water
ArticleModeling of Sediment Transportation in Ichkeul Lakefor the Estimation of the Influence of the Constructions of theReservoirs in the Upper Streams
Mitsuteru Irie 1, * , Hirotoshi Kotegawa 2 , Atsushi Kawachi 3 , Hajel Ouni 4 and Jamila Tarhouni 4
1
2
3
4

*

Citation: Irie, M.; Kotegawa, H.;
Kawachi, A.; Ouni, H.; Tarhouni, J.
Modeling of Sediment Transportationin Ichkeul Lake for the Estimation of
the Influence of the Constructions of
the Reservoirs in the Upper Streams.
Water 2022, 14, 1984. https://doi.org/10.3390/w14131984
Academic Editor: Ian Prosser

Faculty of Engineering, University of Miyazaki, Miyazaki 889-2192, Japan
Maeda Construction Co., Ltd., Tokyo 102-8151, Japan; kotegawa.h@jcity.maeda.co.jp
Token C.E.E. Consultant, Tokyo 170-0004, Japan; kawachi-a@tokencon.co.jp
Institut National Agronomique de Tunisie, Université de Carthage, Tunis 1082, Tunisia;
ouni_hajer@hotmail.fr (H.O.); elmaainat@yahoo.fr (J.T.)
Correspondence: irie.mitsuteru.p2@cc.miyazaki-u.ac.jp; Tel.: +81-2958-7341

Abstract: Rich ecosystems such as estuaries and brackish lakes are vulnerable to the effects of humanactivities and are prone to environmental changes. In particular, the salt environment, which is the
backbone of the environment, might be affected not only by direct modifications such as dredging but
also in ways that were not initially envisioned. Ichkeul Lake, located in the northern part of Tunisia,
is a shallow brackish lake registered as a UNESCO World Natural Heritage Site. The constructionof reservoirs upstream of the inflowing river in the 1980s reduced the amount of freshwater inflow.
That only had been thought to be the cause of the increase in salinity in Ishkeul Lake. On the other
hand, the sedimentation in the reservoirs upstream was remarkable, and the supply of sedimentfrom the reservoirs upstream to the Ichkeul Lake was stopped. Changes in sediment outflow may
have reduced lakebed altitude and enhanced seawater intrusion. However, the environmental
protection measures for the lake so far have focused only on improving the water budget and havenot been quantitatively evaluated for sediment transportation. In this study, we first estimated thewater budget of the lake. Then the re-suspension by wind disturbance in the lake was estimatedfrom the correlation with the wind speed based on laboratory experiments and field measurements.
The outflow of the sediment estimated with these two models was compared with the sedimentvolume trapped in the upstream reservoirs that would have flowed into the lake if there had been
no construction of the dams. Based on this, we evaluated whether the lake is currently erosive or
cumulative. As a result, the estimated annual outflow of sediment to the sea was 4300 tons/year. It
was estimated that the construction of the reservoirs upstream changed the trend of lakebed heightfrom accumulation to erosion.

Received: 4 April 2022
Accepted: 16 June 2022

Keywords: sediment transportation; resuspension; brackish lake; water budget; SWAT

Published: 21 June 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims inpublished maps and institutional affil-

1. Introduction

iations.

In brackish lakes and estuaries, where freshwater and seawater are mixed, the fluctuation of salinity supports the precious habitat of endemic species migrating from both sea
and freshwater areas. Rich ecosystems established under such geographical and hydrological conditions are susceptible to the influence of human activities, and international
conservation actions such as the Ramsar Convention are required. Typical examples are
dredging for navigation or flood control which have environmental impacts due to thechanges in salinity conditions. Miller [1] evaluated the salinity response to dredging under
different forcing regimes for a 75-km segment of the flood-prone Vermilion River locatedin coastal Louisiana, USA. Yuan & Zhu [2] estimated the influences of channel deepening
and widening on the tidal and nontidal circulations of Tampa Bay, based on the numerical
three-dimensional ocean model. They found that the tidal range increased, and the tidal

Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms andconditions of the Creative Commons
Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Water 2022, 14, 1984. https://doi.org/10.3390/w14131984

https://www.mdpi.com/journal/water

Water 2022, 14, 1984

2 of 23

phase decreased from the mouth to the head of the bay after deepening and widening of
the channel. van Dijk et al. [3] showed how dredging changes the natural developmentof estuaries through a combination of experiments in the laboratory and a numerical simulation. They quantified the effect of the increase of shipping draft and sea-level rise on
estuary morphodynamics and habitat suitability. Dias et al. [4] clarified the impact of thegeneral deepening of the lagoon, such as the increase of tidal currents and salt intrusion
through field observations and numerical simulations.
In addition to the environmental impacts of such direct morphological changes, there
are some cases in which the change of the sediment supply through the erosion process
upstream governs the river morphology and shoreline landscape [5]. Sediment supply todownstream rivers worldwide has been dramatically reduced due to dams, especially inthe more recent decades. The rapid flow from dams flashes fine material on the riverbeds
and deepens the channels downstream. Kondolf et al. [6] argued that hydropower dams
trap all bedload and a huge amount of suspended load, releasing sediment-starved flow
downstream. The closure of Aswan High Dam in the Nile River has trapped almost allof the sediment from reaching the Nile River delta [7]. Manwan Dam on the MekongRiver has trapped about 50% of the sediment budget of the river [8]. The development ofwater resources in the upper catchment needs to be considered as a factor of environmental
impacts on the estuary zone.
Ichkeul Lake, located in the northern part of Tunisia, is a shallow brackish lake
registered as a UNESCO World Natural Heritage Site (Figure 1). After the construction of
the dams upstream: Joumine in 1983, Ghezala in 1984, and Sejnane in 1994, an important
fraction of the flow was diverted towards agriculture and domestic uses. Due to thedecrease of the freshwater inflow in rainy winter from the upper stream, the average waterlevel of the lake was lowered and the duration and volume of reverse flow in the dry seasonfrom the sea became longer and larger. The increase in the salinity of the lake affected thedominant aquatic plants and destroyed the habitat of migratory birds. The park was listedon the World Heritage in Danger List from 1996 to 2006.
On the other hand, the sedimentations in the upstream reservoirs are very severe.
Irie et al. [9] estimated the total sedimentation volume in the two large reservoirs upstream
based on bathymetric surveys. The annual average accumulation volume of the sedimentin total was 570,000 tons/year. In addition, due to the structures of the dam bodies andthe grain size characteristics of the solid matter, bottom density currents occur in thereservoirs. During that period, clear water overflows from the spillway of a dam to the lakein contrast to the runoff which has a concentration higher than 1000 ppm into the reservoir.
A large part of the solid matter transported from the upper catchment is trapped in thereservoirs [10]. On the other hand, in winter, the west wind lifts the bed material and theforward flow from the lake to the sea continues. As a result, it is supposed that the height of
the lakebed decreases due to the imbalance of sediment, and parallelly, the lower lake waterlevel enhances seawater intrusion. It is obvious that the decrease in freshwater inflow dueto the construction of the reservoirs was a major factor in the salinity environment of thelake, but such changes in the budget of sediment transportation are also related to changes
in the salinity environment. Since the focus of environmental conservation activities on thelake has been only to improve the water budget so far, the sediment budget has not been
sufficiently evaluated quantitatively.
This study tried to evaluate the sediment outflow based on the calculation of thewater budget of the lake and modeling the resuspension process from the observed
wind data. The Soil & Water Assessment Tool (SWAT) model was applied to the upper
catchment for the estimation of the water inflow to the lake. The outflow in winter fromthe lake to the sea was estimated using the hydraulic calculation with the gradient andwidth of the connecting channel. We assumed that resuspension occurs uniformly in ahorizontal and vertical direction in the lake and that the concentration of the outflowing
water was the same as that in the lake. The influence of the construction of the reservoirs
on the budget of the sediment was discussed using a comparison of the budgets of theWater 2022, 14, x

3 of 25

Water 2022, 14, 1984

3 of 23budget of the sediment was discussed using a comparison of the budgets of the sediment
between the sediment outflow from the lake and the sedimentation in the reservoirs upsediment between the sediment outflow from the lake and the sedimentation in thestream.
reservoirs upstream.

Figure1. Catchments of Ichkeul Lake.
Figure 1. Catchments of Ichkeul Lake.

2. Materials
andMethods
Methods
2. Materials
and2.1. Study Site

2.1. Study Site

Ichkeul Lake is a very shallow brackish lake with an average depth of about 2 m
Ichkeulis a very
shallowbrackishlakerivers
with flow
an averageof about
2 m and2 (Figureandan areaLakeof about
88 km2). Several
into thedepth
lake, andthe total
22(Figureend2). ofSeveralriversflow into
the lake,andtotalcatchment
an catchment
area of about
area88at km
the eastern
the Atlas
Mountains
is about
2132
kmthe
. The
averagearea
at therainfall
easternend of600
theAtlas
is stopaboutfor2132
km2. The
averageannualannualis aboutmm.
It isMountains
an importantmigratory
birds
travelingrainfallabout Europe
600 mm.
It isHolland.
an important
stop for migratory
birds travelingfrom Central
from isCentralandFour migratory
species: greylag
goose, widgeon,
filigulepochard,andFourcoot live
and nestspecies:
on Ichkeul
Lake’swealth.
Hence, IchkeulanEuropeandHolland.
migratorygreylaggoose,
widgeon,filiguleispochard,internationally
important
site
for
these
species.
The
birds’
stopoverprovideshabitatandand coot live and nest on Ichkeul Lake’s wealth. Hence, Ichkeul is an internationally imfood thanks
the twomajorTheaquatic
plantscharacterizing
Potamogeton
portantsite fortothese
species.
birds’
stopoverprovidesIchkeul
habitatLake:and food
thanks to thepectinatus and Ruppia cirrhosa. The Potamogeton were distributed in lower salinity
two major aquatic plants characterizing Ichkeul Lake: Potamogeton pectinatus and Rupconditions (almost 7–9 PSU), while the Ruppia were in high-salinity conditions and exist
piaon
cirrhosa.
TheandPotamogeton
were [suchdistributed
lower salinity(almostthe bottom
in surface water
as 9–11inpracticalsalinityconditions
units (PSU)].
The 7–9
PSU),
while
the Ruppia
werein high-salinityand existthan
on theand inRuppiadistribution
area
is spreading
in a moreconditions
southerly direction
thatbottom
found insurface
water
[such
as
9–11
practical
salinityunits(PSU)].
The
Ruppiadistribution
area isprevious work [11]. In other words, a slight change in salinity conditions can significantly
spreadingin vegetationa more southerly
direction than that found in previous work [11]. In otherchange the
distribution.

words, a slight change in salinity conditions can significantly change the vegetation distribution.
The climate of the site is the typical Mediterranean climate system. In the summer
dry season, the lake water level drops due to little freshwater inflows, while the seawaterflows into Lake Ichkeul from Bizerte Lagoon through the Tindja Canal (red line in Figure1). Bizerte region, where Ichkeul Lake is located, is known for its strong winds, ranging

Water 2022, 14, 1984

reservoirs. Finally, the budget of solid matter was lost. The level of the lakebed decreased
as a result of the excessive outflow. It is considered that the lake water level also dropped
parallelly, causing the lake water level to be lower than sea-level for a longer period.
The results of a sedimentation survey conducted in 2010 at the reservoirs upstreamof the lake [17], show that 17.8 million m3 of sediment was deposited in the reservoir. If
4 of 23
the accumulated sediment was deposited on the entire bed of the lake (an area of about
88 km2), the thickness would be about 20 cm.

