445
1 INTRODUCTION
Estuarineareasareusuallyamenabletoportactivity
developmentduetothefavorablelocation,sheltered
from wave action in most cases. Moreover, natural
greatdepthsarecommonlyfoundinestuaries,which
arealsoimportantforportterminalactivities,asthere
is less need for dredging to allow the
entrance and
mooringoflargercargoships.
In estuaries, interaction of fresh and salt water
causes fine sediments to deposit. Physical and
chemical properties of brackish water allow for fine
particle attraction, due to the presence of sodium
cations.Theseparticlesformheavierflocsthattendto
geteasilydeposited
onthebed.Thisprocessoccursat
different stages, depending on the strength of
chemical bonds formed between particles. One of
these stages is called Fluid Mud, in which chemical
bonds are yetnot strongenough to formlarge flocs
withlowmobility(McAnallyetal,2007).
Fluidmudisan
aqueoussolutionwithrheological
propertiesthatallowforsafenavigationwithlowor
negative under‐keel clearance. Thus, it can be
associated with the Nautical Bottom Concept.
According to PIANC (2014), Nautical Bottom is the
minimum depth in which there can be safe
navigation, without adverse effects in ship control
Fluid Mud and Nautical Bottom
–
Concept and
Application in Itajaí Port Complex (Brazil)
L.M.Pion
HydraulicTechnologicalCenterFoundation,SaoPaulo,Brazil
P.Alfredini
UniversityofSaoPaulo,SaoPaulo,Brazil
ABSTRACT:Consideringthedemandformooringlargerships at Brazilian port terminals,bothprivate and
public, in a scenario of growing exports, engineering interventions that can provide improvements in the
vessel’smaximumalloweddimensionscanrepresentsignificantprofits.Hence,thisworkpresentsanapproach
ofNautical Bottom, definedasthe minimum depth in which ships can navigate without significantadverse
effectsinshipcontrolandmaneuverabilitywithoutphysicaldamage,withthegoalofraisingthemaximum
ship draft allowed in nautical spaces with fluid mud beds. Due to its rheological properties, fluid mud, in
general, allows for vessels navigate with low or negative under keel clearance, respecting the established
NauticalBottomconcepts.Inaddition,fluidmudlayerthicknessatportareascanpossiblyvaryaccordingto
hydrodynamics and sedimentologic variations. This article presents an analysis of fluid mud thickness
variationswithintheItajaíPortComplex
(SantaCatarina,Brazil)turningbasin,wherefluidmudlayersareup
to 2.5 meters thick, by means of analyses of bathymetric surveys and numerical modeling. The Itajaí Port
Complex is located at the Itajaí‐açu river estuary, which presents high variability of river discharge and
suspendedsediments.Frombathymetricsurveys,
itispossibletoobservefluidmudthicknessfrom0.5to2.5
meters. Numerical simulation results indicate suspended sediment load as a main environmental aspect for
fluidmudthicknessvariationsinthestudyarea.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 13
Number 2
June 2019
DOI:10.12716/1001.13.02.24
446
andmaneuverabilityandwithoutsignificantphysical
damageonvessels.
In Brazil, several port terminal locations could
applytheNauticalBottomconceptduetofluidmud
layersnearthebottom,suchastheSantos,Paranaguá
and Antonina ports, the Alumar terminal (Estreito
dos Coqueiros, Maranhão, Brazil) and Itajaí Port
Complex,which
istheobjectofthisstudy.
At the turning basin of the Itajaí Port Complex,
double frequency bathymetries were compared with
specific density measurements, in order to define
whichspecificdensitybettercorrespondstoa33kHz
bathymetric survey, concluding that low frequency
bathymetry surveys, in that area, correspond to
specificdensitiesbetween1,150and1,200kg/m³(Pion
andAlfredini,2014).
TheItajaíPortComplexiscomposedofthepublic
portofItajaíandseveralprivateterminalsinstalledat
theItajaí‐açurivermargins,nearitsoutfall(Figure1).
