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Energy 35 (2010) 1008–1016

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Energy

journal homepage: www.elsevier .com/locate/energy

Environmental costs of a river watershed within the European waterframework directive: Results from physical hydronomics

A. Martınez*, J. Uche, A. Valero, A. Valero-DelgadoCentre for Research of Energy Resources and Consumptions (CIRCE), University of Zaragoza, Marıa de Luna 3, 50018 Zaragoza, Spain

a r t i c l e i n f o

Article history:Received 30 October 2008Received in revised form17 May 2009Accepted 9 June 2009Available online 9 July 2009

Keywords:ExergyPhysical hydronomicsEnvironmental costsRiver basinEuropean Water Framework Directive

Abbreviations: IBC, Inland Basins of Catalonia;exploitation state; FCR, full cost recovery; FS, futurecomponent; IRC, integral replacement cost; NS, natucomponent; OS, objective state; PH, physical hydronoremaining resource cost; SC, service cost; WFD,(Directive 2000/60/CE).

* Corresponding author. Tel.: þ34 976761863; fax:E-mail address: amayamg@unizar.es (A. Martınez)

0360-5442/$ – see front matter � 2009 Elsevier Ltd.doi:10.1016/j.energy.2009.06.026

a b s t r a c t

Physical hydronomics (PH) is the specific application of thermodynamics that physically characterizesthe governance of water bodies, i.e., the Water Framework Directive (WFD) for European Union citizens.In this paper, calculation procedures for the exergy analysis of river basins are developed within the WFDguidelines and a case study is developed. Therefore, it serves as an example for the feasible application ofPH in the environmental cost assessment of water bodies, accordingly to the principle of recovery of thecosts related to water services in accordance with the polluter pays principle, one of the milestones of theWFD. The Foix River watershed, a small river located at the Inland Basins of Catalonia (IBC), has beenanalyzed. Main results, difficulties, and constraints encountered are shown in the paper. Following WFD’squantity and quality objectives previously defined, water costs are calculated and the equivalencebetween the exergy loss due to water users and the exergy variation along the river are also analyzed.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

The Water Framework Directive (WFD) states that it is necessaryto develop an integrated community policy on water. Environmentalconcerns, as well as ecosystem preservation, are the new back-grounds underlying it. The WFD’s end-objective is to achieve a ‘‘goodstatus’’ condition for the whole European water bodies by the end of2015 establishing a programme of measures to that end, with thecorresponding spread of the cost implementation [1]. One of the toolsapplied to reach that objective is the full cost recovery (FCR) principle.Full cost includes, in accordance with the WFD, financial costs of waterservices such as supply, sanitation, and storage, resource costs – asopportunity costs derived from an inefficient or alternative use –, andenvironmental costs regarding the alteration of the physical and bio-logical aspects of water bodies provoked by human activities. Oncethis comprehensive cost of water is calculated, its abatement costmust be allocated among different water users, as the Directiveindicates through the Polluter Pays Principle (Art. 9).

EC, environmental cost; ES,state; IM, inorganic matter

ral state; OM, organic mattermics; PS, present state; RRC,Water Framework Directive

þ34 976732080..

All rights reserved.

The first two terms, the financial and the resource cost, could becalculated from classical economic accountancy. However, the thirdterm is more difficult to evaluate, at least with the current analysistools traditionally used in the context of water management poli-cies. Hence, the assessment of environmental costs for a water bodyrequires the search of new theoretical and applied approaches ableto lead to a comprehensive analysis. The usefulness of those newapproaches demands the definition and calculation procedures ofthe costs to be based on a rigorous quantitative and qualitativeanalysis. This would ensure the homogeneity of the results, so theycould be comparable in space and time. Furthermore, theseapproaches should as well have the ability to aggregate or disag-gregate the results in quantitative and qualitative terms.

Exergy analysis perfectly fits those methodological require-ments. Exergoecology – the application of the exergy analysis forthe assessment of natural fluxes and resources on Earth – wasproposed by Valero in 1998 [2]. The branch of Exergoecologydevoted to watersheds analysis was denominated Physical Hydro-nomics (PH) [3]. It uses general concepts coming from Thermody-namics in order to build exergy profiles of water bodies and toassess the physical costs of natural and artificial water manage-ment. While Thermodynamics is interpreted here as the Arithmeticframework, PH can be understood as the Accounting Principle.

