Climate Change and Gravel-Beach Responses: Hawke s Bay, New Zealand

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1 Conference Proceedings, 2015 Solutions of Coastal Disasters, Boston, MA COPRI, American Society of Civil Engineers Climate Change and Gravel-Beach Responses: Hawke s Bay, New Zealand Paul D. Komar 1 and Erica Harris 2 1 College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, U.S.A; pdkomar@gmail.com 2 AECOM, Seattle, WA 98104, U.S.A. ABSTRACT In 1931 a major earthquake altered elevations along the shores of Hawke s Bay, raised by 2 m at the north end of the study area, decreasing alongshore with 1-m subsidence at the south end. While the uplifted gravel beaches created stable barrier ridges, now developed with homes, concerns are that with projected accelerated rates of rising sea levels and increasing storm wave heights, erosion and overwash impacts will return. Analyses have been undertaken of the measured tides, waves, and calculated swash runup levels on the beaches, combined to yield a record of hourly total water levels at the shore. Its extremes are compared with the elevations of surveyed beaches and gravel ridges, to project future property hazards. In that little more than a decade of measured waves were available for our analyses, the morphologies of the ridges provided evidence for past more extreme storm events and water levels, which had occurred in the 8 decades since the earthquake and land-elevation changes. INTRODUCTION Located on the Pacific coast of New Zealand s North Island, Hawke s Bay experiences natural hazards encompassing essentially all of those that occur globally on ocean shores. The most extreme are those related to its tectonic setting, with catastrophic subduction earthquakes and tsunami having occurred in the pre-historic past, while an earthquake in 1931 within the upper colliding plate resulted in major destruction, having altered the land elevations, tilting the shore such that changes along the coast ranged from 2-m uplift to 1-m subsidence. The changed elevations significantly altered the morphologies of the beaches and backshore properties, having become an important control on their susceptibilities to erosion and flooding. The focus of this investigation has been on the potential hazards enhanced by Earth s changing climate, the projected accelerated rates of rising sea levels, and evidence for increased storm intensities and their generated wave heights. The concern is that in the future the shoreline sites that had become more stable due their uplift by the 1931 earthquake, will again experience impacts of major storms

2 and higher sea levels, while those that had subsided and already experience erosion problems could face catastrophic losses. Our investigations have centered on the Hawke s Bay coast from Tangoio in the north to Cape Kidnappers in the south, Figure 1, the mixed sand-and-gravel beaches of the Bay View and Haumoana Littoral Cells, separated by the Bluff Hill headland within the city of Napier, this being the most heavily developed shore within this region. An earlier report and publication were concerned with the existing erosion problems and their causes (Komar, 2005, 2010), while the present investigation expanded our analyses of the erosion processes to include considerations of future hazards expected from Earth s changing climate (Komar and Harris, 2014). Figure 1: The Bay View and Haumoana Littoral Cells, bounded by headlands within the coast of Hawke s Bay. TECTONIC SETTING AND HAZARDS Being a segment of the Pacific Ocean s Ring of Fire, New Zealand straddles two of Earth s major tectonic plates, the oceanic Pacific Plate that collides with and is subducted beneath the Australian Plate, along the Hikurangi Margin that extends the length of the North Island s eastern shore. Collision of the plates during the pre-historic past generated extreme earthquakes and tsunami, events on a scale comparable to the recent Tohuku event on the coast of Japan. Of more recent occurrences within Hawke s Bay have been earthquakes of magnitudes up to 7 and 8 at shallow depths within the body of the Australian Plate, produced by its compression, the folding and faulting of its rocks. Most

