Modelling he spa io- empo al e olu ion o
3
H
in he wa e s o he Ri e Tagus
A. Baeza
a,
*, E. Ga cı
´a
b
, C. Mi o
´
a
, R. Pe ia
´n
˜ez
c
a
Uni e sidad de Ex emadu a, Facul ad de Ve e ina ia, Dp o. de Fı´sica,
A da. Uni e sidad sn, 10071 Ca´ce es, Spain
b
Uni e sidad de Ex emadu a, Ingenie ı´a Te´cnica Fo es al, Dp o. de Fı´sica,
10600 Plasencia (Ca´ce es), Spain
c
Uni e sidad de Se illa, E.U. de Ingenie ı´a Te´cnica Ag ı´cola,
Dp o. de Fı´sica Aplicada, 1, 41013 Se illa, Spain
Recei ed 7 Ap il 2005; ecei ed in e ised o m 2 Oc obe 2005; accep ed 23 Oc obe 2005
A ailable online 15 Decembe 2005
Abs ac
Measu emen s o i ium speci ic ac i i y le els and o empe a u es in wa e s o he To ejo
´neTagus
ese oi (Spain) showed ha hei adioac i e cha ac e is ics we e basically in luenced by he adioac i e
liquid e luen om he Alma az Nuclea Powe Plan . This en e s he To ejo
´neTagus ese oi ia he
A ocampo cooling ese oi , which exchanges wa e wi h he i s . We s udied he empo al and spa ial
(in wo dimensions) e olu ion o he men ioned pa ame e s o yea s 1997 and 1998. The i ium le els
we e ound o be signi ican ly co ela ed wi h empe a u e. Two nume ical models we e cons uc ed o
a quan i a i e s udy o he i ium le els along To ejo
´n ese oi : a 1D model was used o he dispe sion
o i ium along he whole leng h o he ese oi , and a 2D dep h-a e aged model was used o a de ailed
s udy o he a ea whe e i ium is eleased in o he ese oi . Bo h models sol e he hyd odynamic equa-
ions, o ob ain he cu en s induced by he exchanges o wa e be ween he ese oi s in he Ri e Tagus
and A ocampo, and he ad ec ion/di usion equa ion o calcula e he dispe sion o i ium. In gene al, he
model esul s we e in ag eemen wi h he expe imen al obse a ions.
Ó2005 Else ie L d. All igh s ese ed.
Keywo ds: Rese oi wa e ; T i ium; Tempe a u e; Nume ical modelling; Dispe sion
* Co esponding au ho . Tel./ ax: þ34 927 25 71 53.
E-mail add ess: [email p o ec ed]s (A. Baeza).
0265-931X/$ - see on ma e Ó2005 Else ie L d. All igh s ese ed.
doi:10.1016/j.jen ad.2005.10.004
Jou nal o En i onmen al Radioac i i y 86 (2006) 367e383
www.else ie .com/loca e/jen ad
1. In oduc ion
The quali y o he plane wa e s no ably in luence hei use, wi h he p esence o adionu-
clides being one o he limi ing ac o s. In his sense, he s udy o he i ium con en o di e en
wa e s has a h ee old in e es . Fi s ly, i s uni e sali y, since i ium le els due o na u al o igins
(Kau man and Libby, 1954) may be aised by se e al o de s o magni ude by an an h opogenic
componen (UNSCEAR, 1988; IAEA, 1990; Okada and Momoshima, 1993). Secondly, i s adio-
oxici y, which, while ela i ely low in compa ison wi h ha o o he adionuclides, is 25 000
imes g ea e when he
3
H is in he o m o HTO ins ead o HT (ICRP, 1978). Thi dly, he p ac-
ically indis inguishabili y o hyd aulic sys ems o i ia ed wa e om un i ia ed wa e (Thi-
bodeaux, 1979), so ha his adionuclide may be a good pa ame e o s udying he dynamics
o wa e masses (Fon es, 1983a,b; Baeza e al., 2002), and in pa icula o s udying he spa ial
and empo al dis ibu ion o o he subs ances con ained in hem, whe he conse a i e o no .