Exergy has been successfully applied in water resourcesassessment. In addition to the conventional application of evalu-ating the efficiency of energy-utilization systems and detecting

Nomenclature

a activityb specific exergy (kJ/kg)B absolute exergy (kJ)c velocity (m/s)DG Gibbs free energy (kJ/mol)n number of mols (mol)p pressure (Pa)R universal gas constant (kJ/kg K)T temperature (K)n specific volume (m3/kg)x molar concentrationz altitude (m)

A. Martınez et al. / Energy 35 (2010) 1008–1016 1009

quantitatively the causes of the thermodynamic imperfection,exergy attracts escalating interests in environmental resourceaccounting, environmental-impact assessment, ecological costevaluation, and ecological modelling in recent years [4–10].

Regarding water exergy assessment, Zaleta-Aguilar et al. [11]proposed a simplified analysis of the exergy lost along a rivercourse. Some more specific studies using exergy as the mainoperating tool are those by Hellstorm [12–14], who estimated andcompared the exergy consumption of physical resources in somewastewater treatment plants and sewerage systems. In addition tothat Chen [15] developed a unified objective assessment of waterquality, the chemical exergy-based evaluation method: whilea quantity termed specific standard chemical exergy based on theglobal reference substances might be adopted, an indicator asspecific relative chemical exergy with reference to a spectrum ofsubstances associated with the specified water-quality standard isproposed for water-quality evaluation with more practical impli-cations, resulting in unified objective quantifiers for the carryingcapacity and carrying deficit of water resources. A global waterresources assessment was presented by the authors in theirprevious works [16], taking advantage of the parallelism betweenthe exergy loss and the resources depletion.

2. Methodology. Application of PH to a watershed

The specific exergy of a water body is defined by its mass flowand six measurable parameters characterizing the thermodynamicstatus of water: temperature, pressure, composition, concentration,velocity, and altitude [11]. The exergy method associates eachparameter with its exergy component [17]: thermal, mechanical,chemical, kinetic, and potential (Eq. (1)). Therefore, and starting

bH2O ðkJ=kgÞ|fflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflffl}Total:exergy

¼ cp;H20

�Ta � T0 � T0ln

�Ta

T0

��|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}

Thermal:Ex

þ nH2O ðpa � p0Þ|fflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflffl}Mechanical:Ex

þX

i|fflfflfflfflfflfflþRT0

Xxiln

ai

a0|fflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflffl}Concentration:Ex

þ12

�c2

a � c20

�|fflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflffl}

Kinetic:Ex

þ g ðza � z0Þ|fflfflfflfflfflfflffl{zfflfflfflfflfflfflffl}Potential:Ex

from these components, it is possible to evaluate a water body inquantitative and qualitative terms. The model assumes theapproximation to an incompressible liquid where the exergy isdefined through the mentioned components.where subindex 0 denotes the water properties of the referenceenvironment and a of the water body under consideration. Eachcomponent must be separately calculated. The sum of all thecomponents expresses the specific exergy of the given waterresource and can be understood as the minimum energy requiredto restore the resource from the reference (the Mediterranean Seain the case study presented in this paper). A detailed study of themost suitable reference environment can be found in [18]. Then thetotal exergy of the river will be defined by Eq. (2), and the exergydifference between the two states of the river will be obtained astotal exergies subtraction:

B ðkWÞ ¼ _m ðkg=sÞ , b ðkJ=kgÞ (2)

Furthermore, DB can be divided into the quantitative (t) andqualitative (l) terms [3], as in Eq. (3), where the second-order terms,D _m$D _b, can be neglected:

DByD _m,bþ _m,Db ¼ DBt þ DBl (3)

Taking these equations as the theoretical background, meth-odological tools have been developed in order to calculate thephysical costs of water resources required for the assessment ofWFD environmental costs. In accordance with the polluter paysprinciple and, as it is established in the WFD, the contribution of thedegradation produced by the different uses of water (industry,households, and agriculture) has also been analyzed.

This new methodology is currently being implemented in theInland Basins of Catalonia (IBC), located in the northeast of Spain. Inthis paper, PH has been applied to the river Foix watershed, a smallbasin of about 300 km2 in the southeast of the IBC (Tarragonaprovince). Two levels of analysis are considered: decrease inquantity and quality of water as the water flows and the degrada-tion due to water uses. In the first part of the analysis, the pairquantity–quality gives us the information needed to characterizethe river from an exergy point of view. Then the water uses in thearea are studied to identify the exergy loss due to those uses andthey are included in the first analysis to allocate cost.

2.1. Exergy profile of a river

The exergy profile of the river is a very useful tool that consti-tutes the first step in the exergy cost-assessment procedure [3].Each river status has its own exergy profile. Theoretically, andneglecting the dilution effects in the river mouth, the exergy profileof a river would show a Gaussian bell-shaped curve, coming fromthe product of the specific exergy and the flow (Eq. (2)).

yi

DGf þ

Xe

nebchne

!fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}

Chemical:Ex

(1)

EC

RRC

NS

OS

FS2015

PS

ES

SC

IRC

Fig. 1. Costs required by the WFD to assess environmental costs.