Figure 2. Bathymetry of Ichkeul Lake.
Figure 2. Bathymetry of Ichkeul Lake.

The climate of the site is the typical Mediterranean climate system. In the summer
dry season, the lake water level drops due to little freshwater inflows, while the seawaterflows into Lake Ichkeul from Bizerte Lagoon through the Tindja Canal (red line in Figure 1).
Bizerte region, where Ichkeul Lake is located, is known for its strong winds, ranging from
5 to 9 m/s, but capable of reaching 15 m/s [12]. The most frequent winds blow from theW–NW. During spring and summer, wind speeds are relatively constant, while they arehighly variable in autumn and winter. The strong wind in winter induces high turbidity
in the lake water. Hajer et al. identified the spatial distribution of a water turbidity index,
an indicator of the TSM with multi-date MODIS images. The relationship between thewind conditions and the resuspension from the lakebed was clarified [13]. The criticalwind speed inducing resuspension in the lake was 2.8 m/sec. Such strong wind blows
from the west in rainy winter when the lake water level is higher than the seawater level.
The solid matter resuspended by the wind is outflowing with the forward flow in theconnected channel.
Bizerte Lagoon is so deep (ave. 7 m, Mmax. 12 m) [14] that it is unlikely to beresuspended by the wind. In addition, the strong wind does not blow in the summer when
the reverse flow to the lake occurs. Therefore, the transportation of solid matter in summer
is less in Ichkeul lake. In the winter rainy season, the flow in Tinja channel is forwardfrom the lake to the lagoon, due to the higher water level of the lake with the freshwatersupply from the upper catchment area. At the same time, westerlies blow strongly in
winter, causing resuspension of bottom material [15]. Therefore, the solid matter outflow
from the lake to the lagoon occurs in winter [16], as illustrated in Figure 3.
Before the reservoirs were constructed, the budget of the solid matter in the lake wasin equilibrium with the supply transported by the freshwater inflows from upstream andthe forward outflow through the channel in winter. However, after the construction of
the reservoirs, the solid matter inflows were trapped by the reservoirs as sediments in thereservoirs. Finally, the budget of solid matter was lost. The level of the lakebed decreased
as a result of the excessive outflow. It is considered that the lake water level also dropped
parallelly, causing the lake water level to be lower than sea-level for a longer period.
The results of a sedimentation survey conducted in 2010 at the reservoirs upstreamof the lake [17], show that 17.8 million m3 of sediment was deposited in the reservoir. If
the accumulated sediment was deposited on the entire bed of the lake (an area of about
88 km2 ), the thickness would be about 20 cm.

Water 2022, 14, x
Water 2022, 14, 1984

5 of 25

5 of 23

Figure3.3.Schematic
Schematic images
intrusionandandtransportationof sedimentin Ichkeul
Lake andFigureimagesofofseawater
seawater
intrusiontransportationof sedimentin Ichkeul
Laketypicalimagesof theofwater
surfacein summer
and winter.
Dry season
in summer(Lake< Lagoon:andtypicalimagesthe water
surfacein summerand(a)
winter.
(a) Dryseason insummer(Lake <
Lagoon:seawater
intrusion).
(b) season
Rainy season
in winter> Lagoon:resuspension
bed mateseawater
intrusion).
(b) Rainy
in winter(Lake >(Lake
Lagoon:resuspensionof bedofmaterial)
rial)
without
dams.
(c) Rainyseasonin winterwith dams(Sediment
without
dams.
(c) Rainyseasonin winterwith dams(Sediment
supplysupply= 0). = 0).

2.2.Estimation
Estimationofofthe
the Water
Water Budget
Budget of
2.2.
of thetheLake
Lake
The lake water level has been observed for a long time by the local government in
The lake water level has been observed for a long time by the local government in
Ichkeul Lake, but the inflow and outflow have not been continuously observed. The water
Ichkeul Lake, but the inflow and outflow have not been continuously observed. The water
budget in the lake is estimated based on the following formula:budget in the lake is estimated based on the following formula:
Qin𝑄− Q=±−out
𝑄 − evapo.
− 𝑒𝑣𝑎𝑝𝑜.
=∆V±∆𝑉(1) (1)

where 𝑄
Qin isinflowfromthe catchments,
Qout is𝑄the outflow
from thefrom
lake tothe
Bizertewhere
isthethetotal
total
inflowfromthe catchments,
is the outflow
lake toLagoon,evapo.
istheevaporation
from
the
lake
water
surface
and
∆V
is
the
fluctuation
Bizerte Lagoon, 𝑒𝑣𝑎𝑝𝑜. is the evaporation from the lake water surface and ∆𝑉 is the influcthe volume
the lakeof
water.
tuationin theofvolume
the lake water.
Forthetheestimation
estimation ofof thethe inflows
inflows from
Water
Assessment
For
fromthethecatchments,
catchments,thetheSoil
Soilandand
Water
Assessment
Tool (SWAT) model [18,19] was applied. The input data required for the SWAT model are
Tool (SWAT) model [18,19] was applied. The input data required for the SWAT model aremeteorological data (precipitation, temperature, relative humidity, wind speed and solar
meteorological data (precipitation, temperature, relative humidity, wind speed and solar
radiation) in the basin and the spatial information (elevation, land use, soil distribution)
radiation) in the basin and the spatial information (elevation, land use, soil distribution)that compose the basin. The daily meteorological data (air temperature, dew point, air
thatcomposethe basin.
daily
meteorologicaldata
dew
point,1)airpressure,visibility,
wind The
speed,
precipitation)observed
at (air
Sidi temperature,
Ahmed Air Base
(Figurepressure,visibility,wind
speed,
precipitation)observed
at
Sidi
Ahmed
Air
Base
were downloaded from the National Center for Environmental Information [20]. (FigureThe1)catchments
were downloaded
National
Centerfor Environmental
Information[20]. The
shown in from
Figurethe
1 weredelineatedbased
on ALOS-DSM [21].
Figure 4 shows
catchments
shown
in Figure
1 weredelineated
ALOS-DSM
Figureshows
the land use
distribution
mapfrom thedatabasebasedof theon
EuropeanSpace[21].
Agency[22]4 andtheuse distribution
the databasetheandEuropeanSpaceOrganization
Agency [22]ofand
thelandsoil distribution
map map
from fromthe databaseof the of
Food
Agriculture
thedistribution
map from the database of the Food and Agriculture Organization of
thesoil
UnitedNations [23].
the United Nations [23].

Water2022,
2022,14,
14,1984x
Water

66 of 23
25

FigureFigure 4.
4. (a)(a) LandLand use
use distribution
distribution andand (b)(b) Soil
Soil map
map ofof thethe catchments.
catchments.

Parameter
CNII.mgt
ALPHA_BF.gw
GW_DELAY.gw
GWQMN.gw
CH_N1.rte
CH_K1.rte
CH_N2.rte
CH_K2.rte
SLSUBBSN.hru
ESCO.hru
REVAPMN.gw
RCHRG_DP.gw
GW_REVAP.gw
Sol_AWC.sol
SOL_K.sol
EPCO.hru

The
The inflows
inflows toto eacheach reservoir,
reservoir, estimatedestimated fromfrom thethe budget
budget with
with thethe recorded
recorded intake,intake,spillway,(volumefluctuation)
were
used
for forcalibrationof thespillway,evaporation
evaporationand
andwaterwaterlevel
level(volumefluctuation)
were
used
calibrationofrunoffmodel
parameters
with
SWAT-CUP[24],
thesoftwareoptimizing
theparameters
the runoff model parameters with SWAT-CUP [24], the software optimizing the parameusing
comparison
with anobserveddischarge.
Accordingto the recordsof the management
ters using
comparison
withan observed
discharge.
Accordingto the recordsof the manworksof
these
reservoirs,
almostalloftheannualinflows
were
exploited(intake),
exceptagement works of these reservoirs, almost all of the annual inflows were
exploited(inwhen
the
water
level
reachesthesurcharge
water
level
and
there
is
an
overflowing
throughtake), except when the water level reaches the surcharge water level and there is an overthe
spillway.
In addition,
the inflows
to Ichkeul
Laketoconsistof Lake
not only
theofdischarge
flowing
throughthe spillway.
In addition,
the inflows
Ichkeulconsistnot only
fromthe reservoirs.
There
are someThereblanchesthat donot flowthat
throughthereservoirs.
the discharge
from thereservoirs.
are some
blanches
do notflow
throughThetheapplicabilityof thecalibrated parameters
to theseparametersresidual catchments
should becatchments
evaluated.
reservoirs. The
applicabilityof the calibrated
to these residualSo,
the reliabilityof thewasof
confirmed
as follows:
shouldbe evaluated.
So,parameters
the reliability
the parameters
was confirmed as follows:First, the parameters were calibrated with the inflow to Joumine reservoir. Then theFirst, the parameters were calibrated with the inflow to Joumine reservoir. Then theparameters were applied to the catchment of Sejnane reservoir and the calculated dischargeparameters were applied to the catchment of Sejnane reservoir and the calculated disshowed good agreement with the inflow to Sejnane reservoir. Table 1 shows the ranges ofcharge showed good agreement with the inflow to Sejnane reservoir. Table 1 shows theparameters used for the calibration with SWAT-CUP and the calibrated values. The range
ranges of parameters used for the calibration with SWAT-CUP and the calibrated values.
of parameters for the calibration refers to Mtibaa et al. [25] who studied the upstream area
The range of parameters for the calibration refers to Mtibaa et al. [25] who studied theof the Joumine reservoir.
upstream area of the Joumine reservoir.
Then those parameters were also applied to the residual catchments. The lake water
Table 1. Value ranges and calibrated values identified by SWAT-CUP for the Joumine reservoir catchment.
level was calculated with all these simulated discharges from each catchment and the outflow from Tinja Channel
calculatedwaterlevel Value
did not
Definitionmentioned later. However, the
Value
Range
Calibrated
show
good
agreementwiththeobserved
one.
The
cause
of
the
error
of
the
inflow
Runoff curve number for moisture condition II±1−0.405 is that
Baseflow
recession constant
0–1 to the vast residual
0.968
the parameters
determinedin the Joumine basin were appliedbasin
Groundwater delay
0–50
0.833
where the topography and geology are different from the catchment areas of both reserThreshold water level in shallow aquifer for baseflow
0–500
82.5
voirs.
There
is no recordof discharge
calibrating the model
the residual
Manning’s
roughnesscoefficientfor tributary forchannel
0–0.3 parameters of0.142
Effective
hydraulic conductivity
in tributarychannelwere
alluvium(mm/h)
0–120
100.5 of ancatchment.
Instead, theparameters
determinedbased
on the runoff analysis
Manning’s roughness coefficient for main channel
0–0.3
0.221
other
catchment which is similar in topography and geology
to the residual19.78
catchment.
Effective hydraulic conductivity in main channel alluvium (mm/h)
0–120
The catchment
area
of
Masri
dam
is
in
the
foothills
of
the
Atlas
Mountains
with
Average slope length (m/m)±0.2−0.068Calcisol
Soilevaporationcompensation
factor
0–1
the same as the residual catchment, but it is not in the Ichkeul basin. The runoff0.168
parameters
Threshold water level in shallow aquifer for “revap”
0–100
60.83
were identified
based
on
the
time
seriesofthedischarge
inthemanagement
recordAquifer percolation coefficient
0–1
0.872 of thisdam, andGroundwater
the same parameters
were given to the residual basin“revap” coefficient
0–1 of Ichkeul. 0.685
available
water content
1
0.435
Data onSoil
panevaporation
could be obtained only from ±2008
to 2010. Since
the fluctuSaturated hydraulic conductivity (mm/h):±10.865
ations ofthevaluesbetweenyears
aresmall,
averagevalues
of
the
3
years
on
each date
Plan evaporation compensation factor
0–1
0.402
were used for the other years.
Then those parameters were also applied to the residual catchments. The lake waterlevel was calculated with all these simulated discharges from each catchment and theoutflow from Tinja Channel mentioned later. However, the calculated water level did
not show good agreement with the observed one. The cause of the error of the inflow isthat the parameters determined in the Joumine basin were applied to the vast residual
basin where the topography and geology are different from the catchment areas of bothreservoirs. There is no record of discharge for calibrating the model parameters of theWater 2022, 14, 1984

