2001
Jo˜
ao Miguel
Contribution to the Study of
Sequeira
the Ria de Aveiro Hydrodynamics
Universidade de Aveiro
Departamento de F´ısica
2001
Jo˜
ao Miguel
Contribution to the Study of
Sequeira
the Ria de Aveiro Hydrodynamics
Silva Dias
disserta¸c˜ao apresentada `a Universidade de Aveiro
para cumprimento dos requisitos necess´arios `a
ob-ten¸c˜ao do grau de Doutor em F´ısica, realizada sob a
orienta¸c˜ao cient´ıfica do Doutor Jos´e Fortes, Professor
Auxiliar do Departamento de F´ısica da Universidade
de Aveiro, e do Professor Doutor Ivan Dekeyser,
Pro-fessor Catedr´atico da Universit´e de la M´editerran´ee
(Aix–Marseille II), Fran¸ca
presidente
Doutor Jorge Ribeiro Frade
professor catedr´atico da Universidade de Aveiro
Doutor Daniel Augusto Rodrigues
professor aposentado da Escola Naval de Lisboa
Doutor Ivan Joseph L´eo Dekeyser
professor catedr´
atico do Centre d’Oceanologie de Marseille da
Universit´e de la M´editerran´ee (Aix–Marseille II) – Fran¸ca
Doutor Jes´
us Manuel Pereira Dubert
professor auxiliar convidado da Universidade de Aveiro
Doutor Jos´e Armando Rodrigues Vieira
Director do Danish Hidr´
aulic Institut – Portugal
Doutor Jos´e Fortes do Nascimento Lopes
out the support and a tive parti ipation of many other
people. At this time, I would like to thank everyone who
ontributed to this study.
To Prof. JoseFortes and toProf. Ivan Dekeyser not only
for their s ienti supervision, but also for their trust in
my ability for this task and the freedom they gave me
along these years.
Tomy olleagues,friendsandrelativeswhohelpmeinthe
eld work task for their ompanionship and availability.
TotheDepartamentodeBiologiafortheuseofitss ienti
equipment.
Tothemetalo{me hani andele tri ityte hni iansandto
the administrative personnel of Departamento de Fsi a
for their useful advi es and support.
ToEng. MarioTeles ofHidroproje toforthewater{depth
data used to build the numeri al bathymetry of Ria de
Aveiro.
To my wife, Alexandra, and my mother, Lilia, for their
Apresentar uma ontribui ~aopara a ara teriza ~aoe ompreens~ao do omportamento
hidrodin^ami o da laguna Ria de Aveiro, baseada num estudo experimental e num
estudode modela ~aonumeri a,eo obje tivo deste trabalho.
As ara tersti as hidrologi as da Ria de Aveiro foram investigadas atraves da
realiza ~ao de varias ampanhas de amostragem, tendo sido efe tuadas medi ~oes de
altura de agua, salinidade, temperatura da agua e velo idade da orrente em varias
esta ~oes distribudas aolongo dos quatro anaisprin ipaisda laguna.
Observou{se que a mare astronomi a e a prin ipal a ~ao for adora da ir ula ~ao
de agua na Ria de Aveiro. A mare na embo adura e semidiurna, om uma pequena
omponentediurna,easuapropaga ~aoaolongodalagunaapresentaas ara tersti as
deumaondaprogressivaamorte ida. Foramdis utidaspropriedadesda amadalimite
eos per s verti ais das orrentes de mare na Riade Aveiro foramidenti ados omo
logartmi os. Para diversos lo ais da lagunaforamestimados valores de omprimento
de rugosidade, velo idadede atritoe oe iente de atrito.
Os gradientes longitudinais de salinidade e de temperatura revelaram estruturas
tipi amente estuarinas asso iadasa varia ~aodadist^an ia a embo adura, enquanto os
gradientes transversais e verti ais destas grandezas foram onsiderados desprezaveis
na maioria das situa ~oes. De a ordo om estes resultados a Ria de Aveiro pode ser
onsiderada verti almente homogenea, apesar de alguns anais poderem apresentar
ara tersti as tpi as de estuarios par ialmentemisturados quando o orremelevadas
des argas de agua do e pelos rios.
Atendendoas ara tersti asdaRiadeAveiroforamdesenvolvidos eapli adosa
la-gunamodelos matemati oshidrodin^ami oe de transporte bi{dimensionaisintegrados
ao longo da verti al. Estes modelos foram alibrados e validados, tendo
series temporais destasgrandezas, assim omoa sua distribui ~aohorizontalem
diver-sas fases do i lo de mare, em diferentes ondi ~oes de for amento pela mare, vento
e audal dos rios. Foi dada uma espe ial aten ~ao ao estudo do omportamento da
laguna em ondi ~oes extremas de for amentopelamare astronomi a, onsiderando o
for amentopelamarevivamaximaepelamaremortamnima. A ir ula ~aoeo
trans-porteresidual Eulerianos foramtambemdeterminados onsiderandodiferentes a ~oes
for adoras, de modoaavaliaraimport^an iadestas ontribui ~oes para otransporte de
longotermo. FoiaindadesenvolvidoummodeloLagrangianoparadeterminaro
trans-porte de part ulas, que foi a oplado ao modelo hidrodin^ami o, tendo sido apli ado
para estudar pro essos de dispers~ao e determinaro tempode resid^en ia nalaguna.
Osresultados da modela ~aonumeri a revelaram a ordo om osresultados
experi-mentais, epermitiramaobten ~aodeinforma ~ao omplementarsobreaRiade Aveiro.
Veri ou{se que a mare, que se propaga ao longo dos anais desde a embo adura, e
sentida em toda a Ria de Aveiro. A amplitude da mare diminui om o aumento da
dist^an iaaembo adura,enquantooatrasonosmomentosdepreia{maredebaixa{mar
aumenta. Existeuma onsideravelassimetriadamarenaRiade Aveiro resultante da
in u^en iadiurna,tendo sidoidenti adaszonasdominadas pelos uxos de en hentee
zonas dominadas pelos uxos de vazante. Veri ou{se tambema exist^en ia de mares
quinzenais nalaguna. A extremidade montante do anal de S.Ja into foi identi ada
omo azona de maior ris o de inunda ~ao no aso de uma sobre{eleva ~ao damare de
origem meteorologi a se propagar ao longo da Ria de Aveiro. A maioria das
ara -tersti asda propaga ~aodamarenaRiade Aveiro foram ompreendidas e expli adas
atendendo as varia ~oes dasua geometria e batimetria.
A ir ula ~ao residual induz um uxo de longo termo para o exterior da laguna
atravesdasua embo adura. Episodiosde elevado audaldosriosoudeventosfortese
persistentesaumentamotransporteresidual,e onsequentementearenova ~aodeagua
na Riade Aveiro.
Osresultados domodelo Lagrangiano revelam que numa es ala temporalsuperior
a dois i los de marea permuta entre part ulas provenientes de diferentes anais da
laguna e desprezavel. O tempo de resid^en ia para a zona entral da Ria de Aveiro
e de aproximadamente dois dias, revelando uma forte in u^en ia marinha nesta zona.
A ontribution to the hara terization and understanding of the hydrodynami
be-haviourof Riade Aveiro lagoonispresented, based onanexperimentalstudy,as well
ason anumeri al modellingstudy.
The hydrologi al features of Ria de Aveiro were investigated in several sampling
surveys, where measurements of water level, salinity, water temperature and urrent
velo ity were performed at several stations lo ated along the four main hannels of
the lagoon.
It was observed that astronomi al tide is the main for ing agent driving water
ir ulation in Ria de Aveiro. The tide at the mouth is semidiurnal, with a small
diurnalpattern, and the tidal wave propagation inthe lagoonhas the hara teristi s
of a damped progressive wave. Boundary layer properties were dis ussed and the
verti al pro les of tidal urrents in Ria de Aveiro were identi ed as logarithmi and
des ribed by the lawof the wall. Bottomroughness length, fri tionvelo ity and drag
oeÆ ient were estimated forseveral lo ationsdistributed along the main hannelsof
the lagoon.
Typi al estuarine longitudinal salinity and temperature gradients onne ted with
the distan e to the mouth were identi ed, whereas verti al and transverse gradients
were found unimportant in most ases. A ording to these results, even though Ria
de Aveiro shouldbe onsidered as verti ally homogeneous, some hannelsmay reveal
hara teristi sof a partially mixed estuary,depending onthe freshwater input.
