2015.
The HBV model provides an output time series for several variables, in-
cluding water infiltration, which is assumed here as total groundwater re-
charge (RT). As can be seen in Fig. 5, water infiltration is the water flux
added to the upper groundwater box. A detailed description of the HBV
model can be found in Bergström (1992, 1995) and Seibert (1999).
3.3. Evaluation of careo channels' contribution to total groundwater recharge
Flow rates in five channels —including the Trevélez and Mecina inter-
basin transfer channels, Acequia Real and Acequia Nueva irrigation chan-
nels, and Acequia del Espino careo channel—were measured during the
2014–2015 hydrological year to assess the contribution of the recharge
channel system to the total aquifer recharge in the Bérchules watershed.
In addition to periodical manual flow measurements in these five chan-
nels, the total infiltration capacity along the Acequia del Espino was charac-
terized on the 28th of April 2015, and the careo recharge campaign of this
channel was monitored during its operation in the hydrological year
2014–2015. For this purpose, two gauging stations were installed
(Fig. 6A) at the beginning (i.e., toma; control point 2) and the endpoint
(i.e., Sima de Bérchules; control point 13) of the channel. Both stations
were equipped with an Odyssey™automatic capacitive probe that mea-
sured the water column height in each section with an hourly frequency.
In addition, the water flow rate was measured at both channel points
with an approximately monthly frequency over one year, using a C2-
OTT® small current meter, while applying the area-velocity method to
measure the flow rate through each channel section. Monthly flow rate
data were later correlated with the hourly water column height to derive
hourly flow measures for each section.
The infiltration capacity of the El Espino channel was determined by
gauging the flow rate in thirteen sections along the channel (control points
in Fig. 6A). Fig. 6Brepresentstheflow rate measured for these sections on
the 28th of April 2015. The most permeable intervals of the channel, in
which the infiltration capacity is higher than average, are marked in red
in Fig. 6A and C. They correspond to the channel sections where the flow
rate variation between two consecutive control points is greatest. Fig. 6B
shows the hydrographs of control points 2 and 13 for the hydrological
year 2014–2015.
In this work, the flow rate of the careo channel network in the Bérchules
basin has been monitored during the hydrological year 2014–2015. This in-
formation provided the basis for estimating the volume of water that was
recharged by the careo channel network into the basin during one specific
hydrological year. With this data, however, it is hard to estimate the inter-
annual variability of the careo recharge and its corresponding uncertainty.
To estimate such variability, it is assumed that the annually diverted vol-
ume of surface runoff from the river into the careo channel network is pro-
portional to the annual precipitat ion in the basin. With this as sumption, and
being known both the annual recharged careo volume (RC
ref
[L]) and the
annual precipitation volume (P
Ref
[L]) for a given hydrological year
(e.g., 2014–2015), it is possible to estimate the annual recharged careo vol-
ume time series RC(t) [L] in terms ofthe available annual precipitation time
series P(t) [L] as:
RC tðÞ¼ RCref
Pref

PtðÞ ð2Þ
where t is the hydrological year to which RC is estimated.
Once RC(t) is obtained, the annual natural recharge time series RN
(t) [L] can be evaluated as
RN t
ðÞ¼RT t
ðÞ
−RC t
ðÞ ð3Þ
Fig. 5. General modeling scheme and main modules of the HBV model.
J. Jódar et al. Science of the Total Environment 825 (2022) 153937
6

where RT(t) [L] is the aquifer annual recharge volume time series, which is
calculated by postprocessing the HBV results.
4. Results and discussion
4.1. HBV modeling results
The HBV model adapted by Jódar et al. (2018) for the Bérchules basin
allowed us to simulate the hydrodynamic response of the watershed for
the time interval 1970–2014 and thus evaluate the average basin discharge
for this period as 13.25 hm
3
/year. The seasonal hydrograph at the Narila
gauging station (Fig. 2) shows a temporal delay and a higher baseflow
than would beexpected for a hydrogeological basin developed in materials
of low permeability and subjected to an assumingly pluvio-nival hydrocli-
matic regime, where marked maximums and minimums in river flow
rates are expected in spring and summer, respectively (Beckinsale, 2021).
