Changeset 3404

Jul 22, 2006, 3:14:04 PM (18 years ago)

incorporating more of TD's comments

3 edited


  • production/onslow_2006/report/damage.tex

    r3402 r3404  
    5656ABS housing survey}.
    5757The damage to the residential structures in the Onslow community
    58 is summarised in Table \ref{table:damageoutput}. The percentage
     58is summarised in Table \ref{table:damageoutput}. As expected, the
     59greatest impact is found for the high tide scenario. The percentage
    5960of repair cost to structural value shown is based on the total structural value
    6061of \$71M. Likewise, the percentage of contents loss shown is
    7374&Inundated & Collapsed & Repair Cost
    7475& of Total Value & Losses & of Total Value \\ \hline
    75 HAT & 100 &2&\$8M & 11\%&\$16M & \%16 \\ \hline
    76 MSL & & 1 & \$ &   \% & \$ &  \% \\ \hline
    77 LAT & & & & & & \\ \hline
     76HAT & 100 &2&\$8M & 11\%&\$16M & 16 \% \\ \hline
     77MSL & 0 & 0 & \$0 &   & \$0 & \\ \hline
     78LAT & 0 & 0 & \$0 &   & \$0 & \\ \hline
    8788&Minor & Moderate & Serious & Fatal \\ \hline
    8889HAT & 10's & 10's & 10's & 10's \\ \hline
    89 MSL & &  &  & \\ \hline
    90 LAT & & & & \\ \hline
     90MSL & 0& 0 & 0 &0 \\ \hline
     91LAT & 0&0 & 0& 0\\ \hline
    9697in the future as a number of communities exist in coastal regions of north west WA.
    9798These communities are typically not included in national residential databases
    98 and would be therefore overlooked in damage model estimates.
     99and would be therefore overlooked in damage model estimates
     100We can confirm that Bindi Bindi is not contained in the NBED.
    99101There is one indigeneous community located in this study area as seen
    100 in Figure
    101 \ref{fig:points}. The population of the Bindibindi community is 140
     102in Figure \ref{fig:points}.
     103The population of the Bindibindi community is 140
    102104(18 \% of the Onslow population)
    103105and is situated close to the coast as seen in Figure \ref{fig:points}.
    104 During the HAT scenario, over 1m of water will inundate parts of the community (Figure
    105 \ref{fig:gaugeBindiBindiCommunity}) causing significant impact.
     106During the HAT scenario, over 1 m of water will inundate parts of the community (Figure
     107\ref{fig:gaugeBindiBindiCommunity}) which would cause
     108significant impact.
  • production/onslow_2006/report/execsum.tex

    r3402 r3404  
    1313This report describes the modelling methodology and initial results
    1414for a specific tsunami-genic event as it impacts the Onslow township
    15 and its surrounds. Future studies
     15and its surrounds. In particular, maximum inundation maps are shown
     16and discussed
     17for the event occurring at mean sea level as well as
     18highest and lowest astronomical tide. The inundation results allow
     19estimation of the number of houses inundated and collapsed, as well as
     20the numbers of persons affected. The Onslow township has approximately
     21350 residential structures and a population of around 800.
     22For this specific event at high tide, approximately
     23100 houses are inundated with two of those collapsing. Approximately
     2415-20\% of the population will sustain injuries, including fatalities.
     26Future studies
    1627will present a series of scenarios for a range of return periods to
    17 assist FESA in developing appropriate plans for a range of event impacts.
     28assist FESA in developing appropriate plans for a range of event impacts.
     29This will also allow an assessment of the relative tsunami risk
     30to communities along the NW Shelf of WA.
    1831This report and the decision support tool are the
    19 June 2006 deliverables of the Collaborative Research Agreement
    20 between FESA and GA, Tsunami Impact Modelling for WA .
     32June 2006 deliverables of the Collaborative Research Agreement,
     33Tsunami Impact Modelling for WA, between FESA and GA.
  • production/onslow_2006/report/interpretation.tex

