This paper was presented to the Congreso CARA "Hydrogeology and Water Resources Management: Working together for the future", carried out on March 9-11, 2005 in Managua, Nicaragua. CARA (www.caragua.org) is the Central American Water Resources Management Network.
Introduction
The joint management of surface water and groundwater resources is a
fundamental concept underlying the Spanish Water Act and the European
Union’s new policy concerning water use. However, the practical
application of this concept is not the same in all EU countries, as the
coordinated utilization of various water sources to meet a single
demand is not common practice in the north of Europe, where water is
relatively abundant, while in some southern countries, including Spain,
the gradual introduction of this management technique is being
considered. Specifically, in Spain a nationwide study programme has
been designed and put in place to examine the coordinated utilization
of surface water, groundwater and non-conventional sources of water,
found in 27 water exploitation systems. These are made up of 70
aquifers (of which about 90% are carbonated), 71 reservoirs, 16
large-scale water-channelling networks and numerous wastewater
treatment and seawater desalination plants. This paper presents an
analysis and description of studies carried out in five of these
systems.
Methodology
The methodology used is based on a series of interlinked actions.
According to Sahuquillo and Sánchez González (1983) such
actions can be subdivided as follows:
- Calculate the water inflow (surface and subterranean) in a
natural regime into a water-resource system.
- Characterise the existing hydraulic infrastructure in terms of
both surface storage (reservoirs) and subterranean storage (aquifers),
together with the available means of connecting these elements.
- Analyse the possibilities of using non-conventional resources
(desalinated water and recycled water)
- Quantify the demand for water (both for human consumption and for
other uses).
- Create a mathematical model and a simulation of management
alternatives and calculate guarantee indices.
The programme used for the above modelling was SIMGES (Andreu and
Capilla 1993), designed at Universidad Politécnica de Valencia
(Spain).
The operational steps in this modelling were structured in three stages:
1) Simulation of the current system for managing water resources. The
aim of this is to identify any shortcomings in the system, their extent
and location. The simulation also includes the response of the system
to different hypotheses concerning rising or falling demand, including
meeting the requirements of a minimum ecological water flow. Finally,
an evaluation is made of the pressure exerted by the system on the
water resources most directly related to natural areas of particular
environmental concern.
2) Simulation of the system of water resources for each of the
elements
on which a specific action is proposed or desirable. An individual
analysis is made of the effect produced by each such action, and a
comparative study made of the results that would be obtained. A very
large number of simulations are made during this stage, as one is
required for each of the elements on which a given action is proposed.
3) Performance of a series of simulations to integrate, within a
single
management scheme, some or all of the elements that produced good
results in the simulations carried out in the previous modelling stage.
Water systems analysed and the results obtained
In all the systems that were modelled, various management
alternatives
were simulated to consider a situation of falling demand, resulting
from changes in consumption patterns and/or the more efficient use of
water resources, by the incorporation of technical advances in
distribution systems and irrigation techniques. These simulations also
considered the use of treated wastewater (at least secondary treatment)
for irrigation. In analysing the various management alternatives,
priority was given to the maintenance of ecological volumes of water in
rivers and springs, over and above any other use of the water. A brief
description is given below of the water systems analysed and of the
results obtained.
a) Marina Baja (Alicante): This system consists of two small reservoirs
and various carbonated aquifers, with highly productive wells
(installed pumping capacity: 600-800 L/s). The system supplies water to
meet a drinking water demand of about 24 hm3/year and an irrigation
demand of about 31 hm3/year. This exploitation system is characterised
by the existence of a large resort town (Benidorm) and single-crop
intensive agriculture. Demand, thus, is seasonal, with sharp peaks
during the summer months. The mathematical model created shows that
regulation of the system is improved when two of the aquifers are
pumped directly into one of the reservoirs, when greater use is made of
treated wastewater and when the principal spring in the area is
regulated. The latter regulation involves the use, when necessary, of
water reserves, and so the spring could run dry for long periods of
time, which might adversely affect an area of great natural beauty that
lies downstream. To alleviate this effect, when the springwaters run
dry, some of the water extracted from boreholes would be pumped
directly towards the river course; once it has flowed through the area
to be protected, it can again be extracted and stored in a reservoir
for future use.
b) Costa del Sol Occidental (Málaga): This system is
characterised by the inclusion of some of the most important resort
areas in Spain, where urban water demand is highly variable, both
annually and inter-annually. The changes that occur are both
significant and difficult to quantify, in terms of the size and type of
population to be supplied. The area also features highly productive
agricultural land and specially protected areas of ecological
importance and natural beauty. This combination of economic activities
and conservation interests makes management of the system enormously
complex. The annual demand for water consumption is 187 hm3. To meet
this demand, three water sources are available: surface reservoirs,
groundwater extraction and non-conventional supplies (desalination
plants and wastewater treatment). The model created shows that the
regulation of upstream springs is a more economic alternative, and one
that better ensures the provision of water, than the creation of
surface reservoirs (some proposed, some currently under construction).