The observed hydrological behavior may be due to a high percentage of
groundwater discharge in the total discharge of the watershed. The average
total recharge of the aquiferresulting from themodel application for the pe-
riod 1970–2014 is 12.59 hm
3
/year (Fig. 7A), which represents 28% of the
average rainfall in the basin (667 mm/year) and 95% of the total discharge
of the hydrological system (Jódar et al., 2018). Similar fractions of
Fig. 6. (A) Map representation of the El Espino careo channel. The numbered dots indicate the position of the selected control pointsto measure the channel flow rate. The
yellow spots indicate infiltration zones (simas), and the red sections indicate the most permeable sectors of the channel. Coordinates are expressedin UTM30. (B) Channel
flow rates at the control points 2 (grey line) and 13 (blue line), measured over the hydrological year 2014–2015. (C) Flow rates for all control points measured on the
28th of April 2015. The channel intervals with the highest reductions in flow rate are marked in red; they correspond to the most permeable areas of the El Espino
channel (Modified from Martos-Rosillo et al., 2019b).
Fig. 7. (A) Total, natural and careo recharge estimated for the period 1970–2015. (B) Percentage of both natural and careo recharge concerning total recharge estimated for
the period 1970–2015. The upper and lower box lines correspond to 75 and 25 percentiles, respectively. The bold and dashed lines indicate the mean and median values,
respectively. The dot symbol indicates the variable value for the hydrological year 2014–2015.
J. Jódar et al. Science of the Total Environment 825 (2022) 153937
7

groundwater in the total discharge, only slightly lower than those measured
here, have beenobserved in high mountain watersheds in the Andes, where
the substrate consists almost entirely ofhighly permeable, glacially altered
materials, with ratios of total groundwater discharge to total stream dis-
charge of 72% (Somers et al., 2019), 77% (Saberi et al., 2019) and 80%
(Baraer et al., 2015). Likewise, in the Himalayas, maximum values of
77% are reached (Williams et al., 2016). These high groundwater contribu-
tions to the total streamflow have been also observed in high mountain
karst aquifers, which are known to store and transmit large volumes of
water (Somers and Mckenzie, 2020). In this line, Chen et al. (2018) re-
ported a contribution of 87% in the northern Alps on the Germany/
Austria border, whereas Jódar et al. (2020) reported a contribution of
75% in the Ordesa and Monte Perdido National Park, which constitutes
the highest karst system in Western Europe. Contrary to what happens in
these karstsystems, the permeable outcrops in the Bérchules watershed cor-
respond almost exclusively to weathered materials (Fig. 4B), as most of the
area consists of schists . It seems clear that the elevated groundwater co mpo-
nent of the mean hydrograph (Fig. 2) is partially driven by the artificial re-
charge conducted with the careo channels, as pointed out by Barberá et al.
(2018), who analyzed the isotope content of precipitation, snowmelt,
groundwater, and surface water in the Bérchules Basin.
Rainfall was 509 mm in the hydrological year 2014–2015. This value
represents a reduction of 24% relative to the mean annual rainfall in the
Bérchules watershed for the period 1970–2014 while having an exceed-
ance probability of 64% for the annual precipitation for the same period.
Similarly, the total basin discharge for this period is 5.3 hm
3
, which is a
60% reduction of the average annual discharge for the 1970–2014 period.
The lower discharge value highlights the hydro-climatic stress experienced
in the watershed during the 2014/15 hydrological year. Still, the HBV
model calculates a recharge for this hydrological year of 112 mm (7.62
hm
3
), which isa value below the average recharge value (Fig. 8) and corre-
sponds to 22% of the precipitation recordedfor this period. Deserving men-
tion is the fact that practically all the meteoric water generated in the
headwaters of the Bérchules River was captured and infiltrated by the
careo activities during the 2014–2015 hydrological year.
