title: Hydrodynamic modelling of tsunami inundation in Whitianga

authors: Prasetya, Gegar Sapta

abstract: In 2006, Waikato Regional Council (WRC) provided research funding for the Coastal Marine Group, Department of Earth and Ocean Sciences, University of Waikato, to undertake research on the impacts of tsunami inundation on Whitianga town and harbour.
The main aims of the study are to:
● Identify potential tsunami sources; 
● Establish an understanding of tsunami inundation impacts in Whitianga township and harbour – including the hydrodynamic processes and responses of Mercury Bay, Buffalo Bay, Whitianga Harbour and adjacent land to tsunami wave action; 
● Develop tsunami inundation maps, showing depth and velocity (speed) of tsunami waves; and 
● Provide sound evidence upon which to base community risk mitigation measures – including recommendations for evacuation planning, public education and awareness, protection of infrastructure, management of impacts to marine vessels and future land use planning. 
The numerical model used in this study is the 3DD Suite-Computational Marine and Freshwater Laboratory model (Black, 2001). The model has demonstrated the ability to accurately reproduce tsunami hydrodynamics during propagation and run up on both laboratory and real-world scales. 
There are three primary tsunami sources that could potentially affect Whitianga from the Kermadec Trench, and beyond the New Zealand continental shelf, being: 
1. Mt Healy undersea volcano eruptions (15th Century event); 
2. Large earthquakes along segments 1 and 2 of the Kermadec Trench subduction zone; and 
3. A 1960 Chilean-type earthquake event. 
Each source is modelled, and the results that show the greatest risk and impacts to Whitianga are used as the basis for the hazard maps and hazard zones. 
Modelling results indicate that:
• The Mt Healy type of eruption produced a minimal impact on Whitianga. The tsunami waves generated from this event did not inundate Whitianga. Despite this, strong currents of up to 2.5 m/s were generated inside Buffalo Bay and at the Whitianga Harbour inlet. 
•The Kermadec Trench earthquake scenarios with both positive and negative leading waves, as a result of a subduction fault dislocation along segments 1 and 2, have a significant impact on Whitianga. The waves inundate the coastal area up to 2.5 and 3 km inland for the subduction thrust fault and normal fault events respectively, and affect the entire area of Whitianga Harbour. The normal fault event that produces positive leading waves has more impact than the thrust fault event that produces negative leading waves. 
• The 1960 Chilean-type earthquake event produced tsunami waves that inundated Buffalo Beach Road and houses in Whitianga, as observed by eyewitnesses. Strong currents of up to 5 m/s are generated inside Buffalo Bay and the Whitianga Harbour inlet. 
The modelling indicates that:
• Whitianga would be inundated five times by a Kermadec Trench earthquake scenario, and three times by a 1960 Chilean-type of tsunami 
• For the Kermadec Trench scenario (normal fault), the first waves penetrate Mercury Bay within 75–98 minutes after the fault rupture 
• Regardless of the tsunami source, it takes 11–18 minutes for waves to arrive at the Whitianga foreshore once they have entered Mercury Bay. 
The modelling indicates that the period between waves is 40 – 60 minutes, which is consistent with the 1960 Chilean event. The geometry of Buffalo Bay and Mercury Bay amplify the incoming tsunami waves, and the sea level inside the bay continues to oscillate, even after the sea level outside of Mercury Bay returns to normal. This situation is consistent with eyewitness accounts of the 1960 Chilean tsunami. 
Modelling also shows that strong currents are produced within Buffalo Bay and Whitianga Harbour, as well as during the overland flows - especially in areas adjacent to the Taputapuatea Stream and in the foreshore area between Albert Street and the wharf. The flow speed ranged from 1.5 m/s to 8 m/s for overland flows, and above 8 m/s within the entrance of Whitianga Harbour and in the middle of Buffalo Bay.  
For the first time in New Zealand, a combination of non-ground striking and ground striking LIDAR data was used in modelling tsunami inundation, which increased the accuracy of the modelling results considerably. Inundation flow behaviour and the effect of topography, as well as land use, can be analysed more accurately, and a more precise hazard map can be produced accordingly. 
Mitigation measures suggested to protect the Whitianga waterfront include a combination of enhanced coastal sand dunes and planted forest belts, which could be done along both sides of the Taputapuatea Stream. A stop gate could also be constructed at the entrance of the Taputapuatea Stream to minimise the impact of the tsunami flows upstream. 
With respect to evacuation, it is concluded that due to the lag time between a local event from the Kermadec Trench and wave arrival at the Whitianga foreshore, there is enough time for residents to be evacuated to shelter sites using major roads. Three locations are identified as evacuation shelter sites. These are the marina parking area and Buffalo Beach scenic reserve (both of which are located on high ground adjacent to the high-risk zone), and further inland at the airfield. Vertical evacuation sites are needed inside the high-risk zone, and recommendations on potential locations are provided. It is important that vertical evacuation measures are integrated into community response plans, and that they be reviewed and revised regularly. 
Overland flow information derived from modelling using the ground-striking and non-ground striking LIDAR data provides a basis to influence new development that occurs within tsunami hazard risk zones. Overland flow information also indicates the areas of existing development that need protection from future tsunami events. Risk mitigation may be accomplished through redevelopment, retrofit, coastal defence measures, safety planning for ships and boats, land reuse plans, and also via public education and awareness programmes. 
A major challenge of risk mitigation is to maintain emergency preparedness programmes and procedures when the threat of tsunami is perceived as remote. Periodic exercises are essential to maintain awareness, and regular information should be provided for those occupying tsunami hazard areas. 
Tsunami are rare events, but their impacts on coastal communities can be devastating. It is quite dangerous to believe that the impacts of a tsunami can be completely prevented by man-made structures (Horikawa and Shuto, 1983). However, possible impacts may be minimised through careful design of solutions based on systematic research. An important consideration for risk mitigation works is that they may affect the quality of daily life, and risk mitigation involves choices and trade-offs between risk management and other uses. Video animations of each scenario are provided at regional, intermediate and local scales. The animations cover tsunami wave behaviour during generation, propagation, run up, and overland flows, and may be used to inform land use planning and public education and awareness programmes.