Water 2022, 14, x

7 of 23

residual catchment. Instead, the parameters were determined based on the runoff analysisof another catchment which is similar in topography and geology to the residual catchment.
The catchment area of Masri dam is in the foothills of the Atlas Mountains with Calcisol
the same as the residual catchment, but it is not in the Ichkeul basin. The runoff parameters
were identified based on the time series of the discharge in the management record of thisdam, and the same parameters were given to the residual basin of Ichkeul.
Data on pan evaporation could be obtained only from 2008 to 2010. Since the fluctua8 of 25
tions of the values between years are small, average values of the 3 years on each date wereused for the other years.
The outflow from the lake through Tinja channel was calculated using the Manning equation:
the low water level period (Figure 7). High coefficient of determinations of 0.83 and 0.85
1respectively, were found. When the lake water
falls below the average tide level of
1 2 levelv = R3 I 2(2)0.53 m in Bizerte Lagoon, the tide stop weirn might be closed for the regurgitation of seawater intrusion. As seen in the later figure showing the fluctuation of observed 1/3
flow rate,
where
v is
thewasflow
velocity(m/s),
n is theManningroughness
3/s when
the
flow
rate
0m
the waterlevel
was near0.53 m. coefficient (s/m ), R is
the hydraulic radius (m) and I is the gradient. The channel length and width required for
Regarding the verification of this calculated outflow, there was no record observed
this calculation are 4700 m and 33.7 m, respectively. Hydraulic radius was calculated basedin the field. The validity of the results was evaluated by the reproducibility of the lakeon the depth survey in the cross section shown in Figure 5. The roughness coefficient waswater level obtained at the end of this water budget estimation.
given as 0.024.

Figurelevel observatories
observatorieson
onTinja
Tinjachannel.
channel.
Figure 5.
5. Location
Location ofof thethe waterwater level

There is a tide stop weir at the entrance from the lake to the Tindja canal. The weiris closed when the lake water level is lower than the water level of the lagoon. However,besides the weir, there is the bypass on the right bank, allowing a little reverse flow insummer. Just after the construction of the weir, without the bypass, the tide was stopped
completely in summer, but the evaporation was extreme and the salinity around the weir
became higher than the seawater. Then the bypass was opened for dilution. So that, evenwhen the weir is closed, there is a little reverse flow in summer.
The water levels upstream and downstream of the weir were observed only in 2015.
The flow rate was calculated using the gradient from the water level on the downstreamside of the weir to the average sea level of Bizerte lagoon. Then, the relationship between thewater level of the upstream side of the weir (lake water level) and the flow rate estimatedwith the hydraulic gradient was found as shown in Figure 6. The relationship is for the termof the forward flow when the lake water level is high. In the same way, we also obtained a
relationship with the lake water level for the reverse flow that occurs during the low waterlevel period (Figure 7). High coefficient of determinations of 0.83 and 0.85 respectively,
Figure 6. The relationship between the lake water level and the forward flow calculated from thewerefound. When the lake water level falls below the average tide level of 0.53 m in Bizerte
gradient between the lower WL observatory and seawater level.
Lagoon, the tide stop weir might be closed for the regurgitation of seawater intrusion. As
seen in the later figure showing the fluctuation of observed flow rate, the flow rate was
0 m3 /s when the water level was near 0.53 m.

Water 2022, 14, 1984

Figure 5. Location of the water level observatories on Tinja channel.
Figure 5. Location of the water level observatories on Tinja channel.

8 of 23

Figureflow
calculated
fromthetheFigure 6.
6. TheTherelationshiprelationshipbetween
betweenthe
thelakelakewaterwaterlevel
levelandandthetheforward
forwardflow
calculated
fromgradient
the lowerbetween
WL observatory
and seawaterlevel.
Figure6. between
The relationshipthe lake waterlevel andthe forward flow calculated from thegradient between the lower WL observatory and seawater level.
gradient between the lower WL observatory and seawater level.

Water 2022, 14, x

9 of 25

Figure 7. The relationship between the lake water level and the reverse flow from the lagoon to thelake calculated from the gradient between the lower WL observatory and seawater level.

Figure 7. The relationship between the lake water level and the reverse flow from the lagoon to theRegardingthetheverificationof this calculated
outflow,
thereandwasseawater
no record
observed inlake calculated
fromgradient between
the lower WL
observatorylevel.

the field. The validity of the results was evaluated by the reproducibility of the lake waterlevelTheobtainedat theend of thiswaterbudgetestimation.
volumefluctuationof thelake
on theright side of Equation (1) was converted
Thefluctuation
volume fluctuationof thelevel
lakebasedon theonrightof Equation(1) wasthe
converted
into
into theof the water
thesiderelationshipbetweenwater level
thefluctuation
of
the
water
level
based
on
the
relationshipbetween
the
water
level
and
and the volume of water of the lake (Figure 8) obtained from the bathymetry map shown
theFigurevolumeof watertheof thelake(Figurebathymetry
map showninin
3. Finally,
daily
water
level8)ofobtained
the lakefrom
was thecalculated
and evaluatedwith
Figure3.
Finally,
the
daily
water
level
of
the
lake
was
calculated
andevaluatedwiththethe observed data from 2002 to 2007.
observed data from 2002 to 2007.

Figure 8.
8. TheThe relationshiprelationship between
between volume
volume andand waterwater level.
level.
Figure2.3. Modeling the Sediment Resuspension Driven by Wind
2.3.1. Related Studies on Resuspension
This study consists of three parts: runoff analysis from the upstream region, model-

Water 2022, 14, 1984

9 of 23

2.3. Modeling the Sediment Resuspension Driven by Wind
2.3.1. Related Studies on Resuspension
This study consists of three parts: runoff analysis from the upstream region, modelingof resuspension in the lake and the assessment of outflowing from the lake based on hydraulic estimation in Tinja canal. There are several approaches to the second part while themethods for the first and third parts are standard. Here, we will overview the conventional
approaches regarding resuspension modeling. Bed erosion due to resuspension also affects
the water flows that define the ecosystem and material transportation. So far, research has
been conducted on various lakes [26–28], estuaries [29] and relatively shallow waters along
the coast [30].
The driving force of resuspension is bed shear stress induced by the orbital velocity ofwaves, tidal current, storm surge and wind. In places where orbital velocity and current
exist, such as estuaries and coastal areas, the shear stresses from both are considered linearlyor nonlinearly. Previously, they were obtained as empirical formulas based on laboratory
experiments [31–33]. Soulsby and Clarke [34] proposed a theoretical but practical formulafor estimating total shear stress. On the other hand, shear stress in lakes is often estimatedonly by the orbital velocity because the current velocity is smaller in the lake than theorbital velocity [35]. First, the wave height was estimated from the wind stress, then it wasconverted to orbital based on the linear small-amplitude wave theory.
Wiberg and Sherwood [36] proposed a method to calculate the bed orbital velocity
from the power spectrum of the flow velocity, but there are few studies in which the orbital
velocity was observed. In the case of lakes, taking only wind waves into account, thebed shear stress was often estimated depending on whether the flow regime is laminaror turbulent [37]. Especially in an extremely shallow lake, the flow regime tends to be
turbulent when strong winds continue, due to the passage of low pressure, monsoons andwesterlies. However, few studies observed such typical events due to the difficulty of fieldobservation under severe conditions. Lodahl et al. [38] showed that the critical Reynolds
number was smaller when the oscillating flow and the unidirectional flow coexist in thepipeline than when only the oscillating flow exists. This fact suggests that the flow regime
and bed shear stress change depending on whether there is only oscillating flow or thecoexistence of oscillating and unidirectional flow.
The temporal fluctuation of the turbidity in a shallow lake was described with abox model that considers only the resuspension and the deposition of the fine sedimentparticles. The amount of sediment entrainment was expressed as a function of the bed shear
stress. However, the parameters in the function were defined empirically. Hofmann [39]applied the model of the entrainment in a channel proposed by Garcia and Parker [40] to
the lakebed resuspension in the shallow lake.
On the other hand, direct measurements of the velocity fluctuation in situ could befound. They were taken in a coastal shallow area using Acoustic Doppler Velocimetry(ADV) which measures three-dimensional instantaneous velocity with a high temporalfrequency [41]. Hofmann et al. [39] carried out field observations at the lake with ADV. The
results show a high contribution rate of orbital flow to the bed shear stress.
Sediment exchange and transportation between closed water bodies and river channels
are understood based on two-dimensional or three-dimensional flow observations, remotesensing and modeling in lakes. Hawley et al. [42] discussed the transport mechanismsof SS in Lake Michigan using numerical simulation. Matty et al. [43] investigated thetransportation of SS in Lake Houston. The intensity of the circulation in the lake wasperiodically high enough to transport coarse silt in suspension. Especially in shallow
lakes where sediment transportation affects the hydrological system and environment,
some researchers are paying attention to SS transport. Most of them have focused on
runoff-induced dynamic conditions. Gao et al. [44] evaluated the impact of climate change
and human activities on the sediment exchange process between Changjiang River andPoyang Lake. Zhang et al. [45] observed the fluctuation of the bed level of the lake due
to erosion based on satellite image analysis. Wang [46] combined field data, laboratory

