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 10 Prediction equations for preliminaJ)l estimates of long duration PMP events (mm) in the GSAM zone as a
function of catchment area (AREA, km') and 1 in SO AEP 72 hour rainfall intensity (501", mm/hr).

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12 PMP = 6732-126.9 x 10g,0(AREA) + 434AI0910(501,,) 35 0.85 39 8
24 PMP = 113.1- 3.S11JAREA +404.0J50I" 43 0.91 48 8
36 PMP = 138.5 - 4.055,/ AREA + 4S0.5J 50 I" 42 0.90 56 8
48 PMP = 135.9 -4.414,/AREA + 492.7J50I" 43 0.91 59 8
72 PMP = 125.5 -4,,6S6JAREA + S33.0J5ol" 43 0.88 72 9

Table 11 Prediction equations for preliminaJ)l estimates of long duration PMP events (mm) in the GTSM zone as a
function of catchment area (AREA, km'), distance of the catchment centroid from the coast (COAST, km), latitude of
the catchment centroid (LAT, degrees South), and height of the intervening barrier between the catchment centroid
and the coast (HEIGHT, m AHD).

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JPMP = 40.17 -0.lS7xLAT -4A45Iog,0(AREA)-0269JCOAST
JPMP = 37,,31- 0218 x LAT - 0,,082JAREA - 0212JCOAST - 0.00175 x HEIGHT 85 0.92 1.1 4
JPMP =44.19 - 0260 x LAT -0,,093JAREA - 0,,239'/COAST -0.00214 x HEIGHT 85 0.93 1.2 4
JPMP = SS.86-0.34SxLAT -0.117JAREA -OA57JCOAST -0.00341 x HEIGHT 84 0.92 1.8 5
JPMP = 63.66 - OA04 x LAT - 0.127JAREA - 0.6OSJCOAST -0.00450 x HEIGHT 84 0.89 2.5 6
JPMP ~ 64.94 - 0.335 xLAT - 0.113J AREA - 0.622JCOAST - 0.00298 x HEIGHT 73 0.89 2.4 5
JPMP ~ 68.24 - OA08 x lAT - 0.158JAREA - 0.630JCOAST - D.00324 x HEIGHT 59 0.87 2.4 5
.JPMP =6823 - 0.397 xLAT - 0.163JAREA - 0.S8SJCOAST - 0.00286 x HEIGHT 59 0.89 2.2 5
JPMP = 7223 - 0.440 x LAT - 0.181JAREA - 0.S32JCOAST - 0.00312 x HEIGHT 59 0.91 2.1 4
*Note: Equations for PMP estimates of 120 hours and longer are applicable only to the East Coast Tropical Zone.

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(of either rainfall or floods), must be derived using rainfall-
based procedures. The design details in the following
sections relate mainly to rainfall-based procedures.

In the design event approach described here, it is
assumed that the estimated design flood characteristic
(e.g. peak flood) has the same AEP as its causative design
rainfall. In order to satisfy this assumption it is necessary to
incorporate representative design values of all inputs and
parameters in such a way that they are AEP-neutral. In
practice this commonly requires that a designer selects a
single representative value from a wide range of all design
inputs (such as losses, temporal and spatial patterns, and
model parameters). The joint probability approaches
currently being researched are exp'lCted to perform better
in achieving an AEP-neutral transformation of design
rainfalls to floods (e.g. Beran, 1973; Haan and Schulze,
1987; Weinmann et aI., 1998). Continuous simulation
approaches aimed at achieving the same objective have
also been used (!::alver and Lamb, 1996; Boughton and
Hill, llle7).PraQjilion<lrs are IIIleO~ed to adopt these
more 'holistic' procedures once they have been more fully
tested and become avaiiable as design tODls.

(b) Steps in rainfall-based procedures.

The key input to the procedures is the appropriate
design rainfall information from Section 3. Rainfall excess
must be estimated from the design rainfalls after due
allowance is given to catchment losses. A rainfall-runoff
model must then be used to convert the rainfall excess into
the design hydrograph of direct runoff. Where suitable
rainfall and runoff data are available, the model selected
should be calibrated using observed floods on the
catchment of interest, and where appropriate the parameter
values should be adjusted to help reconcile differences
between design values derived from flood frequency
analysis and rainfall-based methods. In other cases.
design values for the model parameters must be estimated
from calibration on adj acent gauged catchments, regional
relationships, or other relevant information. Where a
concentrated storage, such as a reservoir or lake, can have
a significant impact on the catchment response to rainfall,
allowance must be made for liS effed. Finally, basel10w
must be added to the direct runoff hydrograph where
appropriate. Each of these steps is discussed in the
following sections. In each step, design values from the