Mosul Dam: The Full Story of Its Location, Design, Construction Challenges

Mosul Dam
The Full Story
Nasrat Adamo ( Consulting Engineer)
LTU team

The dam is located 60 Km North west of Mosul and 80 Kilometer
from Syrian and Turkish borders
Mosul Dam
Mosul City
• Mosul Dam Location

Mosul Dam Location
The Dam is 500 Km
north of Baghdad .
This is about 650 km.
along the river channel
route.
The flood wave
resulting from the Dam
collapse could reach
the city within 48
hours
Mosul Dam
Baghdad

Parts of Mosul Dam
Scheme:
Mosul Dam Scheme consists
of three parts:
1. The main Embankment
with the main power station
(750Mw) ,shown at the top
2.The pump storage scheme
(200 Mw) , Upper reservoir is
shown in the middle
3.3. The reregulating dam
located 8 Km. down stream
from the main dam and
provided by (60 Mw) power
station, shown at the bottom
Mosul Dam Scheme

Operation Parameters of Mosul Dam

Mosul Main Dam General Arrangement

General Views of Mosul Dam
Aerial View Down stream View

Geological Factors Influencing Mosul Dam
Safety
1. The Karsts Prevailing in the dam site and reservoir area.
2.The existence of Gypsum / Anhydrite rock formations in
dam foundation alternating with soft marl layers and
weathered and cavernous limestone.
3. The presence of an extensive ground water aquifer
called (Der wadi al malih) aquifer.

Enlarged Google Earth Image Showing Many
Sinkholes in the Upstream Area of the Dam

Sinkholes Present in the Reservoir
(From 2010 Survey)

Geological X-Section along Dam Axis
Geological Cross Section
along the dam axis
showing
Limestone in blue and
violate, gypsum/anhydride
in green , clay and marls in
brown and breccias in pink
and mixed pink with green
and green

Lithological Column of
Beds at Mosul Dam Site
GB3
GB2
GB1
GB0
Of special Importance are
the Gypsum Breccias
Layers (GB) which resisted
grouting during construction
and some parts remained
open and were called
“Windows”. Other parts
opened after reservoir filling
and required continuous
maintenance grouting

Estimated karsts line in the problem area (sections 69-87)
The dots show some of the major grout takes locations

Schematic Diagram showing the formation of
breccias layer
Limestone bed
Gypsum Rock Bed
Breccias Layer

GB3 layer at Spillway bucket foundation
This is GB3 layer which was
uncovered during the
excavation of the foundation of
the spillway bucket .
During first filling of the
reservoir (1986). Seepage
appeared in the right hand side
of bucket. Seepage water
actually originated from the left
side and flowed under the
bucket which caused
dissolution in this layer. This
serious situation required the
construction of a new deep
grout curtain along the whole
length of the left side of the
bucket to stop this flow.

GB3 layer Close
View
This slide shows
closer view of some
of the cracks and
cavities in the GB3
layer uncovered in
the spillway bucket
foundation

Mosul Dam Anti Seepage Measures
• The design considered grouting as the anti seepage measure
to reduce seepage velocities to acceptable limits.
• Literature shows that an equilibrium between Gypsum and its
solution is reached when concentration of solution has 2000
ppm of sulfates. The solution is then saturated and no more
dissolution occurs.
• To reach this equilibrium state the foundation treatment by
grouting should reduce the permeability in the rock mass to
certain low values which makes this saturation possible. These
values are stipulated in the design and expressed in lugeon
units.
• One Lugeon unit( after the Swiss geologist Maurice Lugeon-
1933 ) is defined as the loss of water in liters/minute/one meter
of borehole under a pressure of 10 Kg/square centimeters.
• Blanket grouting and deep grout curtain were performed.

