JPM17b

Nonlinear Dynamics of Tsunami Waves

Efim Pelinovsky

Institute of Applied Physics and Nizhny Novgorod Technical University, Nizhny Novgorod, Russia

The theory of propagation, transformation and runup of tsunami waves taking into account the nonlinearity and the dispersion is reviewed. The available data of real tsunamis demonstrating nonlinear "character" are discussed. The results of laboratory and numerical experiments are reported which point to the necessity of taking into account simultaneously the tsunami wave nonlinearity and dispersion. Models of the tsunami generation are discussed, in particular, a simplified model of tsunami generated by submarine landslides. The nonlinear ray method to simulate the propagation of nonlinear and dispersive tsunami waves in the ocean with bottom irregularities (including random irregularities) is developed. Diffraction, dissipation and waveguide effects are described. Analytical theory of the tsunami wave transformation in the coastal zone and wave runup on beaches is proposed. The conclusions of the theory are compared with the available data on real tsunamis and the results of laboratory and numerical experiments. Developed methods are used for estimating of the tsunami - risk.

JPM17c

SEA LEVEL CHANGE FOR SHANGHAI AND ITS ADJACENT WATERS

Zeng-Hao Qin, Yong-Ping Li and Yi-hong Duan

Shanghai Typhoon Institute, Shanghai,CHINA

Utilizing the historical tide-gauge records(1912-1993) and statistical approaches, two issues, the characteristics of the annual mean sea level changes in the last decades and their long-term amplitudes estimation in the coming years for Shanghai, are dealt with in this paper in the background of the monthly mean sea level change for the northern Pacific.

In general, the mean eustatic sea level (ESL) obviously rises for the Pacific in the twentieth century on the basis of an analysis of the monthly mean ESL records of both tide stations over the Pacific and satellite ocean topography experiment (TOPEX). The average rising rate of the mean ESL differs from part to part and depends on the latitude of the site. The rise of mean ESL was faster for the northern Pacific, covering Shanghai than that for the southern Pacific, whereas the rise of the mean ESL was slower for the eastern Pacific than that for the western Pacific.

Located at the eastern China Sea, the area of fastest rise in mean ESL in the China's coastal waters, the average rate of rise in the mean ESL in Shanghai was approximately 0.9mm per year during the period 1912-1959 and has rapidly increased to 2.0mm per year since 1960. After manipulation of band-pass filter the annual mean ESL for Shanghai varied periodically with predominantly interannual and decade trends included.

A statistical model fitting the variation of the mean ESL is established. It is shown from the model extrapolation that the mean ESL will rise 5cm and 11cm , respectively relative to 1990 for Shanghai by the years 2010 and 2030. As to the current ground subsidence mainly resulting from the over-exploitation of ground water and the average vertical crust deformation and its trend, it is estimated by the scientists from the Shanghai Institute of Rock and Geology that the average subsidence due to the long-term accumulation of ground water will be 10cm and 15cm respectively, relative to 1990 for Shanghai by the years of 2010 and 2030.

The measurements of the average vertical crust deformation by VLBI and their linear extrapolation by the scientists from the Shanghai Observatory, Academic Sinica show that the local crust vertically subsides to 2.0cm and 4.0cm, respectively relative to 1990 for Shanghai in 2010 and 2030.

The sum of the estimations to the mean ESL and average ground subsidence gives a mean relative sea level (RSL) rise of 17cm and 30cm, respectively relative to 1990 for Shanghai by the years of 2010 and 2030. Considering a variety of undetermined factors in mean RSL estimations, the reasonable values of the mean rise in RSL relative to 1990 for Shanghai roughly amount to 15-25cm in 2010 and 25-35cm in 2030.

Finally, the reasons for the mean sea level rise for Shanghai are tentatively discussed.

jpm17d

STORM SURGE INUNDATION MODELLING

Graeme D. Hubbert

Global Environmental Modelling Services, Melbourne, Australia

The GEMS storm surge inundation model has been proven to be extremely stable and accurate and has been used in Australia and overseas for a large number of coastal engineering, risk assessment and real time applications. Various aspects of the modelling techniques have been described previously (see reference list) but this paper presents, for the first time, a full description of the important techniques utilised in the model. The paper will describe the relocatable grid generator, the numerical techniques, the open boundary conditions, nesting algorithm, the wetting and drying technique and the modelling of flow over varying terrain types (such as mud flats, rocks, sand, mangroves etc.).

Many modellers have had difficulty with running ocean models forced by both tides and winds due to the open ocean boundary problem. The traditional specification of tidal heights on open boundaries produces instabilities in this case due to the need to accommodate wind setup on the open boundaries as well. A formulation of the open ocean boundary problem which is stable for joint tidal and wind (even cyclonic) forcing will be described.

