Models
Modelling Philosophy
All investigations are based on a systems approach to the developing of sound model components whereby the essential physics is combined with practical representations of the natural environment. An emphasis is placed on calibration of models to determine the valid ranges of empirical parameters and the verification, wherever possible, that models are representing the real situation. Parameter sensitivity testing is an integral part of any analysis. Best available scientific techniques are selected but an engineering philosophy underpins the implementation so that practical outcomes are obtained which are targeted at client needs. Quality assurance is an essential component of the model development and is manifested in detailed documentation of model design and operation, culminating in evidence of model performance.
Because of a desire to maintain the highest standards of technical credibility, all investigation methodology detail is fully disclosed to clients, who are then encouraged to obtain independent reviews. Workshops and multi-disciplinary approaches are preferred when exploring untried areas. Collaboration is sought with other research or Government groups wherever possible to gain mutual benefits. Formal publishing of techniques has followed as time permits.
Models in Use
The following provides an overview of the main numerical models that are currently available and have been used extensively over the past 15 years:
SEAtide - Real-Time Storm Tide Prediction and Warning Model
A hurricane storm surge forecasting environment capable of rapid (Monte Carlo) scenario generation, mapping and display. Present implementations include the Bureau of Meteorology Northern Territory Regional Office in Darwin and Townsville City.
SURGE - Hydrodynamic Storm Surge Model
A general 2-D (depth integrated) explicit finite difference model of hurricane storm surge with the capacity for overland flooding. This model was developed in the late 1970s and has been used extensively for deterministic storm surge modelling throughout Australia (Sobey et al. 1977; Sobey and Harper 1977; Harper et al. 1978; Sobey et al. 1980; Harper and Sobey 1983). The model is generalised and can be used to represent any coastal location, including reef features.
SATSIM - Surge and Tide SIMulation
A discrete Monte-Carlo statistical model employing tide generation and a parametric hurricane surge model, which can be applied to arbitrary coastal areas. This model was used to establish design water levels along the Queensland coast and also the Northern Territory and parts of Western Australia during the mid-1980s (Harper and McMonagle 1983, 1985; Harper and Robinson 1997). The model was further extensively developed in the late 1980s to include a parametric hurricane wave, wind and 3-D current models (Harper et al. 1989). This provides full (contemporaneous) statistical descriptions of environmental loadings on offshore platforms allowing phase separation at very long return periods (10,000yr). Hurricane wind fields may be specified as NHRP circa 1970 or according to a modified and extended Holland (1980) with overland wind boundary layer effects incorporated for land sites. Extra-tropical cyclones are modelled by scale changes and also the ability to overlay geostrophic asymmetries and synoptic scale interactions.
HARBREM - Rubble Mound Breakwater Model
This empirical model assists in the design of mass-armoured rubble mound breakwaters for harbour protection works (Bremner et al. 1987). The model is based on hydraulic model testing of highly porous breakwater configurations and was developed with the assistance of a Marine Sciences and Technologies Research Grant.
SPECT/ADFA1 - Spectral Hurricane Wave Model
A discrete second-generation 2-D spectral energy model of the generation and propagation of hurricane generated waves (Young and Sobey 1986; Young 1987). This model has been used extensively for deterministic modelling of offshore design criteria in Western Australia and underpins the parametric wave sub-model of SATSIM. The model has been extensively calibrated against more than 30 hurricanes in Australian waters and has also been used for investigations in the Arabian Sea and for the design of a real-time early warning system for port operations (Harper et al. 1993, Harper and Nugent 1994).
MIRAM - Monte Carlo Insurance Risk Assessment Model
A further development of SATSIM since 1992, MIRAM is targeted at insurance loss assessment (Harper 1996a, 1996b). Modules include hurricane wind and storm surge losses as well as severe thunderstorm downburst, hail and tornado losses. The model is discrete and presents a time history of storm behaviour across a region at typically half-hourly (hurricane) and 1 minute (thunderstorm) intervals. Scenario (deterministic) or return period (probabilistic) options are available. Novel terrain and topographic effects for hurricane are derived from Landsat imagery. Model mean and gust wind speed predictions are compared with long term regional airport records to ensure accurate representation of extreme winds. MIRAM has been shown to be very well calibrated against Cyclone Althea (Townsville 1971) winds and insurance industry loss estimates and is capable of representing extreme wind speeds recorded along the Queensland coast (Harper 1997). The thunderstorm model has been calibrated against the January 1985 hailstorm in Brisbane, predicts regional hail day frequencies and reproduces the 50 year record of Brisbane airport winds almost exactly (Harper and Callaghan 1998). It is calibrated against average annual insured losses in the region.