One o he Ibe ian Peninsula hyd ological sys ems ha is mos a ec ed by he p esence o
i ium is he Ri e Tagus. The p incipal eason is ha h ee nuclea powe plan s use i s wa e
o cooling (CSN, 1998). I s cou se is highly egula ed by an almos comple ely coupled se ies
o ese oi s, which a e especially impo an in he i e passage h ough he egions o Ex em-
adu a (Spain) and he Alen ejo (Po ugal), wi h i e ese oi s in 200 km. The au ho s s udied
p e iously, o he yea s 1994e1996, he basic aspec s o he i ium’s spa ial and empo al e o-
lu ion (Baeza e al., 1997), including a ious simple models ha allowed us o unde s and ce -
ain ace s o i s dynamics, such as i s mean ansi speed (Baeza e al., 2001, 2004).
One ac deduced was he impo ance o To ejo
´n ese oi in unde s anding he spa ial and
empo al e olu ion o i ium in his pa o he Ri e Tagus, since he wa e is used no only o
hyd oelec ic powe p oduc ion and i iga ion, bu also o cool he Alma az Nuclea Powe
Plan (hence o h, ANPP) h ough wa e exchanges wi h A ocampo ese oi . In he p esen
wo k, we s udy in de ail he in luence o his wa e exchange on he dis ibu ion o i ium
in To ejo
´n ese oi , using da a o yea s 1997 and 1998. To his end, we collec ed mon hly
wa e samples, in which we de e mined hei empe a u es simul aneously wi h he collec ion.
In his way we we e able o analyze bo h he spa ial dis ibu ion o i ium le els in wo dimen-
sions in To ejo
´n ese oi , ans e sally and longi udinally, and hei empo al e olu ion.
The cu en s caused by he exchange o wa e be ween he di e en ese oi s in his pa o
he Ri e Tagus make i di icul o gi e a de ailed quan i a i e in e p e a ion o he measu ed
i ium le els, in a o m allowing p edic ions o hei u u e e olu ion. A p e equisi e is o con-
s uc app op ia e models o To ejo
´n ese oi . We made a i s app oxima ion by using simple
box models o simula e he empo al e olu ion o i ium le els in he A ocampo (Baeza e al.,
1997) and To ejo
´n(Baeza e al., 2001) ese oi s, in pa icula s udying he a ea whe e he
exchange o wa e wi h he A ocampo ese oi akes place. The p esen wo k desc ibes he
de elopmen o wo new nume ical models o he To ejo
´n ese oi . The i s is a one-dimen-
sional model cons uc ed o ep oduce he la ge scale dispe sion o i ium, co e ing he o al
leng h o he ci ed ese oi . This model canno , howe e , desc ibe he dispe sion o i ium a
a small scale, in pa icula in he a ea o he discha ges om A ocampo ese oi . A highe
esolu ion wo-dimensional dep h-a e aged model was he e o e cons uc ed o his a ea.
The ad ance ep esen ed by hese models is ha hey a e physical models in which he ins an-
aneous cu en s a e ob ained o each poin o he To ejo
´n ese oi and o each ins an o
ime. These cu en s a e hen used o calcula e he i ium dispe sion. Hence, he i ium con-
cen a ions may be calcula ed o any posi ion and ime in his ese oi .
368 A. Baeza e al. / J. En i on. Radioac i i y 86 (2006) 367e383
2. Expe imen al
2.1. S udy a ea
The Ri e Tagus has i s sou ce in he Sie a de Alba acı
´n (Spain), and i s mou h in Lisbon
(Po ugal). I s o al leng h is 1107 km (Fig. 1). The a ea o he Tagus basin is abou
8.1 10
4
km
2
, o which 69% is in Spain. The ANPP, wi h wo 930 MWe PWR- ype uni s is
loca ed on he i e igh bank, in he egion o Ex emadu a and 180 km wes esou hwes o
Mad id. The Ri e Tagus ecei es discha ges om he ANPP (Baeza e al., 1991) and om o he
wo nuclea powe plan s loca ed below 300 km ups eam eJose
´Cab e a and T illo eas well
as se e al smalle con ibu ions om a signi ican numbe o labo a o ies and hospi als (CSN,
1998).
