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NT Remote Communities Storm Tide Study and Inundation Mapping



NT Remote Communities Storm Tide Study and Inundation Mapping


Systems Engineering Australia Pty Ltd

Issued by

Northern Territory. Department of Land Resource Management


E-Publications; E-Books; PublicationNT; J1507-PR001B




Made available via the Publications (Legal Deposit) Act 2004 (NT).; 'This report documents tropical cyclone (TC) storm tide hazard analyses that will provide the basis for reliable risk analyses of major remote towns and indigenous communities on the West Coast, Arnhem Land and Tiwi Islands.' - Introduction


This Storm Surge Study Report was produced with funding provided by the Northern Territory and Australian Governments through the Natural Disaster Resilience Program. 'Numerical Modelling and Risk Assessment' - on cover.; Made available via the Publications (Legal Deposit) Act 2004 (NT).

Table of contents

Executive summary -- Introduction -- The study localities -- Methodology to assess the storm tide hazard -- Simulation model results -- Conclusion -- References -- List of Appendices A-C.




Storm surges; Storm surges; Cyclones; Maps; Mathematical models

Publisher name

Northern Territory Government

Place of publication





vi, 62, 4,3,8 pages : colour illustrations, colour maps ; 30 cm.

File type



Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government



Parent handle


Citation address


Page content

NT Department of Land Resource Management NT Remote Communities Storm Tide Study and Inundation Mapping J1507-PR001B B-2 Systems Engineering Australia Pty Ltd July 2016 B.1 - General This study has presented its analyses of risk in terms of the socalled Return Period (or Average Recurrence Interval ARI). The return period is the average number of years between successive events of the same or greater magnitude. For example, if the 100year return period storm tide level is 3.0 m AHD then on average, a 3.0 m AHD level storm tide or greater will occur due to a single event once every 100 years, but sometimes it may occur more or less frequently than 100 years. It is important to note that in any N-year period, the N-year return period event has a 64% chance of being equalled or exceeded. This means that the example 3.0 m storm tide has a better-than-even chance of being exceeded by the end of any 100-year period. If the 100-year event were to occur, then there is still a finite possibility that it could occur again soon, even in the same year, or that the 1000-year event could occur, for example, next year. Clearly if such multiple events continue unchecked then the basis for the estimate of, say, the 100-year event might then need to be questioned, but statistically this type of behaviour can be expected. A more consistent way of considering the above (Harper 2012) is to include the concepts of design life and encounter probability which, when linked with the return period, provide better insight into the problem and can better assist management risk decision making. These various elements are linked by the following formula (Borgman 1963): T = - N / ln [1 - p ] Where p = encounter probability (0 to 1) N = the design life (years) T = the return period (years) This equation describes the complete continuum of risk when considering the prospect of at least one event of interest occurring. More complex equations describe other possibilities such as the risk of only two events in a given period or only one event occurring. Figure B.1 illustrates the above equation graphically. It presents the variation in probability of at least one event occurring (the encounter probability) versus the period of time considered (the design life). The intersection of any of these chosen variables leads to a particular return period and a selection of common return periods is indicated. For example, this shows that the 200-year return period has a 40% chance of being equalled or exceeded in any 100-year period. The level of risk acceptable in any situation is necessarily a corporate or business decision. Figure B.1, is provided to assist in