TheItajaíPortComplexlogisticsisbasedonthecities
of Itajaí
and Navegantes. This port complex was
responsibleforapproximately900,000TEUstransport
in2015, being the second port in Brazil in container
transportation,aftertheSantosPortComplex.
Itajaí
Itajaí Port
Complex
Figure1.ItajaíPortComplexLocalization
The nautical areas of the Itajaí port complex are
divided in external access channel, internal access
channel and turning basin. At access channels, the
minimum under keel clearance is 15% of ship draft.
At the turning basin, under keel clearance of 0.6
meters is allowed, independently of ship draft.
Maximum ships
LOA allowed to enter Itajaí Port
Complexisabout285meters.
1.1 Itajaí‐açuriver
The Itajaí‐açu estuary is approximately 70 km long,
considering its upper limit next to Blumenau (Santa
Catarina,Brazil),wherewaterlevelvariationsdueto
tidaleffectsarestillobserved,andcoversa15,500km²
drainagebasin.
The average Itajaí‐açu river discharge was
estimatedin228m³/swithstandarddeviationof282
m³/s by Schettini (2002), considering data
measurements collected between 1934 and 1998 at
Indaial(SantaCatarina,Brazil), a citylocated90km
far from the river outfall. The minimum discharge
observed was 17
m³/s and the maximum discharge
measured was 5,390 m³/s. According to the same
author,thislocationrepresentsapproximately70%of
the Itajaí‐açu river drainage basin. The measured
discharges of the Itajaí‐açu river could not be
associatedwithseasonality,asthemonthlymaximum
discharge was measured on February and
October
andthemonthlyminimumdischarge was measured
onAprilandDecember(Schettini,2002).
AttheItajaí‐açu river outfall,the tidal amplitude
variesfrom0.3metersonquadratureto1.2meterson
syzygies, with an average tidal amplitude of 0.8
meters. The mean sea level is approximately 0.57
meters. Meteorological
effects can amplify tidal
amplitudes by 25% (Truccolo, 2009). Water level
measurements can be also significantly modified by
high discharges occurrence (Schettini and Truccolo,
2009)
Salt intrusion in the Itajaí‐açu river estuary is
related to river discharge magnitude. When river
dischargesreachabout300m³/s,saltintrusionoccurs
up
to 18 km from the river outfall. High discharges
(1,000 m³/s or higher) expel salt intrusion from the
estuary(Schettini,2002).However,theItajaí‐açuriver
discharges are lower than its average value most of
time,thussaltintrusioncanbeconsideredpractically
permanent, reaching up to 30 km in low
‐discharge
periods (Schettini and Truccolo, 2009). When the
Itajaí‐açu river discharges reach approximately 500
m³/sthere is an evident saltwedge (Schettini, 2002).
Attheturningbasinarea,salinityvariesfrom30ppt
(bottom)to10ppt(surface)(Medeiros,2003)
The Itajaí‐açu river estuary bed is predominantly
composed
ofclaydeposits,inwhichtheclayfraction
ishigherthan70%(Schettini,2002).Riverdischarges
higherthan700m³/sincreasebedsandfraction,due
to higher flow sediment transport capacity. The
suspendedsolidconcentrationvariesfrom7mg/Lto
500 mg/L when measured at Indaial station,
dependingonriverdischarge
(Schettini,2002).
1.2 Goaloftheresearch
The goal hereby is to describe fluid mud layer
thickness at the turning basin of the Itajaí Port
Complex and its variation through bathymetrical
surveys and analysis of river discharges and
suspended solids. We also aim, by using
hydrodynamicandfinesedimenttransport
numerical
modeling,specificallysoftware Delft3D®, to analyze
environmentalconditionsthatmaycausevariationin
fluidmudlayerthicknessatthislocation.
2 MATERIALANDMETHODS
TheanalysisoffluidmudlayerthicknessattheItajaí
PortComplexwasdevelopedfromdoublefrequency
bathymetric surveys, river discharge and suspended
sedimentdataand
hydrodynamicandsedimentologic
numericalmodeling.