A. Martınez et al. / Energy 35 (2010) 1008–10161010

2.2. WFD objectives and costs definition

The definite objective of PH is to use the physical costs as a guideto allocate the environmental costs proposed by the WFD amongthe different water users. This landmark legislation establishesseveral objective states (OS) for the water bodies by 2015 (in flowand quality) according to the river tipology [19]. Therefore,different costs can be defined depending on the initial and endstatuses of the water body. In addition to the present status (PS) ofwater bodies, there is a natural status (NS) for each water bodycharacterized as if it were unaffected by human degradation;a future status (FS) of water bodies in 2015 in whose definition thetrends of water consumption by diverse uses are considered; anda exploitation status (ES), a hypothetic one that represents thewater bodies situation if the existing sewage plants would notoperate (see Fig. 1). In general terms, the NS of the river wouldpresent the better state of the river and the exploitation state wouldshow the exergy loss due to water uses.

In consequence, and following the WFD indications and theWATECO group guidelines (EU, 2004), it is possible to define thefollowing costs:

– Services cost (SC) or financial cost (FC) is the cost associated tothe present measures that allow water bodies to be in the PSinstead of being in the ES. It comprises supply, sanitation,transport, and storage costs, which at present could be reflec-ted to users in minor or major quantity. The costs of depreci-ation of capital, the costs of financing, the costs of maintenanceand operation, the administrative costs, and other direct costsare also included here.

– Environmental cost (EC) ranges the gap between FS and OS,regarding the alteration of the physical and biological aspectsof water bodies due to economic activities and remainingpollution. Note that according to WATECO Working GroupECO2 and following the ecological concept of the WFD, theresource costs (RCs), initially defined as the opportunity costsof a better use of water, are finally integrated with EC.

– Remaining resource cost (RRC) is the cost which assesses themeasures required to reach the NS starting from OS. Consid-ering the integral water cycle, this last cost has been introducedby completeness. However, the WFD exigences just run untilthe EC, which should be gradually included in the SC of water.

Finally, the integral replacement cost (IRC) is the addition of thethree referred costs, associated to the measures needed to reach the

NS, starting from the ES. Fig. 1 shows these definitions. The IRC linksdirectly with the full cost set out by the WFD as the basis of the FCRprinciple.

It is important to emphasize that ecologic status of water bodiessummarizes a set of physicochemical, biologic, and even hydro-morphologycal indexes and, at present, PH is only capable to dealwith physicochemical features. Biological aspects are still difficultto include, and other knowledge fields would be required.

2.3. Aggregation level of the analysis

A preliminary water network (with about 90 points) was firstlycreated for the complete IBC, with their main water courses, watersupply piping systems, reservoirs, desalination plants, and groundwater bodies [20]. Water-quality data and flows required for the PSwere obtained from available sampling stations. Since quantity andquality sampling stations are independent, special attention wasdevoted to the fact that gauging and quality stations were nearbywithin the river. Then, the exergy values of present water courseswere obtained by the addition of thermal, mechanical, potential,and chemical (organic and inorganic) components.

Unfortunately, the accuracy of that global network resulted notuseful enough to meet the WFD requirements. At that point, it wasconcluded that the analysis should be focused, at least, on the levelof the diverse water bodies charaterized in previous steps under theroadmap of the WFD application (more than 250 water bodies forthe IBC river courses) [21].

2.4. Discrete river profiles

Once the statuses have been well defined in quality and quan-tity, the discrete exergy profile of the river is obtained after thecalculation of its exergy components. The detail in information willbe translated into detail in exergy profile. The ideal input datawould be continuous but it is not feasible. The real sampling data,when exist, provide a discrete database which leads to a discreteriver profile defined by a reduced number of real figures. Since realmeasurements are scarce, a simulation software is needed toextend the discrete profile until the desired number of river reachesfor the study (see Fig. 2). The software used in this work is a surfacewatershed simulator developed by the EPA [22], Qual2kw. It allowsto set the flow and chemical features in each reach of the river fordiverse scenarios. Results help to obtain the discrete exergy profilesfor present, virtual, and OSs of the rivers.

This fragmentation requirement should also be enhanced whenselected measures have to be applied to restore the OS of waterbodies, what is the final target in the WFD. Furthermore, thedownstream effect that any corrective measure has in the river andits adequate mathematical treatment have to be carefully observedin the analysis. The complete exergy profiles of a river status willinclude the upstream effects of applied measures (see Fig. 3). Inaddition to that, catchments and returns are sometimes identifiedin the same reach, so its effects are translated into a quality andquantity loss.