    r3375 r3404  
    11The main features of the
    2 tsunami wave and resultant impact ashore is described in this section.
     2tsunami wave and resultant inundation ashore is described in this section.
    33We have
    4 chosen a number of locations which we believe would be critical
    5 in an emergency situation, such as the hospital and power station; or
    6 effect recovery efforts, such as the airport and docks. These locations
     4chosen a number of locations to illustrate the features
     5of the tsunami as it approaches Onslow and runs ashore.
     6These locations have be chosen as we believe they would
     7either be critical
     8in an emergency situation, (e.g. the hospital and power station) or
     9effect recovery efforts, (e.g. the airport and docks). These locations
    710are described in Table \ref{table:locations} and shown in
    8 Figure \ref{fig:points}. The water's stage and speed are shown
     11Figure \ref{fig:points}. The water's stage and speed
     12at each of these locations are shown
    913as a function of time in the series of graphs shown in
    10 Appendix \ref{sec:timeseries}. Stage is defined as the absolute
    11 water level relative to AHD. Both stage and speed are shown
     14Appendix \ref{sec:timeseries}. It is assumed that the earthquake is
     15generated at the beginning of the simulation, i.e. time = 0 minutes.
     16Stage is defined as the absolute
     17water level (in metres) relative to AHD
     18\footnote{For an offshore location such as Beadon Bay West,
     19the initial water level will be that of the tidal scenario. In the
     20case of MSL, this water level will be 0. As the tsunami wave moves
     21through this point, the water height may grow and thus the stage will represent the amplitude of the wave. For an onshore location such as the Light Tower, the actual water depth will be the difference between
     22the stage and the elevation at that point. Therefore, at the beginning
     23of the simulation, there will be no water onshore and therefore
     24the stage and the elevation will be identical.}. Both stage and speed
     25(in metres/second) for
     26each scenario (HAT, MSL and LAT) are shown
    1227on consistent scales to allow comparison between point locations.
    13 %The graphs show these time series for
    14 %the three cases; 1.5m AHD, 0m AHD and -1.5m AHD so that comparisons can
    15 %be made.
    1628As a useful benchmark, Table \ref{table:speedexamples}
    17 describes typical examples for a range of velocities found in the
     29describes typical examples for a range of speeds found in the
    20 \begin{table}
    2235\caption{Examples of a range of velocities.}
    38 Examining the offshore locations shown in Appendix
    39 \ref{sec:timeseries}, the drawdown prior to the tsunami wave
    40 arriving at the shore can be seen to occur around 230 mins 
    41 (3.8 hours) after the tsunami is generated.
    42 Prior to the drawdown, maximum amplitudes are approximately 50cm at
    43 West of Groyne (Figure \ref{fig:gaugeWestofGroyne}) and
    44 the mouth of Beadon Creek
    45 (Figure \ref{fig:gaugeBeadonCreekmouth}), for example.
    46 The first wave
    47 after the drawdown ranges from approximately 2m in the
    48 west of Beadon Bay (Figure \ref{fig:gaugeBeadonBaywest})
    49 to over 3m in the mouth of Beadon Creek
    50 (Figure \ref{fig:gaugeBeadonCreekmouth}).
    51 The speed
    52 sharply increases at drawdown with further increases as the
    53 wave grows in amplitude.
    54 There is an increased amplitude of approximately 4m found in
    55 east of Beadon Bay for the secondary wave, as opposed to the first wave.
    56 This feature is also evident at the West of Groyne location but
    57 with decreased amplitude.
    58 This may be due to the geography of the bay, including the groyne west of
    59 the creek mouth opening, the local bathymetry
    60 and the direction of the tsunami wave.
     51A tsunami wave typically has a low amplitude and typically travels at 100's of kilometres per hour. The low amplitude complicates the ability to detect
     52the wave. As the water depth decreases, the speed of the wave
     53decreases and the amplitude grows. Another important feature of tsunamis
     54is drawdown. This means that the water is seen to retreat from the beaches