A ordingtoRiadeAveiro hara teristi s,two{dimensionaldepthintegrated
math-emati al hydrodynami and transport models were developed and applied to the
la-goon. These models were alibrated and validated,and then used todetermine water
level, depth mean urrent, salinity and water temperaturefor the entire lagoon. The
instanta-wind andriverfreshwater for ing onditions. Spe ial emphasiswasgiven tothe study
of the lagoonbehaviour in extreme onditions of astronomi al tide for ing,
onsider-ingmaximumspringand minimum neaptide onditions. Eulerianresidual ir ulation
and transportwere also determinedhaving intoa ount several for ing onditions, in
order to evaluate the importan e of these ontributions in the long{term transport.
A Lagragianparti letra kingmodelwas developed and oupledtothe hydrodynami
model, and was applied to study the dispersion pro esses and to determine residen e
time in the lagoon.
The numeri almodelling results are in agreement with the observed in situ data,
and havepermittedtoobtain omplementaryinformationaboutRiade Aveiro. Itwas
found thattidespropagatingfromthemouthofRiadeAveiroarepresentintheentire
lagoon. The tidal amplitude de reases with the distan e from the mouth, while the
phaselaginthehighandlowwaterin reases. Thereisa onsiderabletidalasymmetry
inRiade Aveiro resultingfromthe diurnalin uen e,wherehavebeenfound oodand
ebb dominan e areas. Fortnightly tides are also present in the lagoon. The head of
S.Ja into hannel was identi ed as the higher risk area of ooding in the the ase
of the propagation of a storm surge in Ria de Aveiro. Most of the hara teristi s of
the tide propagation in Ria de Aveiro an be related to the variations in the lagoon
geometry and bathymetry.
Residual ir ulation indu e a long{term out ow through the tidal inlet, whi h
promotesthewaterrenewofthelagoon. Episodesofstrongriversruno orofpersistent
strong winds ause high residualtransport, improvingthe water renewal.
The Lagrangian model results show that the ex hange between parti les oming
from di erent hannels of the lagoon is negligible in a time s ale higher than 2 tidal
y les. Theresiden etime fortheRiadeAveiro entralareaisabout2days,revealing
a strong marine in uen e in this area. At the upper rea hes of the hannels values
A knowledgments i
Resumo iii
Abstra t v
List of Figures xiii
List of Tables xix
1 Introdu tion 1
1.1 Motivation, Aimsand Stru ture of this Work . . . 1
1.2 Nomen lature . . . 8
1.3 Study Area . . . 10
1.3.1 Geomorphology . . . 11
1.3.2 DrivingFor es . . . 13
I Experimental Study of Ria de Aveiro 21 2 Hydrologi al Chara terization of Ria de Aveiro 23 2.1 Introdu tion . . . 23
2.2 Materials and Methods . . . 24
2.2.1 Samplingstrategy. . . 24
2.2.2 Fixed station . . . 26
2.2.3 Moored stations . . . 26
2.3 Results . . . 28
2.3.1 Water mass hara teristi s atthe mouth . . . 28
2.3.2 Tidal propagation . . . 30
2.3.3 Salinity and temperaturetime evolution . . . 35
2.3.4 Salinity and temperaturespatial stru ture . . . 39
2.3.5 TS diagrams. . . 52
2.4 Dis ussion . . . 56
2.4.1 Tidal dynami s . . . 56
2.4.2 Salinity and temperatureevolution . . . 58
2.4.3 Salinity and temperaturestru ture . . . 60
2.5 Con lusions . . . 62
3 Verti al Stru ture of Tidal Currents in Ria de Aveiro 65 3.1 Introdu tion . . . 65
3.2 Materials and Methods . . . 67
3.2.1 Overview . . . 67
3.2.2 Samplingstrategy . . . 68
3.2.3 Meteorologi al onditions . . . 71
3.3 Field Data . . . 72
3.4 Verti alPro les of Tidal Currents . . . 72
3.5 Global Method to EstimateBottomRoughness Length . . . 82
3.6 Drag CoeÆ ient Estimation . . . 84
3.7 Con lusions . . . 85
II Numeri al Modelling Study of Ria de Aveiro 89 4 Mathemati al Modelling of Physi al Pro esses 91 4.1 Introdu tion . . . 91
4.2 General Equations . . . 93
4.2.1 Reynolds equations . . . 95
4.3 ShallowWater Equations . . . 99
4.3.1 General hypothesis . . . 99
4.3.4 Verti ally integrated equations . . . 103
4.4 Heat and RadiativeFluxes Parameterizations . . . 109
5 The Numeri al Model 113 5.1 Introdu tion . . . 113
5.2 Finite{Di eren e Method. . . 115
5.2.1 Con epts and de nitions . . . 115
5.2.2 Consisten y, stability and onvergen e . . . 118
5.3 Integration of the Hydrodynami Equations . . . 121
5.3.1 Dis retizationof the modelequations . . . 122
5.4 Numeri al Algorithmsfor Integration of the Transport Equation . . . . 122
5.4.1 Expli it Numeri alAlgorithm . . . 123
5.4.2 Higher OrderAlgorithms . . . 126
5.4.3 The Flux Corre ted Transport Algorithms(FCT) . . . 129
5.5 Boundary Conditions . . . 133
5.5.1 Open boundaries . . . 133
5.5.2 Closedboundaries . . . 135
5.5.3 Free surfa e and bottom boundaries . . . 136
5.5.4 Moving boundaries . . . 136
6 Model Calibration and Validation Pro edures 141 6.1 Introdu tion . . . 141
6.2 Model Implementation for Riade Aveiro . . . 143
6.2.1 Numeri albathymetry . . . 144
6.2.2 Initialand boundary onditions . . . 147
6.3 Calibration of the Hydrodynami Model . . . 149
6.4 Validationof the Hydrodynami Model . . . 158
6.5 Calibration of Salt and Heat Transport Models. . . 162
6.6 Validationof Salt and HeatTransportModels . . . 164
6.7 Con lusions . . . 168
7 Modelling Tidal Regime of Ria de Aveiro 171 7.1 Introdu tion . . . 171
7.3.1 Tidal urrents pattern . . . 179
7.3.2 Amplitude and phase distributionof tidal urrents. . . 182
7.4 Tides and Tidal Currents Relation . . . 186
7.5 Tidal Asymmetry . . . 188
7.6 Fortnightly Tides . . . 190
7.7 Physi al Parameters Estimation . . . 192
7.7.1 Tidal prism . . . 193
7.7.2 Bulk ushingtime estimates . . . 194
7.8 Study of a Storm SurgeEvent . . . 195
7.9 Salinity and TemperatureHorizontalStru ture . . . 197
7.10 Con lusions . . . 203
8 Eulerian Residual Cir ulation in Ria de Aveiro 207 8.1 Introdu tion . . . 207
8.2 Eulerian ResidualCir ulation . . . 208
8.3 Methodology . . . 209
8.3.1 The Numeri al Model . . . 210
8.3.2 For ing A tions . . . 212
8.4 Results and Dis ussion . . . 215
8.5 Con lusions . . . 220
9 Lagrangian Transport of Parti les in Ria de Aveiro 223 9.1 Introdu tion . . . 223
9.2 Parti le Tra king Model . . . 224
9.2.1 Modelvalidation . . . 226
9.3 Results and Dis ussion . . . 227
9.3.1 Tidal mixing . . . 227
9.3.2 Parti lestra ks . . . 229
9.3.3 Lo alizedemission spots . . . 232
9.3.4 Residen e time . . . 234
9.4 Con lusions . . . 236
B Finite Di eren e Approximation of the Momentum Equations 255
B.1 Dis retizationof the ModelEquations. . . 255
B.1.1 Firsttime step . . . 255
B.1.2 Se ond time step . . . 258
B.2 Numeri al Resolutionof the Finite{Di eren e Equations . . . 260
C Harmoni Constants Determined in Model Calibration 265
1.1 Image ofRiadeAveiro obtainedinAugust1991 bythe satelliteLandsat5 2
1.2 Geographi map of Ria de Aveiro . . . 11
1.3 Average and extreme monthly mean temperatures observed at Aveiro
limatologi alstationforea hmonthoftheyear,fortheperiodbetween
1981 and 1999 . . . 19
1.4 Averageandextrememonthlymeana umulatedpre ipitationobserved
at Aveiro limatologi al station for ea h month of the year, for the
periodbetween 1980 and 1997 . . . 20
2.1 Samplings hedule and strategy . . . 24
2.2 Transverse transe ts lo ation. . . 25
2.3 Pre ipitation, wind intensity and maximum and minimum air
temper-ature in Aveiro meteorologi al station during the surveys (22/05 to
10/07/97) . . . 28
2.4 Transferfun tionusedto lterthewaterlevel,salinityandtemperature
measurements . . . 28
2.5 Time series and omputed spe tral density of the water level, salinity
and temperaturemeasured atthe lagoonmouth . . . 29
2.6 Con urrent water height atthe mouthand atea hstation . . . 31
2.7 Con urrent water height and urrent omponents atea h station . . . . 33
2.8 Ve tor plots of the urrent velo ity atea h moored station . . . 34
2.9 Con urrent salinity and temperature at the mouth and at stations 3,
