FLOOD01798

• County: Statewide
• Title: Australian Rainfall and Runoff 1998, Revision of Book VI - Estimation of Large to Extreme Floods
• Date: 11/28/1998
• Prepared By: Rory Nathan, Sinclair Knight Merz
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Table 3 Summary of procedures to derive Design Floods.

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!;jOOK VI . t:.5t1maUOn 01 Large lO t:.xtreme r-IUUU5

Use ~complete stann- losses for all durations and all AEPs (see Section 4.2.3)

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See recommen-
dations in Book II,
Section 3 and also
more recent
regional loss data
(where available)

Losses to be varied
gradually between those
adopted forthe 1 in 100
AEP events and the PMP
Design Flood

Very low loss rates
applicable for PMP
Design Floods (0 mm IL
and 1 mmlhr CL for many
regions)

Either runoff-routing or unit hydrograph models can be used, examples of
suitable modelling packages being RORB, RAFTS, URBS, WBMN

Calibration to range of flood magnitudes, including reconciliation with design
flood estimates derived from at-site/regional flood frequency and
paleohydrological procedures

Non-linearity in S = kQm relation generally assumed to be 0.8 or 0.85
(depending on catchment characteristics), and adjustment of unitgraph
ordinates required for Rare to Extreme events

Baseflow to be varied
gradually between that
adopted for the 1 in 100
AEP and the PMP Design
Flood

Adopt constant value 20%
to 50% higher than
maximum observed

Derive rainfall-based estimates for range of design rainfall durations and
adopt highest peak discharge from a range of different durations

If credible limit of rainfall extrapolation is 1 in 100 and prErburst temporal
patterns not available, shape factors (Table 7) may be applied to design
floods derived fromlhe PMP, and the 1 in 50 AEP, and 1 in 100 AEP design
rainfalls.

Not applicable

Defined as the limiting
value of flood that could
reasonably be expected to
occur.

AEP-neutral procedures are recommended to ensure that any bias in the AEP
of the transfonnation between rainfall and runoff is minimised. A range of
procedures from the simple to the rigorous are provided

Regional
procedures and
flood frequency
analysis (Book IV,
Sections 1 and 2)

Shape factors may be
used to determine Rare
design estimates
(Table 7)

The credible Jimit of
extrapolation generally
ranges from 1 in 100 to
1 in 5000AEP

At present only
applicable to the GSAM
zone

See Section 4.2.3 (b) and
(d) for generat
recommendations

Genera' guidance in
Sections 4.3.1 - 4.3.3
See Sections 4.3.4

See Sections 4.3.5 and
4.3.6

See Section 4.4

Rainfafl-based
procedures generally
preferred (Section 4.5;
Book Iif, Section 2)

For seasonal floods see
Section 4.6

Procedures applied are
not AEP-neutral and thus
it is not possible to assign
an AEP to the PMF.

Section 5 includes
references to procedures
sufted to the analysis of
uncertainty.

Regional information may
be used to estimate the See Section 4.7
PMP Design Flood
(conservatively assumed
to equal the PM F).