Wave Inundation on the Coral Coast of Fiji

The roaring winds of the Southern Ocean and the Tasman Sea can generate some large swells, big enough to cause inundation on the Coral Coast in the south west of Viti Levu in Fiji, some 3000 km to the north. These inundation events are sometimes associated with tsunami-like long waves that hit the shore and inundate the coast with brute force. These are locally known as loka waves. To understand the origin of the loka waves and how they become so destructive in a fringing reef environment, this research monitored the waves and water levels, for 2 years, at 4 locations across the reef at a pilot site in Maui Bay on the Coral Coast of Fiji. In order to test the size of waves necessary to cause coastal inundation, a validated numerical model, XBeach, was used to simulate the development, propagation and dissipation of these infragravity waves using different water level scenarios. The result of this analysis is intended as a predictive tool to evaluate the risk of coastal inundation from ocean surface waves that can be used to support an early warning system and coastal management tool for both the tourism industry and coastal communities on the Coral Coast

Waves and Coasts in the Pacific - Cost Analysis of Wave Energy in the Pacific

Ocean waves are often cited as an appealing source of renewable energy in the Pacific but the cost effectiveness of wave energy converters (WECs) is deemed unproven and the technology is rarely considered as a reliable renewable energy resource in Pacific Island countries. However, single/stand-alone WECs could be a competitive option against fossil fuel generators because of the high cost of imported fuel. This study analyses the wave energy resource in the Pacific and calculates the potential cost and power generation of a benchmark WEC in Pacific Island countries. The type of WEC chosen depends largely on the environmental and geophysical characteristics of the wave energy site where it is to be deployed. The aim of this study was not to report on the best device for each site but rather to give advice about the islands that could benefit most from wave energy. Therefore, the cost analysis is based on a single WEC – the Pelamis device. The Pelamis device cost presented here serves as a benchmark for comparison with other WECs in different locations. Due to uncertainties and variations in potential costs across the region, the study evaluated the range of costs applicable to the whole region. The costs of the WEC, transport, installation, operation and management, refit and decommissioning are included. Site-specific potential power generation was calculated, based on a realistic power output dependent on the wave conditions. The study found that Pacific islands south of latitude 20oS receive a substantial amount of wave energy with a mean available wave resource above 20 kilowatts per metre (kW/m) and that many other islands also have potential for wave energy extraction with a mean wave resource above 7 kW/m. This study found that a Pelamis device in the Pacific could cost between USD 6,318,000 and USD 14,104,000 to install and can operate for 25 years. The energy produced by such a device could be up to 1200 megawatt hours (MWh) per year for sites exposed to large swells. Using these values, the range of the total lifetime cost of power generation was calculated to be between USD 200/MWh for exposed sites and USD 1800/MWh for more sheltered sites. The corresponding operation and maintenance generation cost are between USD 40/MWh and USD 900/MWh. These costs are on a par with the cost of generation of other renewable energies, such as wind and solar, and, for exposed sites, on a par with the cost of diesel generation. These findings suggest that wave energy is a genuine contender for the development of renewable energy in the Pacific and should no longer be ignored when planning such development; a concerted effort from all stakeholders should be made in order to benefit from this technology. Further deployment in wave technology will reduce the cost of single wave energy devices, and most small Pacific Islands would not need to deploy large-scale wave farms of ten or more devices, as power production would greatly exceed the demand. With expected rises in fuel prices in the next decades, it would be wise to investigate further the potential of wave energy technology. The deployment of WECs in the Pacific could provide an opportunity for the technology to prove itself in the region and attract the attention of investors, policy makers and decision makers to invest in wave energy development in the Pacific . Page | 2 Waves and Coasts in the Pacific Other recommendations are listed below. 1. French Polynesia, the Austral Islands in particular, should investigate potential wave energy sites. On these islands, wave energy generation could become a major renewable energy resource with a relatively low cost that could even compete with fossil fuel. 2. Tonga, Cook Islands and New Caledonia should also investigate wave energy sites and suitable wave energy devices. Wave energy has a great potential for helping these countries reach their renewable energy targets and supply energy more cheaply than other renewable energy resources. 3. Countries with a mean wave energy flux above 7 kW/m should also investigate wave energy hotspots and wave energy device options, especially in exposed locations. There, wave energy may be able to supply a significant amount of renewable energy and help these countries meet their renewable energy targets. However, wave energy in these locations may be more expensive than other types of renewable energy. 4. Countries with a mean wave energy flux of less than 7 kW/m, such as Papua New Guinea and Solomon islands, are unlikely to benefit from wave energy unless a major technological breakthrough makes wave energy devices much more efficient. These countries should therefore not consider wave energy as a significant renewable energy resource. The WACOP project has provided calculations similar to those presented in this study for more than 200 Pacific locations in wave climate reports that should be consulted as an initial assessment of the wave energy resource available.1 The WACOP project also provides a detailed wave climate analysis for Samoa, Rarotonga in Cook Islands, Tongatapu and 'Eua in Tonga, southern Viti Levu in Fiji, Efate in Vanuatu, and Funafuti in Tuvalu. These analyses include wave energy and cost calculations based on the calculations presented in this report