Water 2022, 14, 1984

10 of 23

experiments and numerical simulations to try to understand the variation of SS in Poyang
Lake. However, there are few studies evaluating the volume of transported sediment froma shallow lake to a lower basin based on the modeling of resuspension of sediment andhydrological runoff.
In this study, we observe horizontal two-dimensional velocity with an electromagnetic
current meter that is cheaper than ADV. The vertical velocity was not observed but it
was sufficient for the estimation of the Reynolds number and the bed shear stress in theshallow lake. The correlation between wind speed and Reynolds number was defined
empirically using the observed data while that between Reynolds number and turbidity
was found by laboratory experiment. The sediment outflow from Ichkeul Lake throughthe connecting channel was evaluated using the water exchange in the budget and theestimated turbidity. In this study, all kinds of data for the whole term were not available, but
the field measurements, hydrological modeling and laboratory experiments complement
each other and a long-term evaluation was carried out.
2.3.2. Box Model
Luettich et al. [47] showed the application of a simple box model for the resuspensionof sediment driven by wind in a shallow lake. Assuming well mixing and negligible
horizontal advection, the temporal fluctuation of the averaged concentration of suspended
solids (hereinafter referred to as SS) in the column is expressed by the following equation:hdc= ws ( Es − c)dt(3)where, h is the water depth of the column, ws is the sedimentation speed of suspended
particles (m/s) and Es (kg/m3 ) is the resuspension rate. Assuming that the disturbancecaused by the wind is maintained for a certain period, the sedimentation and resuspension
would be in equilibrium. In that case, the left side of the above equation can be zero.
On the other hand, resuspension occurs only when the bottom shear stress exceeds
the critical tractive stress acts. That is expressed as the following formula:
E = ws Es = M (τ − τcr )n(4)where M and n are constants, τ is bottom shear stress and τcr is the critical bottom shear
stress at which resuspension starts. n is given as 1 in some previous studies [48,49].
On the other hand, the bottom shear stress τ is modeled as a resuspension by theoscillating flow, it is expressed by the following equation:
τw =1
ρw f w Ubw 22(5)

where, ρw (kg/m3 ) is the density of water, f w is friction coefficient and Ubw is the root meansquare of the flow velocity (m/s). The bottom shear stress characteristics vary dependingon the bottom roughness and flow conditions (turbulence/laminar flow) indicated with the
Reynolds number defined by the kinematic viscosity coefficient ν(m2 /s) and predominantperiod T (s) as follows:
U 2T
Rew = bw
(6)2πν
In case of laminar flow (Rew < 150,000) that occurs through all terms in this study, f w
in (5) can be given as 2Rew −0.5 [50]. Through Equations (3)–(6), the concentration of SS
in an equilibrium state in which a constant disturbance continues can be expressed as afunction of the Reynolds number. In this study, the relationship between the two will be
formulated by laboratory experiments in Section 2.3.3, and then we tried to explain the
results of field observations of flow velocities and turbidity, obtained in the center of thelake for a short period in the same manner, as shown in Section 2.3.4.

Water 2022, 14, 1984

11 of 23

2.3.3. Laboratory Experiments

Water 2022, 14, xLaboratory experiments were carried out for formulating the relationship between
the above mentioned Reynolds number and the concentration of SS using a vertical tankand stirring device as shown in Figure 9. The sediment sampled from Ichkeul Lake wasused. Four stirrers were placed over the vertical tank (25 × 25 cm with 1 m depth). The finsof stirrers were placed near the water surface. The sensor of the velocity meter (KENEK,
VMT2-200-04P) measuring horizontal 2D velocities was placed in the center at 40 cm depth
from the water surface, 50 cm above the sediment surface. The sensor of the turbidity12meter
of 25(KENEK, PM-501N) was also placed at the same depth but besides the center. Both thevelocity and turbidity were measured at a frequency of 10 Hz.

FigureFigure 9.
9. Experimental
Experimental setup
setup ofof sedimentsediment resuspension.
resuspension.

as the flow velocity amplitude and T as the predominant period of thebw (cm/s)
2.3.4.UField
Observation
fluctuating velocity were calculated from the continuous measured values under a steady
Flow velocity and turbidity at the center of the lake were observed continuously forequilibrium state with a constant rotation speed of the stirrer. The relationship between
one week in September 2015 and March 2016. A horizontal 2D electromagnetic current
turbidity and SS (mg/L) is calibrated in advance, and the turbidity measurement value ismeter (Infinity-EM, JFE Advantech Co., Ltd., Kobe, Japan) and a turbidity meter (Infinityconverted to SS.
CLW, JFE Advantech Co., Ltd.) were installed at a depth of 50 cm from the bottom of the
The experiments were conducted in summer and winter when the water temperatureslake, the same as the laboratory experiment mentioned above. A place without aquaticwere different, and the water temperature in summer was around 28 ◦ C, while the water
plants was selected
thearoundinstallation.
The
recording
10beginning
Hz for 30ofs
temperature
in winterforwas
10 ◦ C. In
addition,
the wastank performed
prepared atatthe(300
samples)at2
minintervals.
this study gave a uniform predominant period T that might depend on the size of the water
speedsobserved
at 1-hintervals
fromusingMarch
2015water
to March
2016
near thetank. Wind
Therefore,
theweresame
experimentwasconducted
other
tanks
of different
entranceoftheTindjacanal.
sizes, 40 × 40 cm and 1 m in height.

3. Results
Discussion
2.3.4.
Fieldand
Observation
3.1. Estimationof WaterFlow velocity
and Budget
turbidity at the center of the lake were observed continuously forone
in September
2015 and Area
March 2016. A horizontal 2D electromagnetic current
3.1.1.week
Inflowfrom the Catchment
meter (Infinity-EM, JFE Advantech Co., Ltd., Kobe, Japan) and a turbidity meter (InfinityThe calculated discharge from the catchment of Joumine reservoir, calibrated with
CLW, JFE Advantech Co., Ltd.) were installed at a depth of 50 cm from the bottom of the
SWAT-CUP has a good agreement with the observed discharge from September 2008 tolake, the same as the laboratory experiment mentioned above. A place without aquatic
September 2010 as shown in Figure 10. The discharge from the neighboring catchment,
plants was selected for the installation. The recording was performed at 10 Hz for 30 s
Sejnane reservoir, could be reproduced with the same parameter values as Joumine reser(300 samples) at 2 min intervals.
voir catchment, shown in Figure 11. Since the winter season is the rainy season and theWind speeds were observed at 1-h intervals from March 2015 to March 2016 near thesummer season is the dry season in this study site, the figures start from September ofentrance of the Tindja canal.
each year, the beginning of the rainy seasons. Both agreements were quantitatively evaluated with the coefficients of determination, RMSE and NSE in Table 2. Comparing theobserved and calculated values in Figures 8 and 9, the peak flow rate and the recession
phase could be reproduced well. The coefficient of determination of the Joumine basin for2009 is rather low, but 2009 was a dry year and the flow rate was small throughout theyear.

Water 2022, 14, 1984

12 of 23

3. Results and Discussion
3.1. Estimation of Water Budget
3.1.1. Inflow from the Catchment Area

Water
Water 2022,
2022, 14,
14, xxThe calculated discharge from the catchment of Joumine reservoir, calibrated with
SWAT-CUP has a good agreement with the observed discharge from September 2008 to
September 2010 as shown in Figure 10. The discharge from the neighboring catchment,
Sejnane reservoir, could be reproduced with the same parameter values as Joumine reservoir
catchment, shown in Figure 11. Since the winter season is the rainy season and the summer
season is the dry season in this study site, the figures start from September of each13of
13 year,of 25
25
the beginning of the rainy seasons. Both agreements were quantitatively evaluated withthe coefficients of determination, RMSE and NSE in Table 2. Comparing the observed andcalculated values in Figures 8 and 9, the peak flow rate and the recession phase could behilly area of the study site. Finally, the acceptable calculation results of the lake water level
reproduced well. The coefficient of determination of the Joumine basin for 2009 is rather
were obtained as shown in the later chapter.
low, but 2009 was a dry year and the flow rate was small throughout the year.

Figure10. Simulation
Joumine reservoir
reservoir catchment
catchment calibrated
calibrated with
with
Figure 10.
Simulation result
result ofof thethe discharge
discharge fromfrom Joumine
SWAT-CUP.
SWAT-CUP.

Figure 11. Simulation result of the discharge from Sejnane reservoir catchment with the parameters
calibrated
with Joumine
Joumine reservoir
reservoir catchment.
catchment.
calibrated with
Table 2.
2. Evaluation
Evaluation ofof thethe runoff
runoff simulations
simulations forfor thethe catchments
catchments ofof Joumine
Joumineand
andSejnane.
Sejnane.
Table

Catchment
Catchment
JoumineJoumineSejnaneSejnane

Years
Years
(Precipitation)(Precipitation)
2008
2008(836(836 mm)mm)
2009(757(757 mm)mm)2009
2008–20092008–2009
2008(836(836 mm)
mm)
2008
2009
(757
mm)
2009 (757 mm)
2008–20092008–2009

RR222

RMSE
RMSE

NSE
NSE

0.7
0.7
0.58
0.58
0.68
0.68

7.57
7.57
3.46
3.46
5.01
5.01

0.64
0.64
0.52
0.52
0.62

10.73
10.73
7.42
7.42
7.90

0.68
0.68
0.18
0.18
0.63
0.63
0.70
0.70
0.54
0.54
0.65
0.65

0.62

7.90

3.1.2. Fluctuation of Water Level and Volume
The change in the water in the lake was calculated from the inflow and outflow obtained using the above procedure. The evaporation from the lake surface was consideredWater 2022, 14, 1984

13 of 23

Based on these results, the mountainous catchments upstream of the two reservoirs
have similar morphology and hydrological characteristics, so both discharges could be
explained with the same parameters. On the other hand, the residual catchments without
the records of the discharges have different characteristics. As mentioned in Section 2.2,
the parameters calibrated for the hilly catchment with Calcisol soil were given to the lower
hilly area of the study site. Finally, the acceptable calculation results of the lake water level
were obtained as shown in the later chapter.
3.1.2. Fluctuation of Water Level and Volume
Water2022,
2022,14,
14,xx
Water