4.2. Artificial recharge via careo channels
During its operation time between April 1st and May 15th, 2015, the El
Espino channel captured a total volume of 1.99 hm
3
of water from the
Grande de Bérchules River. Of this volume, 82% (1.64 hm
3
)infiltrated
along the course of the channel, while the remaining 18% (0.34 hm
3
)infil-
trated at the end of the channel into the permeable materials ofthe sima de
Bérchules (Fig. 6A).
The total volume of water transferred from the Trevélez to theBérchules
watersheds via the Trevélez-Juviles interbasin transfer channel (Fig. 4A)
was 0.06 hm
3
during the 2014–2015 hydrological year. This volume was
infiltrated completely through the transfer channel into the Bérchules
basin. While this relatively low volume was due to leakages in several of
its sections, the Mecina channel (Fig. 4A) transferred 1.2 hm
3
of water
from the Bérchules River to the Mecina watershed during the same period.
According to local agreements between the Bérchules and the Mecina wa-
tershed communities, not all the water diverted into the Mecina interbasin
transfer channel is transferred to the neighboring Mecina watershed. A part
of the diverted wateris rechargedin the Bérchules watershed. This volume
amounted to 0.57 hm
3
during the 2014–2015 hydrological year. For the
same period, the total water volume diverted from the Bérchules River
into the two main irrigation channels Acequia Real and Acequia Nueva
(Fig. 4A) amounted to 1.44 hm
3
. Unlike thewater channels exclusively ded-
icated to aquifer recharge, part of the water flow in these two irrigation
channelsis for orchards, which cover an area of 0.88 km
2
, thus representing
1.3% of the basin surface (Jódar et al., 2018). Considering that the irriga-
tion season runs from July to September, and assuming a mean evapotrans-
pirationrate of the orchard crops of 5 mm/day (Carpintero et al., 2018), the
corresponding evapotranspiration loss during the irrigation season would
be 0.40 hm
3
, and the estimate of total aquifer recharge with these channels
would be 1.04 hm
3
in the period 2014–2015.
On a whole, the contribution of the five studied recharge channels —El
Espino (1.99 hm
3
), Trevélez (0.06 hm
3
), Mecina (0.57 hm
3
), Acequia Real,
and Acequia Nueva (1.04 hm
3
)—to the total aquifer recharge in the
Bérchules watershed during the hydrological year 2014–2015 was 3.66
hm
3
, which is equivalent to 70% of the river water flow discharge at the
Narila gauging station (5.3 hm
3
) and constitutes 48% of the total aquifer re-
charge estimated for this period (7.62 hm
3
). The natural (i.e., diffuse) re-
charge of the aquifer thus accounts for 52% of the total recharge (Fig. 7).
Furthermore, it should be emphasized that this ancestral form of water
“sowing”increases the total groundwater storage of the aquifer, which in
turn enhances water “harvest”for the following hydrological year(s).
The mean careo and natural recharge for the period 1970–2015 are 4.8
±2.0hm
3
/yr and 7.4 ± 10.6 hm
3
/yr, respectively. In both cases, the var-
iation interval is expressed as the standard deviation of their corresponding
time series. As can be shown, the mean annual recharge and annual vari-
ability associated with the careo activities are 1.5 and 5.3 times lower, re-
spectively than those associated with the natural annual recharge
(Fig. 7A). Nevertheless, the median (i.e., percentile 50%) of the annual re-
charge associated with both the careo and natural recharges is 4.1 hm
3
/yr.
The disparity between the average and median values associated with the
natural recharge is conditioned by the relationship between the natural
Fig. 8. Temporalvariation of annual precipitation from observations, total recharge from the HBV model, and estimated careo and natural recharge.
J. Jódar et al. Science of the Total Environment 825 (2022) 153937
8

and total recharge (Eq.(3); Fig. 1-Suppl. Mat), which in turn is driven by the
linear dependence between the careo recharge and precipitation (Eq. (2)).
As a result, the larger the annual precipitation the larger the difference be-
tween the natural and careo recharges (Fig. 8). In any case, the aquifer re-
charge driven by the careo channels seems to essentially change the
proportions of focused and diffuse recharge. In the case of low tomean an-
nual precipitations, both the careo and natural recharges play a similar role
concerning the total annual recharge, as can be shown in Fig. 7B. As the
careo channels mostly work during the thawing season, this result reveals
the high efficiency of the careo channels driving the aquifer recharge. How-
ever, these results should be considered as a first approach only, given that
they rely on an assumption (Eq. (2)), to be confirmed in future research.