text: Hydrodynamic modelling of tsunami inundation in Whitianga In 2006, Waikato Regional Council (WRC) provided research funding for the Coastal Marine Group, Department of Earth and Ocean Sciences, University of Waikato, to undertake research on the impacts of tsunami inundation on Whitianga town and harbour.
The main aims of the study are to:
● Identify potential tsunami sources; 
● Establish an understanding of tsunami inundation impacts in Whitianga township and harbour – including the hydrodynamic processes and responses of Mercury Bay, Buffalo Bay, Whitianga Harbour and adjacent land to tsunami wave action; 
● Develop tsunami inundation maps, showing depth and velocity (speed) of tsunami waves; and 
● Provide sound evidence upon which to base community risk mitigation measures – including recommendations for evacuation planning, public education and awareness, protection of infrastructure, management of impacts to marine vessels and future land use planning. 
The numerical model used in this study is the 3DD Suite-Computational Marine and Freshwater Laboratory model (Black, 2001). The model has demonstrated the ability to accurately reproduce tsunami hydrodynamics during propagation and run up on both laboratory and real-world scales. 
There are three primary tsunami sources that could potentially affect Whitianga from the Kermadec Trench, and beyond the New Zealand continental shelf, being: 
1. Mt Healy undersea volcano eruptions (15th Century event); 
2. Large earthquakes along segments 1 and 2 of the Kermadec Trench subduction zone; and 
3. A 1960 Chilean-type earthquake event. 
Each source is modelled, and the results that show the greatest risk and impacts to Whitianga are used as the basis for the hazard maps and hazard zones. 
Modelling results indicate that:
• The Mt Healy type of eruption produced a minimal impact on Whitianga. The tsunami waves generated from this event did not inundate Whitianga. Despite this, strong currents of up to 2.5 m/s were generated inside Buffalo Bay and at the Whitianga Harbour inlet. 
•The Kermadec Trench earthquake scenarios with both positive and negative leading waves, as a result of a subduction fault dislocation along segments 1 and 2, have a significant impact on Whitianga. The waves inundate the coastal area up to 2.5 and 3 km inland for the subduction thrust fault and normal fault events respectively, and affect the entire area of Whitianga Harbour. The normal fault event that produces positive leading waves has more impact than the thrust fault event that produces negative leading waves. 
• The 1960 Chilean-type earthquake event produced tsunami waves that inundated Buffalo Beach Road and houses in Whitianga, as observed by eyewitnesses. Strong currents of up to 5 m/s are generated inside Buffalo Bay and the Whitianga Harbour inlet. 
The modelling indicates that:
• Whitianga would be inundated five times by a Kermadec Trench earthquake scenario, and three times by a 1960 Chilean-type of tsunami 
• For the Kermadec Trench scenario (normal fault), the first waves penetrate Mercury Bay within 75–98 minutes after the fault rupture 
• Regardless of the tsunami source, it takes 11–18 minutes for waves to arrive at the Whitianga foreshore once they have entered Mercury Bay. 
The modelling indicates that the period between waves is 40 – 60 minutes, which is consistent with the 1960 Chilean event. The geometry of Buffalo Bay and Mercury Bay amplify the incoming tsunami waves, and the sea level inside the bay continues to oscillate, even after the sea level outside of Mercury Bay returns to normal. This situation is consistent with eyewitness accounts of the 1960 Chilean tsunami. 
Modelling also shows that strong currents are produced within Buffalo Bay and Whitianga Harbour, as well as during the overland flows - especially in areas adjacent to the Taputapuatea Stream and in the foreshore area between Albert Street and the wharf. The flow speed ranged from 1.5 m/s to 8 m/s for overland flows, and above 8 m/s within the entrance of Whitianga Harbour and in the middle of Buffalo Bay.  
For the first time in New Zealand, a combination of non-ground striking and ground striking LIDAR data was used in modelling tsunami inundation, which increased the accuracy of the modelling results considerably. Inundation flow behaviour and the effect of topography, as well as land use, can be analysed more accurately, and a more precise hazard map can be produced accordingly. 
Mitigation measures suggested to protect the Whitianga waterfront include a combination of enhanced coastal sand dunes and planted forest belts, which could be done along both sides of the Taputapuatea Stream. A stop gate could also be constructed at the entrance of the Taputapuatea Stream to minimise the impact of the tsunami flows upstream. 
With respect to evacuation, it is concluded that due to the lag time between a local event from the Kermadec Trench and wave arrival at the Whitianga foreshore, there is enough time for residents to be evacuated to shelter sites using major roads. Three locations are identified as evacuation shelter sites. These are the marina parking area and Buffalo Beach scenic reserve (both of which are located on high ground adjacent to the high-risk zone), and further inland at the airfield. Vertical evacuation sites are needed inside the high-risk zone, and recommendations on potential locations are provided. It is important that vertical evacuation measures are integrated into community response plans, and that they be reviewed and revised regularly. 
Overland flow information derived from modelling using the ground-striking and non-ground striking LIDAR data provides a basis to influence new development that occurs within tsunami hazard risk zones. Overland flow information also indicates the areas of existing development that need protection from future tsunami events. Risk mitigation may be accomplished through redevelopment, retrofit, coastal defence measures, safety planning for ships and boats, land reuse plans, and also via public education and awareness programmes. 
A major challenge of risk mitigation is to maintain emergency preparedness programmes and procedures when the threat of tsunami is perceived as remote. Periodic exercises are essential to maintain awareness, and regular information should be provided for those occupying tsunami hazard areas. 
Tsunami are rare events, but their impacts on coastal communities can be devastating. It is quite dangerous to believe that the impacts of a tsunami can be completely prevented by man-made structures (Horikawa and Shuto, 1983). However, possible impacts may be minimised through careful design of solutions based on systematic research. An important consideration for risk mitigation works is that they may affect the quality of daily life, and risk mitigation involves choices and trade-offs between risk management and other uses. Video animations of each scenario are provided at regional, intermediate and local scales. The animations cover tsunami wave behaviour during generation, propagation, run up, and overland flows, and may be used to inform land use planning and public education and awareness programmes.