The low egime o he Ri e Tagus is con olled h ough a chain o ese oi s. One o hem,
in he egion o Ex emadu a (Fig. 1), is, in cubic hec ome es (1 hm
3
¼10
6
m
3
), he 166 hm
3
capaci y To ejo
´n ese oi , which is he objec o he de ailed s udy o he p esen wo k. I is
42 km long, wi h a mean wid h o 130 m and a mean dep h o 20 m. Immedia ely ups eam, he
500 hm
3
capaci y Valdecan
˜as ese oi is loca ed. The Alca
´n a a ese oi , wi h a no mal ol-
ume o 1600 hm
3
, is si ua ed downs eam om To ejo
´n. The wa e o To ejo
´n ese oi is pe-
iodically pa ially exchanged wi h ha o A ocampo, since he la e is used as he ANPP’s
Fig. 1. Map o he Ri e Tagus wi h he loca ions o he sampling poin s. The loca ion o he dam o each ese oi is
indica ed by <.
369A. Baeza e al. / J. En i on. Radioac i i y 86 (2006) 367e383
seconda y cooling ci cui . The pu pose o he exchange is o main ain A ocampo’s olume
p ac ically cons an a 35 hm
3
(ANPP, 1998) and i s wa e empe a u e su icien ly low o ul il
i s cooling unc ion.
The lowe pa o Fig. 2 shows he empo al e olu ion o he lows be ween he A ocampo
and To ejo
´n ese oi s. The s ong 12-mon h pe iod seasonali y o hese exchanges, as has
been desc ibed in p e ious s udies (Baeza e al., 2001), is obse ed. The uppe pa o he
Fig. 2 shows he mon hly discha ges o wa e be ween he Tagus ese oi s p esen in Fig. 1,
i.e., om Valdecan
˜as o To ejo
´n, and om he la e o Alca
´n a a. I can be seen ha he man-
agemen o he discha ges be ween hese h ee ese oi s is pe ec ly coupled, which, as was
indica ed abo e, is a common cha ac e is ic o all he Ri e Tagus ese oi s. On he o he
hand, his managemen is adically di e en om ha be ween To ejo
´n and A ocampo, since
he obse ed seasonali y in his case is condi ioned by he a ailabili y o wa e in he Tagus
Ri e , which in u n is ela ed o he in ensi y and equency o ain alls in he a ea.
2.2. Sampling
Two sampling p og ams eone mon hly and he o he in ensi e ewe e ca ied ou in 1997
and 1998 in he abo e desc ibed s udy a ea. The in ensi e p og am o sampling was designed o
de e mine he spa ial dis ibu ion o i ium le els in wo dimensions in To ejo
´n ese oi : lon-
gi udinally, o 17 sampling poin s dis ibu ed along he leng h o he ese oi , and ans e -
sally, in he cen e and on he wo banks o he ese oi o each o hose 17 poin s. The
mon hly p og am was o allow us o analyze he empo al e olu ion on he basis o mon hly
DISCHARGES
0
500
1000
1500
1 3 5 7 9 11 13 15 17 19 21 23
1997-1998
1357 9 11 13 15 17 19 21 23
1997-1998
(hm
3
)
(hm
3
)
Valdecañas
To ejón
0
25
50
75
100
A ocampo o To ejón
To ejón o A ocampo
Fig. 2. Uppe pa : mon hly discha ges o wa e om Valdecan
˜as o To ejo
´n, con inuous line, and om To ejo
´n o
Alca
´n a a, do ed line. Lowe pa : mon hly exchange o wa e om A ocampo ese oi o To ejo
´n ese oi , con in-
uous line, and om To ejo
´n o A ocampo ese oi , do ed line.
370 A. Baeza e al. / J. En i on. Radioac i i y 86 (2006) 367e383
eco ds a h ee o he a o emen ioned sampling poin s in To ejo
´n ese oi and a ano he
poin in A ocampo ese oi . Wa e empe a u e was simul aneously eco ded wi h each sam-
ple collec ion.
