Multi-hazard analysis and mapping of coastal Tauranga in support of resilience planning

High growth is increasingly forcing development of hazard prone land in the coastal city of Tauranga. A multi-hazard mapping tool developed to guide strategic growth planning in this natural hazard rich environment gives direct comparison of total hazard levels across the city. By aggregating individual hazards into a summative multi-hazard rating for each part of the city, urban planners and engineers have a decision support tool to aid city planning over the next 100 years. Tauranga growth requires 40,000 new homes over the next four decades in addition to the existing 57,000 homes. This 70% growth must squeeze within tight geographic constraints as Tauranga's 137,000 residents nestle around a harbour and are bound by open coast to the north and steep terrain to the south. This research quantifies Tauranga’s natural hazards of sea level rise, storm surge, coastal erosion, tsunami, earthquake shaking, liquefaction, landslides volcanic ashfall and flooding. Each hazard is spatially represented through hazard maps. Individual hazards are combined into a multi-hazard model to represent the aggregated hazard exposure of each point of the city. The multi-hazard exposure is spatially mapped using GIS allowing an area with tsunami, liquefaction and storm surge as dominant hazards to be directly compared with an area of different hazards such as flooding and landslides. Mapping of these hazards provides strategic input for building city resilience through land use planning and mitigation design. A pilot study area of 25 km2 selected from the Tauranga City Council total area of 135 km2 demonstrates the accumulated mapping approach. The pilot area contains a thorough representation of geology, elevation, landform and hazards that occur throughout the city. Our findings showed the highest aggregated hazard areas in Tauranga are along the coast. As is common with many beach resort towns this corresponds with the most popular living areas. The lower hazard areas suitable for urban growth are distributed mostly away from the open coast in the slightly elevated topography.

The future of the Sundarbans mangroves in India

<p>The Sundarbans Biosphere Reserve is situated near Kolkata in the western part of the Ganges-Brahmaputra Delta. The Sundarbans mangroves together with the areas in Bangladesh are the world’s largest mangrove forest and home to the iconic Royal  Bengal Tiger. It is a Ramsar and World Heritage site. Over the last 20 years the mangroves have retreated from 10 to 50 m/yr along the open coast with the loss of 145 km<sup>2</sup> area of the biosphere reserve , 40% of which constitute the  mangrove forest. This erosion reflects a response to waves in the Bay of Bengaland relative sea-level rise of about  5 mm/yr since 1948 which increased further during the last decade. In percentage terms this observed forest land loss is manageable. However, it will continue and almost certainly accelerate with sea-level rise. As well as open coast erosion, inundation will also occur within the mangroves. Hence over many decades,Sundarbans mangroves will be progressively degraded endangering  their iconic species. We are using these observed data and the Sea Level Affecting Marshes Model (SLAMM)to explore possible trajectories of the Sundarbans evolution under different sea-level rise scenarios and management interventions. The areas to the north are densely populated and increasingly influenced by the expansion of Kolkata. Discussions with stakeholders suggest a managed retreat does not seem feasible or practical due to the large displaced populations.The paper will discuss theinter linkages of the slow onset hazard in a sinking and shrinking delta to explore pathways to achieve sustainable outcomes in south Asian deltas.  </p>

BEACH PLANFORM EQUILIBRIUM, APPLICATION AND METHODOLOGIES FOR CLIMATE CHANGE RESILIENCY CONSIDERATION

Climate change and sea level rise (SLR) present a challenge and added uncertainty for managing coastal areas. Many coastal cities and developed coastal areas are assessing future vulnerabilities to SLR and developing adaptation plans for improved resiliency. Equilibrium conditions for beach planform can be critical to the long-term stability of beaches and dunes fronting coastal cities. In many cases, resiliency and adaptation programs for beachfront areas are based on assumptions of evaluating scenarios of higher water elevations and hydrodynamic forcing under present time topographic and bathymetric conditions. These evaluation parameters suggest that the coastline and existing morphological features are near equilibrium condition and are expected to remain near similar equilibrium over the SLR scenarios under consideration. Such assumptions may be limited to open coast conditions where the beach and the developed coastal planform follows theoretical open coast conditions or constant equilibrium planform. This paper discusses factors influencing beach planform along the Florida Atlantic and Gulf of Mexico coastlines and proposes conceptual methodologies in various applications.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/gWsbmi6VIo0

Spatially variable larval histories may shape recruitment rates of a temperate reef fish

Several long-standing hypotheses purport variation in recruitment to be positively correlated with pelagic environmental conditions that enhance larval growth, survival, and/or delivery to recruitment sites. However, the relationship between recruitment intensity and larval environmental conditions (or more directly, larval condition) is difficult to evaluate and poorly known for most species. We evaluate this relationship for the reef fish Forsterygion lapillum that commonly inhabits rocky reefs throughout New Zealand. We quantified variation in recruitment of F. lapillum using a nested sampling design, and found that the largest source of variation was between 2 nearby regions (a semi-enclosed harbour and an adjacent open coast system). We estimated 'settler condition' as the composite of residual body mass and 2 measurements of larval growth (reconstructed from otolith microstructure) and found that recruitment intensity was positively correlated with settler condition for sites within the harbour, but negatively correlated with settler condition for sites on the open coast. Mean pelagic larval duration of recruits to the harbour was ̃3 d shorter than recruits to the open coast. These results suggest that larval experience and relationships between recruitment and settler condition are spatially variable. We speculate that (1) larval retention within a productive embayment facilitates a positive relationship between recruitment and settler condition while (2) dispersal through a less productive environment drives a negative relationship for replenishment on the open coast. These putative differences may have important implications for patterns of recruitment, the strength of post-settlement density-dependent interactions, and dynamics of local populations.