The application of various types of storm surge models will be discussed with particular reference to the shortcomings of using fixed coastal wall models. Comparisons of fixed coastal wall results with results from a recent return period study using the GEMS inundation model at Karratha on the Australian north-west coast will be presented. Results from the Karratha study are also used to investigate the relationship between tidal heights and storm surge heights at Karratha and determine the validity of using simple linear addition methods rather than jointly modelling the tides with the storm surge.

Finally the method for deriving sea level return periods for a given location by simulating several thousand years of tropical cyclones is described. These results are important for coastal engineering and risk assessment applications and the results for Karratha are again used to highlight key factors which can have significant affects on sea level return periods over quite short distances along the coast.

References

Hubbert, G.D., Leslie, L.M. and Manton, M.J. (1990). A storm surge model for the Australian region. Quart. J. R. Met. Soc., 116, 1005-1020.

Hubbert, G.D., Holland, G.J., Leslie, L.M. and Manton, M.J. (1991). A real-time system for forecasting tropical cyclone storm surges. Wea. and Forc. 6, pp 86-97.

Hubbert, G.D. (1991). Numerical modelling for coastal engineering and environmental studies, Part 1: Tropical cyclone storm surges and waves. Proc. 10th Australasian Coastal and Ocean Engineering Conference, Auckland, N.Z.

Hubbert, G.D. and Smith, S.L. (1994). Storm Surge Inundation Verification During the 1939 Tropical Cyclone at Port Hedland. Proceedings of PACON '94, Townsville, Australia.

Hubbert, G.D. and Leslie, L.M. (1995). Modelling Storm Surge Inundation in Australia and Hawaii. Proceedings of IAPSO 95, Hawaii, USA.

JPM17E

The physical model of generation of tsunami

B.Kapochkin and N.Kucherenko

Odessa, UKRAINE

Forecasts of tsunami generation are of low quality now. Mechanisms of the generation and the movement of tsunami-waves are poorly known. We know that only some of the strong marine earthquakes make tsunami and only some marine seismic zones make tsunami. We have many important questions about the mechanism of a generation of tsunami. In this report we give a physical simulation of the mechanism of the generation of tsunami. Our model gives explanation of many important questions. These are the cause of the generation of tsunami preferentially in the deep water region of the ocean, and after shallow earthquakes. The model explains questions about the generation of tsunami after earthquakes on land and the questions about the waves characterised by the different directions of the tsunami. Our model is based especially on the movement of the transverse waves in the compressible ocean and the effects of exchanging the structure and volume of water with time on the motion of the transverse wave. In the report discuss the problem of the type of tsunami waves. We consider the likeness of the tsunami and a type of Love waves.

JPM17F

The physical model of the generation of tropical cyclones

B.Kapochkin, S. Stepanenko and N.Kucherenko

UKRAINE

The forecast of the time and place of the generation of tropical cyclones is a very difficult problem now, using only statistical models of the mechanism generation of the tropical cyclones. Using the physical mechanism to solve the problem of generation of tropical cyclones gives a new quality to the forecast of tropical cyclones. Our physical model is based on understanding the facts of the genesis of tropical cyclones and the use of new additional information. These are the results of studying the specific conditions forming the weather above marine seismic zones, results of the statistical regularity of the dependence between the seismic activity and the activity of the tropical cyclones.

The theoretical aspects and the results of experiments of studying the formation of the field of surface temperature above active seismic zones is covered in the report. One of these experiments was in the southern part of the Indian ocean in 1986-1987.

The report includes results of the statistical dependence between seismic activity and tropical cyclone activity in time and space, in the Atlantic and Pacific oceans in 1958-1987. This investigation assumes a functional dependence between the weather specific condition above the marine seismic zones and the condition of the generation tropical cyclones.

The process of forming a local surface temperature anomaly above the place with seismic activity is taken into account. In this zone there is upwelling of cold water and exchange of the chemical component composition of the air.

The physical model, is adapted for specific conditions in southern oceans.

jPm17H

storm surges in bangladesh

Anwar Ali

SPARRSO, Dhaka, BANGLADESH

Bangladesh is one of the worst sufferers of tropical cyclones and the associated storm surges. These disasters, originating in the Bay of Bengal in the south, bring catastrophic ravages to life and property in the littoral countries. About 1% of tropical cyclones of the global total hit Bangladesh, but over 50% of the world deaths took place in this country.