3 important was the Hawke s Bay Earthquake in 1931, its epicenter having been on the coast just to the north of our study area. Immediately evident on the day of the event was the rise of the Ahuriri Lagoon to the north of Napier, inland from the Bay View Littoral Cell, nearly all of the Lagoon having rapidly drained into the sea, converted into land that now contains the region s commercial airport (Komar, 2010). An analysis by Hull (1990) of the land elevation changes found a maximum uplift of 2.7 m along the rocky coast north of Tangoio, with the shore of the Bay View Littoral Cell having been raised by about 2 m. Along the shore of the Haumoana Cell south of the Bluff Hill headland within Napier, the uplift progressively decreased with distance alongshore to the south, becoming 0 at about Awatoto midway within that embayed shore (Figure 1), while the communities further to the south subsided by 0.5 to 1 m. This degree land-elevation changes along the length of the study area had a profound effect on the coast s morphologies, having altered the rates and extent of erosion as the processes acted to restore an equilibrium. This is evident in the present-day morphologies of the gravel ridges, and the inherent susceptibilities of their developed properties to erosion and overwash flooding. Figure 2 shows the community of Whirinaki in the northern part of the Bay View Cell, the shore that had experienced 2-m uplift. Prior to that event, this site and nearly the entire length of this shore had been a low-lying gravel spit, backed by the extensive Ahuriri Lagoon, having experienced intense overwash during storms. Construction of homes only became possible following its uplift. During subsequent decades the waves and tides cut a low bluff into the uplifted gravel ridge, Figure 2. Examinations of the decades of surveyed beach profiles dating back to the 1970s demonstrated that there has been little erosional retreat of the bluff in recent decades, its morphology having been acquired primarily during the early years following uplift of this shore (Komar and Harris, 2014). The beach/bluff junction elevations therefore represent comparatively extreme but rare storm events. Figure 2: Beach and elevated backshore gravel ridge in the community of Whirinaki, the Bay View Littoral Cell.

4 The small community of East Clive, Figure 3, is located midway along the shore of the Haumoana Cell, close to the node that experienced essentially no change in elevation at the time of the earthquake, representing the transition from the uplifted shore to its north, subsidence to its south. Not having experienced a change in elevation, it retains the morphology of the pre-quake natural barrier gravel beaches, there being a series of ponds along its landward side. This ridge continues to be overtopped by combinations of high tides and wave swash runup during storms, evident in its morphology. A comparison between the earliest profile surveyed at this site in 1989, as part of a monitoring program, and that in 2010, demonstrated that there has been a net erosional retreat of the beach, with a significant accumulation of gravel on the landward side of the ridge, but with there having been almost no change in the elevation of its crest. Figure 3: The central shore of the Haumoana Littoral Cell, the barrier beach ridge in East Clive where overwash events occur during storms and high tides. As expected the southern stretch of the Haumoana Cell, that had experienced subsidence in 1931, suffers extreme problems with property erosion, illustrated by Figure 4, showing the remains of failed structures installed to protect the homes. Investigations have concluded that this chronic erosion may still in part be a response to this shore s 1-m subsidence, although the main cause in recent decades has been the negative balance in the sediment budget for the shore south of the Tukituki River (Tonkin & Taylor, 2005; Komar, 2010). The gravel on this shore is derived predominantly from the inland mountains, transported to the beach by Tukituki River, the other large rivers reaching this coast having been elevated by the earthquake, cutting off their delivery of gravel to the ocean shores. With the gravel being contributed to the beach only at the southern-most stretch of this shore, the dominant waves from the southeast produce a net northward transport within the Haumoana Cells, redistributing the sediment along the length of its shore. Impacting that transport, significant quantities have been commercially mined from the beach at Awatoto, it being the principal debit in this cell s sediment budget, the cell-wide balance being in the red.

5 Figure 4: Property impacts and failed shore-protection structures in the communities that subsided in 1931 and suffer from a negative balance in the sediment budget. EROSION PROCESSES AND WATER LEVELS The main goal of this study has been to analyze the processes important to property erosion along the shores of Hawke s Bay, directed toward projecting future hazards from climate change. This includes analyses of the Port of Napier s measured tides elevated by storm surges, the trend in relative mean sea levels based on the tide data and satellite measurements, the wave climate documented by the Port s wave buoy, calculations of swash runup levels on the beaches, and evaluations of hourly total water levels from these combined processes. Applying the methodology developed by Ruggiero et al. (2001), the total water levels were then compared with surveyed profiles of the beaches and backshore gravel ridges. Of significance, the profiles themselves contain morphologic evidence for still greater extremes in past erosion events, representing the total water levels of major storms providing a record of extremes during the 80 years since the 1931 earthquake elevated most of this shore. A limitation in our process analyses has been the shortness in the records of measured waves and tides. In particular, the record of waves was limited to little more than a decade, the Port having installed a Triaxys directional wave-rider buoy in August Tide data have been collected since 1989, sufficient to define the general distribution of hourly measured water levels, but not necessarily their extremes elevated by storm surges that occurred during Spring tides. However, supporting our analyses have been past investigation on the coasts of New Zealand, including assessments the magnitudes of storm surges and their extremes (de Lange, 1996), and the development of a deep-water wave climate based on hindcast analyses representing 20 years of storm conditions (Tonkin & Taylor, 2003).