Measuring groundwater recharge is not easy and very much determined
by local conditions. There are different techniques, including lysimeters,
environmental tracers, and water table fluctuations (Custodio, 2019),
which are not easily applied to a high mountain basin context. Moreover,
recharge may include different processes such as diffuse and focused re-
charge or mountain system recharge (Meixner et al., 2016), which occur
at different scales in time and space, and may not be adequately delineated
by point measurements. The role of such hydrological processes in ground-
water recharge is usually estimated by numerical modeling. In this line,
Somers et al. (2018) and LaFevor and Ramos-Scharrón (2021) analyzed
the effects of hillslope trenching on surface water infiltration, the former
in the nonglacierized basin of the Shullcas River Watershed in the Cordil-
lera Central of Perú, and the latter in several subalpine forested catchments
of Mexico, where the mean precipitation is 800 and 827 mm/yr, respec-
tively. In both cases, the origin of the infiltrated water through the dug
trenches was runoff from rainfall, which is produced in several rainfall
events distributed over the rainy season. The increases in total infiltration
driven by the channels were modest, varying between 1.2 and 2.5% of
the total recharge. The discrepancy with the results obtained in the
Bérchules basin, where the mean precipitation is 677 mm/yr, and the
careo recharge represents an increment of 65% concerning the natural re-
charge, may rely on the origin of the meteoric water being infiltrated. In
the case of the Bérchules basin, most of the infiltrated water through the
careo channels corresponds to snowmelt, which provides a continuous
source of water to be infiltrated along the thawing season. As a result, dur-
ing the careo period, the concentrated recharge along the channel network
allows less time for evapotranspiration than that associated with intermit-
tent precipitation generating diffuse natural recharge. Besides, the water
flowing through the careo channels generate a saturated bulb under the
channels that maximizes the infiltration, and hence groundwater recharge
(Appels et al., 2015). Moreover, during the careo period, a daily inspection
and maintenance work of the channel network is carried out to guarantee
its operation without downtime, preventing the bottom of the ditches
from becoming clogged and losing infiltration capacity, as often happens
in ditches and infiltration ponds.
The data presented in this work confirms that using the ancient careo
channels may lead to improvements in water resources management. Similar
aquifer recharge systems can be found in the Andes (South America) where
channels (amunas) are in use since before the arrival of the Spanish in the
15th century (Escolero et al., 2017;Ochoa-Tocachi et al., 2019). Reusing,
and replicating these WSHS would allow quality water recharge in many
aquifers sustainably, at least complementingandevenreplacingwaterman-
agement grey infrastructures. This will improve the availability of local water
resources from both quantitative and qualitative perspectives. Moreover,
these ancient WSHS could be of interest for many Mediterranean high moun-
tain watersheds, such as those found in the Pyrenees (Spain, France), the
Atlas Mountains (Morocco), Mount Etna (Italy), the Dinaric Alps (Croatia),
the Taurus Mountains (Turkey) or Mount Lebanon (Lebanon), especially as
efficient adaptation measures to mitigate the forecasted impact of climate
change on water resources (Abd-Elmabod et al., 2020;Haro-Monteagudo
et al., 2020) and on ecosystems (Peñuelas et al., 2018).
The ancient WSHSs were developed in hillslope areas with a moderately
permeable substrate, where exist both semiarid climate and high interan-
nual variability of precipitation. To replicate the ancient WSHS successfully
in other areas in the world more research is needed, especially in character-
izing the hydro-geo-morphological variables (e.g., basin concavity profile
and the nature and variability of the soil bedrock interface) that control
the efficiency of the careo recharge at the hillslope scale. This knowledge
is still lacking and might be part of future research endeavors in different
basins of Sierra Nevada where the practice of groundwater recharge with
careo channels is still alive (Fig. 1). At this point, it is worth stressing that
to ensure the successful replication of these ancient WSHS, the technical de-
tails are as important as the social aspects, since there must be a community
that needs suchwater resources surplus and is willing to build and maintain
the channel network. (Fig. 1).