2.2.1. Mon hly sampling
E e y mon h, su ace wa e samples we e collec ed a he h ee sampling poin s o he To -
ejo
´n ese oi iden i ied as 1, 7, and 8 in Fig. 1, and a one sampling poin o he A ocampo
ese oi iden i ied as A in he igu e. As was no ed abo e, A ocampo is he cooling ese oi
o he ANPP. The e is a cons an o ced ci cula ion o wa e a a a e o 88 m
3
/s a ound he
sepa a ion dyke cons uc ed in he cen e o he ese oi . As a esul , i s wa e has pe ec ly
homogeneous physicochemical p ope ies (Baeza e al., 1991), so ha poin A is en i ely ep-
esen a i e o he cha ac e is ics o wa e in he ese oi . The loca ions o poin s 1, 7, and 8 in
To ejo
´n ese oi a e he ollowing. Poin 1 is some 10 m om he To ejo
´n dam, on he le
bank o he Tagus. Poin 7 is downs eam he A ocampo dam and close o he ou le om ha
ese oi in o To ejo
´n, on he igh bank o he Tagus. Finally, poin 8 is some 400 m ups eam
o poin 7, on he le bank o he i e and clea ly in he opposi e di ec ion o he na u al low o
he wa e . These las wo poin s a e logically hose ha will be mos in ensely a ec ed by he
mixing o wa e s be ween he To ejo
´n and A ocampo ese oi s, which, as we shall see below,
ha e e y di e en adiological and he mal cha ac e is ics.
2.2.2. In ensi e sampling
In ensi e sampling was ca ied ou on wo speci ic da es: 1997-08-01 and 1998-02-12. As
can be seen in he lowe pa o Fig. 2, he o me da e co esponds o he ime o yea
when he exchange o wa e be ween To ejo
´n and A ocampo ese oi s is maximum, while
he la e is ep esen a i e o he ime o yea when he olumes o exchanged wa e a e ela-
i ely low. On bo h da es, su ace wa e samples we e collec ed in a numbe o longi udinal and
ans e sal ansec s o he To ejo
´n ese oi . Fig. 1 shows he loca ion o he poin s in he
h ee longi udinal ansec s, co e ing he 42 km leng h o he ese oi . The sepa a ion o hese
poin s was kep as homogeneous as possible, excep o a zone o he ese oi ha is especially
p o ec ed because o i s wildli e. The numbe o sampling poin s on he 1998-02-12 da e was
inc eased in ligh o he esul s o he analysis o he 1997-08-01 samples.
2.3. Analy ical me hods
A each sampling poin , 1.5 L o wa e was collec ed in polye hylene bo les, and empe a-
u e was measu ed wi h a p ecision o 0.1 C. A e anspo o he labo a o y, he samples
we e il e ed h ough 0.45 mm po e il e s p io o hei p epa a ion o
3
H assay.
Fo he i ium assay, a 50 mL aliquo was aken and subjec ed o a p ocess o simple dis-
illa ion o elimina e colou a ion, o ganic ma e , and sal s ha migh in e e e wi h he analysis.
The dis illed sample was hen mixed wi h a scin illa ion solu ion o Op iphase Hisa e 3 om
LKB-Wallac a a sample/scin illa o a io o 8/12 (Scho
¨nho e and Hen ich, 1987)in20mL
e lon-coa ed polye hylene ials. T i ium con en was de e mined using a Quan ulus-1220,
LKB-Wallac, liquid-scin illa ion alphaebe a spec ome e . The quenching calib a ion was pe -
o med wi h i ium s anda ds quenched o inc easing deg ees wi h CCl
4
. The backg ound in
he egion o he i ium b-emission was o he o de o 1.5 cpm. The sys ema ically used coun -
ing ime was 1000 min (200 min 5 measu emen cycles). The esul ing Lowe De ec ion
371A. Baeza e al. / J. En i on. Radioac i i y 86 (2006) 367e383

Limi a a 95% con idence o i ium was 0.5 Bq/L and he igu e o me i , (e iciency)
2
/back-
g ound, was 320 (Baeza e al., 1999).
3. Resul s and discussion
3.1. Tempo al e olu ion (1997e1998)
Fig. 3 shows he empo al e olu ion o
3
H le els and he empe a u e a he su ace wa e o
he sampling poin s iden i ied in Fig. 1 as 1, 7, and 8, belonging o To ejo
´n ese oi , and poin
A in A ocampo ese oi . Table 1 lis s he mean alues and anges eco ded a hese sampling
poin s o he ci ed a iables e i ium and empe a u e. The ollowing esul s s and ou .