Mapping shallow groundwater salinity in a coastal urban setting to assess exposure of municipal assets

Study region: Christchurch, New Zealand. Study focus: Low-lying coastal cities worldwide are vulnerable to shallow groundwater salinization caused by saltwater intrusion and anthropogenic activities. Shallow groundwater salinization can have cascading negative impacts on municipal assets, but this is rarely considered compared to impacts of salinization on water supply. Here, shallow groundwater salinity was sampled at high spatial resolution (1.3 piezometer/km2 ), then mapped and spatially interpolated. This was possible due to a uniquely extensive set of shallow piezometers installed in response to the 2010–11 Canterbury Earthquake Sequence to assess liquefaction risk. The municipal assets located within the brackish groundwater areas were highlighted. New hydrological insights for the region: Brackish groundwater areas were centred on a spit of coastal sand dunes and inside the meander of a tidal river with poorly drained soils. The municipal assets located within these areas include: (i) wastewater and stormwater pipes constructed from steel-reinforced concrete, which, if damaged, are vulnerable to premature failure when exposed to chloride underwater, and (ii) 41 parks and reserves totalling 236 ha, within which salt-intolerant groundwater-dependent species are at risk. This research highlights the importance of determining areas of saline shallow groundwater in low-lying coastal urban settings and the co-located municipal assets to allow the prioritisation of sites for future monitoring and management

Mapping shallow groundwater salinity in a coastal urban setting to assess exposure of municipal assets

Study region: Christchurch, New Zealand. Study focus: Low-lying coastal cities worldwide are vulnerable to shallow groundwater salinization caused by saltwater intrusion and anthropogenic activities. Shallow groundwater salinization can have cascading negative impacts on municipal assets, but this is rarely considered compared to impacts of salinization on water supply. Here, shallow groundwater salinity was sampled at high spatial resolution (1.3 piezometer/km²), then mapped and spatially interpolated. This was possible due to a uniquely extensive set of shallow piezometers installed in response to the 2010–11 Canterbury Earthquake Sequence to assess liquefaction risk. The municipal assets located within the brackish groundwater areas were highlighted. New hydrological insights for the region: Brackish groundwater areas were centred on a spit of coastal sand dunes and inside the meander of a tidal river with poorly drained soils. The municipal assets located within these areas include: (i) wastewater and stormwater pipes constructed from steel-reinforced concrete, which, if damaged, are vulnerable to premature failure when exposed to chloride underwater, and (ii) 41 parks and reserves totalling 236 ha, within which salt-intolerant groundwater-dependent species are at risk. This research highlights the importance of determining areas of saline shallow groundwater in low-lying coastal urban settings and the co-located municipal assets to allow the prioritisation of sites for future monitoring and management