2.1 Bathymetricsurveys
The analysis of the turning basin of the Itajaí Port
Complex was based on four different double
frequency bathymetrical surveys (33 – 200 kHz).
447
These data were collected on 30/03/2007, 15/05/2007,
12/07/2007and15/11/2007.
2.2 Riverdischargeandsuspendedsolidsdata
Inadditiontobathymetric surveys, theanalysiswas
basedonriverdischargeandsuspendedsolidsdata,
collected at Indaial (Santa Catarina, Brazil), located
approximately90kmfromtheItajaí‐açuriveroutfall.
These
data were collected over the course of 2007.
Riverdischargeandsuspendedsoliddatawereused
as boundary conditions for the numerical model,
consideringthegoalofjustifyingfluidmudthickness
variations.
2.3 Delft3D®HydrodynamicModule
Delft3D hydrodynamic module simulates non‐
uniformflowsandtransportphenomenausingwater
level variation,
river discharges or meteorological
forcing variables, including density gradient effects,
calculatedfromsalinityandtemperaturedistribution.
This model can be used to predict flow patterns on
shallow regions, coastal, estuarine or lake areas
(Deltares, 2014). In this case, numerical modeling is
based on the continuity equation, the momentum
conservation equation (Navier
‐Stokes) and the
transportequationssolution.
The model solves Navier‐Stokes equations for an
incompressible fluid, considering the Boussinesq
approximation, in which fluid density is considered
to be constant, except for the baroclinic term, which
represents flow variations due to vertical density
gradients (Deltares, 2014). Moreover, the Boussinesq
approximation does
not account for vertical flow
acceleration, considering hydrostatic pressure. This
hypothesis is valid when the horizontal extension is
muchlargerthanflowdepths(Deltares,2014).
Thenumericalsimulationsareperformedthrough
thefinitedifferencemethod,andthespaceisdivided
incellsfromacomputationalgrid.Delft3D®cohesive
sedimenttransportmodel
The Delft3D fine sediment transport model is
based on continuity principle. Considering a certain
control volume, increase of fine sediment
concentration is equal to incoming fine sediment
added to particle generation inside this control
volume(McLaughin,1961).
The model considers eddy diffusivity to be
independent of sediment concentration, which is
a
valid hypothesis considering usual sediment
concentrations found at rivers and estuaries
(Partheniades,2009).Settlingspeed
iscalculatedbased
on sediment concentration, considering that high
concentrationshindersedimentsettling.
Cohesive sediment reference settling speed is a
function of salinity. The presence of salt causes a
reduction in the repulsion force of electrical forces
between clay minerals, inducing flocculation
(Alfredini and Arasaki,2014). These flocs are bigger
andheavier,
sotheytendtosettlefasterthansmaller
particles. Delft3D calculates fine sediment settling
speedbasedonwatersalinity.
3 RESULTSANDDISCUSSION
Results obtained are presented separately, first from
field data analysis and then numerical model
calibration and simulation results. These results are
furtherintegratedinthediscussionsection.
3.1 Comparativesurveys
Comparative surfaces presented high variability of
fluidmudlayerthicknessattheturningbasinofthe
ItajaíPortComplex(Figure3andFigure4).Asitcan
be observed, on 15/05/2007 (Figure 3 (b)) and
05/11/2007 (Figure 4 (b)), the fluid mud layer is
thickerthanwhatwas
observedinotherbathymetric
surveys.In15/05/2007,thefluidmudlayerisupto2.5
metersthickinsomeregionswithintheinterestarea
and most of the turning basin of the Itajaí Port
Complex presents fluid mud layer thickness of
between1and1.5meter.Instead,bathymetricsurveys
from
30/03/2007(Figure3(a))and12/07/2007(Figure
4(a))presentalayeroffluidmudnear thebedthat
does not surpass 0.5‐meter thickness in most of the
turningbasinarea.
ab
Fluid Mud Layer Thickness (m)
Figure3.Comparativesurfaces‐(a)30/03/2007(b)15/05/2007
448
a
b
Fluid Mud Layer Thickness (m)
Figure4.Comparativesurfaces‐(a)12/07/2007(b)05/11/2007
3.2 Modelconceptionandcalibration
The modeled area was defined considering the land
boundaries conceived using the Google Earth®
software. Oceanic boundaries were determined in
ordertoadequatelyrepresenttidewavepropagation
overtheentiremodeldomain.Fluvialboundarywas
defined considering the extension of salt intrusion
and the border was
located at approximately 20 km
fromtheriveroutfall,wheresalinityisapproximately
zero(Schettini,2002).