5. Conclusions
The response of the mean annual hydrograph of the Bérchules River is
not typical of a high mountain river, which should show a nival or at
least pluvio-nival hydrological regime. Instead, it exhibits the characteris-
tics of a river connected to an inertial (slow response time) aquifer. The
Bérchules watershed sits on metamorphic rocks, mainly schists. Neverthe-
less, these materials became permeable as a result ofweathering and glacial
and periglacial alteration processes, which allowed the formation of a shal-
low aquifer. The water from artificial aquifer recharge plus irrigation
returns, both achieved by capturing headwaters from the river with careo
channels, end up slowly discharging into the river. As a result of the re-
charge process, the snow flow peak is eliminated from the hydrograph of
the Bérchules or other watersheds in the Sierra Nevada basins where this
form of water management is practiced.
The obtained results demonstrate that aquifer recharge occurs through
two different processes in the Bérchules watershed: (1) a natural and spa-
tially distributed recharge associated with infiltration of meteoric waters
(rainwater and snowmelt), and (2) an artificial and concentrated recharge
along the course of the careo channels, with irrigation and inter boundary
transfer channels that capture and transport river waters for this purpose.
For the hydrological year 2014–2015, distributed natural recharge and ar-
tificial recharge respectively accounted for 52% and 48% of the total re-
charge of the hydrogeological system.
Although this study is undertaken in a particular watershed in the
southern edge of Sierra Nevada (Spain), the methods are generically appli-
cable to different basins in other geographical settings where dug channels
are used to recharge groundwater. Further study is required to characterize
the behavior of such recharge systems in other geographical conditions as
they may be an efficient adaptation measure against the impact of climate
change.
CRediT authorship contribution statement
J. Jódar: Conceptualization, Formal analysis, Methodology, Data
curation, Investigation, Writing –original draft, Writing –review &editing,
Visualization. T. Zakaluk: Investigation, Writing –original draft, Writing –
review &editing. A. González-Ramón: Conceptualization, Data curation, In-
vestigation, Writing –original draft. A. Ruiz-Constán: Writing –original
draft, Visualization. C. Marín Lechado: Writing –original draft, Visualiza-
tion. J.M. Martín-Civantos: Writing –review &editing. E. Custodio: Con-
ceptualization, Writing –original draft, Writing –review &editing. J.
Urrutia: Writing –original draft. C. Herrera: Writing –original draft. L.J.
Lambán: Writing –original draft. J.J. Durán: Investigation, Writing –origi-
nal draft. S. Martos-Rosillo: Funding acquisition, Project administration,
Conceptualization, Formal analysis, Methodology, Data curation, Investiga-
tion, Writing –original draft, Writing –review &editing, Visualization.
Declaration of competing interest
The authors declare that they have no known competing financial inter-
ests or personal relationships that could have appeared to influence the
work reported in this paper.
J. Jódar et al. Science of the Total Environment 825 (2022) 153937
9

Acknowledgements
This research was undertaken as part of the project “Impact, monitoring
and assessment of global and climate change on water resources in high-
mountain National Parks (CCPM)”, with reference number CANOA-
51.3.00.43.00 and funded by Organismo Autónomo Parques Nacionales
from the Ministerio para la Transición Ecológica y el Reto Demográfico.
The authors thank the Ibero-American Science and Technology for Devel-
opment Programme (CYTED) for its financial support to the network “Wa-
ter Sowing and Harvesting in Protected Natural Areas”(419RT0577). This
work is a contribution to the Research Group RNM-126 of the Junta de
Andalucía. Special thanks goes to the irrigation community in Bérchules
and the Sierra Nevada NationalPark for their collaboration. We also appre-
ciate the support of AEMET and REDIAM, who provided meteorological
and hydrological data. The authors would also like to thank the anonymous
reviewers for their constructive comments and suggestions which led to a
substantial improvement of the paper.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.scitotenv.2022.153937.
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