Waves and Tidal Flat Ecosystems

173 Pages·2003·13.185 MB·English

by  Prof. Eiichi Baba, Prof. Hideo Kawarada, Prof. Wataru Nishijima, Prof. Mitsumasa Okada, Prof. Hiroshi Suito (auth.)

Eiichi Baba, Hideo Kawarada, Wataru Nishijima,
MitsumasaOkada, Hiroshi Suito
Waves andTidal Flat Ecosystems
Springer-Verlag Berlin Heidelberg GmbH
E. Baba, H. Kawarada, W. Nishijima,
M. Okada, H. Suito
Waves and Tidal
Flat Ecosystems
With 144 Figures, 27 in colour
, Springer
PROF. ElICHI BABA PROF. WATARU NlSHIJIMA
Information Exchange Office PROF. MITSUMASA OKADA
Hiroshima University Department of Chemical Engineering
1-3-2 Kagamiyama, Graduate School ofEngineering
Higashi-Hiroshima,739-8511 Hiroshima University
Japan 1-4-1 Kagamiyama
Higashi-Hiroshima, 739-8527
PROF. HIDEO KA WARADA Japan
Faculty of Distribution and
Logistics PROF. HIROSHI SUITO
Systems Department of Environmental
Ryutsu Keizai University and Mathematical Sciences
Hirahata 120, Ryuugasaki Okayama University
Ibaraki,301-8555 3-1-1 Tsushima-naka
Japan Okayama, 700-8530
Japan
ISBN 978-3-642-62444-5 ISBN 978-3-642-55534-3 (eBook)
DOI 10.1007/978-3-642-55534-3
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Preface
In this book, the authors address present-day methodology to explore natural
phenomena. Highly advanced computational fluid mechanics contributes to the
rationalization of experimental work. By taking sandy beach and tidal flat eco
systems as an example, results from interdisciplinary collaboration between envi
ronmental experimentalists and applied mathematicians are presented in an inte
ractivemanner.
In 1994, an environmental study group from Hiroshima University started a
study on tidal flats. Based on fieldwork, they discovered the importance offluid
flow in understanding the biological activities of tidal flats and sandy beaches.
Theyfound that the numberofbacteriaon the seabed strongly correlates with the
amountofsilt (fine sand <50micron). Largerslopes produce smalleramounts of
silt.Theynoted theimportanceofan appropriateslopefor atidalflat wheresound
biologicalactivitiesarecarriedoutontheseabed.
Furthermore, independentlyin 1993, anappliedmathematics groupfrom Chiba
University studied a sliding problem oftwo different media. In 1995, they exten
ded their workto explain apenetration problemfrom one side to the otherin dif
ferent phases. Then, in 1996, the study was extended to wave motion on the slo
pingsandybeach. Atthis momentthis mathematicsgroupdidnotexploityettheir
potentialto explorecoastalenvironmentalproblems.
In 1997,theenvironmentalgroup startedaresearchprojectdealing with theef
fect ofspilledoiloncoastal ecosystems. This projectaims to providemeasures to
counterenvironmentaldisasters suchasthespilledoilin 1997from atankerin the
JapanSea. Inthis study, anewexperimentaldiscovery wasmadeabouttheroleof
waves over a sandy beach. Breaking waves act as a pump to transport fresh sea
waterto the beach. Thus, itbecamepossibleto estimatequantitatively the infiltra
tionofseawaterbywavesintotheseabed.
Even though the waves themselves are only afew centimetershigh, the impor
tance ofwaves was recognized from experimental studies using atidal flat sumu
lator, which contains actual soil from the tidal flat. That is, benthos grows in the
seabedwhen wavesandtidesacttogetheroverthetidalflat. However, the number
ofbenthosdecreases andseagrass growsinsteadwhen the tide aloneacts without
waves. Seagrass prevents the infiltration offresh seawaterinto the seabed. Thus,
it was clearthat different kinds oforganisms flourish under different habitatcon
ditions, i.e., with waves or without waves. Thus waves at the margin of sandy
VI
beaches ortidal flats are an importantfactor for the determination ofcoastal eco
systems.