The computational grid (Figure 5) employed has
14,011 cells, with variable resolution. At the turning
basin of the Itajaí Port Complex, the resolution
employed was of approximately 40 x 20 meters. In
order to
precisely represent estuarine stratification,
themodelwasconceivedwith12verticallayers,with
betterresolutionnearbottom.Layersweredividedin
2‐2‐3‐4‐5‐6‐7‐9‐11‐14‐17‐20%frombottomtosurface.
Figure5.Computationalgrid
The Model bathymetry (Figure 6) was based on
bathymetricaldatacollectedin2007,whichwerealso
used for variation analyses of fluid mud thickness.
For areas which are not covered by bathymetric
surveys, information contained in nautical charts of
the Itajaí Port Complex were used to fulfill model
bathymetry.
Figure6.Modelbathymetry
Oceanic open boundary was forced with
astronomicconstantsextractedfromtheTPXOglobal
tidemodel(EgbertandErofeeva,2002)fortheItajaí‐
açu river outfall area. River boundary was forced
with river discharge data measured at Indaial
multiplied by 1.43, considering that discharges
measuredatIndaial represent approximately 70% of
all
drainagebasin(Schettini,2002)
Bed roughness was set according to the bed
material characteristics. Wave and wind effects are
not representative for sediment transport at the
interest area (Schettini, 2002), so they were not
considered.Salinitywassettozeroatriverboundary
and35pptatoceanicboundary.
Only
one cohesive sediment fraction was
simulated, in order to evaluate sediment
concentrationsnearthebed.Thesedimentproperties
were chosen with the aim of hindering it from
settling,inordertorepresentafluidmudlayerinthe
most accurate way possible. At the river boundary,
suspendedsedimentmeasuredin2007
atIndaialwas
forced. Considering that this sediment is originated
fromthedrainagebasin,finesedimentconcentration
attheoceanicboundarywasconsiderednull.
Waterlevelwascalibratedusingatime‐seriesfor
theItajaíPortComplexgeneratedbytheTPXOglobal
tide model. Current speeds were evaluated
comparing model
results with monthly average
speeds measured by CTTMar (Univali, Itajaí, SC)
between 2006 and 2012.Salinity model results were
calibratedwithlongitudinalsalinityprofilebasedon
measurements at the Itajaí river estuary by Schettini
(2002).Suspended sediment was based on 11 points
inside the turning basin of the Itajaí Port Complex.
449
Model results were compared with suspended
materialmeasurementsperformedbySchettini(2002),
analogouslytosalinitymeasurements.
3.3 Dredgingvolumesestimate
Aiming to analyze variations of fluid mud layer
thickness as precisely as possible, dredged volumes
from the Itajaí Port Complex were calculated. This
estimatewasbasedontotalsedimentcontribution
to
the interest area extracted from model results. The
model estimate was compared to the 2007 annual
total dredged volume estimated by the Itajaí Port
Complex administration (2,000,000 m³). In this case,
theestimated volume pertainstoall nautical spaces.
Dredged volume at the Itajaí Port Complex area
cannot be
precisely determined because water
injectiondredgingisperformedinthisregion.
Themodelestimatedthatapproximately1,500,000
m³ofsedimentcontributedtotheItajaíPortComplex
in 2007 (Figure 7), presenting the same magnitude
order of dredging volumes informed by the port
administration in 2007. It is important to highlight
that
approximately 60% of sediment contribution
occurredbetween15/05/2007and12/07/2007(Table1).