14 of
of 25
25
14
The change in the water in the lake was calculated from the inflow and outflow
obtained using the above procedure. The evaporation from the lake surface was considered
the same as the record of the pan evaporation at Joumine dam office. From the net water
volumechange inlake,
the Thewater
levelof the next
day was sequentiallycalculatedfor
lagoonoccurredoccurred
onthe
28January.
January.
Theerrorerror
betweenthecalculated
calculated
andobserved
observed
waterlevel
level
lagoonon
28
between
the
and
water
the
rainy
season2015 when
we 13
installed
water
level
gaugesin tendency
Tinja channel.
The
inthe
the
secondhalfinshown
inFigure
Figurereachedthe
more
than
10cm
cm
butthethesimilar.
insecond
half
shown
in
13 reached
more
than
10
but
tendency isissimilar.
timeseriesofthecalculated
outflow
from
the
lake
changesmore
slowlythantheinflow
The coefficient
coefficient ofof determination
determination with
with thethe measured
measured water
water level
level was
was 0.89
0.89 andand thethe RMSE
RMSE
The
due
to
the storage
effectwasof thedroughtlake (FigureThelake water
reproduced
from
these
was 0.092.
0.092.
Since 2015
2015
year,12).
probablethatlevel
the accuracy
accuracyof thethe inflow
inflow
wasSince
was aa drought
year,
itit isis probable
that
the
of
calculated
discharges
andthebathymetry
of
the
lake
were
comparedwiththeobserved
was particularly
particularly low
low asas mentioned
mentioned inin Section
Section 3.1.1
3.1.1 andand thatthat errors
errors were
were likely
likely to
to be
be comcomwas
lakewater large.
level in 2015 as shown in Figure 13. The calculation period started when theparatively
paratively large.
lake levelexceeded parameters
the averagewere
sea level
andtotheoutflow fromlake towith
theThe identified
identified
appliedtheforward
longer simulation
simulation
andtheverifiedThe
parameters wereappliedto thelongerandverifiedwithlagoonoccurredon
28
January.
The
error
betweenthecalculated
andobservedwater
the waterwater level
level record.
record. The
The results
results ofof thethe lake
lake water
water level
level calculated
calculated only
only fromfrom precipitaprecipitathelevel in the second half shown in Figure 13 reached more than 10 cm but the tendency istion andand evaporation
evaporation over
over aa long
long term
term were
were compared
compared with
with thethe waterwater level
level observed
observed bybytion
similar. The coefficient of determination with the measured water level was 0.89 and thethe
National
AgencyofProtectionoftheEnvironment(ANPE)[51]
inFigure14.
Therethe National Agency of Protection of the Environment (ANPE) [51] in Figure 14. The reRMSE was 0.092. Since 2015 was a drought year, it is probable that the accuracy of the
producibilityof
ofthethewaterwaterlevel
levelfluctuation
fluctuationin
inthe
thehighhighrainfall
rainfallyear
yearisishigh,high,andandthethewaterwater
producibility
inflow was particularly low as mentioned in Section 3.1.1 and that errors were likely to be
level
fluctuation
couldbe
re-produced
even
over
a
long
period.
level
fluctuationlarge.
could be re-produced even over a long period.
comparatively

Figure 12.
12. The
Thesimulated
simulatedtotal
total inflow
inflow to,to, andand outflow
outflow
from,
the
lake
(2015:
rainy
season).
outflowfrom,from,thethelakelake(2015:(2015:rainy
rainyseason).
season).
Figure13. Thethe SWATSWAT parametersparameters calibrated
Figure 13.
13.
The simulated
simulated lake
lake water
water level:
level: theparameters
calibrated with
with Masri
Masri reservoir
reservoir
Figurecatchment (Hilly(HillyandandCalcisol
Calcisolsoil)soil)were
wereapplied
applied
to
the
lower
catchment.
Theparameters
usedforcatchment
toto
the
lower
catchment.
Theparameters
used
for forthecatchment
andCalcisol
soil)
were
appliedthelowercatchment.
Theparameters
used
themountainous
mountainous
catchment
werecalibrated
with
Jouminereservoir
catchment.
thecatchment
werecalibrated
with
Jouminereservoir
catchment.
mountainous
catchment
werecalibrated
with
Jouminereservoir
catchment.

Water 2022, 14, 1984

14 of 23

The identified parameters were applied to the longer simulation and verified with thewater level record. The results of the lake water level calculated only from precipitation andevaporation over a long term were compared with the water level observed by the National
Figure13.ofThe
simulatedoflake
level: the(ANPE)SWAT parameters
calibrated
withMasri reservoir
AgencyProtection
the water
Environment[51] in Figure
14. Thereproducibilityofcatchment (Hilly and Calcisol soil) were applied to the lower catchment. The parameters used forthe water level fluctuation in the high rainfall year is high, and the water level fluctuation
the mountainous catchment were calibrated with Joumine reservoir catchment.
could be re-produced even over a long period.

Figure 14. The simulated lake water level verified with the long term observed data.

3.1.3. Water Budget of the Lake and Influence of the Reservoirs
Based on the water budget model mentioned above, the annual water budget from2000 to 2018 was calculated. Water intakes and discharge downstream at the reservoirs in
Table 3 were the recorded data in the dam management reports. As mentioned, here thesame values as the average of 2008–2010 pan evaporation at Joumine reservoirs were given
for each year.
Table 3. Annual water budgets from September 2000 to August 2019 under the current state.
(Unit: Million m3 )Current State
Reservoirs
Years(September–August)Intake(Exploitation)

2000–2001
2001–2002
2002–2003
2003–2004
2004–2005
2005–2006
2006–2007
2007–2008
2008–20092009–20102010–20112011–20122012–20132013–2014
2014–2015
2015–2016
2016–20172017–20182018–2019

52
82
92
109
88
165
152
174
158
167
186
193
180
187
199
152
127
141
165

Ichkeul Lake

Evaporation

Disch.
to Downstream

Total
Inflow

Precipitation

Evaporation

Outflow

Reverse
Flow

56
56
56
56
56
56
56
56
56
56
56
56
56
56
56
56
56
56
56

0
0
292
112
268
112
2
3
91
57
1
254
58
48
35
0
0
0
66

99
72
486
393
733
405
290
308
453
336
206
600
283
288
247
125
215
186
324

39
36
58
71
82
49
59
57
74
67
54
77
65
61
59
42
56
69
63

249
309
309
309
309
309
309
309
309
309
309
309
309
309
309
309
309
309
309

29
3
351
227
571
248
152
163
303
205
91
476
162
155
136
26
122
64
179

140
204
115
72
65
103
111
106
86
111
140
109
123
116
139
168
161
117
101

In order to compare the water and sediment budgets between the states with andwithout the reservoirs, the water budgets with the reservoirs were also simulated. The
fluctuation of the simulated lake water level, assuming no upstream reservoirs, is shown as
the red line in Figure 15. Due to the water storage effect of the reservoirs, the inflow was
reduced and the rise in the lake level was suppressed. Especially in drought or moderate
years, when there is almost no spilling from the dam, the difference in the peak of the lakewater level is large. The water budget by year.

16 of 25
Water 2022, 14, 1984

15 of 23

Figure 15.ofTheof thewaterlevelforof thelake for(September
19 years (September
2000–2019).
Figure 15. The simulations
thesimulations
water levelof thelake
19 years
2000–2019).

The effect of the tide stop weir could be confirmed from the ratio of the current state

Table 4. Annual waterof thewithout
simulation
without astheshown
reservoirs.
andbudgets
the simulation
the reservoirs
in Table 4. The total inflow and outflow

Total
Inflow
171
81
408
551
986
537
561
617
732
514
373
695
399
460
391
191
445
330
514

Precipitation
39
36
58
71
Years
(September–August)82
49
2000–2001
2001–2002
59
2002–2003
2003–2004
57
2004–200574
2005–2006
2006–200767
2007–2008
2008–200954
2009–20102010–201177
2011–201265
2012–20132013–201461
2014–2015
2015–201659
2016–201742
2017–20182018–201956
69
63

were drastically reduced by the reservoirs, but the increase in the reverse flow of seawater(Unit:
Millionm3) withwas suppressed to within about 20%. The total inflows andoutflows
estimated
the water budget model
were compared between the current
state andthe case without
Outflow
ReverseFlow
reservoirs.
The
results
duringthewinter,from
1
September
2003
to1
September
Evaporation
Current State
Current State 2006, areshown in Figure 16 as examples. In the case of “without reservoirs”, larger peak discharges/Without
Damsslightly(%) due to the rise
/Without
Dams
were found, and the outflow
increasedof the lakewater (%)
level.

249
88
33
127
Table 4. Annual water budgets of the simulation without the reservoirs.
309
7
46
199
309
434
81
277
Outflow
309
365
62
52
Total
Precipitation
Evaporation
Current
State
Inflow309
823
69
64/without Dams (%)
6588
171 30939 379
249
33102
127
81
36
309
7
46
199
309
397
38
86
408
58
309
434
81
277
551 309
71 442
309
6277
52
37365
986
82
309
823
69
64
54379
537 309
49 563
309
6567
102
561
59
309
38
86
56397
617 30957 367
309
442
3795
77
732 30974 242
309
54125
67
38563
514
67
309
367
56
95
373 309
54 568
309
38105
125
84242
695
77
309
568
84
105
61265
399 309
65 265
309
61110
110
460
61
309
303
51
91
309
303
51265
91
391
59
309
51
124
191 30942 265
309
34124
152
5176
445
56
309
335
36
144
76
34200
330 309
69
309
32152
110
514
63
309
331
54
63
309
335
36
144
309
200
32
110
309
331
54
63

110
103
42(Unit: Million m3 )Reverse138 Flow
Current State
101/without Dams (%)
101
110
103
129
42
138
138
101
128
101
129
117
138
128
113
117
113
103
103
111
111
127
127
112
111
112
112
111
106
160
112
106
160

Water2022,
2022,14,
14,1984
x
Water

17 16
of of2523

Figurethelake:(a)(a)
thethesimulation
of of
the
Figure 16.
16. TheThe simulations
simulationsof
ofthe
thetotal
totalinflow
inflowto,
to,andandoutflow
outflowfrom,
from,
the
lake:
simulation
the current(b) simulation
the simulation
without
reservoirs.
current
statestate(b) thewithout
the thereservoirs.

