Predictive modelling provides an efficient means to analyse the coastal environment and generate knowledge for long term urban planning. In this study, the numerical models SWAN and XBeach were incorporated into the ESRI ArcGIS interface by means of the BeachMMtool. This was applied to the Greater Christchurch coastal environment to simulate geomorphological evolution through hydrodynamic forcing. Simulations were performed using the recent sea level rise predictions by the Intergovernmental Panel on Climate Change (2013) to determine whether the statutory requirements outlined in the New Zealand Coastal Policy Statement 2010 are consistent with central, regional and district designations. Our results indicate that current land use zoning in Greater
Christchurch is not consistent with these predictions. This is because coastal hazard risk has not been thoroughly quantified during the process of installing the Canterbury Earthquake Recovery Authority residential red zone. However, the Christchurch City Council’s flood management area does provide an extent to which managed coastal retreat is a real option. The results of this research suggest that progradation will continue to occur along the Christchurch foreshore due to the net sediment flux retaining an onshore direction and the current hydrodynamic activity not being strong enough to move sediment offshore. However, inundation during periods of storm surge poses a risk to human habitation on low lying areas around the Avon-Heathcote Estuary and the Brooklands lagoon.
In the aftermath of the 2010-2011 Canterbury Earthquake Sequence (CES), the location of Christchurch-City on the coast of the Canterbury Region (New Zealand) has proven crucial in determining the types of- and chains of hazards that impact the city. Very rapidly, the land subsidence of up to 1 m (vertical), and the modifications of city’s waterways – bank sliding, longitudinal profile change, sedimentation and erosion, engineered stop-banks… - turned rainfall and high-tides into unprecedented floods, which spread across the eastern side of the city. Within this context, this contribution presents two modeling results of potential floods: (1) results of flood models and (2) the effects of further subsidence-linked flooding – indeed if another similar earthquake was to strike the city, what could be the scenarios of further subsidence and then flooding. The present research uses the pre- and post-CES LiDAR datasets, which have been used as the boundary layer for the modeling. On top of simple bathtub model of inundation, the river flood model was conducted using the 2-D hydrodynamic code NAYS-2D developed at the University of Hokkaido (Japan), using a depth-averaged resolution of the hydrodynamic equations. The results have shown that the area the most at risk of flooding are the recent Holocene sedimentary deposits, and especially the swamplands near the sea and in the proximity of waterways. As the CES drove horizontal and vertical displacement of the land-surface, the surface hydrology of the city has been deeply modified, increasing flood risks. However, it seems that scientists and managers haven’t fully learned from the CES, and no research has been looking at the potential future subsidence in further worsening subsidence-related floods. Consequently, the term “coastal quake”, coined by D. Hart is highly topical, and most especially because most of our modern cities and mega-cities are built on estuarine Holocene sediments.
The world is constantly changing. Christchurch, New Zealand, has recently experienced drastic changes after earthquakes struck the city. The earthquakes caused the city to physically shake, and the land to sink in some places and rise in others. Now further change is forcast and parts of Christchurch could be under water by 2115 according to experts.
Climate change induced sea level rise is recognised as a international issue with potential impacts for coastal communities all over the world. The Chrischtchurch City Council is required to have a 100-year planning horizon for sea level rise and this means planning for at least one meter, and possibly up to two meters, of sea level rise by 2115. This dissertation investigates the planning response to slow onset disasters, change, and uncertainty, using the example of sea-level rise in Christchurch, and it examines the role of public participation in this. To achieve this, the ways in which planning theory and practice acknowledge uncertainty, and cope with change, were critically analysed along with the Christchurch City Council’s response to the Tonkin and Taylor predictions and modelling. Semi-structured interviews with professionals in natural hazards risk reduction, policy, and planning were conducted, and the previous and proposed Christchurch City District Plans were compared.
Planning for sea level rise in Christchurch provides an example of how planners may cope with slow onset change. The results of this dissertation suggests that the favoured risk reduction strategy for coastal communities in Christchurch is an adaptation strategy, and at present there is no sign of managed retreat being employed. The results also suggests using a planning approach that involves public participation for best results when planning for change, uncertainty or slow onset disasters.