Mosul Dam Anti Seepage Measures
• Two types of grouting works are adopted in Mosul Dam :
• 1. The blanket grouting which extends under the clay core in the main
dam. No blanket grouting is considered under the dam shells.
• 2. The deep grout curtain which extends along the dam centerline
along the whole length and even in the natural ground beyond for the
extensions

Blanket Grouting
• Blanket Grouting covers the contact area of the clay core in the main
dam with foundation rock . It has 10 rows of holes u/s of centerline
and 10 rows downstream of centerline. Rows spacing is 2 meters.
• It is intended to seal all cavities, joints and fissures at the surface and
close preferential seepage lines at the core –foundation interface..
• To create a bulkhead at the top of the curtain and lengthen seepage
path.
• The thickness of blanket shall be 25 meters at the middle and 10
meters at the edges. Spacing of holes is 3 meters in each row with
possibility of split spacing till quenaries depending on permeability
tests results
• 90% of permeability tests results shall have values less than 10 Lu in
the upper 10 meters.
• 100% of all permeability tests shall have values less than 50Lu.

Deep Grout Curtain -1
• Under the main dam the curtain shall have 3 rows of holes at
1.5 meter spacing with possible split spacing. It extends from
section 114 to section 48 with total length of 2376 meters
.Depth is between 80- 100 . It is performed from the grouting
gallery.
Acceptance Criteria:
At the Upper 30 meters
- 90% of test results to have permeability less than 2 Lu..
-100% of test results to have permeability less than 5 Lu.
Below 30 meters
-100% of test results to have permeability values 5-10 Lu.

• Under The saddle dam and fuse plug section ( sections 47 to
15) with total length of 1152 meters the curtain shall have
single line of grout holes. But an additional line of holes was
added after appearance of seepages in this area in 1986.
Acceptance
criteria was to get 90% of permeability test results less than
10 Lu and 100% of all results shall be less than 50 Lu.

• The curtain extension in the left flank of the dam has total
length of 1500 meters. This is a single line curtain with depth
20-30 meters, 3 meters spacing of holes with possible split
spacing. Acceptance criteria was according to the amount of
grout take and the Engineers judgment.
• The curtain extension in the right flank of the dam has total
length of 408 meters. This is a double line curtain for the first
216 meters and single line curtain in the remaining part . The
depth reached was up to 100 meters. 3 meters spacing of holes
with possible split spacing .Acceptance criteria was according
to the grout take and the Engineers judgment.

Problems Encountered During First Filling of
Reservoir (1986-1988) – Seepage in the Left Bank
At the start of impounding the reservoir many springs appeared in
the left bank and at the two sides of spillway bucket. The
discharges were collected and measured . Total quantity was
830 L/second ( on 22nd
march 1986 at reservoir level of 304.6 )
.This could yield 2 cubic meters per second at full reservoir
elevation of 330.
• Chemical testing showed increase in salt content indicating
leaching of gypsum at a rate of 30 tons/day which corresponds
to a volume of 10-15 cubic meters .
• Hydro geological investigation by more open pipe piezometers
and dye tracers indicated that seepage was coming from left
bank of dam and part of it was passing under the spillway’s
bucket towards it’s right side.

Reservoir (1986-1988) – Seepage in the River
Section
• Measurement of seepage water in the river section was done
by collecting it by coffer dam no. 6 in this section. This
cofferdam was used during river diversion, but it was left in
place to collect seepage water from under the dam at the river
section . A weir was added to the coffer dam and used for
seepage water measurements.
Chemical analysis of seepage water indicated an increase in
sulfate concentration as sign of dissolution of gypsum from
under the dam which is the direct result of increased seepage
flow .

Seepage in left side and in River Section
after Guzina (et al.)
- Analysis of these results for the period from February 1986 to
August 1986 was done by Guzina (et al ), this analysis showed
that almost 13000 tons of minerals were leached from the dam
foundations in this period.
-The dissolution Intensity ranged between 42 – 80 t/day
-The following two slides show strong correlation between the
quantity of seepages with water levels while transmissibility
and dissolution of gypsum continued at higher rates than
before .