The paper starts with an inventory of cyclones that formed during the last 100 years or so and hit Bangladesh. Then it discusses the storm surge phenomenon and the various reasons due to which storm surges are so severe in Bangladesh. Using a numerical model developed for studying storm surges in the northern Bay of Bengal, the paper investigates the interaction of storm surges with various phenomena like climate change (rise in sea surface temperature and sea level), fresh water discharge (floods), tides etc., individually and in different combinations in relation to Bangladesh. The paper also recommends some future actions to minimise the affects of cyclones and storm surges in Bangladesh.

JPM17i

TIDES AND STORM SURGES OF THE CENTRAL QUEENSLAND COAST

L.J. Cowen and R.H.J. Grimshaw

Department of Mathematics, Monash University,
Clayton, Australia

The Tropical Cyclone Coastal Impacts Program (TCCIP) was established in 1993, to help focus research and development attention on the substantial problems of managing the growing cyclone risk in Queensland, but also involves the applications of interest to other cyclone affected areas. As a part of TCCIP, the interaction between tides and storm surges along the Queensland coast is being investigated.

To achieve this, a two-dimensional numerical model has been developed and applied to a region along the Queensland coastline, between latitudes 14ƒ S and 24ƒ S.

Initially, the linear shallow water equations were solved using an explicit time-stepping scheme on a rotated latitude-longitude Arakawa B grid. The model was developed using topographies of increasing complexity, and tested with the tidal forcing emulated by Kelvin and PoincarÈ waves. A variety of damped and radiation boundary conditions were employed along the remaining open boundaries.

Realistic bathymetric and tidal data sets of the region were obtained from the Australian Oceanographic Data Centre, the Bureau of Meteorology Research Centre and the National Tidal Facility, and incorporated into the model.

To deal with complex coastlines and islands, land and sea points are differentiated by setting different values of the drag coefficient, c_D. The total depth, H=h+z is used to determine whether a large value (c_{DÆ €} ) is set for land points, or a more typical value, like c_D=0.0025 for sea points should be used.

This area is subject to large tidal ranges because of the amplification of tidal waves, due to the wide, shallow continental shelf. The Great Barrier Reef and Broad Sound, near Mackay, also provide a funnelling effect that further increases the tidal extremes.

These large tidal ranges indicate that nonlinearity is important in the surge-tide interaction. Hence, the nonlinear shallow water equations were then solved, again using an explicit time-stepping scheme. Results from both tide models will be shown and compared against the predicted tides given in the Australian National Tide Tables.

The Holland model for Tropical Cyclones will then be used to drive the storm surge in the nonlinear model, with and without tidal forcing. To further improve the predictive capacity of surge models used in this region, one-way grid nesting, focussing on regions such as Mackay and Townsville, coastal inundation and simultaneous river flow output may also be included.

JPM17J

climate change, storm surges and coastal impacts in australia

Kathleen L. McInnes

CSIRO Division of Atmospheric Research, Aspendale Vic AUSTRALIA

Coastal regions are particularly vulnerable to climatic change brought about by the enhanced greenhouse effect. This is partly due to the projected rise in sea level through thermal expansion of the oceans under global warming, and the associated melting of glaciers and ice sheets. Mean sea level rise, however, is only one of a number of climatic factors which may impact on coastal areas. Temporary and localised sea level increases produced by storm surges are potentially more hazardous and cause severe flooding of low lying coastal areas and can increase the inland penetration of damaging wind generated surface waves. Storm surge inundation may also coincide with extreme rainfall run-off to produce worsened coastal flooding structures.

An assessment of the possible impact of climate change on the coastal zone requires consideration of how the severe weather events, responsible for storm surge generation, may be affected by climate change. In this paper, an overview will be given of the types of weather systems which generate storm surges in Australia and the possible impacts of climate change on these weather systems. Results will be presented from storm surge modelling studies which have been undertaken to examine such issues.

JPM17K

Freak waves generation at the agulhas current

Igor Lavrenov

Arctic and Antarctic Research Institute, St Petersburg, RUSSIA

It is known that dangerous situations arise repeatedly for ships encountering freak waves along the south-eastern coast of South Africa in the Agulhas current. The term ‘freak waves’ pertains to individual asymmetric waves with a crest of extremely high slope, in front of which appear a longer and deeper trough than is observed with ordinary wind waves. The height of such waves can reach 15-20 m and more, sometimes in a relatively calm sea. That is why it is practically impossible to take any precautions. It makes the wave very dangerous. In present article, the case of a ship’s collision with a freak wave is described. It happened with tanker-refrigerator ‘Taganrogskii Zavil’ on 27 April 1985. In the action a seaman was killed by the wave.