The highes ac i i y le els we e eco ded a poin A, as was o be expec ed since his is he
cooling ese oi o he ANPP. Ac i i y le els and hei empo al e olu ion a e consis en wi h
he indings o p e ious s udies (Baeza e al., 2001). The obse ed empo al e olu ion is a con-
sequence o he managemen o hese wa e s, whose egime o exchange wi h hose o he To -
ejo
´n ese oi (see lowe pa o Fig. 2) is condi ioned by he maximum empe a u e ha he
wa e can each o be used o cool he ANPP. Thus, poin A no only had he highes empe -
a u es o all he s udy a ea, bu i also had he na owes ange o empe a u es as well. This is
because in he cold mon hs o he yea , when i is unnecessa y o exchange wa e in o de o
sa is y he he mal equi emen s, i s empe a u e alls o less han ha o he To ejo
´n ese oi
wa e s. The ei e a ed use o he A ocampo wa e as coolan du ing win e is also he eason
why
3
H le els a poin A we e highe in hese mon hs. In pa icula , he e was a signi ican neg-
a i e co ela ion be ween i ium le els and empe a u e a poin A (see he las ow o Table 1).
Fo he h ee poin s sampled mon hly in he To ejo
´n ese oi epoin s 1, 7, and 8 ebo h
i ium le els and empe a u e dec eased om poin 7 o 8, and om he las o poin 1. This is
eadily unde s andable gi en he spa ial loca ion o hese h ee poin s (see Fig. 1) ela i e o he
0
50
100
150
200
250
300
0
10
20
30
40
Sampling poin A Sampling poin 7
0
100
200
300
400
500
1357911131517192123
1997-1998
1357911131517192123
1997-1998
1 3 5 7 9 11 13 15 17 19 21 23
1997-1998
1 3 5 7 9 11 13 15 17 19 21 23
1997-1998
3H (Bq·L-1)
3H (Bq·L-1)
3H (Bq·L-1)
3H (Bq·L-1)
0
10
20
30
T (ºC)
T (ºC) T (ºC)
T (ºC)
H-3
T
H-3
T
H-3
T
H-3
T
600 40
Sampling poin 8
0
50
100
150
200
250
300
Sampling poin 1
0
20
40
60
80
0
10
20
30
40
0
10
20
30
40
Fig. 3. Speci ic ac i i y o i ium and empe a u e measu ed du ing 1997e1998 a sampling poin s A, 1, 7, and 8 o he
s udy a ea.
372 A. Baeza e al. / J. En i on. Radioac i i y 86 (2006) 367e383
local sou ce o i ium and hea in o To ejo
´n ese oi , i.e., he discha ge om he A ocampo
ese oi . Local empo a y inc eases in ac i i y we e di ec ly co ela ed wi h inc eases in he
exchange o wa e be ween he A ocampo and To ejo
´n ese oi s (see lowe pa o
Fig. 2), and he e o e had a s a is ically signi ican posi i e co ela ion wi h ises in To ejo
´n
ese oi wa e empe a u e (see he las ow o Table 1). These empe a u e inc eases o cou se
ha e a na u al componen du ing he ho mon hs, ein o ced by he ci ed exchanges wi h he
ho e wa e in A ocampo ese oi . The coupled egula ed ansi o wa e in his zone o
he Ri e Tagus (see uppe pa o Fig. 2) is ul ima ely esponsible o he anspo o i ium
discha ged in o he To ejo
´n ese oi o wa e s below To ejo
´n dam. This ansi occu s p e -
e en ially du ing win e , so ha i ium is sp ead ou along he men ioned ese oi du ing he
summe mon hs.
3.2. Spa ial e olu ion
To check he e aci y o he o egoing s a emen , we pe o med an in ensi e s udy on he
spa ial dis ibu ion o i ium and empe a u e on wo da es ha we e clea ly iden i iable
wi h he p e iously ypi ied cha ac e is ics o he mon hs o win e and o summe . Resul s
a e p esen ed in Table 2. The able lis s, i s ly, he dis ance o he 17 poin s selec ed along
he leng h o he To ejo
´n ese oi (see Fig. 1) om he ou le o he discha ges om he A -
ocampo ese oi (poin 7). Secondly, o each o he wo sampling da es and each sampling
poin , i lis s he
3
H le el and, in pa en heses, wa e empe a u e in he cen e and nea he
banks.