Thus, it is possible to infer that dredging was
intensifiedinthisperiod.
Sediment Contribution – Itajaí P ort Complex Turning Basin
Cumulative Sediment Contribution (m³)
Ti me
Figure7. Modeled sediment contribution to the turning
basingoftheItajaíPortComplexin2007
Table1. Sediment contribution to the turning basin of the
ItajaíPortComplex
_______________________________________________
ModeledSedimentContributionBetweenBathymetric
Survweys(m
3
)
_______________________________________________
PeriodSediment%from
Contribution(m
3
) AnnualVolume
_______________________________________________
30/03/2007‐15/05/2007 8,1591%
15/05/2007‐12/07/2007 816,37860%
12/07/2007‐08/11/2007 242,32018%
_______________________________________________
3.4 Numericalsimulationsresults
From model results (Figure 8), it was possible to
concludethatsuspendedfinesedimentconcentration
isnotrelatedtotidalcycles.Variationsofsurfaceand
bedfinesedimentconcentrationarenotcorrelatedto
syzygiesorquadraturestandards.
0
0.05
0.1
0.15
0.2
0.25
0
0.2
0.4
0.6
0.8
1
1.2
1.4
10/04/2007 15/04/2007 20/04/2007 25/04/2007 30/04/2007 05/05/2007 10/05/2007
SuspendedSedimentConcentration(kg/m³)
Waterlevel(m)
WaterlevelandSuspendedSedimentConcentration
WaterLevel Av erageCo nc entr at ion‐ Bot tom Av erageCo nc entr ation‐ Supe rfa ce
Figure8. Water level and Suspended Sediment
Concentration
Comparison between river discharges and
sediment concentrations showed that surface layer
sediment concentrations slightly raise when river
discharges are over 400 m³/s (Figure 9). However,
sediment bed concentrations seem not to be directly
relatedtoriverdischarges.
0
0.05
0.1
0.15
0.2
0.25
‐200
‐100
0
100
200
300
400
500
600
10/04/200700:00 15/04/200700:00 20/04/200700:00 25/04/200700:00 30/04/200700:00 05/05/200700:00 10/05/200700:00
Suspended SedimentConcentration(kg/m³)
Rive rDischarge (m³/s)
RiverdischargeandSuspendedSedimentConcentration
RiverDischarge AverageConcentration‐Bottom AverageConcentration‐Superface
Figure9. River discharges and Suspended Sediment
Concentration
Thus, suspended sediment concentration was
comparedtosuspendedsedimentloadattheturning
basin of the Itajaí Port Complex (Figure 10). From
theseresults,itcanbestatedthatsuspendedsediment
concentration is directly related to suspended
sediment load. Suspended sediment load peaks
generally cause an immediate increase in surface
sediment
concentrations, followed by a delayed
increase of bottom sediment concentrations. This
delay is justified by the necessary interval for the
suspendedsedimenttosettle.Hence,thevariationof
fluid mud layer thickness was analyzed using the
suspended sediment load parameter, in addition to
sedimentconcentration.
450
0
0.05
0.1
0.15
0.2
0.25
‐0.004
‐0.002
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
10/04/2007 15/04/2007 20/04/2007 25/04/2007 30/04/2007 05/05/2007 10/05/20 07
SuspendedSedimentConcentration(kg/m³)
SuspendedSedimentLoad(m³/s)
SuspendedSedimentLoadandSuspendedSedimentConcentration
SuspendedSedimentLoad AverageConcen tration ‐Bottom AverageConcentration‐Superface
Figure10. Suspended suspended sediment load and
concentration
Fluidmudlayer thickness analysis was based on
thefollowing simulated periods: between 15/03/2007
and15/04/2007,01/05/2007and01/06/2007,28/06/2007
and 20/10/2007 and 20/11/2007. The results are
expressedinFigure11.
Before 30/03/2007 (Figure 11 (a)), there were low
suspended sediment loads and, consequently, low
sediment concentrations at the surface and
bottom.