6 The development of a deep-water wave climate to be applied in our assessments of the Hawke s Bay hazards proved to be a challenge, it having been decided that it would be based primarily on the hourly measurements collected by the Port s buoy, but then compared and calibrated with the hindcast assessments. A principal problem was that the buoy is located in 16-m water depth, not the desired deep-water measurements required to define a wave climate. This was exacerbated by the dominant and highest waves reaching Hawke s Bay having predominantly been generated by storms far to the south, occurring in the waters between Antarctica and New Zealand. The waves important to the coastal hazards therefore undergo significant refraction as they travel from deep water to the shores of the littoral cells, those recorded by the buoy having been reduced to varying degrees from their deep-water significant wave heights (!"#s). Important to our hazard assessments was the development of a deep-water wave climate in which the distributions of!"#s and periods, originally derived from the Port s buoy, have been calibrated so they are reasonably equivalent in magnitudes to those based the deep-water hindcast analyses, specifically that of Tonkin & Taylor (2003) for Hawke s Bay. Our analysis therefore compared the histogram of deep-water!"#s, initially calculated from the buoy data, with the histogram of deep-water!"#s from the hindcast analyses, thereby empirically accounting for the effects of refraction on the buoy s hourly measurements. The convergence of the data involved the correction of the Port s data, increasing its mean!"# of 0.92 m by a factor of 1.91, so it agreed with the 1.76-m mean!"# from the hindcast analyses, in effect on average accounting for the refraction of the dominant waves arriving from the southeast. This ratio was then used as an empirical correction factor for the entire histogram based on the buoy data, increasing the entire range of!"#$. Figure 5: Histograms of deep-water!"#s derived from the Port s buoy, the numbers of observations graphed on both linear and log-scale axes.

7 The resulting histogram for the distribution of hourly-measured!"#s is presented in Figure 5, graphed using both linear and log scales for the numbers of observations. The log plot is informative in applications to hazard assessments in that it emphasizes the rare occurrences of extreme!"#s (Komar and Allan, 2007). The lower axis in the graph is for the original data from the buoy, the upper Corrected axis being the revised values based on the 1.91 empirical factor. It was found that this procedure yielded reasonable agreement between the revised magnitudes of the deep-water!"#s derived originally from the Port s buoy, and those based on the wave hindcast analyses; the modes of mostfrequent occurrence were respectively 1.2 and 1.4 m, with maximum!"# magnitudes of 9.9 and 8.6 m. This level of agreement was considered to be acceptable in defining a unified deep-water wave climate, such that the Port s buoy data could be used in evaluating hazard assessments for Hawke s Bay (Komar and Harris, 2014). Values of the wave-swash runup levels (their vertical components) were calculated from the hourly combinations of deep-water!"#! and periods, the Port s buoy measurements corrected to their deep-water equivalents. The formula of Stockdon et al. (2006) was applied, representing diverse beach morphologies, although uncertainties remain in this application to the Hawke s Bay mixed sand-and-gravel beaches. The formula depends on the beach slope, that for the beaches within the littoral cells are consistently close to 0.1 (1-in-10). The resulting calculated swash runup levels are strongly dependent on the extent of wave refraction, and therefore vary systematically along the shores of the littoral cells, the runup levels being greatest on the exposed beaches of the Bay View Cell with its shore facing directly into the dominant waves, whereas more refraction is experienced on the Haumoana Cell, and with the lowest swash runup levels occurring at the southern ends of both cells due to sheltering by headlands (and the Port s breakwater). According to our calculations, in the absence of refraction the mode of most frequent runup levels is about 1.5 m, the maximum being about 5 m during the most extreme storms. More realistically, with the expected extent of refraction on the Haumoana shore, the mode of most frequent swash runup would be a level of about 0.4 m, the maximum being a vertical 1.5 m, the horizontal extent of the swash respectively being 4 and 15 m. Therefore, a large range of potential swash runup levels of the waves exists, reaching these shores, being a major contributor to the total water levels during storms that are responsible for occurrences of property erosion and overwash. The levels of the tides can also be a significant factor in causing beach and property erosion on the coast of Hawke s Bay, the maximum predicted range being about 2 m, potentially increased by a storm surge of 1 to 1.5 m (de Lange, 1999). Analyses of 20- years of measured tides were undertaken to derive a histogram of its hourly water levels, the result being strongly bimodal, resulting from the semidiurnal variations (Komar and Harris, 2014). The overall distribution was skewed to higher values by occurrences of storm surges, the most extreme measured elevations having been on the order of 2.25 m, 0.25 m above the predicted Highest Astronomical Tide (HAT). However, the surge that produced those extremes undoubtedly would have been substantially greater since they did not actually occur during the HAT predicted level, or necessarily even during a spring tide.