3.2.
Driven by
by WindWind
3.2. Modeling
Modeling ofof Resuspension
Resuspension Driven
3.2.1.
Experiments andand Field
Field Observation
Observation
3.2.1. Results
Results ofof Laboratory
Laboratory Experiments

Water 2022, 14, xInthe rotation
rotation speed
speedofofthe
thestirrer
stirrerwas
waskept
keptconstantconstantsoso
In thethe laboratorylaboratory experiment,
experiment, thethatwere inin equilibrium
equilibriumand
andthetheturbidity
turbidityapproachedapproachedthat thethe resuspension
resuspension andand settlement
settlement wereasymptoticallytoaconstant
value.
In
the
exampleoftherecord
of
SS
and
flow
velocity
asymptotically to a constant value. In the example of the record of SS and flow velocity
shownin
Figure17,
therotation
speed
of
the
stirrerisincreasedinfour
steps.
SS
shown in Figure 17, the rotation speed of the stirrer is increased in four steps. The The
SS inincreases
as
the
flow
velocity
increases.
The
periodduringwhich
themeasuredSS
wascreases as the flow velocity increases. The period during which the measured SS was stastableat eachstage
analyzed.
The predominantperiodwas obtainedby Fourier
ble at eachstage
waswasanalyzed.
The predominantperiodT wasTobtainedby Fourier
analanalysisofthefluctuationoftheabsolute
flow
velocity
from
the
flow
velocity
in two25 horizonysis of the fluctuation of the absolute flow velocity from the flow velocity 18
in oftwohorizontal
directions
measuredby the current
themeanroot squaremean squareof thebw flow
tal directions
measuredby the current
meter, meter,
and theandroot
Ubw ofUthe
flowvelocity
was obtained.
velocity
was obtained.
It was expected that the turbulence intensity (Rew) and SS would correlate, but therelationship would change depending on some factors because the state of the sedimentsurface seemed to change depending on the water temperature. First, when all the experimental results are shown in the same plot in Figure 18, the effect of water temperaturethat was initially expected was not large, and SS and turbulence intensity were in a linear
relationship.
The relationship between Rew and SS observed in the field was also investigated. The
hourly average of T, 𝑈 and Reynolds number were estimated from the time series ofvelocity observed in the field in September 2015 and March 2016 as shown in Figure 19.
The period in which SS was stable for about an hour was extracted, and the relationships
with the turbulence intensity and wind speed in the meantime were evaluated. The turbulence increased more in March when the westerlies occurred than in September, andthe sediment was highly resuspended. No significant fluctuations were observed in the
predominant period T in the field observation results, suggesting that the increase in the
Reynolds number is highly dependent on 𝑈 .
The relationships between the Reynolds number and SS obtained from the results offield observations were shown as x marks in Figure 18. Those were on the same linear line
as the results of the laboratory experiment. It is considered that the formulation of therelationship between the Reynolds number and SS in the laboratory experiment can reproduce the state of resuspension driven by wind in the field.
FigureExampleof results
the laboratory
experiments.
T asbars
the were
blue bars
wereobtained from
Figure17.17.
Exampleof resultsof theof
laboratory
experiments.
T as the blue
obtainedfromthethefluctuationof thewith Fourier
analysis.
fluctuationof velocity
the velocity
with Fourier
analysis.

It was expected that the turbulence intensity (Rew ) and SS would correlate, but the relationship would change depending on some factors because the state of the sediment surface
seemed to change depending on the water temperature. First, when all the experimental
results are shown in the same plot in Figure 18, the effect of water temperature that was
initially expected was not large, and SS and turbulence intensity were in a linear relationship.

Water 2022, 14, 1984

Figure 17. Example of results of the laboratory experiments. T as the blue bars were obtained fromthe fluctuation of the velocity with Fourier analysis.

17 of 23

FigureThe
relationshipbetweenturbulent
intensityintensity(Rew) and(Rethewconcentrationof suspended of suspended solids.
Figure18.18.
The
relationshipbetweenturbulent) and the concentration
solids.

The relationship between Rew and SS observed in the field was also investigated. The
hourly average of T, Ubw and Reynolds number were estimated from the time series ofvelocity observed in the field in September 2015 and March 2016 as shown in Figure 19. The
period in which SS was stable for about an hour was extracted, and the relationships withthe turbulence intensity and wind speed in the meantime were evaluated. The turbulence
increased more in March when the westerlies occurred than in September, and the sediment
was highly resuspended. No significant fluctuations were observed in the predominantperiod T in the field observation results, suggesting that the increase in the Reynolds
number is highly dependent on Ubw .

Figure 19. Results of the field observations: (a) September 2015 (b) March 2016.

The relationships between the Reynolds number and SS obtained from the results offield observations were shown as x marks in Figure 18. Those were on the same linear
line as the results of the laboratory experiment. It is considered that the formulation of
the relationship between the Reynolds number and SS in the laboratory experiment can
reproduce the state of resuspension driven by wind in the field.

Water 2022, 14, 1984

18 of 23

3.2.2. Relationship between Wind and Reynolds Number
The relationship between the wind speed observed in the field and the Reynolds
number indicating the turbulence intensity hourly observed in the field is shown as the
red rectangle in Figure 20. As the wind speed increased, the turbulence intensity increased
exponentially. The coefficient of determination for the relationship was 0.90. However, thehourly wind data were not observed in the long term, while the daily average wind speed
was available from the NOAA [51] database. Therefore, the relationship between the daily
average of the Reynolds numbers and wind speed was obtained from the above hourly
observed data. It is shown as the blue triangles in Figure 20. Even the daily averaged
Reynolds number and wind speed showed the same relationship.

Water 2022, 14, x

20 of 25

Figure 20. The relationship between the wind velocity and Reynolds number observed in the field.

Another concern is the location of the observatories. Sidi Ahmed Air Base, the observatory of NOAA, is located in Bizerte city which has a different wind speed from the lake.
The wind speed downloaded from NOAA and the average daily wind speed observed near
the lake for the two weeks when the hourly data were obtained were not equal but werehighly correlated, with a coefficient of determination of 0.946 as shown in Figure 21. The
temporal fluctuation of the Reynolds number was estimated from the daily wind speed data
downloaded from NOAA through the two relationships identified in Figures 20 and 21.
The time series of SS estimated from the NOAA wind velocity data was verified by the comparison with the daily average SS measured in the field from 6 September to 11 Septemberand 20 March to 24 March (Figure 22) The daily averaged concentration of SS was wellFigure 20. The relationship between the wind velocity and Reynolds number observed in the field.
reproduced,
especially in winter.
2

Figure 21.
comparisonof windvelocities
betweenbetween
Sidi Ahmed
Base andTinja
channelfor channel for
Figure21.TheThe
comparisonof windvelocities
SidiAir
Ahmed
Air
Base
and Tinja
the observation
periods.
theobservation
periods.

of the lakebed was decreasing,enhancing the seawater intrusion from the lagoon duringin the simulation without the reservoirs was higher than the current state, as shown inthe summer season.
2000
Figure 24.

SS(mg/L)

2000

1500
SS(mg/L)

Water 2022, 14, 1984

Using a combination of the water budget model and the wind resuspension model,
the sediment transportation from the lake through Tinja channel was estimated for bothcases: the current state and that without reservoirs, using the rainfall and wind speed dataof theSediment
Outflow
as 3.2.3.
inputEstimation
values. The
timeseries of
SS was estimated from the daily average wind speed.
Usingofa combinationof risethe watermodellevel
and inthethewind
resuspension
model,
The change
SS due to thein thebudget
lake watercase
without thereservoirs
19 offor23
Figure 21. The comparison of wind velocities between Sidi Ahmed Air Base and Tinja channel
thenotsediment
transportationfromthe lakethroughTinjachannelwas estimatedforsettlement
bothwasnecessarytoconsiderbecauseitisassumedthattheresuspension
andthe observation periods.
the current
stateinandwithout reservoirs,
usingconstant
the rainfall
and wind
speed
data day.
of cases:
the sedimentwere
anthatequilibrium
state under
wind
speed
for eachas
input
values.
The
time
seriesofSS
wasestimated
from
the
daily
averagewind
speed.
Therfore, the same time series of SS shown in Figure 23 was used for both simulations
The change of SS due to the rise in the lake water level in the case without the reservoirs
with/without
the reservoirs. Due to the increase in the water outflow to the lagoon, thewas not necessary to consider because it is assumed that the resuspension and settlement
sediment outflow in the simulation without the reservoirs was higher than the currentof the sediment were in an equilibrium state under constant wind speed for each day.
state,as shown
in Figure24. of SS shown in Figure 23 was used for both simulations
Therfore,
the sametime series
The annual
water
thewatersediment
transportation
with/without
thecumulative
reservoirs. Due
to discharge
the increaseandin theoutflow
to the lagoon, fromthe thelake
tothelagoon
for
each
year
were
calculated(Figure25).
Indrought
years,
the total
sediment outflow in the simulation without the reservoirs was higher than the current
amountofshown
sediment
outflowstate, asin Figure24. decreases as the amount of water discharge decreases. In thisannual cumulative
dischargecatchment
and the sedimentfromthe bestudy, The
the sedimentyield in water
the upstream
was nottransportation
estimated with
SWAT
lake
to
the
lagoon
for
each
year
were
calculated(Figure25).
Indrought
years,
thetotalcause we could not obtain the observed data for calibration, but the SS concentration in
sediment outflow
decreases as thewaterdischarge
decreases.
In thistheamountlake isofconsidered
to be independent
ofamountthat ofofthe
inflow
in suchlarge andshallowstudy,
thesediment
yield
in
the
upstream
catchmentwasnotestimatedwithSWAT
belakes. It was modeled as being highly dependent on wind disturbance intensity. The availFigure we
22. Thedaily
theobserved
concentration
offor
SS in
the lake in the
periods estimated
cause
could
notaverageobtainofthecalibration,
butobserved
the SS concentration
in
able
data
theofinflowof thedatasolidmattertointhelake
is sedimentation
Figure22.representing
The daily average
the concentrationof SS inthe lakethe observed
periods estimatedin thefromlakewindvelocity
data. to be independent of that of the inflow in such large and shallow
theisconsideredfrom wind Before
velocitythedata.construction of the dams, the trapped sediment in the reservoirs wasreservoirs.
lakes. It was modeled as being highly dependent on wind disturbance intensity. The avail3.2.3.
Estimationof the to
Sediment
Outflowtheablesupplysedimentlake.
data ofrepresenting
thetheinflowof the solid matter to the lake is sedimentation in the
Usingacombination
of
the
water
budgetmodel
and thewind resuspension
model,wastheThe
orange
bar
in
the
right
Figureis theannualaveragesediment
accumulationinreservoirs. Before the construction of the
dams,
the
trappedsediment
in the reservoirs
sediment
transportation
from
the
lake
throughTinjachannelwasestimatedforbothcases:
thethereservoirs,
calculatedfromthebathymetricsurvey
[38].
As
it
was
largerthan
theoutsupply of sediment to the lake.
theof
current
state barandinthatwithout
reservoirs,
using therainfall
and
wind
speed
data inasHowflow
theorange
sediment
bothcases,
the islaketendedto deposit
sediment.
The
the
right
Figuretheoriginallyannualaveragesediment
accumulation
input
values.
The
time
seriesofSS
wasestimated
from
the
daily
averagewind
speed.
The
the after
reservoirs,
calculatedwere
from constructed,
the bathymetric[38]. supply
As it waslarger than tothetheoutever,the reservoirs
thesurvey
sediment(equivalentorangechange
of
SS
due
to
the
rise
in
the
lake
water
level
in
the
case
withoutthereservoirs
wasflow
ofbeenthe sedimentin bothcases,
originally tended
deposit sediment.
Howbar)hadalmost cut
off dueto thethe lake
sedimentationin theto
reservoirs
while thesediment
not necessary to consider because it is assumed that the resuspension and settlement of theever, after
the reservoirs
were constructed,
thebalance
sediment
supply(equivalent
to andthe orange
outflow
continues.
Asaresult,thesediment
of
the
lake
is
negativethealtitudesediment were in an equilibrium state under constant wind speed for each day. Therfore,
bar)
had
been
almost
cut
off
due
to
the
sedimentationinthereservoirs
while
the
sedimentof thethe same
lakebedtheseawaterfrom thelagoon during
timewasseriesdecreasing,enhancing
of SS shown in Figure 23
wasused for intrusion
both simulations
with/without
continues. As a result, the sediment balance of the lake is negative and the altitude
theoutflow
summerseason.
the reservoirs. Due to the increase in the water outflow to the lagoon, the sediment outflow

1500

1000
1000

500
500

0
2003 09/1

2003 9/1

2004 9/1

2004 9/1

2005 9/1

2005 9/1

2006 9/1

2006 9/1

Figure 23. Turbidity in the lake estimated from the daily wind velocity at Sidi Ahmed Air Base.
Figure 23. Turbidity
Turbidity in the lake estimated from the daily wind velocity at Sidi Ahmed Air Base.
FigureBase.