SEACATD - Catastrophe Model: Deterministic
A further generalised development of MIRAM for testing tropical cyclone building loss functions (in collaboration with the James Cook Cyclone Testing Station, Townsville, as part of the Tropical Cyclone Coastal Impacts Program - TCCIP).
References
Bremner W, Harper B A and Foster D N, (1987) The Design and Construction of a Mass Armoured Breakwater at Hay Point, Australia, Proc Seminar on Unconventional Rubble Mound Breakwaters, NRCC, Ottowa, Sept.
Harper B A, Sobey R J and Stark K P, (1978) Sensitivity Analysis of a Tropical Cyclone Surge Model, in Noye B J (ed) Numerical Simulation of Fluid Motion, North-Holland, pp 371-381.
Harper B A and Sobey R J, (1983) Open Boundary Conditions for Open Coast Hurricane Storm Surge, Coastal Engineering 7, pp 41-60.
Harper B A and McMonagle C J, (1983) Greater Darwin Storm Surge Study - Part 3: "Extreme Water Level Frequencies", Northern Territory Department of Lands under direction Maritime Works Branch Department of Housing and Construction, Blain Bremner and Williams Pty Ltd, Sept, 120 pp.
Harper B A and McMonagle C J, (1985) Storm Tide Statistics - Methodology, Beach Protection Authority of Queensland, Blain Bremner and Williams Pty Ltd, Jan, 120 pp.
Harper B A, Lovell K F, Chandler B D and Todd D J, (1989) The Derivation of Environmental Design Criteria for Goodwyn 'A' Platform, Proc 9th Aust Conf Coastal and Ocean Engin, I E Aust, Dec.
Harper B A, Mason L B and Bode L, (1993) Tropical Cyclone Orson - A Severe Test for Modelling, Proc 11th Australian Conference on Coastal and Ocean Engineering, IEAust, Townsville, Aug, pp. 59-64.
Harper B A, and Nugent S W, (1994) Port Early Warning System Concepts, Proc Asian and Australasian Ports and Harbours Conf, EADA, Kuala Lumpur, Sept.
Harper B A, (1996a) Risk Modelling of Cyclone Losses, Proc Annual Engineering Conf, IEAust, Darwin, April.
Harper B A, (1996b) The Application of Numerical Modelling in Natural Disaster Risk Management, Proc Conf Natural Disaster Reduction NDR'96, Gold Coast, Sep.
Harper B A, (1997) Numerical Modelling of Extreme Tropical Cyclone Winds, Proc 4th Asia Pacific Sympos on Wind Engin, Gold Coast, July.
Harper B A and Robinson D A, (1997) Storm Tide Threat in Queensland, Proc 13th Australasian Conf Coastal and Ocean Engin, IPENZ/IEAust, Christchurch, Sept.
Harper B A and Callaghan J, (1998) Modelling of Severe Thunderstorms in South East Queensland. Proc. Sixth Australian Severe Storms Conference, Bureau of Meteorology, Brisbane, Aug.
Holland, G J, (1980) An Analytic Model of the Wind and Pressure Profiles in Hurricanes. Mon. Wea. Rev., 108, 1212-1218.
Sobey R J, Harper B A and Stark K P, (1977) Numerical Simulation of Tropical Cyclone Storm Surge, Department of Civil and Systems Engineering, Research Bulletin No. CS14, James Cook University, May, 300 pp.
Sobey R J and Harper B A, (1977) Tropical Cyclone Surge Penetration Across the Great Barrier Reef, Proc 3rd Aust Conf Coastal and Ocean Engg, I E Aust, Melb, pp 58-63.
Sobey R J, Harper B A and Mitchell G M, (1980) Numerical Modelling of Tropical Cyclone Storm Surge, Proc 17th International Conf Coastal Engg, Sydney, pp 725-745.
Young I R and Sobey R J, (1986) Hurricane Wind Waves - A Discrete Spectral Model. ASCE Journal of Waterway, Port, Coastal and Ocean Engineering, Vol. 112, No. 3, 370-389.
Young I R, (1987) A General Purpose Spectral Wave Prediction Model. Res. Rep. No. 16, Univ College, Australian Defence Force Academy, Canberra, Jan.