8 The erosion and flooding hazards depend on the total water levels (!"#s) achieved by the summation of the measured tides and wave-swash runup levels on the beaches, particularly their extremes during storms, and in the long term by the rise in sea levels. This dependence on the!"#$ is the basis for the model developed by Ruggiero et al. (2001), which calculates the hourly combinations of tides and wave runup, the interest of our process analyses for Hawke s Bay therefore primarily being on the frequency distribution of the!"# elevations. Its distribution will differ from site to site along this coast, depending on the shore s exposure to the waves and the extent to which refraction has reduced the runup levels, while the measured tide is assumed to be the same at all sites. Accordingly, the total water level is calculated as!"# =!! +!!!!% where!! is the elevation of the measured tide, which includes its enhancement by storm surges, while!!!!% represents the hourly evaluated swash runup (vertical component) with the coefficient!! governing the extent of reduction produced by wave refraction. Figure 6: Examples of!"# distributions based on the Hawke s Bay hourly measured waves and tides, for a series of!! values representing increased nearshore waves and swash runup levels.

9 Our analyses of the!"#s for Hawke s Bay were limited to the 11 years during which there were simultaneous hourly measurements of waves and tides. Distributions were calculated at 0.1 increments for the range!! = 0.1 through 1.0, representing sites that are well sheltered to those fully exposed to the waves, having experienced little reduction in runup due to refraction or sheltering by headlands. Example distributions are graphed in Figure 6 for!! = 0.4, 0.7, and 1.0, in sequence representing increasing waves reaching the shore due to smaller degrees of refraction, resulting in higher swash runup levels and!"# elevations. The respective contributions by the tides versus the wave swash runup is evident in the form of the distributions, for!! = 0.4 being dominated by the tides with a noticeable bi-modality from its contribution, essentially lost in the second graph for!! = 0.7, while the bottom distribution with!! = 1.0 represents a shore that is fully exposed to the waves with minimal refraction. EXISTING AND FUTURE HAZARDS The above analyses yielded climates for the processes important to property impacts on the Hawke s Bay shore, the measured deep-water wave heights and periods, wave-swash runup levels on the beaches, tides, and total water levels (tides plus runup), directed toward assessments of their potential extremes responsible for severe erosion and flooding. Applying the model analysis methodology developed by Ruggiero et al. (2001) to evaluate past and future impacts, comparisons have been undertaken of the total water levels with profile surveys of the beaches and backshore gravel ridges. Important to the management of the Hawke s Bay beaches, particularly assessments of their multidecadal trends of erosion versus accretion, has been a monitoring program with its emphasis placed on the collection and analysis of annual surveys of beach profiles at a large number of stations along the shores of the Bay View and Haumoana Littoral Cells (Komar, 2005, 2010). To meet our objectives, six representative sites were selected for analyses, three from each of the littoral cells. For each site the elevations of the beach/bluff junction level and the top of the backshore ridge were determined from their surveyed profiles, to be compared with the evaluated!"#s, involving a choice of the!! dependent histograms illustrated in Figure 6, a selection that provided a reasonable match between the maximum!"# and evidence from the profile for water levels during past major storm events. This selection also considered the degree of exposure of that profile site to the waves, the expected extent of wave refraction that would have reduced the wave heights and swash runup levels. A comparison between the analyzed!"#s and surveyed profiles is shown in Figure 7 for two profile sites within the Haumoana Cell, HB06 being a profile from East Clive that had not experienced an elevation change caused by the 1931 earthquake, while HB10 is from the Napier shore where uplift amounted to on the order of 1.5 m, evident in the higher elevation of the gravel ridge at that site. As seen in Figure 3 and discussed earlier, with a crest elevation just over 3 m RL, the ridge at East Clive has experienced overtopping during storms when the swash runup combined with high tides. As such, having experienced both recent erosion and overtopping, its morphology can be expected to correspond to our analyses based on recent measurements of the waves and tides,