2.5. From the physical to the economic costs

The exergy gap between the two states gives an idea about howfar the river is from the desired final state. As an example, theenvironmental cost could be defined as the difference between theexergy of the river at the objective state and its status by 2015 (Eq.(4)). The integral (discrete sum) has to be done along the river, i.e.,in the set of reaches comprising the river,

HW#1 FOIX

HW#2 PONTONS

HW#4 QUEROL

HW#3 LLITRÁ

1

2

3

4

9

5

7

6

8

10

11

SAMPLING STATION

FO000J125

SAMPLING STATION

FO005

SAMPLING STATION

FO010C091

SAMPLING STATION

FO015J008

SEWAGE PLANT VILAFRANCA PENEDES

IND. PACS DEL

PENEDES

PONTONS

QUEROL

AIGUAMURCIA

FOIX IRRIGATION CATCHMENT

SEWAGE PLANT

CASTELLET I LA GORNAL

SEWAGE PLANT

CASTELLVI DE LA MARCA

FOIX DAM

Fig. 2. Scheme of a general river basin to be applied in Qual2kw model.

A. Martınez et al. / Energy 35 (2010) 1008–1016 1011

ECth ¼X

i¼ reaches

QOS,DbOS � QFS2015

,DbFS2015

i (4)

At this point, the ECth just represents the theoretical exergy cost,the exergy loss provoked by humans that moves away the riverfrom the desired objective state. The real cost (EC*) to fill the gapbetween both the river statuses has to be still calculated. Since thedifference between the exergy of fuels and products determines theirreversibility in a system, exergy efficiency is the ratio betweenthe fuel(s) and product(s). Then, the unit exergy cost (k) is theinverse of the exergy efficiency, and it is calculated as the ratiobetween the exergy needed to produce a resource (fuel, F) and theexergy of the resource in which the interest is focussed (product, P),Eq. (5),

k ¼ FP

(5)

In consequence, the real environmental cost in energy units,EC*, can be immediately obtained as indicated by the followingequation:

EC* ¼ k$ECth (6)

Finally, if the cost needs to be given in economic units, energyunits (J) can be easily translated into monetary units (V) using thenational average energy price according to the energies mix.

2.6. Relationship between the IRC and the degradationdue to water users

The IRC (SCþ ECþ RRC) accounts for the existing distancebetween the natural state of the river and the state that the riverwould present if none of the water treatments after using wasconsidered. Then, it represents a global degradation along the rivercourse.

Focussing the analysis on the water users system boundary, thedegradation provoked by water uses can be defined as shown bythe following equation:

DBuses ¼X

i

DBi ¼X

i

Bi;cat �X

i

Bi;ret (7)

River Length

B (kW)

1 2 3 4 5 6 7

OS

PS

Downstream effect

mouthsource

Measure

Fig. 3. Discrete profile of a river when simulation models are used, and downstreameffect of an applied technique.

A. Martınez et al. / Energy 35 (2010) 1008–10161012

where i stands for the number of uses. It is also considered that, insome cases, as ,for instance, interbasin water transfers, only thecatchment (cat) or the return (ret) are accounted for.

The DB has been defined in this way (cat-ret) because it isassumed that the quality in the return flow will be lower than the

Water uses characterization

ΔB (MWh/yr) -Exergy-Related-Dissag

ΔB* (MWh/yr) -Real ex-Related-Dissag

Economic cost (€/yr) - Real econo-Dissagrega

Dissagregation in quantity (t) and quality (l)

Cost alloca

Fig. 4. PH’s methodo

quality in the catchment (Db¼ bcat – bret> 0). The same argumentwas applied to the quality component since a small amount of thewater delivered is consumed and then it does not return to thewatershed (DQ¼Qcat – Qret> 0).

Then, Eq. (7) can be written and calculated by its components(quantity and quality), and afterwards the contribution of each use towater-quality degradation (or water loss–quality degradation) can beused to divide the water costs among the different water users,

DBuses ¼X

i

ðDQ$bcat þ Qret$DbÞiþX

j

ðDQ$bcat

þ Qret$DbÞjþX

zðDQ$bcat þ Qret$DbÞz (8)

where i represents the number of domestic water uses, j thenumber of industrial uses, and z the number of agricultural uses. Inbroad outline, the cost allocation for quantity and quality compo-nents will be different: uses that usually damage the water qualitydo not necessarily reduce the available amount of water.

