Abstract
Darbandikhan Dam is one of the vital dams in Iraq that contributes to the flow
of water and provides water reserves for multiple purposes. However, its collapse
poses a major risk to the stability of the surrounding water and environmental
system, which may lead to severe water shortages and pollution and threaten
residents' livelihoods. Therefore, it is necessary to assess the damage caused by the
failure of the dam and develop plans and mechanisms to reduce the resulting losses.
This research studies probability of the collapse of Darbandikhan Dam to identify
and describe flood risk areas and thus understand the potential impacts of this
collapse on the downstream area to protect people, institutions, and agricultural
regions.
There are many reasons for the collapse of dams. Still, in this research, the
focus was on the most dangerous scenario for Darbandikhan Dam more than on the
cause, which is the dam collapse due to the phenomenon of overtopping, where the
reservoir is filled to the level of the dam crest. The research relied on the computer
modelling method to analyse the data, using a 2D unsteady HEC-RAS model and
with the help of the GIS software to prepare the digital data and maps necessary,
such as DEM and land use, with a resolution of 12.5 m and 10 m, respectively.
The RAS-Mapper tool was used in the HEC-RAS software to create cross
sections of the Diyala River course to adjust the river course. The hydraulic data
obtained from the Iraqi Ministry of Water Resources were entered, and visual
inspection with the aid of satellite photos was used to perform the model calibration
and verification process due to the lack of field data. A good match was obtained
after comparing the hydraulic model results with the satellite images. The breach
parameters were predicted using the available regression equations founded in HEC
RAS. The Von Thun and Gillete equation was chosen to find the dimensions of the breach opening because it works best for the conditions at Darbandikhan Dam. The
bottom of the breach was 205 m wide, the sides were 0.5 slope, and it took 1.75
hours to form.
After running the model and implementing the hypothetical collapse of the
dam through the HEC-RAS software, the peak value of the breach outflow discharge
at the dam site reached 381128.6 m3 /s, which caused the flooding of an area of
approximately 8200 km2 , including Hemrin Lake. The flood maps showing the
hydraulic characteristics of the flood were produced through the RAS-Mapper tool
in HEC-RAS, where the depths, velocities, and arrival time values in the closest city
(Sirwan) were (17.5–58) m, (2-22) m/s, and (0.13-0.6) hours, respectively, while in
the farthest city (Al-Aziziyah) were (0-0.5) m, (0-0.3) m/s, and (165-228) hours. In
addition, a sensitivity analysis was performed for flood discharge and flood depth to
breach parameters because of its importance in analysing dam collapses. The
greatest sensitivity of the flood discharge and flood depth values was to breach
bottom width and the least to breach formation time.
This study enhances the understanding of the risk associated with dam
collapse. It guides decision-makers on how to take proactive measures to reduce the
negative impacts of dam collapse. The study's results contribute to the effective
policy and procedure implementation to ensure the security of communities adjacent
to Darbandikhan Dam and help preserve water resources that are the lifeblood.
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