The environmental experiment group needed rationalization of their experi
mental results from a theoretical standpoint. The Chiba University mathematics
group was informed ofthe flow phenomenon observed in experiments by one of
the environmental study groups in 1998. These experimentalresults attracted and
inspired the mathematics group to exploit the large potential to explore the flow
phenomenon inside the seabed. They then extended their analysis to treat fluid
flow in variousenvironmentssuchas air, wetsandanddrysand. Itwasfound that
mathematically simulated flow behaviour inside a sloping beach well explained
observedphenomena. Thus, theflow phenomenaobserved by theeinvironmented
studygroup wererationalized.
Theeinvironmental studygroupcontinuedtheirworkandfound thatspilledoil
over a sloping beach prevents the infiltration of fresh seawater into the seabed,
causingashortageofoxygen. Therefore, thebenthos suffers.
The mathematics groupextendedtheirworkto simulatebahaviourand decom
position of spilled oil based on Navier-Stokes equations with the Bingham fluid
modelfor oil. Multi-phaseflow analyses were made. In this study, decomposition
of spilled oil by bacteria is simulated as a chemical reaction. Thus, natural phe
nomena around the margin of land, in other words, the margin of different dis
ciplinary research fields are being explored by collaboration of experimentalists
andapplied mathematicians. Thedevelopmentofthis workin thefuture is highly
expected to further our understanding ofcoastal ecosystems and to contribute to
sound engineering approaches in the construction of artificial tidal flats and co
astlines.
March2003
EiichiBaba
HideoKawarada
MitsumasaOkada
Thefollowing authors contributedtothis book:
Chapter1;W. Nishijima
Chapter2;E. Baba
Chapter3;H. KawaradaandH. Suito
Chapter4;M. Okada
Chapter5;H. KawaradaandH. Suito
Chapter6;M. Okada
Chapter7;H. Kawaradaand H. Suito
Chapter8;H. KawaradaandH. Suito
Chapter9;H. KawaradaandH. Suito
Table of Contents
1 What isatidal flat?.......................................... 1
1.1 Introduction.............................................. 1
1.2 Function and structure of natural and man-madetidal flats ... 2
1.2.1 Pysico-chemical characteristics...................... 2
1.2.2 Hydrauliccharacteristics .. .......................... 5
1.2.3 Biomass ofbacteria and macrobenthos 5
1.2.4 Respiration rates of microorganisms ................. 8
1.2.5 Discussion......................................... 8
1.3 Key factors todetermine atidal flatcharacteristic. ........... 10
1.3.1 Transferexperiments.. ........ ........ .. .. .. .. .. ... 10
1.3.2 Relationship between silt content and bacterial
population 12
1.4 Fluid flow on atidal flat 15
1.4.1 Outline ofstudy sites. .... .. ... ..... .. ... .. ... .. .... 15
1.4.2 Shearstress. .. .. .. ... ... .. ... .. ... .. ... .. ... .. .... 16
1.4.3 Sedimentation ofsand. ............................. 18
1.4.4 Discussion......................................... 20
2 Effectsofwaves and tide on tidal flat ecosystems ............... 23
2.1 Introduction.............................................. 23
2.2 Method of experimentson internal flow in seabed 24
2.2.1 Flow visualization inside sandy beach................ 24
2.2.2 Wave and tide control ............................... 25
2.2.3 Quantification of seawaterinfiltration in sandybeach .. 25
2.3 Role ofwave andtide on seawater infiltration in sandy beach. 26
2.3.1 Fresh seawater infiltration ........................... 26
2.3.2 Silt movementbywave action 28
2.4 Role ofwaveand tide on ecosystems in tidal flats 29
2.4.1 Measurementof seawater infiltration intidal flat. ...... 29
2.4.2 Observation of benthicorganisms intidal flat simulators 32
2.5 Concluding remarks....................................... 38
VIII TableofContents
3 Unified modelforwave breaking action. ....................... 41
3.1 Introduction 41
3.2 Mathematical model. ...................................... 42
3.2.1 Notationsand geometry 42