To summarize the explained methodology, a conceptual diagramis presented in Fig. 4. Starting from the river profile of the river in itsdifferent states and from the several exergy cost definition, theminimum energy (DB) among the defined states is calculated.Secondly, it is translated into real exergy requirements by comparingtheoretical with real energy consumptions consumed by the appliedwater treatment technologies. Afterwards, the energy price is intro-duced to obtain the economic costs of such correction measurementsto go from the initial to the objective state of the river.

differences among river profiles to SC, EC, SC,

regated in ΔBt and ΔBl

ergy distance among river profiles to SC*, EC*, SC*,

regated in ΔBt, and ΔBl

mic cost of covering the exergy differenceted in ΔBt, and ΔBl

tion among users

logy summary.

-250-200-150-100

-500

50100150200250300

Jan Feb Mar Abr May Jun Jul Ago Sep Oct Nov Dic

M Wh/month

EC RRC SC

Fig. 6. Chemical term of the EC, RRC, and SC costs, associated to water consumption(DBch,t).

A. Martınez et al. / Energy 35 (2010) 1008–1016 1013

From a different perspective, it is know that the river degrada-tion was provoked by water users. The quantity and quality featuresof those uses were introduced in the methodology to allocate thepreviously calculated costs among diverse sectors.

3. The case of the Foix Basin

3.1. Main geodata, river reaches, and Qual2kW simulation

Foix watershed is a quite small basin (301.3 km2) located at thenortheast of Tarragona, the southern province of the IBC. Its totallength is 163.8 km, and it has three main tributaries: Marmellar,Pontons, and Llitra. Average annual contribution of the river is only9.47 hm3, corresponding to an average flow of 0.3 m3/s.

Foix Basin was divided into 11 water reaches, following theguidelines suggested by the WFD’s experts attending to hydro-geomorphological criteria. Finally, four river courses can be clearlyidentified within the watershed. The main one is the Foix Head-water, formed by reaches 1, 2, 5, 8, 10, and 11. The Pontons Head-water (reaches 3 and 4) is located east to the main headwater. TheMarmelar Headwater, west side of the watershed, is constituted byreach 9 and it joins the main course before Foix Dam (reach 10) and,finally, Llitra is formed by reaches 6 and 7, in the east area of thewatershed.

Only two sampling stations provided water-quality measure-ments for the Foix Watershed. However, four sampling stations

2.25

2.30

2.35

2.40

2.45

2.50

bch

,IM

(kJ/kg

)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Q (m

3/s)

0100200300400500600700800

1 2 5 8 10 11

1 2 5 8 10 11

1 2 5 8 10 11

Bch

,IM

(M

Wh

)

PS FS ES OS NS

Fig. 5. Exergy profile of the Foix River in January, attending to its flow (Q), its salinity(bch,IM), and the total exergy (Bch,IM¼Q�bch,IM), for several statuses: present, projected2015–future, exploitation, objective and natural status.

measured its flow for the last 50 years. To overcome those infor-mation restrictions, the Qual2kw model was used to simulate thewatershed. First, the figures (quantity and quality) for each stretchof the river in the PS of the river were obtained. Then, all the neededriver states were also simulated in order to calculate the minimumexergy costs.

3.2. Exergy profiles and minimum costs

The main exergy components for each one of the explained riverstatuses have been calculated. These components are separatelypresented because different restoration technical measures will beapplied. The term IM (inorganic matter) groups inorganic salts andpure water contributions, i.e, the conductivity, and the OM standsfor the organic matter in the water flow.

The discrete exergy profiles for the Foix Basin were calculatedfor each month. As an example, Fig. 5 shows the chemical specificexergy (b) profile of the Foix River in January, attending to itssalinity, for all the considered states. The flow profile (Q) and thetotal exergy (B) – following Eq. (2) – are also presented. Fora better interpretation, only the main water course (reaches 1, 2, 5,8, 10, and 11) has been drawn: stretches 3 and 4 flow into 5,reaches 6 and 7 into 8, and reach 9 into 10, where the Foix Dam isemplaced.

Once all the exergy profiles of the river states (ES, PS, FS, OS, andNS) are established, the next step was to calculate the minimumcosts defined in Section 2.2 as the exergy loss DB existing betweenthe two given exergy profiles.

Next figures summarize the three costs defined in Section 2.2(EC, RRC, and SC) along the river, disaggregated into its quantitative(Figs. 6 and 7) and qualitative (Figs. 8 and 9) terms. These bars

-500-400-300-200-100

0100200300400500

Jan Feb Mar Abr May Jun Jul Ago Sep Oct Nov Dic

M Wh/month

EC RRC SC

Fig. 7. Potential term of the EC, RRC, and SC costs, associated to water consumption(DBp,t).