10 including the!"#s graphed in Figure 7. A reasonable match between the process climates and surveyed ridge elevation is seen in Figure 7 to be achieved for a 13.7-m RL!"#, the maximum in the!! = 0.6 histogram that also reasonably accounts for the expected extent of refraction of the dominant waves arriving at that site from the southeast. As further confirmation, this!"# also accounts for the beach/bluff junction elevation identified on the HB10 Napier profile, presumable representing erosion of it s bluff during the same extreme storm event that had resulted in overtopping of the gravel ridge at East Clive. Figure 7: Comparisons between the!"#s and beach junction elevation (HB10) and ridge crest (HB06) for beach profiles within the Haumoana Cell. Profiles analyzed in the central to northern stretch of the Bay View Cell, having been elevated by about 2 m during the 1931 earthquake, show little if any erosional retreat of its bluff surveyed by the monitoring program that began in the 1970s, suggesting that it s erosion occurred mainly in the decades immediately following the earthquake. The beach/bluff junction elevations are uniformly at 16.5-m RL elevation, the implication again being that they were eroded during the same major storm event. With the waves potentially having experienced little refraction, that shoreline being oriented toward the dominant waves arriving from the southeast, the!"# magnitudes were based on!! = 1, yielding a mean!"# of 11.6 m and maximum of 15.1 m according to the histograms illustrated in Figure 6 (Komar and Harris, 2014). This maximum storm-generated water level, based on the limited process measurements, is 1.4 m lower than the surveyed junction elevations. While there are uncertainties in the methodologies being applied in calculating the!"#s, the likely explanation for this difference is the limited data available for the measured waves and tides, the 15.1-m!"# during those 11 years representing less extreme events than the storms recorded in the ridge-profile morphologies. However, with that 15.1-m!"# elevation based on actual measurements, a projection of the 100-year extreme event could be on the order of at least 16 m RL. A

11 match between the processes and morphology could also be empirically achieved if!! is increased to about 1.2, thereby providing a possible empirical correlation between combinations of tides, swash runup levels, and wave heights, accounting for the inferred 16.5 m RL of past extreme!"# magnitudes, produced by rare storm events that occurred in the distant past, more severe than represented by the recent process measurements. With time and the collection of additional measurements of waves and tides, and improvements in analysis methodologies applied to calculate the!"#s, the magnitudes of extreme events should become better established, supporting direct process-based matches. Analyses in Figure 7 for sites within the Haumoana Cell represented the present-day conditions, the existing mean level of the sea and the wave climate based on 11 years of hourly measurements. Projections of future hazards extending through the 21st century required that we account for climate controls on the projected rise in sea levels, and any trend of increasing storm intensities and the heights of the waves they generate. Important is whether the barrier gravel ridges, having been raised by 1 to 2 m at the time of the 1931 earthquake, will continue to provide protection to shore-front properties. The 20-year tide gauge record from the Port yielded a regression rate of increase of 2.0 mm/yr, while data from a program of GPS measurements of land elevation changes demonstrated a trend of subsidence, but at a negligible rate (Komar and Harris, 2014). Our inclusion of the projected accelerating rates of rising sea levels and its elevation reached by the year 2100 have been based on considerations of the IPCC 2007 projections, and on the more extreme rates derived by Rahmstorf (2007) and other recent investigations. The results for an Average Assessment, representing the most probable increase, indicated that by the year 2050 the relative sea level could rise by about 30 cm above its elevation in 2000, and by 2100 the rise could amount to on the order of 90 cm. The High Assessment indicated that the increase could amount to 50 cm by mid-century, as much as 130 cm by the end of this century. Based on those results, in our analyses directed toward future hazards projections for Hawke s Bay, a rise of 1.1 m was adopted for the increased sea level for the year 2100, a value between the Average and High projections. The result is that the mean sea level would be raised from its present elevation of 10.0 m RL to 11.1 m RL. This extent of sea-level rise relative to the beach and property elevations can be envisioned in Figure 7 for the Haumoana Littoral Cell, simply by raising the!"# lines in the graph by 1.1 m. As expected, the most dramatic consequence would be on the low-elevation profile of survey site HB06, on the shore of East Clive, the rise in the Max!"# line relative to the crest elevation of the beach ridge clearly expected to produce frequent and intense overwash events, resulting in a landward migration of the barrier ridge by 10s of meters. For the survey sites having higher backshore elevations, profile HB10 from Napier (Figure 7) and those in the Bay View Littoral Cell, applications of a geometric model to evaluate the extent of retreat of the wave-eroded bluff (the beach/backshore junction) predicted property losses on the order of 10 m for this 1-in-10 beach slope, significant but not catastrophic considering there is a wide Reserve with homes set well back from the shore (Figure 2).

