FLOOD04994

• County: Statewide
• Community: na
• Basin: Statewide
• Title: Guidelines on Selection of Acceptable Flood Capacity for Dams
• Date: 3/1/2000
• Prepared By: Australian National Committee on Large Dams
• Floodplain - Doc Type: Educational/Technical/Reference Information

I'
II
I
I
I'
II
II
II
,I
II
I'
II
I'
, II
II
1\ I
,I
,I
I
I

on when this is appropriate is provided in
sub-sections 3,7.5 and 7,2, Book VI.

(ii) The level of experience of operators, and
history of gate problems and malfunctions
during operation, and under test, should be
included in the risk study and joint probability
considerations.

(iii) If there are dam/s upstream the potential
for a cascade effect should be assessed,

(iv) The extent of concurrent floods in
tributaries downstream of the dam will relate
to flood control procedures and assessment of
dambreak flow conditions. Simple procedures
are presented for those design situations in
which the issue of concurrent floods is of
minor importance, though more rigorous
procedures (similar to the joint-probability
approach used for the detailed consideration of
initial reservoir levels) can also be used (sub-
section 8.5, Book VI).

9.3. Flood Mitigation Dams.

Dams with significant flood mitigation storage
should be assessed as specific cases. Selection
of design floods relate to two main aspects:

(i) Hydrologic safety of the dam,
What initial flood, and potential
consequent floods, must be accommodated
without failure, relevant to the appropriate
consequences and risk level?

(ii) Selection of flood storage
volume.
What volume is required for flood control
relative to the appropriate degree of
downstream flooding control? This
involves balancing economics of dam
construction with flood protection to a
required risk level. It is limited to a
maximum inflow sequence that can be
economically justified, with recognition
that protection cannot be provided against
all floods.

(Refer Appendix 2, sub-section A2.1O).

9.4. Construction FkllXJs.

9.4.1. Construction Flood Practice.

There is no consistent, or appropriate
international practice or standard for risks
associated with handling floods during
construction, be it for river diversion during,
construction of a new dam, or flood
management during remedial works for an
existing dam.

The main concern in the past in assessing river
diversion provisions during dam construction
to minimize potential damages and delays to
the construction works, an economic
consideration, rather than specifically consider
risk to life downstream.

Risks to construction workers are covered in
general by appropriate occupational health and
safety regulations and penalty rate provisions
in wages, with the acceptance of higher risks
on construction projects.

The overall perception of dam engineers has
been that higher risk levels are acceptable
during short term construction periods as
compared with the long term risks from the
completed structure.

Construction flood provisions are also very
site specific, and normally there would be
flood forecasting and warning arrangements
for at least site protection.

ANCOLD 1986 gave guidance on selection of
construction floods (refer Appendix A, sub-
section A2.8), with the diversion flood based
on equivalence in flood probability over the
construction period to the recommended
design flood for the relevant consequences,
including risk to life, for the completed dam
assuming a nominal 100 year life. The
guidelines at that time were basically related to
river diversion during construction of new
dams.

I

ANCOW Guidelines on Selection of an Acceptable flood Capacity for Dams 23