Seepage at left side and River Section
After Guzina (et al.)
Reservoir Water level
(Feb. – Aug 1986)
Seepage Discharges
(Feb – Aug. 1986)

Seepage at left side and River Section of Dam
After Guzina (et al.)
Variation of Trsmissibilty
(Feb. –Aug.) 1886
Soluble Salt Concentration
(Feb.- Aug.) 1986

Reservoir (1986-1988) - Seepage
• In the left bank the seepage water was reduced and controlled
by strengthening the left side curtain by adding another row of
grout holes, constructing a new 600 meter long deep curtain
along the left side of spillway chute to cut the flow under the
spillway’s bucket.
The springs were collected in three measuring points and
all small seeps were covered with filter material.
• In the river section efforts continued to maintain the deep grout
curtain
• Observations, measurements and chemical testing were
continued .

Locations of Seepage Water Collection Points

Seepage from left abutment (photos taken in 2003)
The situation was stable with continuing dissolution .
Discharge showed strong correlation with reservoir water
level

Sinkholes and Dissolution Phenomena
• Indications of sinkholes and dissolution tunnels were first
observed after beginning of first filling.
• An Inspection of reservoir rim in September 1986 when
reservoir level was drawn down to elevation 309 from elevation
316.4 . This level was reached during the previous winter. The
inspection discovered many sinkholes at a distance of 150
meters from the dam right abutment.
• One very large sinkhole was also discovered 1.0 km away from
the first group of sinkholes.
• These indicated a dramatic dissolution of gypsum layers which
were exposed on the shoreline.
• In view of the uncertainty of how these sinkholes would
develop an intensive grouting program was carried out to
strengthen the right bank grout curtain extension.

In March 2002 a large
dissolution tunnel was
discovered in a gypsum/
anhydrite layer in the
right bank of the
reservoir . The height of
the cave was 1.3 meters
with a floor level of 315
compared to 330. which
was the maximum
operation water level

Sinkholes and Dissolution
Phenomena
At the same time a ground
fissure started to open
gradually at a location
close to the right
abutment of the dam and
developed in a large crack
as shown. The soil mass
on the right showed
sliding movement towards
the boats platform in the
reservoir . One theory
stipulated that this slide
movement was initiated
by a dissolving gypsum
layer underneath.

During the operation
years of the reservoir ,
sinkholes developed
downstream at the right
bank about 900 meters
from the toe of the dam.
Four sinkholes developed
in a linear arrangement
during 1992-1998. The
rate of annual settlement
of these sinkholes ranged
between 0.25- 0.35 meters
with a total value of 5
meters
It has been suggested that
they are formed as a
result of underground
water flow and
dissolution of gypsum
layer.

Sinkhole SD2 . Picture shows concrete
slab settlement at contractors yard
SD2 after full development .Compare
its size to telephone pole length

One spring on the same
alignment of sinkholes
was uncovered after
spillway flood discharge
had removed the upper
river terrace sediments. It
is believed that this spring
belonged to the same
phenomena as the
sinkholes formation .
The formation of the
sinkholes and the spring
indicated an underground
flow and the formation of
gypsum dissolution
channel.

• It is believed that the flow from (Wadi Dermalih) underground
aquifer at the right bank in addition to fluctuation of tail water
level downstream of main dam due to the operation of the
reregulating dam had caused the formation of a solution
channel in an existing gypsum layer resulting in these
sinkholes. The collapse of their roofs occurred after
connecting with infiltrated rain water. The spring also had
originated from the same dissolution channel. The water of the
spring and the sinkholes had the same quality and sulfate
content of the (Wadi DerMalih) underground aquifer.

The existence of (Wadi
Dermalih) under ground
aquifer was established
during the construction of
the underground caverns
and tailrace tunnel of the
PS scheme . The
excavation of the caverns
was only possible after
completing grout shields
and drainage tunnels
around them. This photo
shows the huge spring
which had erupted from a
gypsum- breccias layer
during the tailrace tunnel
excavation . A great
amount of grouting was
done to plug this spring

It is an established fact that (Wadi Der Malleh) aquifer is of a huge
extent and it runs under the river aquifer independent from it . It
is fed from all the sinkholes and seepage paths and solution
tunnels in the upstream area and from the reservoir.
The flow of this aquifer is rich with sulfate indicating passage
over and through gypsum layers causing further dissolution.
The flow finds its way to the downstream at various locations
posing a constant threat to the stability of the dam itself
through the possible formation of more sinkholes .