-250

-200

-150

-100

-50

0

50

Jan Feb Mar Apr May Jun Jul Ago Sep Oct Nov Dic

M Wh/month

EC RRC SC

Fig. 8. Chemical exergy term (OM) component of the EC, RRC, and SC costs, associatedto the loss of quality in water (DBchOM,l).

Table 1Minimum exergy cost (IRC) and real exergy cost (IRC*), after including the restoringmeasurements.

DBt,pot DBt,IM DBt,OM DBl,pot DBl,IM DBl, OM

Exergy cost (MWh/yr)SC 0 0 0 0 21 –1843EC 1323 0 0 0 141 –149RRC 3298 1293 69 0 54 –196IRC 4621 1293 69 0 216 –2188Exergy cost*(MWh/yr)SC* 0 0 0 0 93 –8203EC* 9167 0 0 0 628 –664RRC* 22,857 7113 379 0 240 –870IRC* 32,024 7113 379 0 962 –9738

A. Martınez et al. / Energy 35 (2010) 1008–10161014

compute the exergy losses of the whole basin and they were drawnfor each month.

It is important to remark that the potential term appears only inthe quantitative portion because the average altitude of each waterreach remains constant independently of its flow. Therefore, for thepotential component of exergy, Eq. (3) becomes DByDBm.Regarding that portion, it is clear that RRC is the most represen-tative because it includes the water lack between NS and OS. Theflow in NS is understood as the original flow of the river withoutany anthropogenic presence, and the flow in the OS is defined foreach river by the competent regulation organism, meeting the WFDrequirements. For July and August, the flow legally defined for theOS is higher than the NS for this river and, therefore, negativeresults are obtained in these months. This case is a clear example ofcontradictions sometimes adopted: the OS for this river in thementioned months is higher than the stream actually flowing in theriver even without any external use. The quantity term of the SC iszero for all the months because no consumption in the wastewatertreatment plants has been considered and, accordingly, flows in theES and PS are equal.

Having looked at the quantity component, as SC compares thestatus of a river with and without sewage plants, the quality ofwater will be considerably different. For this cost, highest bars willbe found in Fig. 8, since they account for the exergy losses associ-ated to OM. However, regarding the salts content (Fig. 9), EC is themost important one because higher salinity losses are foundbetween OS and PS, which are the states limiting the EC, as shownin Fig. 1.

This analysis has been carried out for all the exergy componentspresented in Eq. (1), always attending to the separated study of thequantity and quality contributions. A summary of the results ispresented in the upper part of Table 1.

-5

0

5

10

15

20

Jan Feb Mar Apr May Jun Jul Ago Sep Oct Nov Dic

M Wh/month

EC RRC SC

Fig. 9. Chemical term (IM) component of the EC, RRC, and SC costs, associated to theloss of quality in water (DBchIM,l).

3.3. Real exergy costs and economic cost of water

Although all the three contributions to the IRC were calculatedin this study, the main attention was focused on the environmentalcost of water (EC), since it is the main WFD requirement. Theminimum exergy costs have been calculated as exergy differences.When the river quality or quantity features want to be restored bymeans of the best available technology (that will be included inthe Plan of Measures to reach the WFD objectives by 2015), theunavoidable cost due to real processes irreversibility must beincluded.

A complete study for obtaining the unit exergy costs (k) ofdifferent water treatment plants in the area of study was carriedout. Desalination and pumping unit exergy costs were used toobtain the real environmental cost (EC*) for the quantity compo-nents. On the other hand, the unit exergy cost of the water treat-ment plants provided information to deal with the qualitycomponent of the EC*. The complete study covers all the exergyflow analyses within the water plants and exceeds the purpose ofthis paper. A more detailed information can be found in [23].

The results for real exergy costs (noted with *) are presented inthe low part of Table 1. IRC* is divided in the three explainedcomponents (SC*, EC* and RRC*). Environmental cost (EC) is givenin bold and the quantity and quality terms are given separately.

The energy price was included in the analysis in order to linkenergy and economics. The environmental cost of water within theFoix Basin rises until about 1.8 MV.

3.4. Water cost allocation among users

Total demand in the Foix Basin is about 42 hm3/yr. The main usersare industry (about 9.4 hm3/yr), households (about 10.1 hm3/yr),and livestock and irrigation (about 22.9 hm3/yr). One of the mostspecific characteristics of the Foix Basin is that groundwater isextensively used.