I can be obse ed ha he esul s we e adically di e en in he condi ions iden i ied as
summe (sampling da e 1997-08-01) and win e (sampling da e 1998-02-19). The summe sam-
ples showed a good ans e sal mixing in bo h i ium le els and empe a u es a each sampling
poin . Indeed, he maximum ela i e ans e sal a ia ion was 13.8% o
3
H and 5.2% o em-
pe a u e, bo h co esponding o poin 17. Likewise, he o e all spa ial homogenei y was also
e y signi ican . In pa icula , omi ing he ac i i ies and empe a u es measu ed a poin 17
which is 12.4 km away in he opposi e di ec ion o no mal wa e low in he ese oi , we
can conside ha he es o he ese oi has a well de ined i ium le el and empe a u e in
he condi ions ha we e iden i ied as summe . In pa icula , o ha sampling da e, he alues
we e 56.6 3.2 (SD) Bq/L and 29.2 1.5 (SD) C, espec i ely. The wo pa ame e s we e
closely co ela ed, wi h a co ela ion coe icien o 0.880 a a signi icance le el quan i ied by
he alue o he pa ame e p¼510
4
.
Table 1
Mean alues and anges o i ium and empe a u e eco ded du ing yea s 1997 and 1998 in wa e s o A ocampo es-
e oi (poin A), and To ejo
´n ese oi (poin s 1, 7, and 8)
Sampling poin A 1 7 8
3
HSD (Bq/L) 270 144 22 19 101 77 57 63
Range
3
H (Bq/L) 59e496 1.4e6.0 2.4e243 1.2e199
TSD (C) 28 5185218207
Range T(C) 19e36.2 9e26.5 10e30.5 10e28.5
Co ela ion
3
HeT(signi icance le el) 0.774 (<0.0001) 0.676 (0.0003) 0.484 (0.0165) 0.711 (<0.0001)
De ails o he co ela ion be ween hese wo pa ame e s, a he ou sampling poin s ha we e selec ed o he s udy o
he empo al e olu ion, a e also gi en.
373A. Baeza e al. / J. En i on. Radioac i i y 86 (2006) 367e383
Table 2
De ails o he wo in ensi e sampling campaigns, iden i ying he dis ance (m) o each sampling poin om he ou le o wa e discha ged om A ocampo ese oi in o
To ejo
´n ese oi
No a ion Dis ance (m) Sampling 1997-08-01 Sampling 1998-02-19
Le side Cen um Righ side Le side Cen um Righ side
1þ28 600 53 3 (26.0) 54 3 (26.5) 56 3 (26.0) 1.5 1.5 (11.5) 1.5 1.5 (11.5) 1.5 1.5 (11.5)
2þ13 100 58 3 (27.0) 58 3 (27.0) 61 4 (27.0) 17.5 2.0 (10.5) 17.7 2.0 (10.5) 17.8 2.0 (10.5)
3þ2600 56 3 (28.7) 55 3 (29.0) 56 3 (29.0) 34 3 (11.0) 16.6 1.9 (10.0) 10.7 1.7 (11.0)
4þ1600 57 3 (29.0) 58 3 (29.5) 57 3 (29.0) 44 3 (11.5) 48 3 (12.0) 7.6 1.7 (11.0)
5þ600 57 3 (29.5) 58 3 (29.5) 60 4 (30.0) 32 3 (12.0) 87 5 (13.0) 58 4 (12.0)
6þ300 53 3 (30.2) 57 3 (30.5) 56 3 (30.0) 88 5 (13.5) 111 6 (14.0) 81 5 (13.0)
70 594 (31.0) 58 3 (31.5) 55 3 (32.0) 3.7 1.6 (10.0) 229 11 (18.5) 371 18 (24.0)
8400 58 3 (30.5) 54 3 (30.5) 55 3 (30.5) 1.6 1.5 (10.0) 2.5 1.5 (10.0) 1.5 1.5 (9.5)