12, 16,35,48 and 57 . . . 36
2.11 Salinityandtemperatureverti alpro lestemporalevolutionforstations
3, 12,16,35, 48,57,60and 66 . . . 38
2.12 Salinityandtemperatureverti alpro lestemporalevolutionforstations
73,76 and 79 . . . 39
2.13 Salinity and temperature ross{se tional stru ture measured one hour
after the high tide for stations1 to22 . . . 40
2.14 Salinity and temperature ross{se tional stru ture measured one hour
after the high tide for stations23 to40 . . . 41
2.15 Salinity and temperature ross{se tional stru ture measured one hour
after the high tide for stations41 to58 . . . 42
2.16 Salinity and temperature ross{se tional stru ture measured one hour
after the high tide for stations59 to77 . . . 43
2.17 Salinity and temperature ross{se tional stru ture measured one hour
after the high tide for stations78 to80 . . . 44
2.18 Salinity and temperature ross{se tional stru ture measured one hour
before the high tide for stations 1to 22 . . . 45
2.19 Salinity and temperature ross{se tional stru ture measured one hour
before the high tide for stations 23to40 . . . 46
2.20 Salinity and temperature ross{se tional stru ture measured one hour
before the high tide for stations 41to58 . . . 47
2.21 Salinity and temperature ross{se tional stru ture measured one hour
before the high tide for stations 59to77 . . . 48
2.22 Salinity and temperature ross{se tional stru ture measured one hour
before the high tide for stations 78to80 . . . 49
2.23 Salinity and temperature horizontal stru ture for Ria de Aveiro one
hour after the high tide atthree di erentlevels . . . 50
2.24 Salinity and temperature horizontal stru ture for Ria de Aveiro one
hour before the high tide at three di erent levels . . . 51
2.25 Temperature{salinity urvesfortheverti alpro lesmeasuredinmoored
and xed stations . . . 52
2.26 Temperature{salinity spatial evolution inthe main hannels . . . 53
3.1 Assembly used to measure urrent verti al pro les . . . 70
3.2 Pre ipitation, wind intensity and maximum and minimum air temper-ature in Aveiro meteorologi alstation duringthe survey (1to 24/06/98) 71 3.3 Verti alpro les oftidal urrents measured inRiade Aveiro atstations 3, 12,16 and 35 . . . 73
3.4 Verti alpro les oftidal urrents measured inRiade Aveiro atstations 48, 57,60and 66 . . . 74
3.5 Verti alpro les oftidal urrents measured inRiade Aveiro atstations 73, 76and 79 . . . 75
3.6 Velo itypro lesmeasured inRiadeAveiro atstations3,12,16and35, represented ina semi{logs ale . . . 77
3.7 Velo ity pro les measured in Ria de Aveiro at stations 48, 57, 60 and 66, represented ina semi{logs ale . . . 78
3.8 Velo ity pro les measured in Ria de Aveiro at stations 73, 76 and 79, represented ina semi{logs ale . . . 79
3.9 Correlations between the fri tion velo ity squared and the referen e velo ity squared for allthe stations . . . 86
4.1 Geographi al referential OXYZ.. . . 94
4.2 Time evolutionof a propriety p . . . 96
4.3 Lagoonse tionusedtode nethewater surfa eand thebottom bound-ary onditions . . . 104
5.1 Re tangular grid geometry . . . 116
5.2 Representation of the di erent nite{di eren e approximations . . . 118
5.3 Spa e{staggered grid . . . 122
5.4 Grid used toapproximate the transportequation . . . 130
5.5 Bottom pro le in anarea whi h over/dis over depending on the tidal amplitude . . . 136
6.1 Ria de Aveiro bathymetry obtained from a general survey arried out in 1987/88 . . . 145
6.3 Computed spe tral densities using observed and modelgenerated time
series for stations A toL . . . 151
6.4 Computed spe tral densities using observed and modelgenerated time
series for stations M toV. . . 152
6.5 Comparison of time series of water height for stations A to L, used in
the hydrodynami model alibration . . . 153
6.6 Comparison of time series of water height for stations M toV, used in
the hydrodynami model alibration . . . 154
6.7 Distributions of tidal amplitude and phase for M 2 , S 2 , N 2 , P 1 , K 1 and O 1
tides plottedfor ea hstation . . . 157
6.8 Comparison of time series of water height for some stations from 3 to
79,used inthe hydrodynami model validation. . . 159
6.9 Comparison of time series of along ow dire tion velo ities for some
stations from3 to79,used inthe hydrodynami modelvalidation . . . 160
6.10 Comparison of time series of water ow for stations 3, 57, 66, 73, 76
and 79, used inthe hydrodynami modelvalidation . . . 161
6.11 Timeseries ofsalinityand temperaturemeasured atthelagoonmouth,
and used as boundary onditions for the West open boundary . . . 163
6.12 Comparison of time series of salinity for stations 3, 12, 16, 35, 48, 66
and 73, used inthe transportmodel alibration . . . 164
6.13 Comparison of time series of temperature for stations 3 to 73, used in
the transport model alibration . . . 165
6.14 Comparison of time series of salinity for some stations from 3 to 79,
used in the transport modelvalidation . . . 166
6.15 Comparison of time series of temperature for some stations from 3 to
79,used inthe transport modelvalidation . . . 167
7.1 Phase and amplitude distributions for the M 2 , S 2 and N 2 onstituents . 174
7.2 Phase and amplitude distributions for the P 1 , K 1 and O 1 onstituents . 175
7.3 Delayrelativetothemouthofthelo alhighandlowwater inneaptide
and in spring tide onditions . . . 176
7.4 Tidal form numberF . . . 177
7.7 Tidal urrents pattern, shown atintervalsof two lunarhours . . . 181
7.8 Phase and amplitude distributionfor the M 2
tidal urrent . . . 183
7.9 R MS speed distribution forthe extremeneap and springtide onditions183
7.10 Delay relative to the mouth high and low water of the lo al urrent
inversion in neap tide and inspring tide onditions . . . 185
7.11 Tidal velo ities determined at 24 stations distributed along the main
lagoon hannels . . . 185
7.12 Phasedi eren ebetweenthetidesandthe urrentsfortheM 2
onstituent187
7.13 Phase andamplitudedistributionfortheM 4
onstituentand
asymmet-ri al oeÆ ients . . . 188
7.14 Amplitudeand phasedistributionfor theM sf
onstituent andphase of
the spring{neapenvelope . . . 192
7.15 Computed tidal prisms at23 ross-se tions of Ria de Aveiro, at
maxi-mum spring tide, minimum neap tide and mean tide . . . 194
7.16 Waterlevelatthetide{gaugeusedtofor ethemodelattheopen
bound-ary in neap and springtide onditions . . . 196
7.17 Waterleveldistribution inRiadeAveiro (normaland stormsurge
for -ing), and the water height diferen e between these two situations, for
neap and springtide onditions . . . 198
7.18 Horizontalsalinitypatterns, shown atintervalsof three lunarhours, in
typi alWinter and Summersituations . . . 200
7.19 Horizontalwatertemperaturepatterns,shownatintervalsofthreelunar
hours, in typi alWinter and Summersituations . . . 202
8.1 Comparison between the water elevation omputed by the numeri al
model and the extreme results of the analyti al modelfor re tangular
hannelswith 7 and 11km length . . . 212
8.2 Meanmonthlyvaluesofthesurfa ewindintensityatthemeteorologi al
station n o
547 (S.Ja into) . . . 214
8.3 Wind rosesforea hseasonatthemeteorologi alstationn o
547 (S.Ja into)214
8.4 Residual velo ity urrent indu ed by tidal for ingand rivers runo . . . 216
9.1 Distan e from the parti le position to ea h one of the nearest velo ity
ells . . . 225
9.2 Comparison between the traje tories determined by the Lagrangian model and obtained solving the analyti alequations . . . 227
9.3 Parti les position timeevolutionsequen e forparti lesreleased inea h grid ell . . . 228
9.4 Alongtimeevolutionofthepositionofparti lesreleasedatfourdi erent areas of the lagoon . . . 230
9.5 Tra ksofparti lesreleasedinadja entgridpointsatfourdi erentareas of the lagoon . . . 231
