12.2 Dam Breach Consequences
179
rheology could change dramatically for changing tailings properties including degree
of saturation, consolidation, and the increased presence of clay minerals.
12.2.2 Breach Size
Continuing with the dam/dykes example, the next step of a risk analysis involves the
evaluation of breaches which lead to downstream consequences. The first step is of
course to determine the breach size.
The literature shows that dam breach size models rely on many assumptions and
are mostly based on geometry of the embankment and retained water levels/volumes
(Franca and Almeida 2004; Morris 2005; Zagonjolli and Mynett 2005; USBR 1988).
In a 2013 study by Nourani and Mousavi (2013), 142 embankment dam breach
data were collected from reliable references and dam breach equations analyzed.
Dimensional analysis and multiple regression were used to predict maximum outflow
from earth dam breach.
Uncertainty of empirical relations was determined using appropriate statistically
method. The following general results were derived by (Nourani and Mousavi 2013)
from collected data by studying 142 embankment dam breaches (Eq. 12.3):
2 ∗ h d ≤ B m ≤ 3 ∗ h d
(12.3)
where B m = average breach width (m); h d = dam height (m); B top /B bottom = 1.13–1.64
width at top, bottom of the breach.
If we note as V w the water volume above break point of bottom (m
3 ) and h b the
height of water above breach bottom the analyses performed in the study yielded the
following regression (Eq. 12.4):
B m = 2.2839 ∗ V
0.0635
w
∗ h
0.8481
b
with r = 0.918
(12.4)
Please note that many of the necessary data are Space Observable or retrievable,
by querying historic imagery databases.
The final step is to develop a breach outflow analysis and through that to evaluate
the downstream consequences. Let’s note that unless major changes intervene it is
not necessary to redo a dam break analysis each time the risk assessment is updated,
but variations in land use and density, which are all space observable will generate
possible significant changes in consequences.
179
rheology could change dramatically for changing tailings properties including degree
of saturation, consolidation, and the increased presence of clay minerals.
12.2.2 Breach Size
Continuing with the dam/dykes example, the next step of a risk analysis involves the
evaluation of breaches which lead to downstream consequences. The first step is of
course to determine the breach size.
The literature shows that dam breach size models rely on many assumptions and
are mostly based on geometry of the embankment and retained water levels/volumes
(Franca and Almeida 2004; Morris 2005; Zagonjolli and Mynett 2005; USBR 1988).
In a 2013 study by Nourani and Mousavi (2013), 142 embankment dam breach
data were collected from reliable references and dam breach equations analyzed.
Dimensional analysis and multiple regression were used to predict maximum outflow
from earth dam breach.
Uncertainty of empirical relations was determined using appropriate statistically
method. The following general results were derived by (Nourani and Mousavi 2013)
from collected data by studying 142 embankment dam breaches (Eq. 12.3):
2 ∗ h d ≤ B m ≤ 3 ∗ h d
(12.3)
where B m = average breach width (m); h d = dam height (m); B top /B bottom = 1.13–1.64
width at top, bottom of the breach.
If we note as V w the water volume above break point of bottom (m
3 ) and h b the
height of water above breach bottom the analyses performed in the study yielded the
following regression (Eq. 12.4):
B m = 2.2839 ∗ V
0.0635
w
∗ h
0.8481
b
with r = 0.918
(12.4)
Please note that many of the necessary data are Space Observable or retrievable,
by querying historic imagery databases.
The final step is to develop a breach outflow analysis and through that to evaluate
the downstream consequences. Let’s note that unless major changes intervene it is
not necessary to redo a dam break analysis each time the risk assessment is updated,
but variations in land use and density, which are all space observable will generate
possible significant changes in consequences.