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2D simulations for sediment management options during Wadi flash floods in Sidi Salem Dam〇Mouhanned JABBERI, Sameh Ahmed KHANTOUSH , Sumi TETSUYA

bathymetric survey. The methodology includes anI.

Introduction:

extensive simulation covering all flood events between

Tunisia's climate, marked by arid periods and intense

2006

and2017,

utilizingTelemac2dforfloods, leads to increased erosion and sediment yield inmorphodynamical analysis. The sediment boundary

rivers, impacting reservoirs. Sidi Salem Dam (SSD)

condition determination employs Ghimire et al's

depicted in figure 1, crucial for water security, has lost

approach, relying on bed shear stress calculation due to30% of its initial capacity due to sedimentation. The

data unavailability. The calibrated model exhibits goodchallenge is intensified by the reservoir's unique

agreement with the 2017 bathymetric survey.

morphology and the current emphasis on waterIII.

retention over sediment control during droughts. This

After calibrating SSD numerical model, thestudy aims to address the rising sedimentation issue bysedimentation dynamics analysis unveiled distinct flow

formulating

strategies,

patterns influenced by the reservoir's morphology, withaccounting for the dam's distinctive features, diversea significant portion of sediment depositing far

rainfall patterns, and complex dynamics of upstream

upstream before reaching the reservoir wall. This

reservoir management.

underscores the inefficiency of current reservoir

effective

management

Sediment dynamics assessment

operations.
N

Cumulative

bed

evolution

indicates

preferential deposition zones that vary across reservoir
regions from upstream to downstream. Region-specificanalysis depicted in figure2, identifies uniquedeposition

characteristics,including

embayment

deposition in Region 1, bank-oriented deposition in
Region 2, axial deposition in Region 3, and deltaic
behavior at the boundary between Regions 3, 4, and 5.

Thickness (m)Figure 1: Study Area LocationII.

Objectives and methodology

The study focuses on assessing and proposing
tailored control measures for sediment management inN

the reservoir. Data limitations lead to estimations forsediment-related data, necessitated by the absence ofhistorical data. Calibration relies on the 2017

Figure 2: Simulated Cumulative Sediment Thickness in m

These results emphasize the need for tailored

Cumulative sediment volume results in figure 5

management strategies, suggesting that a uniform

indicated varied deposition and erosion patterns acrossapproach

regions and options.

may

not

be

optimalforeffective

sedimentation control across the entire reservoir.

1

Sediment control options:

The sediment management assessment for the Sidi
Salem reservoir utilized both long-term and eventbased analyses. The long-term projection depicted infigure3 indicates a substantial loss of nearly 50% of theinitial capacity by 2040, prompting the exploration ofalternative strategies.

50%

Volume (Mm3)700600400300200100198719891991199820022006200920122015201920232027203120352040
Sediment Volume

Region 1Region 2
Option1

Option2

Region 3
Option3

Region 4
Option4

Region 5

Option5

Figure 5: Cumulated Volume change per reservoir region

Water Volume

Option 5 showcased superior performance in20%

evacuating sediment from the most affected regions,10%

specifically Region 1 and Region 3. In contrast, Option

0%

cdepicted in figure 4, revealing that Option 5, featuring
a bypass tunnel with a diversion weir and a dredging
channel, demonstrated optimal performance allowing
to recover 30% of the silted storage. The efficiency ofeach option was assessed based on the reservoir's
specific characteristics and silted capacity.

50.98

52.66

50

�𝟎𝟎.𝟖𝟖 < 1

52.1

Storage Effeciency
53.27

55.25

30
20
10

Option3

Option4

Conclusion:

The study's findings reveal that sedimentation
patterns in the reservoir are strongly influenced by bothmorphology

Option5

Figure 4: simulated flushed sediment volume per option.

andcurrent

operational

strategies.

Conventional sediment control measures, unsuitable
for arid conditions due to potential water loss, are notrecommended. The optimal approach advocates for a
combination

ofmanagement

options,emphasizing region-specific strategies within the35%

reservoir. Specifically for Sidi Salem Dam, the30%

installation of a bypass, coupled with dry dredging

25%

during the drought season in the upstream region,

20%

emerged as the most effective solution for storage

15%

recovery.

10%

Option2

V.

40%

40

Option1structure.

tailored80(𝑽𝑽𝑽𝑽�𝒗𝒗𝒗𝒗𝒗𝒗+𝑽𝑽𝑽𝑽)

dredging, exhibited a more uniform pattern with
influenced by the currents from the bottom outlet

five sediment management options were evaluated-∞ <2, involving sediment flushing combined with channel
notable erosion in region 4 and 5, particularly

In event-based testing with flash flood scenarios,

Sediment Volume Out (Mm3)-430%

Figure 3: Simulated predicted Storage Evolution

0-3

40%

50060-260%

80070-1-5

900

00
Cumulative volume change (Mm3)

IV.

5%