3.2.2 Conservation of massfortotal flow system 44
3.2.3 Conservation of momentum fortotal flow system 44
3.2.4 Surface blocking effect to seawater due to
accumulated materialson the beach ................. 45
3.3 Unified model fortwo-phase flow with surface blocking effect. 46
3.4 Numerical results 47
3.4.1 Correlation between wave breaking action on a
sloping beach and internalflow ofasandy beach ..... 47
3.4.2 Flow pattern and infiltration area of seawater in
sandybeach ....................................... 48
3.4.3 Time averagedflow underthe beach. ................ 50
3.4.4 Surfaceblocking effectto seawater 51
4 Oil pollution: human damages on hydraulic regime in sandy
beach ecosystems. ......................................... 53
4.1 Introduction....... ... .. ... .. ... .. ... .. ... .. ... .. ... .. .... 53
4.2 Infiltration of stranded oils into sandy beach sediments by
waves and tides 54
4.2.1 Waves andTides ................................... 54
4.2.2 Volumeofstranded oils ............................. 57
4.2.3 Tidal Cycles andtemperature 57
4.2.4 Viscosityofoil. ..................................... 58
4.2.5 Weathered and dispersed oils ....................... 60
4.3 Effects ofthe penetrated oils into sandy beach sediments
on seawater infiltrationby waves 65
5 Theoretical studyofoil pollution 71
5.1 Introduction 71
5.2 Behaviorofspilled oil in the surfzone " 71
5.3 Mathematical model. .. .. ... ..... ..... .. ... .. .... .... .. .... 72
5.3.1 Notationsand geometry 72
5.3.2 Conservation of massforatotal flow system 73
5.3.3 Conservation of momentumforatotal flow system 74
5.3.4 Unified equationsof motionforathree-phase flow 75
5.3.5 Adhesive phenomena ofoil on asandy beach 76
5.4 Unified model forthree-phase flow with adhesion. ........... 76
5.5 Numerical results ......................................... 78
5.5.1 Process ofdriftingashore ofspilled oil 78
5.5.2 Deformation ofoil 81
5.5.3 Adhesion and sliding phenomena between oil and
water in asandybeach 81
TableofContents IX
5.5.4 Infiltration phenomena of oil into atidal flat or sea
bed duetothe tidal motion ... ....................... 86
5.5.5 Blocking effect by penetrated oil on the internal flow
in sand 86
6 Oil pollution: human damage on hydraulic regime and benthic
communities in tidal flat ecosystems........................... 93
6.1 Introduction.............................................. 93
6.2 Penetration ofstranded oils into tidal flat sediments bytides.. 95
6.3 Effects of the penetrated oils into tidal flat sediments on
seawater infiltration bytides. ............................... 97
6.4 Effects ofoil spill on seawater infiltration and macrobenthic
community in tidal flats 100
6.4.1 introduction 100
6.4.2 The tidal flat simulator 101
6.4.3 Effectsofoil spill ontidal flat ecosystem 105
6.4.4 Macrobenthiccommunity 106
7 Decomposition mechanism ofspilled oil by bacteria 109
7.1 Introduction 109
7.2 Notations 109
7.3 Characteristics ofoil decomposition into water 110
7.3.1 Reactivity condition 111
7.4 Incompressibilitycondition foratotal flow system 111
7.5 Biological contribution to satisfy reactivity condition 112
7.6 Unified model forthree-phase flow with decomposition 113
7.7 Numerical results " 114
8 Breaking waves and ecosystem dynamics 117
8.1 Introduction 117
8.2 Mathematical modeling 117
8.2.1 Mathematical description ofaeration dueto breaking
waves 117
8.2.2 Modelingforecosystem dynamics 120
8.3 Coupling scheme between waves and ecosystem dynamics.. 121
8.4 Numerical results 122
8.4.1 Aeration due to breaking waves 122
8.4.2 Simulation ofecosystem dynamics 122
9 Methodologies fortheoretical studies 127
9.1 Introduction 127
9.2 Mathematical methodologies 127
9.2.1 Distribution theoreticapproach to multi-phaseflow 127
9.2.2 Anti-smearing devicefornumericalfree surface 134
9.3 Numerical methodologies 135
X TableofContents
9.3.1 Discretized model forthe total system 135
9.3.2 Two-phase free surface flow with large density
difference 137