92400 54 3 (29.5) 56 3 (29.5) 53 3 (29.5) 3.9 1.6 (10.5) 5.0 1.7 (9.5) 4.4 1.6 (10.0)
10 2900 52 3 (28.0) 51 3 (29.0) 53 3 (29.0) 3.7 1.5 (11.0) 3.8 1.5 (10.0) 1.5 1.5 (9.5)
11 3900 No da a No da a No da a 3.3 1.6 (10.0) 3.0 1.5 (10.0) 2.0 1.5 (10.0)
12 4900 60 4 (30.3) 67 4 (30.2) 61 4 (29.0) 2.2 1.5 (9.5) 2.5 1.5 (9.5) 2.4 1.5 (9.5)
13 6400 No da a No da a No da a 2.9 1.5 (9.5) 3.8 1.5 (9.5) 2.8 1.6 (9.5)
14 7900 No da a No da a No da a 2.2 1.5 (9.5) 2.2 1.5 (9.5) 2.2 1.5 (9.5)
15 8900 No da a No da a No da a 2.2 2.0 (10.5) 1.5 1.5 (9.5) 2.5 1.5 (9.5)
16 11 400 No da a No da a No da a 1.5 1.5 (9.5) 1.5 1.5 (9.5) 2.6 1.6 (9.5)
17 12 400 2.2 1.3 (19.0) 2.0 1.3 (19.0) 2.3 1.3 (20.0) 1.5 1.5 (9.5) 1.5 1.5 (9.5) 2.8 1.6 (9.5)
The sign þo indica es whe he i is in he same di ec ion o he opposed one, espec i ely, as he no mal ad ance o he wa e in he To ejo
´n ese oi . The able lis s, o
each o he wo sampling da es, he
3
H le els (Bq/L) and, in pa en heses, he empe a u e (C) o he su ace wa e close o he wo banks and in he cen e o he ese oi .
374 A. Baeza e al. / J. En i on. Radioac i i y 86 (2006) 367e383
Wi h espec o he spa ial dis ibu ion in he To ejo
´n ese oi de e mined on he sampling
da e ypical o win e condi ions, i.e., when he e was a small low o ela i ely wa m wa e
om he A ocampo ese oi con aining ela i ely high le els o i ium, as well as a la ge wa-
e low in he di ec ion o he na u al cu en in his ac o he Ri e Tagus, he ollowing ac s
may be obse ed. Fi s ly, he adioac i e and he mal con ibu ions om he A ocampo dis-
cha ges we e only no able in a limi ed po ion o he To ejo
´n ese oi . This zone was in
he di ec ion o he na u al ad ance o he wa e , also a ou ed by he di ec ion o he A o-
campo discha ge canal on he igh bank o he Ri e Tagus a poin 7. One obse es in Table
2 ha i was p ecisely a ha poin whe e he highes empe a u e and
3
H ac i i y we e de ec ed.
Bo h he ans e se and he longi udinal homogenei ies o hese pa ame e s in he To ejo
´n es-
e oi wa e ha e disappea ed unde he ope a ing condi ions ha we e iden i ied as being yp-
ical o win e . Indeed, du ing hese win e mon hs, he impac o he A ocampo discha ges was
only pa ially de ec able downs eam om he ou le poin in o he To ejo
´n ese oi . I could
no e en be de ec ed a he head o he ese oi , as indeed was he case on he summe da e o
ou in ensi e sampling. None heless, he wo pa ame e s e
3
H ac i i y and empe a u e ewe e
again pe ec ly co ela ed, e lec ing hei common o igin in he discha ges om A ocampo
in o he To ejo
´n ese oi . The co ela ion coe icien was 0.974, wi h a signi icance le el
quan i ied by he alue o he pa ame e p¼10
4
.