9.6 Zonesa e ted bylo alizedemissionof parti lesafter3daysofsimulation233 9.7 Contours of tidal-mean residen e time for passive parti les released in ea h grid ell . . . 234
B.1 Grid used to approximate the X momentumequation . . . 256
B.2 Grid used to approximate the ontinuity equation . . . 258
B.3 Grid used to approximate the Y momentum equation . . . 259
B.4 Rowfromthe omputationaldomainused todeterminethe valueofthe unknowns U and . . . 261
2.1 Station hara teristi sanddataa quisitionpro edures forthe rstsurvey 25
2.2 Harmoni analysis results for water height measured at the mouth of
Ria de Aveiro . . . 30
2.3 High water and low water delays relative to the mouth and di eren e
between the amplitude at the mouth and atea h moored station . . . . 32
3.1 Station hara teristi s and survey time s heduled . . . 69
3.2 Typi alvalues ofthe roughnesslength,z 0
andthe drag oeÆ ient,C 100 for di erent bottomtypes . . . 82
3.3 Bottomroughnesslength,z 0
,estimatedbytheglobalmethod,andtotal
roughness element,K b
, for ea h station . . . 84
6.1 Bottomfri tion oeÆ ient . . . 150
8.1 Residual transport indu ed by the rivers runo , wind stress and tide
through the main se tionsof the prin ipallagoon hannels . . . 218
A.1 Chara terization of the verti al pro lesmeasured at station 3 . . . 244
A.2 Chara terization of the verti al pro lesmeasured at station 12 . . . 245
A.3 Chara terization of the verti al pro lesmeasured at station 16 . . . 246
A.4 Chara terization of the verti al pro lesmeasured at station 35 . . . 247
A.5 Chara terization of the verti al pro lesmeasured at station 48 . . . 248
A.6 Chara terization of the verti al pro lesmeasured at station 57 . . . 249
A.7 Chara terization of the verti al pro lesmeasured at station 60 . . . 250
A.8 Chara terization of the verti al pro lesmeasured at station 66 . . . 251
A.9 Chara terization of the verti al pro lesmeasured at station 73 . . . 252
C.1 Harmoni analysis results omparisonof eldand modelgenerated
wa-ter leveldata (M 2
and S 2
onstituents) . . . 266
C.2 Harmoni analysis results omparisonof eldand modelgenerated
wa-ter leveldata (N 2
and P 1
onstituents) . . . 267
C.3 Harmoni analysis results omparisonof eldand modelgenerated
wa-ter leveldata (K 1
and O 1
Introdu tion
1.1 Motivation, Aims and Stru ture of this Work
Theimportan eofthe lagoonsystems andof the oastalwatermasseswas re ognized
a long time ago not only by the s ienti ommunities but also by the water side
populations. Thesesystemsa tasinterfa esbetweenlandandsea,withafundamental
roleintheregulationofthetransportbetweentheirenvironments. Duetothisinterfa e
positionthesee osystemarehighlyvariableandri h,supportingimportante onomi al
a tivities. These areas are open systems, where the ex hange with o eans, rivers and
atmosphere o urs with di erent time s ales and where several fa tors in uen e the
elements y le, as well as their transferen e to the o eans [Forstner and Wittmann,
1981℄. ThemanagementoftheseareasnearlyalwaysinvolvediÆ ultde isionsandthe
need to nd some ompromise solutions. Sometimes it is essential to on iliate and
harmonizea tivitiesthat apparentlyare in ompatibleinthe samegeographi area. A
large numberof the problems that a e t the lagoons and the oastal areas havetheir
origin inlarge geographi zones, that are not on ned toits land{seaboundary. Few
ofthesesystemsevolvesnaturally,be ausemostofthemaresubmittedtothepresen e
of the human a tivities.
Ria de Aveiro is a remarkable lagoon whi h onstitutes a very important area in
the Portuguese oast (Figure 1.1), with an adja ent surfa e of about 250 km 2
. It is
the most extensive lagoonsystem in Portugal and the one most dynami in terms of
physi al and biogeo hemi al pro esses. It is onne ted with the sea through a single
Figure1.1: Imageof Riade Aveiroobtained inAugust 1991by thesatelliteLandsat5,
evolution,spe iallyduetothefrequentworksinthe lagoonmouth. Biologi allyit an
be onsidered asbeing ri hinnutrients andorgani matter,and therefore onstitutes
ahighly produ tive environment. This e osystem is hara terized by the existen eof
a large diversity of spe ies. Borrego [1996℄ refers that 64 spe ies of shes, 12 spe ies
ofamphibia,8 spe ies ofreptiles, 173 spe ies ofbirds and 21spe ies of mammalwere
identi ed in Riade Aveiro.
It providesnatural onditions forharbour, navigationand re reation fa ilitiesand
itis also a pla e of dis harge of domesti and industrial wastes. It o ersgood
ondi-tionsforagri ulturaldevelopmentalongitsbordersandforthesetupofalargenumber
ofsmalland mediumindustries operating inthe hemi al,engineering and transport,
metallurgy,textiles, lothes andfootwear, foodanddrink, and paperandpulp se tors
[Borrego etal.,1990℄. Thereare a onsiderablenumberof semi{professionaland part
time shermen who e onomi ally depend on the produ tivity of the lagoon waters.
Nowadays there is onlya small number of operational saltpans omparing with
pre-vious de ades. Meanwhile an in reasing number of re overed pans for aqua ulture
purpose impliesthat in anear future this a tivity may be e onomi ally promising.
More than 300 000 people live around the lagoon and its hannels (1981 ensus
[Re et al., 1991℄); this on entration in a smallarea brings up several environmental
and pollution problems. Industry, agri ulture and shery, urbanization, tourism and
several other a tivities are partially or totally dependent on this e osystem. Due to
the development of some of these a tivities the lagoonis being subje t toa
onsider-able pollution stress. As examples, the most en losed and remotearms of the lagoon
show evidentsigns of advan edeutrophi ation, some ommunities and animalspe ies
have survival problems,thereismi robiologi al ontaminationfromlargedis hargeof
untreated sewage and there is industrial pollution [Moreira et al., 1993℄. The latter
in ludes the euents of a onsiderable number of light industries s attered
through-out the area of a hemi al omplex. As onsequen e, onsiderable on entrations of
mer ury near the lo ation of these industries was measured in Ria de Aveiro [Hall,
1982; Pereira, 1996℄.
The harbour reveals astrongdevelopmentinlastyearsdue tothein reasing
num-ber of industries in Aveiro region. It is the terminal point of a main road onne ting
Aveiro with the entralzone of Spain, whi h anti ipateits future expansion.
freshwa-a tion of the tides. The water movements and the turbulent mixing resulting from
the a tion of the di erent driving for es onstitute interesting problems in the
hy-drodynami domain. The main ir ulation featuresde ne the transport of suspended
materialsand the erosion ordepositionthat o urs inthe lagoon. The distributionof
suspendedsedimentsand thewater hemi al ompositionare importantindi esinthe
hara terization of the environment of the lagoon.
The study of this kind of problems must be based upon an understanding of the
biologi al, hemi al and geologi al pro esses, whi h are highly dependent on the
la-goon's hydrodynami s, and implies the existen e of an extensive data set on erning
water quality and physi alparameters.
To hara terizeandunderstanda oastalsystemitisfundamentaltohavedatawith
a goodspatialand temporalresolution. Duetothe human andmateriallimitationsit
isdiÆ ulttohaveenoughinformationprovidedby eldmeasurements. Analternative
istoestablishasystemofnumeri almodelswhi hdes ribethe systeminordertohave
more information about it. The numeri al models represent the natural systems in
a simpli ed mode, and if orre tly used an be very useful to study the pro esses
o urring in omplex environments.
The irregular geometry of Ria de Aveiro and the omplexity of the system of
equations whi h des ribe the water movements and hara teristi s inside the lagoon
requiretheuseofa uratenumeri almodels,whi hallowadetailedinformationabout
the system.