year: 2015-01-15

title: Offsetting of CO₂ emissions by air capture in mine tailings at the Mount Keith Nickel Mine, Western Australia: Rates, controls and prospects for carbon neutral mining

authors: Wilson, Siobhan A.

subjects: Carbon accounting

abstract: The hydrated Mg-carbonate mineral, hydromagnesite [Mg₅(CO₃)₄(OH)₂•4H₂O], precipitates within mine tailings at the Mount Keith Nickel Mine, Western Australia as a direct result of mining operations. We have used quantitative mineralogical data and δ¹³C, δ¹⁸O and F¹⁴C isotopic data to quantify the amount of CO₂fixation and identify carbon sources. Our radiocarbon results indicate that at least 80% of carbon stored in hydromagnesite has been captured from the modern atmosphere. Stable isotopic results indicate that dissolution of atmospheric CO₂ into mine tailings water is kinetically limited, which suggests that the current rate of carbon mineralization could be accelerated. Reactive transport modeling is used to describe the observed variation in tailings mineralogy and to estimate rates of CO₂ fixation. Based on our assessment, approximately 39,800 t/yr of atmospheric CO₂ are being trapped and stored in tailings at Mount Keith. This represents an offsetting of approximately 11% of the mine's annual greenhouse gas emissions. Thus, passive sequestration via enhanced weathering of mineral waste can capture and store a significant amount of CO₂. Recommendations are made for changes to tailings management and ore processing practices that have potential to accelerate carbonation of tailings and further reduce or completely offset the net greenhouse gas emissions at Mount Keith and many other mines.