In February 2002 one
sinkhole at the left bank
appeared suddenly . It
was located at 150 m
from the downstream toe
of the dam .It was due to
the dissolution of
gypsum layer by seepage
water originating from
under the embankment at
further left.
The sudden collapse of
the roof occurred as a
result of the infiltration of
drainage water from a
nearby camp

This sinkhole had a depth
of 15 meters and a diameter
of 15 meters at the bottom.
It was put under
observation and filled later.
Although the initial sinkhole
was filled with 1200 m³ of
loose sandy gravel, the
settlement continued. A
further 3000 m³of material
were required to fill the
sinkhole completely in two
separate filling operations
in May 2003 and October
2004. By March 2005 there
had been a further
settlement of about 0.5 m.

The dotted line shown
on this aerial view
indicates the general
alignment of sinkholes
downstream of the
dam. This suggests
some correlation with
underground
geological feature .
As a result of sinkholes
activity the maximum
operation water level
was reduced to 319 .
Instead of 330 .

The sinkhole formation
In Mosul dam is a slow
and dangerous process
connected to seepage
and underground flow
within gypsum/anhydrite
layers and their
dissolution. This could
happen anywhere under
and around the dam
where conditions are
favorable. The danger
results from their
unpredictable and
sudden formation. This
requires intensive
observation of ground
water movement.

Problems encountered in the grout Curtain
Construction and Maintenance
• It was an established fact at the end of 1985 that grouting of some parts of
the grout curtain did not succeed in obtaining the grouting design criteria.
• These areas where in the gypsum breccias (GB) layers which resisted
grouting due to their complex composition.
• All types of grouting methods, materials and techniques were tried with no
positive results.
• So at the beginning of the impounding of the reservoir in 1985 some parts
in the curtain were still open and others were temporarily closed while all
efforts to seal them failed. These areas where called the “windows”.
• As the level of the reservoir was raised the newly built hydrostatic
pressure opened new windows in the curtain. Even the temporarily closed
windows were opened again.
• This created a very critical situation and an intense atmosphere at the site,
as every one knew that dissolution of gypsum was continuing at higher
rates.

• To cope with this situations large cavities had to be plugged. Many trials on
various mixes were conducted to have a workable thick mix. Finally a sandy
mix (SS) was reached in which sand was added to the normal cement-
bentonite mix at a ratio of 2:1
• Such grout mix was used when large quantities of normal mix grout did not
give the required result.
• In situations where fast action was required to fill very large cavities in a short
time very large quantities of both types of mixes had to be transported and
pumped in short periods of time. This resulted in devising a large production
and injection process which was called “Massive Grouting” or “Enlarged
Grouting”
• This involved the driving of three vertical steel pipes from the crest of the dam
through the core to the grouting gallery. Grout mix was delivered by truck
mixers to the pipes heads and pumped down to the gallery which was then
remixed and distributed to the grout holes using high pressure hoses.

• The sand and cement were batched in the concrete batching plant ,loaded
in the truck mixers then bentonite slurry was added in the grout mixing
plant before transporting to the delivery pipes on the dam crest.
• This industrial production and injection processes succeeded in reaching
an injection rate up to 20 cubic meters per hour.
• A verbal report mentioned that one cavity took more than 5000 tons of
grouting materials in a continuous operation before it was finally closed.
• In 1987 every one realized that the dissolution of gypsum within the
breccias layers would continue indefinitely and the grouting process
should also continue as a routine maintenance processes.
• Grouting operations stopped on 8th
August 2014 when ISIS occupied the
site. Although they where driven away on the 18th
of the same month the
operations were not resumed to the same level as before up to now.
• The quantity of solid materials injected in this work reached a quantity of
95500 tons up to August 2014.