The exergy degradation due to those uses has been obtained bycalculating the exergy gap between the catchments and theirreturns to the river by each water user. Table 2 shows the degra-dation sharing among users. An important difference betweenquality and quantity degradation can be observed: as expected, the

Table 2Environmental cost allocation among the different water uses in the Foix Water-shed, separated into quantity (t) and quality (l).

V/yr t l t l

Domestic 39% 90% 505,969 419,566 925,535Industrial 2% 5% 29,228 24,426 53,654Agricultural 59% 5% 769,335 21,369 790,704

1,769,892

A. Martınez et al. / Energy 35 (2010) 1008–1016 1015

domestic sector accounts for 90% of the water-quality losses.However, the water consumption is mainly due to irrigation (60%).

3.5. Significant features of the Foix watershed

The application of PH to the Foix watershed has presented someshortcomings, mainly related to the required input information. It isworth to analyze them in order to properly prepare future casestudies:

– Diverse catchments and (diffuse) return flows could occur inthe same river stretch simulated in Qual2kw, which returnsonly a mean value representing the whole stretch. Thus,a higher disaggregation level is required to deal with theaccurate balance in the river.

– Exergy losses due to dilution of diverse streams have to betaken into account, at least for the chemical (salinity) term.

– The natural self-depuration of the river supposes that a lowerdegradation will be found in the organic matter componentwith respect to the exergy extracted from diverse uses.

– Since most uses come from aquifers in the case of Foix Basin,simulated flows at present conditions (PS) are sometimeshigher than the flow in the NS, leading to confusion with theRRC and its theoretical definition.

– Theoretical return coefficients for water uses were selected (forinstance, a 10% for irrigation). Salinity and organic mattercontents increase after the water uses. Because of the lack ofinformation in some returns, those values were estimated fromdiverse literature sources. On the contrary, present gaugingstations and sewage plants were, respectively, taken forQual2kw simulator to calculate diverse river profiles.

4. Conclusion

The methodology associated to PH could be useful for theassessment of the quantity and quality degradation of surfacewaters. The equivalence between the exergy loss due to uses andthe exergy variation along the river underlines the main usefulnessof PH: it allows charging the cost of restoring water bodiesaccording to the degradation provoked by water users. Thisdegradation is measured in terms of quality, but also in quantity(the water really consumed is actually not returned to the envi-ronment), and has obviously a physical cost.

However, some corrections are still needed in the direction ofadapting the specific conditions of each river. For instance, theintensive use of groundwaters or surface waters coming fromneighbouring basins makes the flow in the present state of the riverhigher than the flow in the natural state (as in the case of the FoixRiver), perverting the definition of RRC and EC.

The lack of trustful real information is always a handicap for PH.However, although the information would be good enough for thereal status, pressure-impact models are always required to simulatethe hypothetic states (FS and OS) demanded by the WFD. Evenpressure-impact (P-I) models information could not be enough ifseveral catchments and returns are contained in the same simu-lated stretch. Another P-I model able to include aquifer interchangewith the River Basin could also be necessary for some areas. Inaddition to that, the lack of real data regarding the water degra-dation after its use makes difficult the total equivalence betweenthe exergy loss in water courses and water uses as well.

To conclude, an important aspect to underline is that exergy iscapable of measuring in physical units the damage, unifying theeffects in energy units. What is more, PH allows seeing interestingeffects such as the degradation occurring in the conceding basin ina watershed transfer, or the weight of the consumptive users (not

only the pollutant ones), which are not taxed within the presentwater tariffs.

Acknowledgments

The authors want to thank the efforts of the Catalan WaterAgency’s initiative of connecting Physics with Economy for theassessment of water costs. Besides, the authors greatly acknowl-edge the financial support given to this paper, which is under theframework of the IDERE RþDþI Project (ENE2007-067191),financed by the Spanish Ministry of Education and Science.

References

[1] European Union. Directive 2000/60/EC of the European Parliament and of theCouncil establishing a framework for the Community action in the field ofwater policy; 2000. Available at: http://ec.europa.eu/environment.

[2] Valero A. Thermoeconomics as a conceptual basis for energy-ecologicalanalysis. In: Ulgiati S, editor. Advances in energy studies. Energy flows inecology and economy. p. 415–44. Available at: http://circe.cps.unizar.es; 1998.

[3] Valero A, Uche J, Valero A, Martınez A. Physical hydronomics: application ofthe exergy analysis to the assessment of environmental costs of water bodies.The case of the Inland Basins of Catalonia. Energy [in press]. Corrected proofavailable online 30 October 2008. Available at: http://www.elsevier.com/energy.

[4] Jorgensen SE, Nielsen SN, Mejer H. Energy, environ, exergy and ecologicalmodelling. Ecol Model 1995;77:99–109. Available at: http://www.elsevier.com/locate/ecolmodel.