Christchurch shallow groundwater quality survey dataset

Shallow groundwater quality and level across the low-lying coastal city of Christchurch, New Zealand were surveyed at a high spatial resolution (1.3 piezometers/km²) in the spring of 2020. The groundwater quality parameters recorded across 99 piezometers include specific conductance, temperature, pH, and dissolved oxygen, following the pumping of approximately three bore volumes. Additionally, 27 out of 99 piezometers were analysed for chloride concentration and alkalinity as calcium carbonate. This dataset is useful to explore shallow groundwater conditions and how these might impact co-existing subsurface infrastructure and ecosystems. Furthermore, this dataset provides a valuable point of comparison against future changes, for example due to increased seawater intrusion, pollution events, or groundwater level rise

The influence of reef topography on storm-driven sand flux

Natural formations of rock and coral can support geologically controlled beaches, where the beach dynamics are significantly influenced by these structures. However, little is known about how alongshore variations in geological controls influence beach morphodynamics. Therefore, in this study we focus on the storm response of a beach (Yanchep in south Western Australia) that has strong alongshore variation in the level of geological control because of the heterogeneous calcarenite limestone reef. We used a modified version of XBeach to simulate the beach morphodynamics during a significant winter storm event. We find that the longshore variation in topography of the reef resulted in: (1) strong spatial difference in current distribution, including areas with strong currents jets; and (2) significant alongshore differences in sand flux, with larger fluxes in areas strongly geologically controlled by reefs. In particular, this resulted in enhanced beach erosion at the boundary of the reef where strong currents jet-exited the nearshore

On the resilience of small-island freshwater lenses: Evidence of the long-term impacts of groundwater abstraction on Bonriki Island, Kiribati

© 2018 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license: http://creativecommons.org/licenses/by-nc-nd/4.0/ This author accepted manuscript is made available following 24 month embargo from date of publication (June 2018) in accordance with the publisher’s archiving policy.Groundwater on islands occurs in the form of freshwater lenses that serve as an important water resource for local inhabitants. These lenses are highly vulnerable to salinization due to natural recharge variations and groundwater abstraction. Determining the sustainable yield from freshwater lenses is challenging because the lens response during drought periods and the long-term effects of pumping are both difficult to predict. The exceptionally detailed and long data record for Bonriki Island of the Tarawa atoll (Kiribati) made it possible to develop a three-dimensional variable-density model of the island. Field data and modelling results highlight the strong control of rainfall variability and pumping on the temporal dynamics of the freshwater lens. The model reproduces the salinity observations in both monitoring and pumping wells reasonably well, and provides a rare example of physically based island simulation based on an extensive data set. It enables the analysis of freshwater volume and fluxes of submarine groundwater discharge, which is impossible based on the field observations alone. Under natural as well as abstraction conditions, submarine groundwater discharge responds rapidly and almost proportionally to recharge. Theoretical model scenarios with scaled abstraction rates show that lens contraction caused by pumping is a nearly linear function of the total pumped volume, whereby the abstraction rate and the timing of depletion are approximately inversely proportional. Modelling indicates that when monthly recharge inputs fall below around 2500 m3/d (i.e., a flux of 1.7 mm/d) plus the abstraction rate, the lens tends to contract. Thus, despite the highly distributed and extensive abstraction network on Bonriki Island, a significant amount of recharge is eventually lost to submarine groundwater discharge. The long-term freshwater storage trend indicates that Bonriki Island’s lens is still contracting after 27.5 years of pumping, and lens thinning is threatening to impact the water supply salinity. This means that even permeable, small islands like Bonriki may take at least two decades to realise new equilibrium conditions that reflect pumping stresses, which is an important consideration in assessing the sustainable yield of small islands, in particular those less resilient to pumping than Bonriki

El ciclo Kondratiev : mito o realidad ?

International audienc

Les cycles longs du capitalisme, un point de vue sur soixante dix ans de débats

International audienc