It is frequently ne essary to foresee the variation of the physi al parameters
dis-tribution in the lagoon as a onsequen e of human interventions whi h hange its
geometryor hydrauli hara teristi s. Commonexamplesare the dredging operations
performedinseveral hannelsorthe hangeof the freshwater in owdue tothe
build-ing of river dams. These type of questions an be best answered through the use of
an a urate and reliable numeri al model able to reprodu e the transport and
mix-ing pro esses o urring in the lagoon as answer to di erent for ing onditions in its
boundaries. Therefore, with the use of this kind of tool it is possible to foresee the
evolution of the lagoon as answer to di erent human interventions or for ing
ondi-tions. Itisalsopossibletoperformsimulationswhi hprovidedatato omplementthe
information obtained by eld work. With these results it is possible to hara terize
theXX entury,but mostoftheresear honthisimportant oastalsystemwas arried
outmainlysin ethe eighties. This resear hwasdone essentiallyinthe biology,
hem-istry,geologyandenvironments ien es, ondu tingtothepresentationofseveralPhD
thesis about Ria de Aveiro in the last years [Queiroga, 1995; Cunha, 1999; Pereira,
1996; Teixeira, 1994; Silva, 1994℄. However, almost there wasn't systemati resear h
in the physi al and in the numeri al modelling domains. At the nal of the eighties
Instituto Hidrogra o [1988/1991℄ performed several surveys to measure physi al
pa-rameters in Ria de Aveiro in an attempt to hara terize this system, but this data
never originate a omprehensive report about the lagoon. Matos [1988℄ performed a
study about the salttransportme hanismsin Ria de Aveiro, using data measured in
asinglestation. Rodrigues[1989℄and Teles etal.[1990℄ developed anumeri almodel
of Ria de Aveiro, as well as Hidromod more re ently, but they were essentially used
to study parti ular problems on erning the management of the lagoon, rather than
being used to perform extensive studiesabout this system.
A full and extensive physi al hara terization of this lagoon is essential to
under-standnotonlythephysi alpro esses,butalsotogivethesupporttotheotherresear h
domains. One of the aims of this workis to ful llthis gap.
Theaimsof thisworkare to ontributeforthe hara terization andunderstanding
of the dynami al behaviour of Ria de Aveiro, as well as of the dominant pro esses
there o urring, and to develop a system of numeri al models able to reprodu e and
predi tthe lagoon evolution.
Thedes riptionofthetemporalandthreedimensionalspatialdistributionof
salin-ity and temperature, the hara terization of the temporal evolution and of the
hori-zontaland verti alstru tures ofthe tidal urrents, aswellasthe determinationofthe
Eulerian residual urrents and transport in this lagoon are some of the obje tives of
this work. To study the propagationof the tidal wavethrough the lagoon hannelsin
typi alandinextremefor ing onditions andtoevaluateand toidentify possible
on-sequen es and riti al areas inside the lagoondue to the generation of a storm surge
atthe Portuguese oast arealsopurposes ofthiswork. Anotheraimofthis studyisto
determinetheLagrangiantransportofpassiveparti lesreleasedin riti alareasofthe
lagoon,in ordertobetter understand the mixingbetween water masseswith di erent
origins and to evaluate the danger and onsequen es of possible pollution episodes
and through a numeri almodellingexer ise.
Theobje tivesofthisworkarealsorelevantforsomelo alandnationalinstitutions,
who re ognizethe needstoin reasethe knowledgeabout theRiade Aveiro system, in
ordertoimproveitsmanagement. Consequently,thereferredobje tivesareimportant
not onlyin the s ienti domainbut also inthe e onomi one.
This work is divided in two di erent parts, one on erning the eld results and
analysis and another related to the development and appli ation of the numeri al
model.
Chapter one presents the Introdu tion, where are des ribed the motivation, aims
and stru ture of this work. Also a dis ussion about the proper nomen lature used
to designate and lassify Ria de Aveiro is presented. This hapter in ludes a general
presentationofthestudyareaanddis ussesthemainfor inga tionsdrivingthelagoon
dynami s.
Chapters 2and3 onstitutethe PartI of this work. In Chapter 2thehydrologi al
hara terization of Ria de Aveiro in Summer is presented, using salinity, water
tem-perature, water level and urrent values measured during several surveys performed
in the lagoon. With these data the water mass hara teristi s at the lagoon mouth
and at several other pla es distributedby the main lagoon hannelsare analyzed and
dis ussed. Spe ial attention is dedi ated to the tidal propagation, to the time
evolu-tion ofthe salinityand ofthe watertemperatureatspe i lo ations,aswellastothe
salinity and temperature spatial distribution. Relevant results are the water olumn
verti al homogeneity, as well as the hara teristi longitudinal gradients observed in
ea h one of the main hannelsand its onne tion with the lagoonfreshwater inputs.
Chapter 3 des ribes the verti al stru ture of the tidal urrents observed inRia de
Aveiro. A ording tothe measured verti alpro les itwas possible toadjust
logarith-mi pro lesto all the tidal urrents observed. Two alternative methods were used to
estimate the bottom roughness length in several pla es distributed through the main
lagoon hannels. Thefri tion velo ity andthe drag oeÆ ient were alsoestimatedfor
ea h one of the pla es.
Chapters 4 to 9 onstitute the Part II of this work, and des ribe the numeri al
modelling study of Ria de Aveiro. Chapter 4 dis usses the mathemati al modelling
of physi al pro esses in shallow water systems. The hydrodynami and transport
simpli-radiative uxes parameterisationsadopted inthe heat transportmodelare presented.
Chapter 5 on erns the presentation of the numeri al model used in this work.
Some on epts and de nitions related to the nite{di eren e method and the
dis- retizationpro edures are dis ussed. The dis retizationand integration of the
hydro-dynami and transport equations are dis ussed. The boundary onditions adopted in
this work are alsoreferred.
Chapter 6 presents the results of the models alibration and validation and is
referred the models implementation for Ria de Aveiro. The nal results reveal that
both models are able toreprodu ea urately the evolution of Ria de Aveiro.
Chapter 7isdedi atedtothemodellingstudy ofthetidal regimeofRiadeAveiro.
Resultsofseveral simulationsinextremespringandneaptide onditionsarepresented
and dis ussed. The harmoni onstants for the water level and tidal urrents were
determined for the entire lagoon. The tidal urrents pattern is dis ussed, as well as
the relation between tides and tidal urrents. Tidal asymmetry and fortnightly tides
are dis ussed with the help of the water level harmoni onstants. Several physi al
parameters hara terizing Ria de Aveiro are determined, as well as the tidal prisms
in extreme tidal onditions. In this hapter it is also performed the study of the
propagation of a storm surge event in the lagoon, and are identi ed possible areas
with high risk of ooding. Finally, are presented salinity and temperature horizontal
distributions,underdi erent onditionsoffreshwater input, inordertoobtaintypi al
Summerand Winter des riptions. The results reveal that most of the features of the
tide propagationinRia de Aveiro may be explainedby the variationsinits geometry
and bathymetry.
Chapter 8 presents the results of the Eulerian residual ir ulation and transport
in Ria de Aveiro under di erent for ing onditions. The alibration of the model to
the wind for ing it is also performed in this hapter. Residual transport is dire ted
outward of the lagoon, improving the lagoonwater renewal. Somefeatures identi ed
inthe residual ir ulation may be explainedby geometryand bathymetryvariations.
Chapter 9 develops a Lagragian model of transport of passive parti les and it is
performeditsvalidation. Thismodelisusedtostudy mixinganddispersionpro esses,
aswellastodetermine theresiden e timeinRiadeAveiro. Inhightimes ales almost
thereis noex hangebetween parti lesreleased indi erent hannels, howeverinshort
Finally, Chapter 10 synthetizes the main on lusions of this work and introdu es
some new ideas and new propositions for future work.
1.2 Nomen lature
Through time, several designations have been used to refer Ria de Aveiro, and even
a tually there is some ambiguity about whi h designation to adopt to refer Ria de
Aveiro. Thetermsha {delta,half{delta,"ria"( oastalembayment),estuary, barrier{
island and oastallagoonare often found todesignate Riade Aveiro, and thereforeit
is importantto larify the meaning of these di erent nomen latures.
The term ha {delta was introdu ed at the beginning of the entury by German
geographers [Teixeira, 1994℄,who found morphologi alsimilitudesbetween Aveiro
re-gion and the lagoons (ha ) lo ated onthe Balti , wherethe tide is almost inexistent
[Davies, 1977℄. The existen e of Vouga river, dis harging intoRia de Aveiro, leads to
the expression ha {delta,whi hmeansabayoralagoon lledinby uvialsediments.
The subsequent domain of the anglo{saxon terminology was probably responsible by
the hange of the term to half{delta [Teixeira, 1994℄, whi h probably has the same
meaning. A ording to Ria de Aveiro hara teristi s these terms should not be used
to designate it.
A ording toWright [1978℄ a delta orresponds to subaerialor submarine oastal
a umulations of uvial sediments adja ent or lose to water lines that reate them,
in luding deposits whi h were shaped by the a tion of various marine agents, waves,
urrents ortides, but where the importan eof uvialsediments ontributionex eeds
the re{mobilization apa ity of the dynami agents. In Ria de Aveiro the tidal
pro- esses are mu h more important than the uvial sedimentation. These onditions
signi antly di er from the sedimentar regimes asso iated with delta environments,
and thereforethe term delta relative toRia de Aveiro should be avoid.
