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The 10 km stretch of foreshore between two of New Zealand's largest cities Wellington and Hutt City is a crucial infrastructure corridor combining cycleway, road and rail, as well as sub-surface utilities. Recent storm events have caused significant damage to, and overtopping of, the current rock revetment structure resulting in the rail line being undermined and closed for extended periods. Future proofing the foreshore is integral for the longevity and function of this corridor and the Te Ara Tupua Alliance have been tasked with redeveloping it. UNSW Water Research Laboratory (WRL) undertook a large physical modelling program (over a 100 individual tests) to assist optioneering for a range of coastal protection designs. 2D flume testing was conducted to assess both the stability and overtopping performance of rock and concrete armoured (modified XblocPlus) revetments and vertical walls equipped with sloped crown walls. All tests were conducted using irregular wave time series derived from several spectral conditions. Analysis of wave buoy records showed that both wind waves and swell entering the harbour could be expected to impact the project area. As such, sensitivity testing for overtopping was conducted using custom-generated bimodal conditions with different wind/swell ratios. Physical model testing results showed that overtopping volumes were highly sensitive to the long period wave component within the bimodal spectrum. The findings of this extensive physical modelling program highlight the limitations of standard empirical methods for assessing overtopping under bimodal wave climates, the importance of extending beyond conventional unimodal wave climates when designing coastal structures, and the importance of using on-site wave data to best model potential overtopping volumes and safely optimize designs. [ABSTRACT FROM AUTHOR]

The use of single layer, concrete armour units for coastal edge protection in place of rock is becoming increasingly common. Revetments constructed from these units can provide benefits of a reduced footprint, reduced material usage and transport costs as suitable rock becomes increasingly difficult to source, and reduced construction timeframes. XblocPlus® units have been adopted as the primary armouring for a major shared-path infrastructure project within Te Whanganui-a-Tara, Wellington Harbour. The Ngā Ūranga ki Pito-One Project comprises a 4.5 km shared (pedestrian/cycling) pathway between Ngā Ūranga and Pito-One. The XblocPlus® units are patternplaced interlocking armour concrete units that remain stable at steep slope angles while providing high coastal performance. However, these units have had limited application in seismically active regions. Therefore, the behaviour of the individual armour units and overall revetment during, and following seismic activity was assessed in detail to assess performance and enable development of a post-seismic inspection and repair strategy. The response of a revetment to seismic shaking, particularly the interlocking of the individual XblocPlus® units and interaction with the ground profile below is complex and could not be determined using a single method or model. Therefore, a suite of complementary models was used to assess the behaviour of individual components and combined performance of the revetment asset under the design earthquake events. This paper describes the various physical and numerical models used to determine performance and to inform the design and repair strategy of XblocPlus® revetment. The physics-based model Unreal Engine was calibrated against uni-directional testing on a physical shake table and run for 3D design earthquake timeseries to assess how the individual XblocPlus® units reacted to shaking. Limit equilibrium and time history finite element modelling were carried out to understand how the ground profile supporting the revetment might perform. These results were then used in the 3D physics-based model in Blender to determine the unit response to slope deformation. The XblocPlus® response to shaking and slope deformation was combined to create a post-seismic revetment condition, which in turn was tested by physical modelling in a wave flume against to assess hydraulic stability performance under moderate storm events (i.e., before a repair could be enacted). Following this, an inspection and repair strategy was developed. [ABSTRACT FROM AUTHOR]

The Te Ara Tupua Ngā Ūranga ki Pito-One (Ngauranga to Petone) Project comprises a 4.5 km shared (pedestrian/cycling) pathway between Ngā Ūranga (Ngauranga) and Pito-One (Petone) in Te Whanganui-a-Tara, Wellington. The Project will be located on the seaward side of the State Highway 2 and the rail corridor and will provide safe walking and cycling infrastructure as well as enhancing the resilience of the transport corridor. The Project involves temporary and permanent works in and adjacent to the coastal marine area, including multiple rock and concrete armour revetments, ūranga (landings), seawalls, offshore habitats and culvert extensions, and will result in over 5 Ha of permanent marine habitat loss. To avoid, minimise and compensate for the impact on the marine environment, a number of innovative ecological enhancements have been incorporated into the Project design. Two rock armour offshore habitats will provide undisturbed roosting habitat for coastal avifauna. 235 little blue penguin nesting boxes will be incorporated within the revetment and Ūranga. Gravel beaches will be nourished to provide 10-25 years of resilience to future sea level rise. Over 240 ECOncrete® tide pools will be integrated in clusters within the intertidal bench of the rock revetments and offshore habitats, providing habitat and water retaining features for marine life as well as foraging habitat for coastal birds. Finally, some 1850 XblocPlus® units, that form part of the revetment, will be ecologically enhanced using increased surface complexity. The integration of these ecological enhancements within the design was developed in collaboration between ecologists, landscape architects, engineers and mana whenua and drew inspiration from the existing ecology, coupled with cultural narrative. This project will be the first application of many of these ecological enhancement features in New Zealand. The features will improve the ecological value of the coastal pathway and provide a more resilient marine ecosystem within Te Whanganui-a-Tara (Wellington Harbour). The project provides a case study for how ecological features can be successfully implemented into coastal infrastructure and an opportunity to measure the ecological performance of these features in a New Zealand context, so that future installations can more accurately predict the ecological gains likely to be achieved when balancing against unavoidable biodiversity losses. [ABSTRACT FROM AUTHOR]