text: Offsetting of CO₂ emissions by air capture in mine tailings at the Mount Keith Nickel Mine, Western Australia: Rates, controls and prospects for carbon neutral mining The hydrated Mg-carbonate mineral, hydromagnesite [Mg₅(CO₃)₄(OH)₂•4H₂O], precipitates within mine tailings at the Mount Keith Nickel Mine, Western Australia as a direct result of mining operations. We have used quantitative mineralogical data and δ¹³C, δ¹⁸O and F¹⁴C isotopic data to quantify the amount of CO₂fixation and identify carbon sources. Our radiocarbon results indicate that at least 80% of carbon stored in hydromagnesite has been captured from the modern atmosphere. Stable isotopic results indicate that dissolution of atmospheric CO₂ into mine tailings water is kinetically limited, which suggests that the current rate of carbon mineralization could be accelerated. Reactive transport modeling is used to describe the observed variation in tailings mineralogy and to estimate rates of CO₂ fixation. Based on our assessment, approximately 39,800 t/yr of atmospheric CO₂ are being trapped and stored in tailings at Mount Keith. This represents an offsetting of approximately 11% of the mine's annual greenhouse gas emissions. Thus, passive sequestration via enhanced weathering of mineral waste can capture and store a significant amount of CO₂. Recommendations are made for changes to tailings management and ore processing practices that have potential to accelerate carbonation of tailings and further reduce or completely offset the net greenhouse gas emissions at Mount Keith and many other mines.

year: 2014

title: The marine reservoir effect in the Southern Ocean: an evaluation of extant and new R values and their application to archaeological chronologies

authors: Petchey, Fiona

subjects: ∆R

abstract: The last phase of human colonisation of the south-west Pacific occurred around the 12th Century AD amongst the islands of the subtropical and temperate zones of the Southern Ocean (i.e., Norfolk Island, the Kermadec Islands, New Zealand and the Chatham Islands) (Fig. 1). Archaeological evidence indicates that initial colonisation of the region was rapid, possibly taking less than 100 years. Unfortunately, the chronology of these events has been largely reliant on charcoal radiocarbon determinations that have not been successful in delineating these changes. This paper investigates the use of marine shell for radiocarbon dating as an alternative to charcoal, with specific focus on variation in the marine 14C reservoir (specifically the ∆R) of Raoul Island (Kermadec Islands), Norfolk Island and Chatham Island (Fig. 2). Results from known-age, pre-AD 1950 shellfish indicate that ∆R values south of the South Pacific Convergence Zone are low compared to those recorded for islands within the South Pacific generally (Fig. 1) (see Petchey et al.in press). An average ∆R value of –19 ± 13 14C yr is recorded for Raoul Island and –49 ± 10 14C yr for Norfolk Island. These values are attributed to heightened absorption of atmospheric CO2 in this region. Extant published ∆R information from New Zealand (Fig. 2A) also suggests a low average ∆R value for these southern waters, but the range of values indicates that considerable variability is possible because of the complex interplay of currents around the New Zealand coastline. In contrast, results from Chatham Island are more variable and much higher (average ∆R = 134 ± 83 14C yr). Stable oxygen and carbon isotope data support the hypothesis that these ∆R values are caused by upwelling and mixing of 14C-depleted water along the Chatham Rise. Comparison of marine and charcoal 14C determinations from archaeological sites on Raoul Island support, within the limits of the available data, the ∆R values obtained, but further analysis is required to establish the stability of this value over time.

text: The marine reservoir effect in the Southern Ocean: an evaluation of extant and new R values and their application to archaeological chronologies The last phase of human colonisation of the south-west Pacific occurred around the 12th Century AD amongst the islands of the subtropical and temperate zones of the Southern Ocean (i.e., Norfolk Island, the Kermadec Islands, New Zealand and the Chatham Islands) (Fig. 1). Archaeological evidence indicates that initial colonisation of the region was rapid, possibly taking less than 100 years. Unfortunately, the chronology of these events has been largely reliant on charcoal radiocarbon determinations that have not been successful in delineating these changes. This paper investigates the use of marine shell for radiocarbon dating as an alternative to charcoal, with specific focus on variation in the marine 14C reservoir (specifically the ∆R) of Raoul Island (Kermadec Islands), Norfolk Island and Chatham Island (Fig. 2). Results from known-age, pre-AD 1950 shellfish indicate that ∆R values south of the South Pacific Convergence Zone are low compared to those recorded for islands within the South Pacific generally (Fig. 1) (see Petchey et al.in press). An average ∆R value of –19 ± 13 14C yr is recorded for Raoul Island and –49 ± 10 14C yr for Norfolk Island. These values are attributed to heightened absorption of atmospheric CO2 in this region. Extant published ∆R information from New Zealand (Fig. 2A) also suggests a low average ∆R value for these southern waters, but the range of values indicates that considerable variability is possible because of the complex interplay of currents around the New Zealand coastline. In contrast, results from Chatham Island are more variable and much higher (average ∆R = 134 ± 83 14C yr). Stable oxygen and carbon isotope data support the hypothesis that these ∆R values are caused by upwelling and mixing of 14C-depleted water along the Chatham Rise. Comparison of marine and charcoal 14C determinations from archaeological sites on Raoul Island support, within the limits of the available data, the ∆R values obtained, but further analysis is required to establish the stability of this value over time.

year: 2008