• The dam works were followed by an international Board of Experts
(IBOE) from 1979 at the stage of the planning report preparation up to
the end of maintenance period in 1989 .They held meetings with all
parties involved and issued 34 detailed reports with remarks and
recommendations. The grout curtain problems were discussed and
reported in details
• In 1987 the problems on the grout curtain induced the contractors to
seek advice from Binnie & Partners as an external consultants who
made a detailed study on the problem and explored possible
solutions.
• The study included a theoretical analysis of the mechanism of gypsum
dissolution. It also considered the use of many alternative grouting
materials and additives . But these were all rejected on technical or
economical reasons or both.
The study then explored the possibility of using many
alternatives of using upstream barriers.

Problems encountered in the grout Curtain Construction and
Maintenance
First Alternative was the
blanketing of the dam u/s as
shown. Such blanket would
be installed only by drawing
down the reservoir.
Blanketing the bed may be
done without drawing down
the reservoir, but success
depends on the entry points
of seepage to the foundation
and lengthening the
seepage path.
Blanketing the bed may be
done by dropping bentonite
pellets through vertical pipes
and then covering with sand.
This is done only in small
ponds and cannot be relied
upon in a large project as
Mosul Dam.

Problems encountered in the grout Curtain Construction and Maintenance
Second Alternative was
to construct a positive
cutoff from the upstream
berm of the dam or a
new grout curtain from
the toe . The difficulty of
the positive cutoff
solution is in the
combination of the depth
and the hardness of
pervious strata. The grout
curtain assumes to have
better geology in the new
location which is not the
case . Both solutions
require the drawing down
of the reservoir.

• A general conclusion from Bennie & Partners study was; that
there was no recommended practical solution for the grouting
problem but only to continue the curtain maintenance by
improving the mixes and injection procedures ( as shown earlier
here) to combat large dissolution areas. With good ground water
observation using the piezometers in the grouting gallery, early
warning and intervention can be achieved. The three major
consequences of this study were:
1. It gave new dynamics to the grouting tests program already
initiated at the site to look for new mixes and injection methods.
2. It introduced the concept of (Maintenance Grouting) as a long term
safety and repair procedure and abandon the idea of constructing
the ideal curtain which confirms exactly to the design criteria and
so relieving the contractors from this obligation.
3. It emphasized the importance of piezometric observations as a
mean of checking local solution channels for prioritizing the repair
work.

• In a continuing effort by the owner to look for alternative
solutions. The expert Mr. Mariotte from Geoconncel examined
the site and submitted his report with the following proposals:
• a) strengthening the grout curtain in the problematic areas by
additional rows of grout holes ,one in the u/s of the curtain and
slightly inclined to the u/s, the second in the downstream of the
curtain and slightly inclined to the d/s the third is vertical in the
center. The sequence was to grout the central row followed by
the u/s row and then the d/s row. Finally the central row was to
be re-drilled and grouted using silica gel.
• b) the second proposal was to construct a tunnel along the
length of the chalky series from which grouting would be
performed.
• c) the third proposal was to construct a series of tunnels and
galleries to replace risky materials.

• d) the fourth alternative was to construct a diaphragm from the
u/s berm connected to concrete facing, OR a diaphragm from
the crest through the core u/s of the gallery after removing the
top rock cover as shown.

• Comments of the IBOE on Mariotte’s report
• The Board did not object to alternative (a) as machinery and
grouting capacity was available.
• The Board thought that (b) and (c) were very specialized
solutions and need further studies to prove their technical and
economical feasibility in addition to the need of new machinery
and were dismissed due to time shortage.
• The Board considered solution (d) as undesirable as it
required the lowering of the reservoir for an extended period of
time (2-3 years) which was required for implementation.

Badush Dam
A flood wave study in the
event of Mosul Dam failure
was prepared by the Swiss
Consultants Consortium in
1984-1985. Details of this
study and its conclusion are
given later.
The great magnitude of
Human and material losses
induced the ministry of
irrigation after the observed
problems on the deep grout
curtain, to initiate in 1987 the
design and construction of
Badush Dam as a protection
dam, to retain Mosul dam
flood wave completely in
case of failure.
The dam site is located d/s of
Mosul Dam 15 kilometers
north of Mosul city.