Figure 24. The flux of SS outflowing from the lake to the lagoon: (a) the simulation of the current

Figure24.
The
flux
outflowing
fromthethelakelakelagoon:(a) simulation
the simulation
the current
FigureThe
fluxofofSSSS
outflowing
from
to to
thethelagoon:(a) theof theofcurrent
state(b)24.
thesimulation
without
the dams.
state(b)(b)
thethesimulation
the dams.
dams.
state
simulationwithout
without the

The annual cumulative water discharge and the sediment transportation from the lake
to the lagoon for each year were calculated (Figure 25). In drought years, the total amountof sediment outflow decreases as the amount of water discharge decreases. In this study,

Water 2022, 14, 1984

Water 2022, 14, x

20 of 23

the sediment yield in the upstream catchment was not estimated with SWAT because we
could not obtain the observed data for calibration, but the SS concentration in the lake
is considered to be independent of that of the inflow in such large and shallow lakes. It
was modeled as being highly dependent on wind disturbance intensity. The available data
22 of 25
representing the inflow of the solid matter to the lake is sedimentation in the reservoirs.
Before the construction of the dams, the trapped sediment in the reservoirs was the supplyof sediment to the lake.

Figure25.
25.Comparison
Comparisonbetween
between the cases
discharge
andandFigurecaseswith/without
with/withoutdams:
dams:(a)(a)Annual
Annualcumulative
cumulative
discharge(b)
runoff.
(b)Annual
Annualcumulative
cumulative sedimentsediment runoff.

The orange bar in the right Figure is the annual average sediment accumulation in the
4. Conclusions

reservoirs, calculated from the bathymetric survey [38]. As it was larger than the outflow ofIn this study, the water budget of the brackish lakes and the resuspension caused by
the sediment in both cases, the lake originally tended to deposit sediment. However, afterwind
disturbanceweremodeledthe
forsedimentevaluationof thechanges in
sediment
the reservoirs
wereconstructed,
supply(equivalent
to thethe orangebar)outflow
had
due
to
the
constructionofthereservoirs.
Thesediment
outflow
from
the
lake
was estibeen almost cut off due to the sedimentation in the reservoirs while the sediment outflow
matedonly withmeteorologicalas input,
relativelyand
easy
obtain. ofcontinues.
As a theresult,the sedimentdatabalanceof thewhichlake isis negative
thetoaltitude
modelingenhancingof the water
budget, theinflows
fromcatchments
were
the Regarding
lakebed wasthe
decreasing,
the seawater
intrusion
fromthethelagoonduring theestimated
using
SWAT,
and
the
outflowwasestimatedfromthehydraulicgradient
besummer season.

tween the lake water and the seawater level. Finally, the fluctuation of the lake water level
Conclusions
in4.thelong term was reproduced.
In thisstudy, the water
budgetof lakethe brackishlakes andthe aresuspension
The
resuspension
processin thewas describedwithsimple box caused
model bywithwind
disturbanceweremodeledforevaluationofthechangesinthesediment
outflowdue
fixed lakebed altitude in this study. We formulated the relationships between the wind,
to the constructionof thereservoirs.
The sediment
the onlakelaboratory
was estimatedturbulent
intensit, andsediment
resuspension
on outflow
the lake,frombased
experionly
withthemeteorologicaldata
asinput,
whichisrelatively
easy
toobtain.
ments and field measurements. A uniform relationship between the turbulence intensity
Regarding themodeling
ofboththe water
budget,from thewere
and resuspension
wasfound inthe resultsof thethe inflows
experiments
andcatchments
the field measureestimated using SWAT, and the outflow was estimated from the hydraulic gradient between
ments, while the wind and the turbulence intensity were formulated based on the results
the lake water and the seawater level. Finally, the fluctuation of the lake water level in theof field observations. The concentration of the SS in the lake was estimated only from thelong term was reproduced.
wind speed
data.
The resuspension process in the lake was described with a simple box model withThe
sediment
transportation
outflowing
from thewas simulated
using
combifixed lakebed altitudein this study.
We formulated
thelakerelationships
betweenthe awind,nationof theaboveandtwosedimentmodelings.
Comparedtheannualsedimentationin theturbulent
intensit,
resuspension
onto
the
lake,
basedaverageon laboratory
experiments
upstream
reservoirs,
IchkeulLaketendedtodepositsediments
beforethereservoirs
wereand field measurements. A uniform relationship between the turbulence intensity andconstructed.
However,aftertheconstruction
of
the
dams,
the
inflowofsedimentfromresuspension was found in both the results of the experiments and the field measurements,theinflowing
was thealmostcut off,
and it were
was estimated
the
of of
sediment
while the riverwind andturbulence
intensity
formulatedthat
based
onoutflow
the results
field
observations.
The concentrationof theSSthe
in thewaslevelestimated
only and
fromthethesaltwater
wind
might
be excessive.
It was suggested
thatlakelakewater
decreased
speed data.
intrusion
to Ichkeul Lake increased as the lakebed was eroded.
The
transportation
outflowing
fromthethelakeupstream
was simulatedusing werea com-notIn thissedimentstudy, theinflows of thesediment
fromcatchments
bination
of
the
above
two
modelings.
Comparedtotheannualaveragesedimentationinsimulated in the budget. Whether the sedimentation tendency is erosive or cumulative
the discussed
upstream reservoirs,
Ichkeul Laketendedto deposit
before inthethereservoirs
wasusing comparison
to theannualaveragesediments
sedimentation
upstream
wereconstructed.
However,aftertheconstruction
of
the
dams,
the
inflowofsediment
fromreservoirs. An alternative would be to compare with a more accurate estimate of soilyield
the inflowing river was almost cut off, and it was estimated that the outflow of sedimentin the catchments using SWAT instead of the annual average sedimentation of the upstream reservoir. However, we could not obtain the sediment load observed in the field
for the verification of the results calculated using SWAT. In addition, the change of thealtitude of the lakebed due to erosion or sedimentation was not considered and its steadystate as the same bathymetry as that observed in 2015 was assumed. If the sedimentation

Water 2022, 14, 1984

21 of 23

might be excessive. It was suggested that the lake water level decreased and the saltwater
intrusion to Ichkeul Lake increased as the lakebed was eroded.
In this study, the inflows of the sediment from the upstream catchments were notsimulated in the budget. Whether the sedimentation tendency is erosive or cumulative
was discussed using comparison to the annual average sedimentation in the upstream
reservoirs. An alternative would be to compare with a more accurate estimate of soil yieldin the catchments using SWAT instead of the annual average sedimentation of the upstream
reservoir. However, we could not obtain the sediment load observed in the field for theverification of the results calculated using SWAT. In addition, the change of the altitude ofthe lakebed due to erosion or sedimentation was not considered and its steady state as thesame bathymetry as that observed in 2015 was assumed. If the sedimentation tendency
continues, as in the absence of dams, salt intrusion will be more restricted. On the contrary,
if the sedimentation of the dam continues as it is and the elevation of the lake bottom
continues to decrease, the salinity of Ichkeul Lake will be even higher due to the significant
reverse flow from Bizerte Lagoon.
Currently, the environmental conservation of Ichkeul Lake is planned only withthe focus on its water budget and the regulation of the lake water level. However, thelakebed depression due to the imbalance of the sedimentation also has a certain negativeenvironmental impact on Ichkeul Lake. In further studies, it is expected to allow SWAT orother river basin scale models to be calibrated based on field observations of wash load
and to assess soil yield in the catchments more precisely. In addition, to consider specificmeasures against the sediment budget imbalance, such as relocation of the sediment in thereservoirs to the lake, it is necessary to develop a model that can reproduce the changes
in lakebed altitude caused by resuspension and sedimentation processes and evaluate thechanges in saltwater inflow more accurately. This study, which showed that the tendency
of sediment movement changed to erosive after the construction of the reservoirs in the
upstream area, was the initiation for a more detailed examination.
Author Contributions: Conceptualization, M.I. and J.T.; methodology, M.I.; validation, M.I. and H.K.;
formal analysis, M.I. and A.K.; investigation, M.I., A.K. and H.O.; resources, M.I. and J.T.; data curation, M.I., H.K. and H.O.; writing—original draft preparation, M.I., H.K. and A.K.; writing—review
and editing, M.I.; visualization, M.I. and H.K.; supervision, M.I., A.K. and J.T.; project administration, M.I.; funding acquisition, M.I. All authors have read and agreed to the published version of
the manuscript.
Funding: This research was partially supported by a Japan Society for the Promotion of Science(JSPS) Grant-in-Aid for Scientific Research (A) 15H02634.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.

References
1.
2.
3.
4.

5.
6.
7.

Miller, R. Forcing uncertainty and salinity response to dredging in a tidal freshwater river. Int. J. River Basin Manag. 2021, 1–9.
[CrossRef]
Yuan, R.; Zhu, J. Saltwater Intrusion in the Pearl River Estuary. J. Coast. Res. 2015, 316, 1357–1362. [CrossRef]
van Dijk, W.M.; Cox, J.R.; Leuven, J.R.; Cleveringa, J.; Taal, M.; Hiatt, M.R.; Sonke, W.; Verbeek, K.; Speckmann, B.; Kleinhans,
M.G. The vulnerability of tidal flats and multi-channel estuaries to dredging and disposal. Anthr. Coasts 2020, 4, 36–60. [CrossRef]
Dias, J.M.; Pereira, F.; Picado, A.; Lopes, C.L.; Pinheiro, J.P.; Lopes, S.M.; Pinho, P.G. A Comprehensive Estuarine HydrodynamicsSalinity Study: Impact of Morphologic Changes on Ria de Aveiro (Atlantic Coast of Portugal). J. Mar. Sci. Eng. 2021, 9, 234.
[CrossRef]
Anthony, E.; Brunier, G.; Besset, M. Linking rapid erosion of the Mekong River delta to human activities. Sci. Rep. 2015, 5, 14745.
[CrossRef]
Kondolf, G.M.; Rubin, Z.K.; Minear, J.T. Dams on the Mekong: Cumulative sediment starvation. Water Resour. Res. 2014, 50,
5158–5169. [CrossRef]
Milliman, J.D.; Syvitski, J.P.M. Geomorphic/Tectonic Control of Sediment Discharge to the Ocean: The Importance of Small
Mountainous Rivers. J. Geol. 1992, 100, 525–544. [CrossRef]

Water 2022, 14, 1984

8.
9.
10.
11.
12.
13.
14.
15.