4. The modelling s udy
4.1. 1D model
The use o a longi udinal model o s udy he dispe sion o i ium in he whole To ejo
´n
ese oi is jus i ied by i s na owness and shallowness ela i e o i s leng h (see he Sec ion
2.1). Also, discha ges om A ocampo a e designed o achie e a apid mixing o he pollu-
an s bo h in dep h and ans e sally. Thus, we a e dealing, essen ially, wi h a one-dimensional
dispe sion p oblem. Indeed, 1D models ha e been ound o be adequa e ools o s udying
he dispe sion o pollu an s in channeled egions and i e s (Ab il and Abdel-Aal, 2000; Ab il
e al., 2000; P andle, 1974). The hyd odynamic equa ions a e sol ed o ob ain he cu en s
along he ese oi o he ime pe iod o in e es . In he p esen case, he ad ec ion/di usion
dispe sion equa ion o i ium is sol ed simul aneously. The 1D hyd odynamic equa ions a e
(P andle, 1974)
dS z
þ ðAuÞ
xdxQ¼0
u
þu u
xþg z
xþCd
ujuj
hþz¼0
whe e Sis he ho izon al su ace a ea, z he heigh o he wa e su ace abo e he mean le el, u
he wa e eloci y along he xdi ec ion, A he c oss-sec ion a ea o he ese oi , g he accel-
e a ion due o g a i y, Q he ex e nal low o wa e en e ing/lea ing he ese oi a each poin ,
and ha dep h pa ame e de ined as h¼A/bwhe e bis he wid h o he ese oi . The bed ic-
ion coe icien is de ined as
Cd¼g
C2
h
375A. Baeza e al. / J. En i on. Radioac i i y 86 (2006) 367e383
e olu ion o he le els o i ium in he ese oi s o A ocampo and To ejo
´n hence depends
s ongly on he managemen o hei wa e s. The empo al e olu ion o he wa e empe a u e
is also condi ioned by he na u al e olu ion o he en i onmen al empe a u e. The wo magni-
udes consequen ly p esen ed seasonal a ia ions wi h an annual pe iod, which we e six mon hs
ou o phase in he A ocampo ese oi , and pe ec ly synch onized a he h ee sampling
poin s ha we e sys ema ically analyzed in he To ejo
´n ese oi .
Fo he s udy o he spa ial e olu ion o i ium in he To ejo
´n ese oi , we ca ied ou in-
ensi e sampling a nume ous poin s o he ese oi on wo da es clea ly ypical o win e and
o summe . In win e , due o he minimal exchange o wa e wi h he A ocampo ese oi and
o he la ge wa e low in he na u al di ec ion o he Ri e Tagus wa e s, he To ejo
´n ese oi
was ound o beha e in a o m simila o a i e wi h a quasi-na u al low egime. Consequen ly,
he ela i ely insigni ican inpu s o i ium and hea om he A ocampo ese oi undamen-
ally a ec ed he a ea close o and downs eam om he discha ge poin (poin 7 in ou s udy),
wi h majo ans e se and longi udinal g adien s in bo h empe a u e and i ium ac i i y. On
he con a y, in summe , he To ejo
´n ese oi was ound o beha e in a o m simila o
a lake, since he e we e minimal lows o wa e om Valdecan
˜as ups eam, and in o Alca
´n a a
downs eam. The exchange o wa e wi h he A ocampo ese oi , whe e he i ium le els and
he empe a u e a e highe , was maximal a ha ime, howe e . In hese condi ions, bo h he
3
H
and he hea di used p ac ically o e he whole To ejo
´n ese oi , wi h he consequen longi-
udinal and ans e sal homogeniza ion o hese wo magni udes.
A 1D model o he To ejo
´n ese oi was de eloped o s udy he beha iou o i ium. In
gene al, he model yielded a empo al e olu ion o i ium speci ic ac i i ies along he ese oi ,
and i ium p o iles along he leng h o he ese oi o he wo in ensi e sampling campaigns,
ha we e in ag eemen wi h he measu emen s. I was necessa y, howe e , o use a la ge alue
o he di usion coe icien du ing he summe mon hs. A 2D model o he elease a ea was
de eloped o s udy he beha iou o i ium nea he ANPP discha ge poin . I was ound
ha he di e en dispe sion pa e ns measu ed in Feb ua y and Augus ( ans e se g adien s
and mixing o i ium, espec i ely) we e ep oduced wi h a single o mula ion o he di usion
coe icien implemen ed o e a 2D domain. The di e en beha iou in win e and summe
a ises om di e ing egimes o wa e ci cula ion in hose wo seasons.
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