     55before a tsunami wave impacts that location. Other features
     56include reflections (where the wave is redirected due to the influence
     57of the coast) and shoaling (where the wave's amplitude increases ...).
    62 The maximum speed found for the offshore locations occur at the West of
    63 Groyne location (Figure \ref{fig:gaugeWestofGroyne}).
    64 The speeds at west and east of Beadon Bay are quite similar
    65 (Figure \ref{fig:gaugeBeadonBayeast} and Figure \ref{fig:gaugeBeadonBaywest}).
    66 However, there are increased amplitudes (from drawdown to maximum
    67 amplitude), in the eastern location which is in shallower water than the western
    68 location.
    69 Subsequent drawdowns are seen as the multitude of waves which make up the
    70 event propagate towards the shore.
     59These features are seen in these scenarios, and are consistent
     60for HAT, MSL and LAT. There is a small wave, followed
     61by a large drawdown and then a large secondary wave. These
     62features are illustrated in Figure \ref{fig:gaugeBeadonBayeest}
     63where a small wave can be seen at around 200 mins. For the HAT
     64case (shown in blue), the amplitude
     65of the wave at this location is around 0.5 m\footnote{In this
     66scenario, the initial water level is 1.5 m, which means that
     67the actual amplitude is the difference between the stage value
     68and the initial water level; 2.? - 1.5).
     69The drawdown of around 4 m (i.e. 2.? - -2) then occurs at around 230 mins
     70(i.e. 3.8 hours after the event has been generated), before
     71the second wave arrives with an amplitude of over 3 m (i.e. 4.? -
     72-1.5). A further wave
     73is then evident a short time later (around 270 mins)
     74which further increases the amplitude to over 4.5 m (i.e. 6.? - -1.5).
     75These features are replicated at each of the offshore points (those
     76points with negative elevation as shown in Table \ref{table:locations}).
    72 %At some gauge locations, these
    73 %subsequent waves cause significantly increased inundation than that of
    74 %the first wave. This is particularly seen at the Beadon Creek Docks,
    75 %West of Groyne and Beadon Creek locations.
     78The wave amplitude is typically greater
     79for those locations which are in the shallowest water. For example,
     80the maximum wave amplitude at the Beadon Bay East location
     81(Figure \ref{fig:gaugeBeadonBayeast}) is over
     824.5m where the water depth would normally be 3.56 m. In the
     83Beadon Bay West location (Figure \ref{fig:gaugeBeadonBaywest})
     84where the water depth would normally be 4.62 m,
     85the maximum wave amplitude is much less (around 3 m). The wave amplitude
     86at the West of Groyne location (Figure \ref{fig:gaugeWestofGroyne})
     87is not greater than that seen
     88at the Beadon Bay East location, even though the water depth is
     89much less, at 2.11m. This is probably due to its proximity
     90to the groyne\footnote{A groyne is a man made structure to combat
     91coastal erosion.}
     92which has impeded the tsunami wave to some degree. However, the
     93maximum speed found amongst the locations is at the West of Groyne
     94point which is in the shallowest water.
    77 It is evident that the sand dunes west of
    78 Onslow are very effective in halting the tsunami wave,
    79 (see Figure \ref{fig:MSL_max_inundation}).
    80 There is inundation between the western sand dunes at high
    81 tide, Figure \ref{fig:HAT_max_inundation}, however, this water
    82 penetrates from the north east (via
    83 Onslow town centre) rather than seaward. (The DEM indicates that
    84 this area is under 1.5m AHD which is automatically deemed to be inundated
    85 at HAT.)
    86 The same feature is evident for the sand dunes east of Onslow.
     96The speed of the tsunami sharply increases as it moves onshore. There
     97is minimal inundation found at the locations chosen, with the Bindi Bindi
     98community receiving the greatest inundation for all tidal scenarios.
     99At HAT, the community would receive over 1 m of inundation with
     100the water moving through the community at approximately 16 m/s. Referring
     101to Table \ref{table:speedexamples}, a person in this location could
     102not outrun this water movement. A small amount of water is found