16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.

22 of 23

Lu, X.X.; Siew, R.Y. Water discharge and sediment flux changes over the past decades in the Lower Mekong River: Possible
impacts of the Chinese dams. Hydrol. Earth Syst. Sci. 2006, 10, 181–195. [CrossRef]
Irie, M.; Kashiwagi, K.; Ujiie, K.; Nsiri, I.; Bouguerra, S.; Tarhouni, J. Feasibility of Exploitation of the Sediment in the Reservoirs
for the Sustainability of Surface Water Resource in Tunisia. J. Jpn. Soc. Civ. Eng. Ser. G 2012, 68, II41–II46. [CrossRef]
Irie, M.; Kawachi, A.; Nsiri, I.; Tarhouni, J. Observation of floodwater behavior and sedimentation in the reservoir. J. Jpn. Soc. Civ.
Eng. Ser. B1 2013, 69, 247–252.
Hata, T.; Irie, M.; Kawachi, A.; Tebakari, T. Evaluation of sediment solidification ability using in situ microbial functions in Ichkeul
Lake, Tunisia. Euro-Mediterr. J. Environ. Integr. 2016, 1, 2. [CrossRef]
Barhoumi, B. Biomonitoring Pollution of the Bizerte Lagoon (Tunisia) by Comparative Analysis of Contamination Levels andEcotoxicity of Sediments and Biota. Ph.D. Thesis, Université de Bordeaux, Bordeaux, France, 2014. (In French).
So, S.; Khare, Y.; Mehta, A. Critical wind and turbidity rise in a shallow Florida lake. WIT Trans. Ecol. Environ. 2013, 169, 13.
[CrossRef]
Béjaoui, B.; Harzallah, A.; Moussa, M.; Chapelle, A.; Solidoro, C. Analysis of hydrobiological pattern in the Bizerte lagoon(Tunisia). Estuar. Coast. Shelf Sci. 2008, 80, 121–129. [CrossRef]
Ouni, H.; Kawachi, A.; Irie, M.; Ben’Barek, N.; Hariga-Tlatli, N.; Tarhouni, J. Development of water turbidity index (WTI)
and seasonal characteristics of total suspended matter (TSM) spatial distribution in Ichkeul Lake, a shallow brackish wetland,
Northern-East Tunisia. Environ. Earth Sci. 2019, 78, 228. [CrossRef]
Hata, T.; Irie, M. Evaluation of sediment solidification ability using in situ microbial functions in Ichkeul Lake, Tunisia. J. Jpn. Soc.
Civ. Eng. Ser. G 2013, 71, 125–133. [CrossRef]
Irie, M.; Taga, S.; Tarhouni, J.; Fuji, M. Trial Production of Porous Ceramics Filter Made from Sediments in Water Reservoirs for
Sustainable Use of Surface Water Resource in Arid Land. Int. J. Environ. Sci. Dev. 2017, 8, 549–556. [CrossRef]
Van Liew, M.W.; Garbrecht, J. Hydrologic Simulation of the Little Washita River Experimental Watershed Using SWAT. J. Am.
Water Resour. Assoc. 2003, 39, 413–426. [CrossRef]
Briak, H.; Mrabet, R.; Moussadek, R.; Aboumaria, K. Use of a calibrated SWAT model to evaluate the effects of agricultural BMPs
on sediments of the Kalaya river basin (North of Morocco). Int. Soil Water Conserv. Res. 2019, 7, 176–183. [CrossRef]
National Centers for Environmental Information (NOAA). Available online: https://www.ncei.noaa.gov/data/global-summaryof-the-day/access/ (accessed on 31 March 2022).
ALOS World 3D. Available online: https://www.eorc.jaxa.jp/ALOS/en/aw3d30/data/index.htm (accessed on 31 March 2022).
ESA CCI Land Cover 20 m Map of Africa. Available online: http://2016africalandcover20m.esrin.esa.int/download.php(accessed on 31 March 2022).
FAO Map Catalog. Available online: http://www.fao.org/geonetwork/srv/en/metadata.show?id=14116 (accessed on
31 March 2022).
SWAT-CUP. Available online: https://www.2w2e.com/home/SwatCup (accessed on 31 March 2022).
Mtibaa, S.; Hotta, N.; Irie, M. Analysis of the efficacy and cost-effectiveness of best management practices for controlling sedimentyield: A case study of the Joumine watershed, Tunisia. Sci. Total Environ. 2018, 616–617, 1–16. [CrossRef]
de Vicente, I.; Cruz-Pizarro, L.; Rueda, F.J. Sediment resuspension in two adjacent shallow coastal lakes: Controlling factors andconsequences on phosphate dynamics. Aquat. Sci. 2010, 72, 21–31. [CrossRef]
Wang, P.; Hu, B.; Wang, C.; Lei, Y. Phosphorus adsorption and sedimentation by suspended sediments from Zhushan Bay, Taihu
Lake. Environ. Sci. Pollut. Res. 2015, 22, 6559–6569. [CrossRef] [PubMed]
Hamilton, D.P.; Mitchell, S.F. An empirical model for sediment resuspension in shallow lakes. Hydrobiologia 1996, 317, 209–220.
[CrossRef]
Zhu, Q.; van Prooijen, B.; Wang, Z.B.; Ma, Y.X.; Yang, S.L. Bed shear stress estimation on an open tidal flat using in situ
measurement. Estuar. Coast. Shelf Sci. 2016, 182, 190–201. [CrossRef]
Wright, L.D.; Boon, J.D.; Kim, S.C.; List, J.H. Modes of cross-shore sediment transport on the shoreface of the Middle Atlantic
Bight. Mar. Geol. 1996, 96, 19–51. [CrossRef]
Grant, W.D.; Madsen, O.S. Combined wave and current interaction with a rough bottom. J. Geophys. Res. Oceans 1979, 84,
1797–1808. [CrossRef]
Garcia, M.; Parker, G. Experiments on the entrainment of sediment into suspension by a dense bottom current. J. Geophys. Res.
1993, 98, 4793–4807. [CrossRef]
Soulsby, R.L.; Hamm, L.; Klopman, G.; Myrhaug, D.; Simons, R.R.; Thomas, G.P. Wave-current interaction within and outside thebottom boundary layer. Coast. Eng. 1993, 21, 41–69. [CrossRef]
Soulsby, R.L.; Clarke, S. Bed Shear-Stresses under Combined Waves and Currents on Smooth and Rough Beds; Report TR 137; Defra
project FD1905; Hydraulics Research: Wallingford, UK, 2005.
Zikhali, V.; Tirok, K.; Stretch, D. Sediment resuspension in a shallow lake with muddy substrates: St Lucia, South Africa.
Cont. Shelf Res. 2015, 108, 112–120. [CrossRef]
Wiberg, P.L.; Sherwood, C.R. Calculating wave-generated bottom orbital velocities from surface-wave parameters. Comput. Geosci.
2008, 34, 1243–1262. [CrossRef]
Carlin, J.A.; Lee, G.-H.; Dellapenna, T.M.; Laverty, P. Sediment resuspension by wind, waves, and currents during meteorologicalfrontal passages in a micro-tidal lagoon. Estuar. Coast. Shelf Sci. 2016, 172, 24–33. [CrossRef]

Water 2022, 14, 1984

38.
39.
40.
41.
42.
43.
44.

45.
46.
47.
48.
49.
50.
51.

23 of 23

Lodahl, C.R.; Sumer, B.M.; Fredsøe, J. Turbulent combined oscillatory flow and current in a pipe. J. Fluid Mech. 1998, 373, 313–348.
[CrossRef]
Hofmann, H.; Lorke, A.; Peeters, F. Wind and ship wave-induced resuspension in the littoral zone of a large lake. Water Resour.
Res. 2011, 47. [CrossRef]
Garcia, M.; Parker, G. Entrainment of Bed Sediment into Suspension. J. Hydraul. Eng. 1991, 117, 414–435. [CrossRef]
Verney, R.; Deloffre, J.; Brun-Cottan, J.-C.; Lafite, R. The effect of wave-induced turbulence on intertidal mudflats: Impact of boat
traffic and wind. Cont. Shelf Res. 2007, 27, 594–612. [CrossRef]
Hawley, N.; Harris, C.K.; Lesht, B.M.; Clites, A.H. Sensitivity of a sediment transport model for Lake Michigan. J. Great Lakes Res.
2009, 35, 560–576. [CrossRef]
Matty, J.M.; Anderson, J.B.; Dunbar, R.B. Suspended sediment transport, sedimentation, and resuspension in Lake Houston,
Texas: Implications for water quality. Environ. Geol. Water Sci. 1987, 10, 175–186. [CrossRef]
Gao, J.H.; Jia, J.; Kettner, A.J.; Xing, F.; Wang, Y.P.; Xu, X.N.; Yang, Y.; Zou, X.Q.; Gao, S.; Qi, S.; et al. Changes in water andsediment exchange between the Changjiang River and Poyang Lake under natural and anthropogenic conditions, China. Sci. Total
Environ. 2014, 481, 542–553. [CrossRef]
Zhang, S.; Liu, Y.; Yang, Y.; Sun, C.; Li, F. Erosion and deposition within Poyang Lake: Evidence from a decade of satellite data.
J. Great Lakes Res. 2016, 42, 364–374. [CrossRef]
Wang, H.; Kaisam, J.P.; Liang, D.; Deng, Y.; Shen, Y. Wind impacts on suspended sediment transport in the largest freshwater lakeof China. Hydrol. Res. 2020, 51, 815–832. [CrossRef]
Luettich, R.A.; Harleman, D.R.F.; Somlyódy, L. Dynamic behavior of suspended sediment concentrations in a shallow lake
perturbed by episodic wind events. Limnol. Oceanogr. 1990, 35, 1050–1067. [CrossRef]
Mei, C.C.; Fan, S.; Jin, K. Resuspension and transport of fine sediments by waves. J. Geophys. Res. 1997, 102, 15807–15821.
[CrossRef]
Sanford, L.P.; Halka, J.P. Assessing the paradigm of mutually exclusive erosion and deposition of mud, with examples from upper
Chesapeake Bay. Mar. Geol. 1993, 114, 37–57. [CrossRef]
Soulsby, R.L. Dynamics of Marine Sands: A Manual for Practical Applications; Thomas Telford Publishing: London, UK, 1997.
L’Agence Nationale de Protection de l’Environnement (ANPE). Rapport sur le Suivi Scientifique au Parc National de L’ichkeul Annee
2006–2007; ANPE: Tunis, Tunisia, 2008.