Nevertheless, any use that is made of groundwater must be compatible
with maintaining water quality within areas subject to special
protection.
c) Sierra de Baza (Granada): This rural system is situated in one of
the poorest areas in Spain. At present, it is constituted of a single
aquifer, although plans exist to construct a reservoir with a capacity
of 10 hm3 , in order to guarantee water supplies for current
agricultural use and to increase the area of irrigable land by 500 ha.
The aquifer lies beneath a protected natural space. The model shows
that the reservoir, alone, is insufficient to guarantee the stated
objectives, and so current volume of pumped groundwater must be
increased to cover the deficit. Nevertheless, sustainable use of the
aquifer and protection of the natural space can only be ensured when
the increased area of irrigated land is limited to 100 ha.
d) Vinalopó (Alicante): This water system is comprised almost
entirely of aquifers, most of which have been over-exploited since the
1960s and that provide 90% of the water consumed (123.3 hm3/year). 54%
of the water regulated by this system is consumed within its geographic
boundaries, while the rest meets an external demand, in nearby coastal
areas where tourism is a significant activity. Of the 16 aquifers
making up the system, only nine are close to equilibrium, while two
present an exploitation/recharge coefficient of around 600%, for
another three it is 200% and for a further two it is 150%. To overcome
the imbalance, water will be introduced into the system from a
neighbouring catchment area (the Júcar basin). The water will be
transported 150 km by means of a system channelling 80 hm3/year of
continuous flow for 6 months a year (October to March). The model shows
that, by these means, regulation and water-supply guarantees are
improved, but even better results could be obtained by making use of
aquifer storage capacity by applying artificial recharge procedures to
part of the water transferred from Júcar. This could be possible
if the outer-system demand is met changing the current water source by
desalinated water obtained from boreholes located a short distance from
the coast, and by increasing the use made of treated wastewater for
irrigation (currently just 8%) up to 20%. If all the above measures
were successfully implemented, pumping from the aquifers could be
reduced by 68 hm3/year and all but one of the aquifers that are
currently over-exploited would return to equilibrium. This does not
mean, however, that in the short term water levels would return to the
levels that existed before exploitation began, or that water would
again be discharged from the aquifers’ natural drainage points. The
models created to analyse the above hypotheses show that recovery times
are very long, up to 200 years in some aquifers, and that in some cases
a large increase is needed in the volume of water to be artificially
recharged. The latter situation must be addressed in the near future,
taking into account the goals of the European Framework Directive on
Water, which sets out as a priority objective to ensure the good status
of inland water, both quantitative and qualitative. To meet this
target, it will be necessary to transfer a greater volume of water
during the period necessary for aquifers to recover. Once this aim has
been achieved, a system can be established to exploit aquifers on the
basis of sustainable use.
e) Quiebrajano-Víboras (Jaén): This system is made up
of 15 aquifers and 2 reservoirs, each of which is located on a
different river course. One of the rivers flows over saliferous
Triassic rocks, and so the reservoir water, proceeding from a number of
aquifers located upstream, is contaminated and must be desalinated. The
other reservoir is constructed over a permeable base, through which
water escapes to recharge the aquifer. The mathematical model shows
that, from both economic and environmental standpoints, indirect
recharge followed by pumping from the aquifer is preferable to sealing
the base of the reservoir, because the recharge derived from the
reservoir helps to increase the volume of water drained by the aquifer.
In turn, this favours the maintenance of the ecological flow of the
river at certain sectors and during particular periods of special
interest for the environment. Moreover, it is feasible to exploit the
water derived from indirect recharge downstream, using other regulation
installations. As regards the first reservoir, here we recommend direct
use of the water, by pumping directly from the upstream aquifers,
rather than storing the water in the reservoir and subsequently
extracting the salt from it, as the water quality thus obtained is much
better for human consumption. It should be borne in mind, however, that
this operation might adversely affect some springs and sectors of the
river course of particular ecological interest. Such problems could be
overcome by programming artificial aquifer recharge operations and by
regulating some springs by pumping water from boreholes and later
channelling some of it into the aquifers that supply the rivers.
References
Andreu, J. and Capilla, J. 1993. El modelo de gestión de
cuencas
SIMGES. In:Andreu J (ed.) Conceptos y métodos para la
planificación hidrológica. CIMNE. Barcelona. 298-321.
Sauquillo, A. and Sánchez González, A. 1983.
Metodología para la realización de estudios de
utilización conjunta de aguas superficiales y aguas
subterráneas. Boletín de Informaciones y Estudios, 43,
1-95.
Organization name: Instituto Geológico y Minero de España (IGME)
Street address: c/ Ríos Rosas 23
City: Madrid
Postal code/ZIP: 28003
Country: Spain
E-mail: jm.murillo@igme.es
Web: http://www.igme.es
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