     103at the hospital (? cm). Whilst this seems minimal, the water is moving
     104at around 6 m/s which could dislodge items such as trolleys and
     105wheelchairs if the water was able to enter the hospital.
     107The geography of the Onslow area has played a role in offering
     108some protection to the Onslow community. The tsunami wave is
     109travelling from the north west of the area. Most of
     110the inundation along the coast is that which is open to this
     112The sand dunes west of Onslow
     113appear to have halted this tsunami wave
     114(see Figure \ref{fig:MSL_max_inundation}) with limited
     115inundation found on the town's side of the dunes.
     116The inundation within the community has occurred due to the
     117wave reflecting from the beach area west of the creek and
     118returning towards the Onslow town itself. 
     119There are also sand dunes east of the creek which have also
     120halted inundation beyond them.
    87121Currently, we do not model changes
    88122to the bathymetry or topography due to effects of the water flow.
    89123Therefore, we do not know whether these sand dunes would withstand the
    90124transmitted energy of the tsunami wave.
    91 The tsunami wave penetrates the river east of Onslow with a wave height
    92 over 2m at the mouth
    93 (Figure \ref{fig:gaugeBeadonCreekmouth})
    94 and inundation
    95 exceeding 1m found at the Beadon Creek south of dock location (Figure
    96 \ref{fig:gaugeBeadonCreeksouthofdock}).
    97 The wave penetrates the river east of Onslow with increasingly
    98 greater inundation between the -1.5m AHD and 1.5m AHD simulations.
    100 As expected, there is greater inundation at 1.5m AHD. The major road
     126Water features such as rivers, creeks and estuaries also play a role
     127in the inundation extent.
     128The tsunami wave penetrates the creek east of Onslow with a wave height
     129over 2 m at the mouth
     130(Figure \ref{fig:gaugeBeadonCreekmouth}) for the HAT scenario.
     131Inundation exceeds 1 m at the Beadon Creek south of dock location (Figure
     132\ref{fig:gaugeBeadonCreeksouthofdock}) suggesting that the wave's
     133energy dissipates as inundation overflows from the creek. A large
     134tidal flat region surrounds the southern parts of the creek and
     135it is evident that the inundation is essentially caught in this
     138As expected, there is greater inundation at HAT with increased
     139extent. The major road
    101140into Onslow, the Onslow Mount Stuart Rd, remains free of inundation for
    102 all simulations with a small amount of inundation evident at HAT at
     141all tidal scenarios with a small amount of inundation evident at HAT at
    103142the intersection with Beadon Creek Rd. Beadon Creek Rd services the wharf in the
    104 river which becomes increasingly inundated as the initial condition
    105 changes from 0m AHD to 1.5m AHD. Only the
    106 entry to the wharf on Beadon Creek Rd is sufficiently inundated to
    107 stop traffic at -1.5m AHD.
    108 At 1.5m AHD however, essentially the entire road would be impassable.
     143creek which becomes increasingly inundated as the tide height
     144increases. The only road sufficiently inundated at LAT is Beadon
     145Creek Rd near the entry to the wharf. This road during the HAT
     146scenario would be impassable as the water depths are consistently
     147over 1 m with a maximum water depth of around 2 m found close to
     148the wharf.
    110150There is significant inundation of at
    111 least 2m on the foreshore of Onslow for 0m AHD and 1.5m AHD.
    112 The inundation extent increases as the initial condition increases above 0m AHD,
    113 reaching the southern boundaries of
    114 the road infrastructure in the Onslow town centre.
     151least 2 m on the foreshore of Onslow for MSL and HAT.
     152The inundation extends further as the tidal heights increase. 
     153At HAT, the inundation reaches the southern boundaries of
     154the road infrastructure in the Onslow town centre. 
     155The airport remains
     156free of inundation for each tidal scenario. Section \ref{sec:damage}
     157details the impact estimates to the residential infrastructure.
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