Regional variation in larval retention and dispersal drives recruitment patterns in a temperate reef fish

Although there is wide appreciation for the influence of variable larval transport on recruitment, few studies have investigated the relationship between recruitment intensity and the origin(s) of recruits. We evaluate this relationship for the common triplefin Forsterygion lapillum in Wellington Harbour (a semi-enclosed bay) and the adjacent open coast of North Island, New Zealand. As the harbour is productive, with many F. lapillum adults, we predicted the harbour would be an important source of recruitment for both regions. We estimated larval origins and dispersal histories using embryonic and larval otolith chemistry, respectively, with differences in otolith elemental composition consistent with birth and/or development in either harbour or open ocean waters. In the harbour, recruitment was greatest when locally spawned larvae were retained. Although large recruitment pulses to the open coast were comprised mostly of larvae originating from the open coast, 72 % of all recruits to the south coast were actually spawned in the harbour. Dispersal of larvae from the harbour was frequent, but in low numbers, and was unrelated to opportunities for transport from the harbour. Given recent evidence for differences in larval growth between regions, we suggest that (1) faster larval growth combined with nearshore larval distributions result in high recruitment to the harbour and moderate, but demograph-ically important, dispersal from the harbour to the open coast. In contrast, we suggest that (2) the combination of strong tidal currents in Cook Strait and slower larval growth result in lower recruitment and greater transport of larvae among open coast populations. The mechanisms that underlie such context-dependent dispersal have important implications for patterns of connectivity. © Inter-Research 2010.

Regional variation in larval retention and dispersal drives recruitment patterns in a temperate reef fish

Although there is wide appreciation for the influence of variable larval transport on recruitment, few studies have investigated the relationship between recruitment intensity and the origin(s) of recruits. We evaluate this relationship for the common triplefin Forsterygion lapillum in Wellington Harbour (a semi-enclosed bay) and the adjacent open coast of North Island, New Zealand. As the harbour is productive, with many F. lapillum adults, we predicted the harbour would be an important source of recruitment for both regions. We estimated larval origins and dispersal histories using embryonic and larval otolith chemistry, respectively, with differences in otolith elemental composition consistent with birth and/or development in either harbour or open ocean waters. In the harbour, recruitment was greatest when locally spawned larvae were retained. Although large recruitment pulses to the open coast were comprised mostly of larvae originating from the open coast, 72 % of all recruits to the south coast were actually spawned in the harbour. Dispersal of larvae from the harbour was frequent, but in low numbers, and was unrelated to opportunities for transport from the harbour. Given recent evidence for differences in larval growth between regions, we suggest that (1) faster larval growth combined with nearshore larval distributions result in high recruitment to the harbour and moderate, but demograph-ically important, dispersal from the harbour to the open coast. In contrast, we suggest that (2) the combination of strong tidal currents in Cook Strait and slower larval growth result in lower recruitment and greater transport of larvae among open coast populations. The mechanisms that underlie such context-dependent dispersal have important implications for patterns of connectivity. © Inter-Research 2010.

Spatially variable larval histories may shape recruitment rates of a temperate reef fish

Several long-standing hypotheses purport variation in recruitment to be positively correlated with pelagic environmental conditions that enhance larval growth, survival, and/or delivery to recruitment sites. However, the relationship between recruitment intensity and larval environmental conditions (or more directly, larval condition) is difficult to evaluate and poorly known for most species. We evaluate this relationship for the reef fish Forsterygion lapillum that commonly inhabits rocky reefs throughout New Zealand. We quantified variation in recruitment of F. lapillum using a nested sampling design, and found that the largest source of variation was between 2 nearby regions (a semi-enclosed harbour and an adjacent open coast system). We estimated 'settler condition' as the composite of residual body mass and 2 measurements of larval growth (reconstructed from otolith microstructure) and found that recruitment intensity was positively correlated with settler condition for sites within the harbour, but negatively correlated with settler condition for sites on the open coast. Mean pelagic larval duration of recruits to the harbour was ̃3 d shorter than recruits to the open coast. These results suggest that larval experience and relationships between recruitment and settler condition are spatially variable. We speculate that (1) larval retention within a productive embayment facilitates a positive relationship between recruitment and settler condition while (2) dispersal through a less productive environment drives a negative relationship for replenishment on the open coast. These putative differences may have important implications for patterns of recruitment, the strength of post-settlement density-dependent interactions, and dynamics of local populations.