Instead, in the period close to 15/05/2007 (Figure 11
(b)), simulation results indicate an increase of
sediment concentration near the bed, according to
suspended sediment load variations for the same
period.
In July 2007 (Figure 11 (c)), immediately before
12/07/2007, the model results indicate a suspended
sediment load and,
consequently, a sediment
concentrationpeak,mainlynearbedlayers.
In November 2007 (Figure 11(d)), the highest
Itajaí‐açu river discharges were measured, causing
peaksofsuspendedsedimentloadand,consequently,
high suspended sediment concentrations at surface
andbedlayers.
3.5 Discussion
Comparative surfaces conceived from bathymetric
survey data indicated that the
field data
measurementson 15/05/2007and 05/11/2007showed
a thicker fluid mud layer than others surveys, with
thickness up to 2.5 meters in some areas within the
turningbasinofthe ItajaíPortComplex. Instead, on
30/03/2007and12/07/2007,fluidmudlayerthickness
did not present thickness higher than 0.5
meters in
mostoftheinterestarea.
From model results, it was possible to identify
suspendedsedimentloadasthemainenvironmental
conditioner to the concentration of suspended
sedimentintheinterestarea,bothatthesurfaceand
bottomlayers.Suspendedsedimentloadisafunction
of river discharges and suspended
sediment
concomitantly,soanincreaseinoneofthesevariables
does not necessarily entail an increase in suspended
sedimentload,ifthereisadecreaseintheotherone.
However, it is possible that high flow speed may
causebedmaterialremobilization,raisingsuspended
sedimentconcentrationsindependentlyofsuspended
sediment
loadcontributiontotheinterestarea.
Considering a bathymetric survey conducted on
30/03/2007, in which fluid mud layer thickness did
not reach 0.5 meter, low suspended sediment load
valueswereobserved,justifyinglowfluidmudlayer
thickness. Yet, simulation results for a period
immediately before 15/05/2007 indicated higher
suspended sediment concentrations
near bottom
layers, justifying an increase on fluid mud layer
thickness.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
‐0.0025
‐0.00125
0
0.00125
0.0025
0.00375
0.005
0.00625
0.0075
24/03/2007 26/03/2007 28/ 03/2007 30/03/2007 01/04/2007 03/04/2007 05/04/2007 07/04/2007
Concentration(kg/m³)
Suspendedsedimentload(m³/s)
Suspendedsedimentloadandconcentration‐ March/2007
SuspendedSedimentLoad Averageconcentration‐Bottom Averageconcentration‐Surface
a
0
0.05
0.1
0.15
0.2
0.25
‐0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
08/05/2007 09/05/2007 10/05/2007 11/05/2007 12/05/2007 13/05/2007 14/05/2007 15/05/2007 16/05/2007
Concentration(kg/m³)
Suspendedsedimentload(m³/s)
Suspendedsedimentloadandconcentration‐ May/2007
SuspendedSedimentLoad Averageconcen t ration‐ B ott om A ver ag e concentration ‐S urfa ce
b
0
1
2
3
4
5
6
‐0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
03/07/2007 05/07/2007 07/07/2007 09/07/2007 11/07/2007 13/07/2007 15/07/2007 17/07/2007 19/07/2007 21/07/2007
Concentration(kg/m³)
Suspendedsedimentload(m³/s)
Suspendedsedimentloadandconcentration‐ July/2007
SuspendedSedimentLoad Averageconcen tration ‐ B ottom A ver ag econc ent ra tion‐ S urface
0
1
2
3
4
5
6
7
8
9
‐0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
31/10/2007 01/11/2007 02/11/2007 03/11/2007 04/11/2007 05/11/2007 06/11/2 00 7
Concentration (kg/m³)
Suspendedsedimentload(m³/s)
Suspendedsedimentloadandconcentration‐ November/2007
SuspendedSedimentLoad Averag e conc entra ti on ‐B ott om Averag ec onc ent ra tio n‐S urfa ce
c
d
Figure11.Suspendedsuspendedsedimentloadandconcentration‐(a)March2007(b)May2007(c)July2007(d)November
2007
451
In July 2007, model results indicated peaks of
suspended sediment load and, consequently, high
suspended sediment concentrations near the bed in
the period just before the 12/07/2007 bathymetric
survey.Thisresultisnotconsistentwithfielddata,in
which the fluid mud layer observed did not exceed
0.5meterin
mostofinterestarea.However,between
May and June 2007, an 815,000 m³ sediment
contribution was estimated, representing 60% of all
2007contribution.Thus,itispossiblethatasignificant
part of all 2007 dredging estimations (2,000,000 m³)
wasperformedinthisperiod.Asthisdredgingisnot
representedin
themodel,itmaybethecauseofthis
incongruence.