The term "ria" ( oastal embayment) de nes a oastal shape orrespondent to a
re{entran e,resultantfromthe submersionby the seaof theterminalzoneof a uvial
network [Granja,1996℄. These hara teristi sareusually asso iatedwiththe Gali ian
"rias", but are not found in Riade Aveiro.
The nomen lature on erning lagoonand estuary environmentsis alsorather
estu-although widely used onne ted to sand stru tures, distinguished in meso and
mi- rotidalregimesoflowenergy,wherethereareseveralbars onne tingthesea andthe
lagoonenvironments [Hayes, 1979℄, is inherentto the lagoonde nition.
The oastal lagoon on ept an be de ned as a depressed oastal zone under the
high tide level of spring tides, o upied by salt or bra kish water, relatively shallow,
separated by the sea by a sand orgravel barrier, onne ted at least intermittently to
the o ean by one or more restri ted inlets and usually shore{parallel [Granja, 1996;
Lankford,1977;Kjerfve,1994℄. A ordingtoBird[1982℄ina oastallagoonthe width
ofmarineentran esathightideislessthanone fthofthetotallengthoftheen losing
barrier.
The term estuary wasde ned by Cameron and Prit hard [1963℄: "an estuary is a
semi{en losed oastal body of water whi h has a free onne tion with the open sea
and within whi h sea water is measurably diluted with freshwater derived from land
drainage". This de nitionisstilla epted andgenerallyusedby several otherauthors
[Elliot,1978; S hubel and Kennedy, 1984; Carter,1988℄
A ordingtotheselastde nitionsthemaindi eren es between thelagoonandthe
estuary environments is the ne essary presen e of a barrier in the former and of an
importantwater lineinthese ond, althoughea honeof thesefeatures an bepresent
inboth environments.
In its a tual on guration Riade Aveiro an be onsidered as a bar built estuary
inPrit hard lassi ation[Prit hard, 1967,1989℄. Under the riterionsestablished by
Ni holsandAllen[1981℄andLankford[1977℄itisdiÆ ultto lassifyRiadeAveiro.
A - ordingtoits hara teristi sitshould be lassi edasanintermediatelagoonbetween
type I (di erential erosion pro esses dominated) and type II (di erential terrigenous
sedimentation pro esses dominated) in Lankford [1977℄ lassi ation [Freitas, 1996℄.
InNi hols andAllen[1981℄ lassi ationRiadeAveiro hassome hara teristi softhe
type Clagoon(partially losed lagoon),but probablyitshouldbe lassi edastypeA
(estuarine lagoon), hara terizedas being dominated by tidal and river pro esses.
Although Ria de Aveiro ould be lassi ed as an estuary, in this work it is
on-sideredalagoon, onsidering essentiallythe hara teristi sof thebarrierseparating it
fromthe sea and of its single tidal inlet. This lassi ationis in a ordan e with the
oneproposedbyFreitas[1996℄toRiade Aveiro. A ordingtoBarnes [1980℄thewater
of Ria de Aveiro as a lagoon, be ause the water olumn an be onsidered verti ally
homogeneous, ex ept lose tothe rivers mouths during strongrainy periods.
Thereare several works published about Riade Aveiro whereit is learly referred
that the term "ria" must be avoidin its nomen lature. Considering the de nition of
the term itobviously shouldnot beused. However, aftermany years of use this term
a tually is not used as a lassi ation of this oastal zone, but as a personal noun.
Therefore, the oastalzoneadja enttoAveirointhisworkisreferredasRiadeAveiro,
and itis lassi edas a oastal lagoon.
1.3 Study Area
Ria de Aveiro is ashallow oastallagoononthe Northwest Atlanti oast ofPortugal
(40 Æ
38'N,8 Æ
45'W), separated fromthe sea by a sand bar. It has a very irregularand
omplex geometry (Figures 1.1 and 1.2), hara terised by narrow hannels and by
the existen e of signi ant intertidal zones, namely mud ats and saltmarshes. It is
onne ted with the Atlanti through an arti ial hannel, opened inthe beginningof
the XIX entury; on rete blo ks and ro k jetties x the sea entran e. It ex hanges
most part of its water with the o ean by tidal input a ross this narrow entran e, 1.3
km long, 350 mlarge and 20 m deep. There is a small arti ialheadland (Tri^angulo
Divisor das Correntes) dividing the entran e hannel in two di erent arms. Due to
this feature the tidal prism of a owing tide is separated in two ows: a small one
owing intoMira hannel and a se ond and more important one owing to the other
hannels, namely S.Ja into and Espinheiro hannels.
The lagoon has a maximum width of 8.5 km and its length measured along the
longitudinalaxisis45km[Oliveira,1988;Reis, 1993℄. Inaspringtide water overs an
areaof83km 2
athightide, whi hisredu ed to66km 2
atlowtide. Theaveragedepth
of the lagoonis about 1 m, ex ept in navigation hannels where dredging operations
are frequently arried out. Due to the small depth and to the tidal wave amplitude
there are zones, espe ially along the borders of the lagoon and in its entral area,
whi h are alternatelywet and dry duringea h tidal y le.
Due tothe omplexity of Riade Aveiro geomorphology,of the tidal e e ts and of
the seasonal variability of the freshwater dis harges, the lagoon has a very omplex
1.3.1 Geomorphology
Morphologi allyRiadeAveiroisare entgeologi alfeaturehavingexperien edin ision
during an i e age and subsequent ooding. A narrow sand bar started to separate a
formerbay,extendinginitiallyfromEspinhoto ap Mondego,fromthe sea inthe11 th
entury. The posterior evolution of this en losed area ulminated with the omplete
isolation of the water mass in the 17 th
entury, leading to the arti ial opening of
the present mouth in the entral area of the lagoon in 1808 [Abe asis, 1961℄. Ria
de Aveiro developed until the present days by sedimentation with material from the
oastalerosionentering thelagoonmouthand bydepositionof solids arriedby rivers
present tenden y is tosilt up.
The present on guration of Ria de Aveiro is essentially fun tion of the
hydro-dynami pro esses driving the transport, erosion and deposition of sediments. The
humana tionis alsobeinganother determinantfa tor initsevolution,spe iallysin e
the intervention to arti ially x the sea entran e and the onsequent works in the
harbour and entran e hannels.
In the a tual on guration this system in ludes the mouths of Vouga river and
of several other small freshwater ourses, whi h originally dis harge in the former
bay. The topography of the lagoonis therefore highly omplex, with several hannels
radiating from a single onne tion to the sea. The upper rea hes of several hannels
are progressively transformed inthe bed of the tributary rivers.
Ria de Aveiro morphology an be des ribed as anarbores ent system of hannels
withhighlongitudinaldevelopment,organizedbysu essiverami ationsfromasingle
onne tion with the sea. The lagoon has four main bran hes radiating from the sea
entran e (Figure 1.2): Mira, S.Ja into, Ilhavo and Espinheiro hannels. The Mira
hannelis anelongated shallowarm, with20 kmlength, and isthe se ond hannel in
terms of average width with amaximum value of 1km. It runs southward parallel to
the oast from the inlet and re eives ontinuous freshwater input at its far end from
a small system of ponds and rivers. A ording to Moreira et al. [1993℄ this hannel
behaves like a tidally and seasonally poikilohalineestuary with a salinity range from
35.1to0.0. Watertemperaturede reasealongthe hannelfromthe mouthtowards its
far extremity during the old season(13.5 {8.5 o
C); aninverse and morepronoun ed
trend wasobserved during thehot season (14.5{ 24.7 Æ
C).S.Ja into hannelis about
29kmlongandisthemostimportant hannel on erningaveragewidthandlength. It
runs northwards paralleltothe oast,wide and deepatthe mouthbut hanging form
and behaviouras itextends tothe North, givinga omplexnetwork of bays, hannels
and deadarms of variable depthand shape. Dis harging atthe North of this hannel
there are two small rivers, Caster and Gonde. The Ilhavo and Espinheiro hannels
runs together at their begins, pointing East towards the town of Aveiro. They are
frequently dredgedintheir rstkilometres lose tothe mouthtoadepthofabout 7m
to allowships movement. Ilhavo hannel afterturnssouthward and it isthe narrower
and shorterofthemain hannels, withalengthof15kmand amaximumwidthof200
at Laranjo bay. It is a short hannel with about 17 km length whi h give a omplex
network of smalldead arms. Two rivers, the Vouga and Antu~a, dis harging into the
East side of the lagoon ontribute toa majorsour e of freshwater.