The Te Ara Tupua Ngā Ūranga ki Pito-One Project comprises a 4.5 km shared (pedestrian/cycling) pathway between Ngā Ūranga and Pito-One in Te Whanganui-a-Tara, Wellington with dual outcomes of rail/road corridor resilience improvement and mode shift. The project presented the challenging design requirements of managing the safety of shared path users through a coastal edge design that is controlled by tight geometric (elevation and toe position) constraints, a range of unique edge protection structures, and a bimodal wave climate. This challenge was addressed through site and design specific physical and numerical modelling, data driven overtopping analysis and a forecast model development for safety management during operation. The range of edge protection structures proposed include XblocPlus armour unit revetments, rock armour revetments with mid-tide berms of varying width, and vertical concrete seawalls with return crest walls. The present empirical guidance on overtopping performance of these structure configurations is not widely developed in literature, at least with sufficient reliability to inform design on this project. An additional complicating factor was a bimodal wave climate, the swell component of which was discovered to have a significant effect on anticipated overtopping flows. As such, structure- and site-specific physical modelling was undertaken to inform the overtopping analysis at the UNSW Water Research Laboratory. The results of the physical model tests were used to develop sitespecific, data-driven formula based on relationships between relative overtopping and relative freeboard, as presented in the EurOtop manual. These relationships were used to understand overtopping potential along the project site both now and in the future through development of a 30-year overtopping timeseries. In parallel, a two-layer phase resolving, non-hydrostatic XBeach solver was calibrated to match the wave transformation of the bi-modal wave climate and physical model overtopping results allowing wave conditions and resultant overtopping flows to be extracted anywhere along the project site. This was used to inform design crest levels future adaptation timeframes and options, and to develop an overtopping forecast model to inform path warnings and closure during operation. The results of this analysis highlighted the importance of understanding site-specific influences on overtopping flows, not all of which are able to be fully understood through adoption of standard empirical overtopping formula. [ABSTRACT FROM AUTHOR]

Modern-day coastal engineering faces two key challenges: firstly, providing adequate protection under anthropogenic increases in sea level, and secondly, reducing environmentally detrimental engineering practices that are further driving changes to the climate. With this, nature-based solutions that minimise detrimental environmental effects whilst providing sufficient protection are increasing in their uptake. At present, the application of these nature-based engineering strategies is restricted to low-energy wave environments with minimal spatial constraints. Hybridisation (combined use of nature-based and traditional hard engineering strategies) enables the use of these nature-based principles in higher-energy and urban environments. This paper explores the use of hybridisation with coastal vegetation, by exploring the ability of vegetation to attenuate wave overtopping flow on the crest of coastal defence structures. Physical modelling experiments were conducted in the University of Auckland's wave flume with a small-scale sloped seawall retrofitted with model vegetation on the crest of the seawall. This preliminary testing found that the model vegetation reduced mean overtopping discharges by 60-80% when evaluated against their nonvegetated counterpart. Numerical model testing was conducted by calibrating to and expanding on the physical model analysis. This was achieved by implementing a one-dimensional non-hydrostatic XBeach model. Numerical model testing used a multiple linear regression analysis to test the sensitivity of the wave overtopping response to various vegetation parameters. From this, the reduction in mean overtopping flow due to the incorporation of vegetation was found to be most strongly correlated to vegetation width, stem density and stem diameter, with increases in any of these parameters leading to substantial decreases in mean overtopping flow. Both the physical and numerical model testing were limited by their use of idealised structure and vegetation parameters. However, despite these limitations, this study provides a framework for future testing that should seek to further solidify the wave overtopping performance of this hybrid strategy. [ABSTRACT FROM AUTHOR]

Wave overtopping occurs as waves pass over the coastal edge and flow onto the land behind. This can result in a hazard to vehicles and pedestrians and flooding or damage to the built environment. To date, predictive formulae for overtopping have been primarily developed in a laboratory setting. Comparatively few studies involve the field measurement of overtopping because environmental conditions such as wind and water levels have a large influence on the overtopping rate (amongst many other factors), and the measurement of overtopping discharge is practically difficult due to enormous spatial and temporal variation in overtopping volumes. This paper discusses key challenges for local government coastal managers in New Zealand relating to overtopping hazard, highlighting a need for pragmatic guidance on monitoring, application within an adaptive management, and assessment of Relative Sea Level Rise (RSLR) effects on future hazard. Two methods to measure wave overtopping in the field were investigated in this study; using either catch devices that measure volume, or camera monitoring. This paper shows, by considering a site along Tamaki Drive in Auckland, how monitoring and measurements of overtopping is important as part of the Ministry for the Environment (MfE) recommended Dynamic Adaptive Policy Pathway (DAPP) approach to managing associated hazards. Finally, this study shows how future overtopping hazards associated with RSLR can be assessed by remodelling incremental rises applied to historic water level records. It is found that even small amounts of RSLR can dramatically increase the exposure of coastal communities to overtopping hazards. [ABSTRACT FROM AUTHOR]