Furthermore, it is significant to emphasize that
dredging procedures are also limitations for other
periods analysis. The dredging at the Itajaí Port
Complex is performed through water injection,
aiming at the remobilization of bed material, so it
cannot be represented simply
as bed material
removal, once dredging procedures in this case can
alsoincreasesuspendedsedimentconcentrationnear
thebed.
The model presented hereby, besides yielding
resultsconsistentwithfielddata,wasconceivedand
calibrated based mostly on bibliographic references
and global models. For a more comprehensive
analysis, further data would
be necessary, such as
current speeds and water level time‐series and
suspended sediment measurements within the
interest area. Moreover, it is important to monitor
occasionalmeteorologicaleffects,suchaswaterlevel
increases, which can change flow pattern and
influencesedimenttransport.Plus,fluidmudspecific
densityvariationsshouldbeanalyzed,
inadditionto
rheologicalpropertiesmeasurements.
4 CONCLUSIONS
Considering a scenario in which ship drafts tend to
increaseinordertomeetthedemandsforexportsof
Brazilianproducts,fluidmudnavigationrepresentsa
profitable possibility. Due to low efficiency of the
dredging procedures in muddy bottoms, these
procedures can
be significantly expensive without
bringing the expected results in enhancing nautical
spacedepths.
TheapplicationoftheconceptofNauticalBottom
depends, also, mandatorily, on an approval by the
maritimeauthority,sothatitcouldbepossiblethata
homologated maximum ships draft will come to
consider fluid mud layers, evidently
always
prioritizingnavigationsafety.
FluidmudlayersattheturningbasinoftheItajaí
Port Complex presented high variability along 2007,
with thickness measurements varying between 0.5
and 2.5 meters according to bathymetric double
frequency surveys. Previous results allow for the
determination of the most influential hydrodynamic
and sedimentological processes
upon fluid mud
thickness variation at the turning basin of the Itajaí
Port Complex. Modeled results showed that this
thickness varies according to suspended sediment
loadvariations,whicharefunctionofriverdischarges
and suspended sediment. As the Itajaí‐açu river
dischargespresenthighvariability,withnoseasonal
patterns, it is
not possible to establish fluid mud
thicknesspredictionssuchasamonthlyestimate.
An aspect that must be highlighted concerns
dredgingactivities.Asthereisnoinformationabouta
dredging schedule over the analyzed period, these
procedures, hence, can cause undetectable effects.
Furtheranalysisshouldevaluatetheconsequencesof
dredging
procedures over fluid mud layers, such as
thereductionoffluidmudlayersandbedfluidization
duetowaterinjection.
Also, model results were based basically on
bibliographic references and global models’ data. In
this case, it must be emphasized that further data
should be collected in order to check and,
mainly,
improve hydrodynamic and sediment transport
modelaccuracy.
Furthermore, it is important to highlight that, in
addition to verifying the causes of formation of and
variations in fluid mud layers, further work is
necessary in order to apply the Nautical Bottom
concept. An interdisciplinary study should be
developed, covering fast‐
time and real‐time
maneuveringsimulationsandphysicalscaledmodels,
to verify the effects of local fluid mud layers upon
vessels, which have to be coupled to numerical
maneuveringmodelsinordertoobtainthedesirable
accuracy
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