A theoretical model of the freak wave’s appearance as a result of the wind wave transformation in the Agulhas current is given. Results obtained in the article indicate that the unusual nature of the current velocity distribution for the Agulhas current forces refraction of the south-west swell which propagates over a wide area of the south-western part of the Indian Ocean in such a way that it turns toward the side of the maximum in the current velocity. The swell is captured, intensified by the counter-current, and localised in the neighbourhood of the maximum velocity, propagating along the south-east Africa. As a result, there is a significant concentration of wave energy density, i.e., a focussing takes place in the area mentioned which promotes abnormal wave formation. The superposition of swell waves by the current with wind sea promotes the shape of the wave and the suddenness of its formation.

JPM17l

CLIMATE CHANGE, CLIMATIC HAZARDS AND POLICY RESPONSES IN AUSTRALIA

A. Barrie Pittock

CSIRO Division of Atmospheric Research, Aspendale, Victoria, AUSTRALIA

Australia is a developed country situated largely in the tropics and subtropics, between approximately 11 and 43ƒS, in a predominantly oceanic hemisphere. It is subject to large climatic variability and extremes, including the effects of the El NiÒo Southern Oscillation (ENSO), frequent droughts and floods, wildfires, tropical cyclones, and severe storms leading to coastal storm surges, hail and wind damage.

Historically, heatwaves, tropical cyclones, and floods have caused the most fatalities, while hail damage is the greatest source of insurance claims (residential flooding is generally not covered by insurance).

This paper briefly reviews the state of the science on possible changes in the frequency, intensity and location of climatic hazards, and some policy responses. In general, the scenario for future changes in climatic hazards due to climate change is still quite uncertain, but significant progress is being made in some areas, notably ENSO-related flood and drought years, and tropical cyclones. The reliability of scenarios for relatively small spatial-scale events such as tropical cyclones, which in principle can be modelled using high resolution regional models, remains highly dependent on the reliability of the global climate models at the regional scale.

Realistic policy responses require a holistic approach to climate change impacts, adaptation and mitigation, including the involvement of stakeholders. This applies particularly to developing policies in regard to the potential impacts of extreme events on major infrastructure and development in Australia. Hazard reduction is especially cost effective in new developments where engineering standards and siting can be readily modified before large investments are made. Targeted education programs that aim to increase awareness of climatic hazards, and of methods of avoiding or coping with them, should be developed and implemented. The cost of climatic hazards may be a significant item in any calculation of the costs and benefits of greenhouse gas emission reductions.

JPM17M

how forecast errors impact evacuation decisions for tropical cyclones in the u.s.

Wilson A. Shaffer and Brian R. Jarvinen

Techniques Development Laboratory, Office of Systems Development, National Weather Service/NOAA, Silver Spring, Maryland, USA
National Hurricane Center, Tropical Prediction Center, National Centers for Environmental Prediction, National Weather Service/NOAA, Miami, Florida, USA

Evacuations along the East and Gulf Coasts of the United States because of the threat of tropical cyclones typically require 18 to 24 hours to complete. The average forecast position error of a hurricane is approximately 185 km for a 24hr forecast in these areas. In addition, skill in forecasting intensity changes is minimal.

Since the greatest threat to human life from tropical cyclones has historically been due to coastal flooding, U.S. evacuations are being conducted for areas threatened by surge flooding. These areas have been defined by using the results of the U.S. National Weather Service’s Sea, Lake and Overland Surges from Hurricanes (SLOSH) model. This model is run in a simulation study mode, where storm surges from many tropical cyclones of varying track direction, landfall location, and intensity are computed. Compositing techniques are used to produce useful products to aid coastal emergency managers.

As track and intensity forecasts are improved, the U.S.’s evacuation program will be modified to take advantage of this increased accuracy. Ideas will be presented which will challenge the emergency management community. Instead of using predetermined evacuation zones based on a series of computer simulations, emergency managers will be receiving from the NWS and responding to the results of composites based on fewer, more specific storm tracks. This will permit the evacuation of fewer people from critical coastal areas, but will challenge the emergency management community to be more responsive and focused on specific areas being threatened.

JPM17N

good examples of bad coastal practices

Wilson A. Shaffer

Techniques Development Laboratory, Office of Systems Development, National Weather Service/NOAA,Silver Spring, Maryland, USA

The United States developed many of its "barrier islands" long before current building practices, evacuation requirement, or land management concepts were implemented. As a result of this development, coupled with sea-level rise and numerous recent storms, many coastal communities are threatened by shoreline erosion. Steps have been taken to reduce the impact of storms, but these are also expensive and often counterproductive. The cost to the U.S. of maintaining the current coastline is increasing each year.

Two areas hold promise for minimizing the effects of coastal storms: land-use planning and building codes. Examples will be presented, based on recent hurricanes along the U.S. coastline, of how both land-use and building codes impact coastal evacuations in the U.S. Proper planning can allow construction in coastal areas while protecting residents from the life-threatening hazards of tropical cyclones.