Badush Dam
• Fast track method was employed for the Investigations and design of
the dam. The geological investigations showed good foundation
composed of sound limestone rocks.
• A mathematical model for Badush Dam was done which was checked
by a physical hydraulic model . These models established the
maximum water level after filling with the Mosul Dam flood wave.
Badush dam was designed to have enough free volume to contain this
wave fully
• A power house was also designed to utilize the head a available
between the reregulating Mosul Dam power station and Badush site
providing an installed capacity of 170 Mw .

Badush Dam
• The dam consisted of an earth fill embankment with a central concrete
structure which groups together the power station, the lower gated
spillway and the un-gated spillway at the crest .In normal operation
the gated spillway had the capacity to pass a maximum discharge of
8000m³/ second .This is the maximum routed discharge from Mosul
dam . It is the maximum discharge that can be passed through Mosul
city without flooding it. The following table gives the main design
parameters for Badush Dam

Badush Dam Design Parameters
Description Before Mosul
Dam failure
After Mosul Dam
failure
Remarks
Normal Operation
Water Level (masl)
245 - Consistent with
the reregulating
dam power station
operation
Maximum Operation
Water Level (masl)
250 307.22 Passing a
maximum
discharge of 8000
m³/sec
Dam Crest Level 312 312
Freeboard (m) 62 4.78

Badush Dam
• Construction of the dam was started on the 1st
of January 1988 ,but it
was halted at the end of 1990 due to the economic embargo imposed
on Iraq after the occupation of Kuwait. The percent of completion was
then 30- 40%.
• Badush dam is thought by so many experts as the only 100% safety
measure protecting Tigris river basin from the consequences of Mosul
Dam failure.

Badush Dam
• In 2008 a desk study based on a Mathematical model was done to
confirm the design levels and the flood protection function of Badush
Dam as it was originally designed.
• The study showed that all assumptions and results in the original
design were correct.
• This study went further to study a staged construction of Badush
Dam.
• The suggested first stage was to build the dam to an intermediate level
of 260 masl to allow the operation of Badush Dam power station as
stipulated by the original design and allowing the normal operation of
the Mosul Re-regulating Dam.
• The next stage was to raise the Badush dam to its full height to take
up the flood protection function.
• The most critical question that must be answered now Is: when this
second stage shall be done before it is too late to do any thing at all?

Badush Dam- Staged construction

Mosul Dam safety reviews during operation
• First general safety review was done in 1995 by two Bulgarian experts, who
stayed for two months at site. Operation records were examined with all
instrumentation readings ,piezometric observations and geodetic
measurements carried on all parts of the dam in addition to seepage quantities
salt content analyses.
• Grouting operations and all available data on grout consumption at various
locations, grout mixes, grout takes and pressures used were all checked.
• Their report included various conclusions and recommendations which can be
summed up as follows:
• 1. Avoid impounding above el. 330 for a very long time.
• 2. Increasing the width of the deep grout curtain by performing two additional
rows of inclined grout holes ; One at the u/s and the other at d/s of the curtain.
• 3. Continuing the maintenance grouting program as before as a routine work
and continue instrumentation readings and seepage and salt content checking.
• 4. Increase the number of the peizometers at d/s side of dam.
• 5. carry out a dynamic analysis for the dam stability.

• In 2003 Iraq was occupied by allied forces from USA and Britain. A
team from USACE inspected the site to investigate its safety
situation. As a result an urgent contract was signed between the
Projects Contracting Office (PCO) of the Coalition Provisional
Authority (PCA) and Washington Group International & Black and
Veatch JV The terms of reference included:
i) The compilation
of all available data on Mosul Dam and reviewing them.
• ii) Conduct site visits and meetings with site and Ministry's’
personnel .
• iii) Perform additional Studies as required.
• Iv) Forming Panel of top Expert to study every thing and give
advice and recommendations.