The entral area of Ria de Aveiro re eives not only the more signi ant inputs
of freshwater, but also the highest sediment inputs as well as important inputs of
pollutants. In this area was found signi ant mer ury a umulation in the bottom
sedimentsofthe hannels losetoanindustryof austi sodaand hlorine[Halletal.,
1987℄.
Riade Aveiro isthereforeasingulare osystem, e ologi allyand e onomi allyvery
important, with areas of freshwater, bra kish water and salt water, leading toa high
biotope variety.
1.3.2 Driving For es
Coastallagoonsexperien efor ingfromtides,riverinput,windstress,pre ipitationto
evaporationbalan e, andsurfa e heat balan e[Kjerfve,1994℄, andrespond di erently
tothese for ing a tions.
InRiadeAveirothereisa ontinuouswatermassex hange betweenthe o eanand
the lagoonthrough itsmouth due tothe penetration of the o eani tidalwave, whi h
propagates a ross the ontinental shelf from South to North along the West oast of
Portugal [Fiuza, 1984℄. The propagation of the tidal wave in the lagoon onjugated
withfreshwater in owsinsome hannels ontrols thewater massbehaviourinsideRia
de Aveiro.
The freshwater input varies ommonly between 3 and 60 m 3
s 1
and during the
rainy Winter season maximum in oming ood ows an in rease up to 820 m 3
s 1
[Borrego et al., 1990℄. The total mean river dis harge during a tidal y le into the
lagoonwas estimated as about 1.810 6
m 3
[Moreira etal., 1993℄. The tidal prism at
the mouthin a spring tide with atidal range of 2.48 m isabout 7010 6
m 3
[Vi ente,
1985℄. A ording to Barrosa [1979℄ the lagoon ex hanges with the o ean volumes of
water rangingfrom2510 6
to9010 6
m 3
duringatidal y le, for tidal amplitudesof
1to 3m, respe tively. The freshwater input fromthe rivers is thereforeusually small
omparativelytothe saltwater inputs fromthe tides(2% to 7.2%),and thereforethe
the freshwater omingfromthe rivers is enoughtodilutethe saltwaterinthe lagoon.
Theunique hara teristi sofRiadeAveiroare duetotheextensivesandbaralong
the shore that separate the lagoon from the sea. This sand bar originates a lagoon
with a dimension mu h higher than the area where the main river dis harge and by
this reason there are several otherrivers dis hargingintothe lagooninzones far from
the mouth of Vouga river. Therefore, Ria de Aveiro water mass is in uen ed by the
freshwater ontributionof several auentrivers dispersed by the lagoon.
During periods that last from a few hours to a few days, the wind, whi h is very
signi ant in Aveiro, indu es important driving e e ts on the lagoon ir ulation,
es-pe ially lose to Laranjo bay and in S.Ja into hannel, the largest water surfa e of
the lagoon. Insome oodperiods,espe iallyinWinter months, the gravitational ow
must alsobe onsideredinthe omprehensionof the lagoon ir ulation, be ausethere
is asigni antfreshwater input intothelagoon,establishing highdensity gradientsin
Ria de Aveiro. The pre ipitationtoevaporationbalan eand the surfa e heat balan e
are alsoimportantdriving fa torsduringsmallperiodsofextremevalues,spe iallyfor
salt and heat balan es at the shallowfar end of the lagoon hannels.
Tides
The tidal wave in Ria de Aveiro is a wave for ed by the o eani tide. The tidal
wave propagates along the West Portuguese oast with an average delay lose to 2
hours relative tothe moon way by the lo almeridian. The most importantharmoni
onstituents have semidiurnal periodi ity (M 2
and S 2
), originatingsemidiurnal tides
with a smalldiurnal inequality, owing to the diurnal period onstituent. The syzygy
tides have an amplitude lose to3 m, while the quadrature ones have approximately
half of that amplitude [Silva, 1994℄. At the lagoon mouth the tidal wave presents
lo al hara teristi s, whi h reveal an in rease in the delay moon{tide and a de rease
in itsamplitude,whi his thelowest observed atthe West Portuguese oast[Instituto
Hidrogra o,1990℄.
The hara teristi s of the tide atthe lagoonmouth have been hanging along the
time due tothe ontinuous works performedat the entran e hannel. The tidal wave
penetrationinRiade Aveiro isa tually fa ilitateddue totheseworks. Measurements
performed at the lagoon mouth in 1905 show tidal ranges between 1.45 m (spring
tidal rangewas referred re ently as0.6 m(neap tides), and the maximum tidal range
as about 3.2 m (spring tides), orresponding to a maximum and a minimum water
level of 3.5 and 0.3 m, respe tively [Dias et al.,1999℄. The tides at the mouth of the
lagoonare predominantlysemidiurnal(M 2
onstituentdominan e),withameantidal
rangeof about 2.0 m. A ordingto thesesvalues Riade Aveiro is amesotidallagoon
[Davies, 1964℄. Tidal urrents inside the lagoon have a maximum speed of about 1.0
ms 1
[Vi ente, 1985; Dias et al., 2000℄. The energy transmitted by the tidal wave is
fundamentalin the establishment of the water ir ulation in Riade Aveiro.
The tidalprisminea honeof themain hannelsrelativetoitsvalueatthe mouth
isabout38%for S.Ja into hannel,26%for Espinheiro hannel,10% forMira hannel
and 8% for Ilhavo hannel[Silva, 1994℄.
Rivers
In Ria de Aveiro tidal urrents are predominant relatively to the urrents due to the
rivers dis harges. However, the freshwater inputsare very important inthe
establish-ment of the salinitypatterns and inthe residual ir ulationof the lagoon[Dias etal.,
1999℄. Therefore it is relevant to hara terize the freshwater inputs of this lagoon.
A signi ant part of the freshwater inputs into the lagoon o ur in small periods of
oods, and onsequently the average ows are not verysigni ant to hara terize the
freshwater distribution inthe lagoon.
Vouga River Themouth ofVouga riverislo atedinthe entralarea ofthe lagoon
and therefore its freshwater in ow is determinant in the establishment of the salinity
eld of this lagoon. Vouga is the main river dis harging into Ria de Aveiro with an
areaof itshydrograpi basin of2425 km 2
[Fariaand Ma hado, 1977℄. 69% ofthe area
drainedby Riade Aveiro orrespondstoVougariver[Silva,1994℄. It dis hargesinRia
de Aveiro through a long hannel (Rio Novo do Prn ipe) lose to Ca ia and it has
three tributaryrivers,
Agueda, Certima and Caima.
Thefreshwater owfromVougaisthehighestfromtheriversdis harginginRiade
Aveiro, but there are no systemati measurements allowinga omplete des ription of
itsannualevolution. Thereis astudy [Vi ente, 1985℄presenting values orrespondent
to ood ows for periods of 25 and 100 years of 3400 and 4100 m 3
s 1
, respe tively.
sta-[1968℄ usingdata olle tedinCa ia by CompanhiaPortuguesa de Celulose, wherethe
maximum daily owsforreturnperiodsof1,5,10and25years wereestimatedas505,
875, 960 and 1020 m 3
s 1
. The average owfor Vouga riveris referred as29m 3
s 1
by
Cunhaetal.[1974℄and as25m 3
s 1
byBorrego etal.[1990℄,buta ording toVi ente
[1985℄ this value isunderestimated, whi h is in agreement with anaverage ow of 67
m 3
s 1
referred by Fonse a et al. [1988℄. The minimum ows o ur during dryness
periods in the Summer months. A ording to Castanho [1968℄ the minimum ows
are higher than 1 m 3
s 1
and Vi ente [1985℄ refers that they are lower than 2m 3
s 1
.
Meanwhile Silva [1994℄ estimated average ows for August and Septemberof 4.2 and
4.3 m 3
s 1
, respe tively.
If ex eptionally strong pre ipitation o ur during dry periods it is expe ted that
the freshwater ow from Vouga river will strongly in rease. However, due to the
existen e of a paper mill fa tory in Ca ia whi h uses the freshwater from the river
in its produ tion pro esses, every years a dam river is build down the fa tory in the
hannel onne ting the Vouga river with the lagoon in order to prevent the salinity
intrusioninthe drynessperiods. Thisdam isusuallybuildinMay orJune, depending
on the freshwater ow of Vouga river, and destroyed by the river when its ow is
strong enough. The dam also regulates the Vouga river ow preventing high river
ows into the lagoon, and therefore from May/June to O tober/November there is
a permanent, small and almost onstant freshwater ow from Vouga river. If strong
pre ipitation o urs during this period the freshwater input into the lagoon slightly
in rease, be ause the dam isnot watertight,but thesevalues are not so strongas the
ones that would have been registered for pre ipitationso urring duringWinter.
