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 19 Design burst loss estimates for
events between 1 il) 100 AEP and the PMP.

4.8
3.5
2.5
1.2
0.6
0.4
0.2

2.9
2.6
2.4
2.0
1.6
1.5
1.2

information, i.e. using rainfalls with a limit of extrapolation of
1 in 100 AEP. The input design burst rainfalls are listed in
Table 12.

Design losses for the 1 in 50 AEP and 1 in 100 AEP
events are obtained by frtting to the flood frequency
estimates (as described in Section 6.3.1), i.e. an IL, of 10
mm, and a CL of 3.5 mmlhr. Loss values for intermediate
events are obtained using the log-log interpolation
procedure (Equation 7). The values of L, and L" and y,
and Y, are shown in the 2" and 3" rows of Table 19 for
both initial and continuing losses, and interpolated values
for the 1 in 2000 AEP and 1 in 50000 AEP events are
shown in the 6th and 81h rows.

The design floods are derived using the routing
parameters obtained from calibration, i.e. a k, of 27 and an
m of 0.8. In order to construct a flood frequency curve it is

10000

-+-- Design burst, credible limit 1:100 AEP
____ Design burst, using eRG-FORGE
---lk- Design stoon, using eRG-FORGE
- . - Flood-based regional estimate

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t:SOOK VI - t:.stlmallon 01 Large to t:xtreme I-Iaocts

necessary to determine the critical duration for each AEP of
interest. Normally the critical duration decreases with AEP,
though for simplicity it is assumed here that the 24 hour
duration is critical for all AEPs. The resulting flood
frequency curve is shown in Figure 13 (using filled diamond
symbols).

6.3.3 Estimates Based on Design Rainfall Bursts
With a Limit of Extrapolation of 1 in 2000
AEP

This example is similar to that presented in Section
6.3.2, the only difference being that CRC-FORGE rainfall
estimates are now incorporated, i.e. the limit of rainfall
extrapolation is 1 in 2000 AEP. The input design burst
rainfalls are listed in Tables 16 and 17.

Loss values for intermediate events are again obtained
using the log-log interpolation procedure (Equation 7). The
interpolated values are shown in Table 19.

The resulting flood frequency curve is shown in Figure
13 (using filled square symbols). It is seen that
incorporation of the CRC-FORGE rainfalls yields a lower 1
in 2000 AEP flood peak, and that when cOlJ1bined with the
Siriwardena and Weinmann interpolation procedure a less
conservative flood frequency curve is obtained.

6.3.4 Estimates Based on Design Rainfall
Storms With a Limit of Extrapolation of 1
in 2000 AEP

Rather than use design burst rainfalls with
conservatively low losses, this example presents the results
for the situation in which pre-burst temporal patterns are
available (see Sections 3.9.1c and 4.2.1b for more general
comments).

The pre-burst temporal pattern for the 1 in 100 AEP and
PMP 24 hour events are shown in Figure 14. The pre-burst

-.

2

1

0.5

0.2 0.1 0.05 0.Q1
Annual Exceedance Probability (%)

0.0001

0.001

Figure 13 Flood frequency curves derived using four design approaches,