• A comprehensive report was submitted in august 2005 . It contained the
following :
• i) Evaluation of the existing condition of the dam.
• Ii) Review of the SC (1984- 1985) dam break flood wave study report.
• Iii) Memorandum on the review of the SC Mosul Dam seismicity study.
• Iv) Mosul Dam Potential Failure mode Analysis Study.
• v) Emergency Action Plan ( issued under separate cover)
• vi) Analysis and recommendations by the panel of Experts

• One of the most important parts of the report was the study on the
“ Potential Failure Mode Analysis (PFMA)”. This was done by
WII/BV JV, URS Corporation experts in addition to Skip Hendron
( Professor Emeritus, University of Illinois)
• The study followed the guidelines of the he US Federal Energy
Regulatory Commission (FERC).
• It was concluded that there are thirteen possible failure modes for
Mosul Dam. these were grouped into three categories according to
their greatest significance considering need of awareness,
potential for occurrence, magnitude of consequence, and
likelihood of adverse response.
• The failure modes of the highest potential ( Category 1) given in
the study are listed in the following table and the likelihood of
their occurrence are also given.

Failure Mode No Description Category Basis For category
Assignment
N1 Usual Loading
Shallow
Foundation Seepage in
the Main Valley
1 Judged to be possible,
and also judged to
develop with limited or
no warning of
development
N2 Usual Loading
Intermediate Depth
Foundation Seepage in
the Main Valley
and also judged to
no warning of
development
N3 Usual Loading
Deep Foundation
Seepage in the Main
Valley
and also judged to
no warning of
development

-The other ten failure modes were considered either
physically possible but unlikely to progress to failure or
very unlikely.
-It was established in the
analysis that the three (N) failure modes were all related
to geology of the dam foundation. They may result from
the formation of cavity/cavern under the dam in one of
the (GB) layers at various depths with the resulting
increased seepage flows either at the dam/foundations
interface or at depth and the consequent subsidence of
one section of the dam. This would result in large flow of
water through the dam body and washing it away.

• -The adverse conditions leading to such an event is one or
more of the following
a) The presence of one the (GB)
layers in which the cavity/cavern forms.
b) No grouting under the dam shell and
doubts on the blanket grouting conditions under the core.
c )The possibility of the development of sinkholes very close
to the upstream or downstream toes of the dam.

• The WII/BV panel of experts recommendations may be summarized as
follows:
• “1. The 1984-1985 dam break study is still applicable today as it was at
the time when it was done .
• 2. The Badush Dam Construction is the only reliable solution which
provides 100% security to the Tigris river valley below Mosul dam in
case of its failure. This failure of Mosul Dam is judged possible to
develop with limited or no warning of development
• 3. The continuation of the grouting maintenance program is
important and necessary to increase the useful life of the dam as long
as possible. The grouting however does not eliminate the possibility
of failure
• 4. The proposal for diaphragm wall construction is not feasible
technically and economically. It is not safe, very costly and involves
very high risk to the dam and it threatens its stability.”

• In 2006 the ministry of water resources ( previously the ministry of irrigation)
formed another panel of experts mainly from Harza Engineering (USA) which
ihad become part of MWH global since 2001 to perform yet another general
safety review.
• In addition to the grouting works another very important issue considered was
the ground water movement in the left bank and possibility of sinkholes
formation.
• One detailed hydro geological survey at the left bank d/s of the dam was
recommended in addition to another ongoing geophysical survey that was
carried out by the Geological Survey of Iraq .
• The new hydrological survey was done using geo-radar which required drilling
of many boreholes to carry out the tests and measurements.
• This survey did not give conclusive results except the active movement of
ground water which originated from seepage from under the dam left bank.

• The only decision that this panel could come up with was to limit the
maximum operation water level to 319 instead of 330. This was an
arbitrary choice based on the reservoir water level at that time,
pending further revision on new findings which did not come . This
level is consider now as sacred by many even without knowing how it
was fixed!!!!!!
• The resulting new maximum operation water level means the loss of
about 40% of the live storage capacity every year.
• The questions are : do we need now to reduce this level further in the
light of the present adverse developments? And to what extent?