Antu~a River Antu~a river is the se ond more important river dis harging in Ria
de Aveiro. Its hydrograpi basin has an area of 146 km 2
[GRIA, 1990℄. This river
dis harges in the eastern area of the lagoon, in Laranjo bay, lose to the mouth of
Vouga river.
Thefreshwater owfromAntu~ariverintoRiadeAveiro hasbeen hara terizedby
Brigada de Hidrometria do Baixo Mondego. The data measured in the hydrometri
station of Ponte da Minhoteira are very extensive and onstitute the more omplete
sour e of informationabout the ow froma river dis harging inRia de Aveiro. This
average ow between 1978 and 1990 was 3.5 m 3
s 1
at Ponte da Minhoteira. Silva
[1994℄estimated that this value orresponds toa freshwater ow dis harging intothe
lagoon of 4.5 m 3
s 1
, whi h is in agreement with the values referred by Hall et al.
[1985℄ and Duarte [1992℄. Borrego etal. [1990℄ refer a smaller average annual owof
2 m 3
s 1
. In a study performed by Gabinete de Qualidade de Vida [1993℄ maximum
and minimum ows for Antu~a river of 50 m 3 s 1 in Winter and 0.5 m 3 s 1 at the end
of the dryness season are referred, respe tively.
South end of Mira hannel The freshwater dis harged to the far end of Mira
hannel orresponds to the se ond highest area drained into Ria de Aveiro, with an
areaof302 km 2
[Silva,1994℄. This freshwater sour eis omposedby asmallsystemof
ponds and rivers withorigin inCantanhede region, and runningfromSouth toNorth
untilthe South end of Mira hannel.
Theinformationaboutthe owsdrainedby Mira hannelarealmostnon{existent.
The only information on erns areferen e of an average ow of 7.8 m 3
s 1
[Queiroga,
1995℄, and some single measurements performed by Silva [1994℄ in 1990 and 1991,
revealingvaluesbetween0.21m 3
s 1
attheendofJulyand3.15m 3
s 1
atthebeginning
of April.
Bo o river Bo oriverdis harges atthe South end of Ilhavo hanneland drains an
area of 104 km 2
. Ilhavo hannel also drains several small water lines, relative to an
area of 85 km 2
[Silva, 1994℄. The only values found for the freshwater ow relative
to this basin were also presented by Silva [1994℄ and are relative to measurements
performedinthe same periodreferred before. This measurementswere doneinPonte
da Ou a ( orrespondent to a basin of 84 km 2
) and the values found were in luded
between 0.00 m 3
s 1
atthe dryness season and amaximum value of0.47 m 3
s 1
atthe
beginningof April.
North end of S.Ja into hannel The Caster river, with a basin of 71 km 2
, and
theGonderiver, withabasinof 49km 2
, dis hargeatthefarend ofS.Ja into hannel.
The onlywater owvalues found for these rivers were measured by Silva [1994℄. The
minimum ows measured for Caster and Gonde rivers were 0.08 m 3 s 1 at the end of Septemberand 0.01m 3 s 1
attheendofJulyandofSeptember, respe tively,whilethe
Wind
Thewindregimeisanimportant limati fa tor on erningthedynami ofthe oastal
zonewhereRiadeAveiroislo ated. Inthisareathewindistypi alofthe oastalareas
of the mean latitudes, in eastern margins of large o eans, dire tly onne ted to the
latitudinalmigrationofthe subtropi alfrontand dependentofthe A oresanti y lone
dynami [Fiuza et al., 1982℄. Its more importantfeature is the high frequen y of the
winds blowing from North and Northwest dire tions. They o ur more than 40% of
the times, with average velo ities of 20 kmh 1
[Faria and Ma hado, 1977℄. These
northern winds are hara teristi of the Summer season, and are generated by the
A ores anti y lone and by the thermaldepressions existing over Iberian Peninsula at
this season. In the Winter the wind regime is more variable,with strong u tuations
in dire tionand intensity [Fiuza,1982℄.
Besides the yearly variation there is a typi al lo al breeze regime, with a daily
periodi ity,resulting fromthe thermalgradientbetween the o eanand the ontinent.
Typi ally,inthe oastal zone,during the day thereis asea breezeblowing fromWest
to Northwest ( alled "nortada"), with in reasing intensity in the afternoon. During
the night the breeze rotates to East or Southeast (land breeze), and usually has a
lowerintensity than during the day. The lo al breezee e t is moreevident when the
regional ir ulation is not signi ant, spe iallyin the Summer when the sky is lean
[Pires, 1986℄.
The wind stress a ting on the sea surfa e generates a oastal drift predominantly
form North to South[Silva,1991℄, with important onsequen es on the oastalzone.
Temperature and pre ipitation
The annual average air temperature in Ria de Aveiro region a ording to Fonse a
etal.[1988℄is 14.7 Æ
C, with minimumand maximumaveragevaluesof 8and 10 o
Cin
Winter, and 18and 20 o
C inSummer, respe tively.
Amorere entstudyperformedusingdatameasuredatUniversityofAveiro
lima-tologi alstationfrom1981to1999byAlves[2000℄revealdi erent values. Theannual
average temperaturedeterminedinthis study is13.8 o
C, the minimum andmaximum
average values for Winter months are 5.9 and 11.6 o
C, and for Summer months are
14.7 and 20.3 o
Figure 1.3: Average and extreme monthly mean temperatures observed at Aveiro
limatologi al station for ea h month of the year, for the period between 1981 and
1999 [Alves, 2000℄.
limateofthis regionis lassi edassubtropi al,sin e theaverage temperatureinthis
regionishigherthan10 o
Cinmorethan 8months oftheyear, andatleastinamonth
the average temperature is lower than 18 o
C. Considering that the highest monthly
average temperature is lower than 22 o
C this region is over the in uen e of the mild
Summermediterranean limate,notation Csb inKoppen lassi ation [Jansa, 1968℄.
The annual average pre ipitation in Aveiro region is 913.5 mm [Fonse a et al.,
1988℄. 75%ofthis pre ipitationo urduringthe rstsemesterofthehydrologi alyear
(O tobertoMar h), while5%o urintheSummerquarter. Thehighestpre ipitation
in the Winter is due to the frequent presen e of old and maritime polar air masses,
whi h originate low pressure y lones over the Atlanti oast. In the Summer the
displa ementoftheA oresanti y lonetohighestlatitudes reatesablo kingsituation,
obstru tingthe arriving of pre ipitationthrough the North [Manso etal., 1996℄.
The valuesmeasured forthemonthlya umulatedpre ipitationatthe
limatolog-i alstationofUniversityofAveirofrom1980to1997arepresented inFigure1.4[Neto
and Vaz, 2000℄. The annual average pre ipitation dedu ed from these measurements
is884.9 mm. Duringthis period at least avery low monthly value for allthe months
oftheyearhas beenobserved, showing thatduringalltheyearlargesequen es ofdays
withoutpre ipitation an ex eptionallyo ur.
determined by Faria and Ma hado [1977℄ using data from 1931 to 1960 has been
found to be 610 mm. Loureiro et al. [1986℄ determined the value of 730 mm for the
basin around Ria de Aveiro (3635 km 2
), whi h means that the pre ipitation an be
onsidered higher than the evapotranspiration inthis region.
Figure 1.4: Average and extreme monthly mean a umulated pre ipitation observed
at Aveiro limatologi al station for ea h month of the year, for the period between
Experimental Study of Ria de
Hydrologi al Chara terization of
Ria de Aveiro
2.1 Introdu tion
Despite the e onomi al, so ial, environmental and s ienti importan e of Ria de
Aveiro there has been no previous hydrologi al measurements overing the whole
la-goon until this present study. The more general hydrologi al measurements existing
before were performed by Instituto Hidrogra o in 1988/89 [Instituto Hidrogra o,
1988/1991℄. Costa [1990℄ resumed the informationobtained in those surveys, but the
original data are still unpublished and not available. Matos [1990℄ performed a salt
balan estudyfor this lagoon, on luding thatithas the behaviourofa verti ally well
mixed estuary.
The most omprehensive work on erns biologi al, hemi al, geologi aland
envi-ronmental resear h. Moreira et al. [1993℄, Queiroga et al. [1994℄, Cunha [1999℄ and
Silva[1994℄performedsomelo alisedmeasurementsofwatertemperature,salinityand
urrentsandTeixeira[1994℄summarizeddispersedata olle tedthroughtheyears
on- erningRia de Aveiro hydrology.
The aim of this Chapter is to study tide and urrent properties as well as to
hara terize the horizontaland verti al stru tures of salinity and temperature in Ria
de Aveiro during an early Summer period. To a hieve these purposes two di erent
observational surveys have been arried out. In this hapter water level, salinity,
