Environmental Engineering Reference
In-Depth Information
v
1
v
IZ
c
IZ
i
The contribution of a given defence asset to the
expected annual damage (EAD) is then calculated
using the standard formula:
c
d
1
¼
ð
15
:
3
Þ
where: C
IZ1
¼
total economic damage associated
with the i
th
adjacent Impact Zone during the flood
event (this equates to the damage within the Im-
pact Zone itself and to those Impact Zones that
receive floodwater from the i
th
adjacent Impact
Zone); v
1
¼
volume discharged into the i
th
adjacent
Impact Zone from defence d
1
during the flood
event; andv
IZj
¼
totalfloodvolumedischargedinto
the i
th
adjacent ImpactZoneduring thefloodevent.
The defence contribution to the residual risk
conditional on the load (l) (based on all system
states, m, sampled for load, l) can then be estab-
lished simply for defence d
1
as follows:
c
d
i
l
X
n
l
i
þ
l
i
þ1
2
l
i
þ
l
i
1
2
EAD
d
1
p
i
p
i
i
¼2
ð
15
:
5
Þ
where EAD
¼
Expected Annual Damage, and n
¼
number of load conditions considered.
As the volume of water discharged into the
floodplain is a function of the defence system
state, the state of the defence assets (failed/not
failed) is also monitored. The contribution to risk
arising from a single defence asset can be further
disaggregated into the contribution due to an ul-
timate limit state failure (i.e. breach in the case of a
linear defence asset, or pump or gate failure) or
serviceability failure (i.e. overtopping in the case
of a linear defence asset, or capacity exceedence in
terms of a pump) (Fig. 15.9).
m
l
X
m
l
1
c
d
1
l
c
d
1
j
ð
15
:
4
Þ
j
¼1
where c
d
1
l
¼
mean consequence associated with
the loading condition l for a specified defence (d
1
).
400
Contribution to risk (overtopping)
350
Contribution to risk (breaching)
300
250
200
150
100
50
0
1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0
Unique Asset Number
Fig. 15.9
Risk attributed to individual assets can be further disaggregated into the contribution from ultimate (e.g.
breach) and serviceability (e.g. overtopping) limit states (taken from the Thames Estuary). Expected annual damage
(EAD)