Mosul Dam last update
• The American interest in Mosul Dam safety did not cease even after
receiving WII/ BV report in 2005. In 2007 USACE issued a new study
underscoring the dangerous situation of the dam. On 1st
May 2007 an
official letter signed by the American Ambassador in Baghdad and
David Petraeous the US army commander in Iraq was sent to the
Prime Minister warning from the worsening dam conditions and the
expected coming catastrophe asking to take necessary precautions to
resume Badush Dam construction and to alarm the population. This
letter was discarded by the latter and no action was taken.
• The dam was again focus of USACE attention after the site was
recovered from ISIS at the end of August 2014 and a new warning was
made at the end of 2014 urging to empty the reservoir and to warn the
population downstream of the dangers.

Mosul Dam last update
• . In February 2015 the dam was under surveillance by an
interagency team lead by the USACE which carried out
site measurements and observations using high
precision remote sensing equipments. Their findings
were included in late 2015 report which was updated in
January 2016 and sent to the Iraqi government. The
findings were alarming and may be summarized in the
following:
i) There were signs of increased formation of caverns and
sinkholes under the dam .
ii) Increased concentration of sulfates in the seepage
water indicating increased dissolution of gypsum.
iii) Sign of increased settlement in the grouting gallery and
cracks opening.

US Interagency team findings
Cameras and remote
sensing were used for
the observation of the
movement of markers
installed on the dam
body and structures
for early warning.

Cracks monitor of monolith
76/75 of the grout gallery
reported displacement of
(0.05” – 0.15” )
Investigation of movement
showed they were not
caused by on site activity
such as nearby works that
might affect reading
calibration issues or thermal
expansion.
The only reasonable
conclusions is that they are
caused by settlement
The lower sketch indicates
the location of these
monoliths

These plots give recorded
cumulative settlement in
the grouting gallery
sections 69,75,80, 84 from
1986 till end of 2015.
Indications are that
settlement is continuing at
various rates in these
section.
Photographs indicate
signs of distressed of
concrete.

According to the
relative Risk
classification of all
USACE Dams .
Mosul Dam would
plot at the shaded
red box at the upper
right corner
indicating extreme
risk

US Interagency team Conclusion

Our conclusions
• 1. Mosul dam site is not the best of sites for a dam of Mosul Dam
magnitude; on the contrary it suffers from severe problems due to the
presence of badly jointed and cavernous soluble gypsum/anhydrite
layers, gypsum breccias layers, weathered and jointed limestone and
soft marls. The creation of the reservoir has accelerated the
dissolution processes and has lead to the formation of sinkholes.
• 2. During construction it was clear that the gypsum breccias layers
were very much resistant to the grouting of the deep curtain zone
under the dam and much work was done to fill the resulting
caverns and solution channels in this zone by maintenance
grouting. But no one knows for sure of the magnitude of
dissolution that may be occurring under the shells of the dam or
even under the consolidation grouting which was done under the
core. The formation of active sinkholes in the reservoir is evident
from the last bathymetric survey conducted in 2010.

Our conclusions
• 3. This lack of knowledge leads to the belief that whatever grouting
that may be done in the grout curtain zone there may be other
places under the dam body where the formation of active
sinkholes may be occurring. If any of such sinkholes develops
near to the dam base then a portion of the dam will sub side
leading to the initiation of large flows through the dam body and
causing the complete washing away of the dam in a very short
time
• 4. This risk factor is a real one but no one knows exactly when
such an event can occur. When this does happen the resulting
flood wave is of unimaginable magnitude due to the human and
material losses it can inflict on the country of Iraq.

Our conclusions
• 5. In facing such situation we have worked out some solid
recommendation which I should leave to be spelled out in the next
session.
Thank You

Mosul Dam: The Full Story of Its Location, Design, Construction Challenges

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