[5] Rosen MA, Diner I. Exergy-cost-energy-mass analysis of thermal systems andprocesses. Energy Conv Manage 2003;44:633–1651. Available at: http://www.elsevier.com/locate/enconman.

[6] Dincer I. Technical environmental and exergetic aspects of hydrogen energysystems. Int J Hydrogen Energy 2002;27:265–85. Available at: http://www.elsevier.com/locate/he.

[7] Gong M, Wall G. On exergy and sustainable development, Part-2: indicatorsand methods. Exergy – Int J 2001;1(4):217–33. Available at: http://www.inderscience.com.

[8] Wall G. Conditions and tools in the design of energy conversion and manage-ment systems of a sustainable society. Energy Conv Manage 2002;43:1235–48.Available at: http://www.elsevier.com/locate/enconman.

[9] Szargut JT. Optimization of the design parameters aiming at the minimizationof the depletion of non-renewable resources. Energy 2004;29:2161–9. Avail-able at: http://www.elsevier.com/energy.

[10] Chen GQ. Scarcity of exergy and ecological evaluation based on embodiedexergy. Commun Nonlinear Sci Numer Simul 2006;11:531–52. Available at:http://www.elsevier.com/locate/cnsns.

[11] Zaleta-Aguilar A, Ranz L, Valero A. Towards a unified measure of renewableresources availability: the exergy method applied to the water of a river.Energy Conv Manage 1998;39(16–18):1911–7. Available at: http://www.elsevier.com/locate/enconman.

[12] Hellstrom D. An exergy analysis for a wastewater treatment plant – an estimationof the consumption of physical resources. Water Environ Res 1997;69(1):44–51.Available at: http://www.wef.org.

[13] Hellstrom D, Karrman E. Exergy analysis and nutrient flows of varioussewerage systems. Water Sci Technol 1997;35(9):135–44. Available at: http://www.iwaponline.com/wst/toc.htm.

[14] Hellstrom D. Exergy analysis of nutrient recovery processes. Water Sci Technol2003;48(1):27–36. Available at: http://www.iwaponline.com.

[15] Chen GQ, Ji X. Chemical exergy based evaluation of water quality. Ecol Model2007;200(1–2):259–68. Available at: http://www.elsevier.com/locate/ecolmodel.

[16] Martınez A, Uche J, Bayod A, Rubio C. Assessment of the world fresch waterresources through energy requirements in desalination technologies. In:Proceedings of Euromed 2008 conference, Dead Sea 9–13 November 2008,Jordan.

[17] Wall G. Exergy – a useful concept within resource accounting. Report No. 77-42, Institute of Theoretical Physics, Chalmers University of Technology andUniversity of Goteborg, Sweden. 1997. Internet version available at http://exergy.se/goran/thesis/paper1/paper1.html.

[18] Martınez-Gracia A, Uche J, Valero A, Valero-Delgado A. Chemical exergyassessment of organic matter in a water flow. In: Proceedingsof the 6thBiennial International Workshop Advances in Energy Studies, Graz 29 June–2July 2008, Austria.

[19] Catalan Water Agency. Caracterizacion de masas de agua y analisis del riesgode incumplimiento de los objetivos de la directiva marco del agua (2000/60/CE) en las cuencas internas de Cataluna. In: Spanish. Departament de mediAmbient i Habitatge, Generalitat de Cataluna; 2005. Available at: http://www.gencat.cat/aca.

[20] Uche J. Aplicacion a las Cuencas Internas de Cataluna del enfoque termoeco-nomico propuesto. In Spanish. Workshop Communication. Workshop "Costos i

A. Martınez et al. / Energy 35 (2010) 1008–10161016

comptes de l’aigua a Catalunya en relacio amb la Directiva marc de l’aigua(DMA)", 18–19 June 2007, Barcelona, Spain.

[21] Catalan Water Agency. Regionalizacio del sistema fluvial a les ConquesInternes de Catalunya. Aplicacio de la Directiva Marc en Polıtica d’Aigues de laUnio Europea. Available at: http://www.gencat.cat/aca 2002. Document deSintesi[in Catalan].

[22] Environmental Protection Agency of the US (EPA). Qual2kw model. Usersguide; 2007. Available at: http://www.ecy.wa.gov/programs/eap/models.html.

[23] Martinez A, Uche J, Rubio C, Carrasquer B. Exergy cost of water supply andwater treatment technologies. In: Proceedings of the 2009 EDS conferenceandexhibition on desalination for the environment, clean water and energy, 17–20May 2009, Baden-Baden, Germany.