12 Evidence also exists for there being climate-controlled increases in storm intensities and the heights of the waves they generate along the Hawke s Bay coast, the trend in the latter yielding a regression rate of m/yr, amounting to about a 10-cm increase over the 11-year time scale of measurements (Komar and Harris, 2014). This represents a 6% increase in the average!"#s, (0.06% per year), being in approximate agreement with the results found by Young et al. (2011) for 25-years of satellite measurements offshore from Hawke s Bay, having found increases in both the extreme wind speeds and!"#s. The possibility therefore exists that there will continue to be an increase in storm-wave heights experienced on the coast of Hawke s Bay during this century, producing higher swash runup levels by the year 2100, adding to the rising sea levels. In view of the potential importance of including this climate-controlled process in future hazard assessments, order-of-magnitude estimates were added, a 10% trend of increasing wave swash runup levels, corresponding approximately to the increase in the wave heights measured by the Port s buoy and over a longer span of time by the satellite data. The increases in both sea levels and storm-wave runup are estimated to yield a maximum!"# to be on the order of 15 m RL on the Haumoana Cell s shore, it being evident in Figure 7 that this would represent an extreme increase compared to the existing elevation of the ridge crest, producing overwash events that are likely to breach this stretch of shore, resulting in extensive inland flooding. Although this 15-m maximum TWL would not exceed the elevation of the barrier ridge at Napier (profile HB10 in Figure 7), its erosion would expected to be substantial, also the impacting the shores of the Bay View Littoral Cell. And of course, this increase would be expected to produce near catastrophic impacts to the southern shore of the Haumoana Cell, which is already experiencing significant erosion (Figure 4). ACKNOWLEDGEMENTS Thanks to Gary Clode, Mike Ayde, Neil Daykin and Craig Goodier of the Hawke s Bay Regional Council for their encouragement and for providing measurements of waves and tides, critical to our analyses. Thanks also to Mr. Richard Reinen-Hamill of Tonkin & Taylor Ltd., for his thoughtful insights in reviewing our reports. REFERENCES de Lange, W. P. (1996) Storm surges on the New Zealand coast. Tephra, 15, Hull, A. G. (1990) Tectonics of the 1931 Hawkes Bay earthquake. New Zealand Journal of Geology and Geophysics, 33, Komar, P. D. (2005) Hawke s Bay, New Zealand: Environmental Change, Shoreline Erosion and Management Issues. Report for the Hawke s Bay Regional Council, 244 pp. Komar, P. D. (2010) Shoreline evolution and management of Hawke s Bay, New Zealand: Tectonics, coastal processes and human impacts. Journal of Coastal Research, 26 (1),

13 Komar, P.D., and J.C. Allan (2007) A note on the depiction and analysis of wave-height histograms. Shore & Beach, 75 (3), 1-5. Komar, P.D., and E. Harris (2014) Hawke s Bay, New Zealand: Global Climate Change and Barrier-Beach Responses. Report for the Hawke s Bay Regional Council. Rahmstorf, S. (2007) A semi-empirical approach to projecting future sea level rise. Science, 315, 368. Ruggiero, P., P.D. Komar, W.G. McDougal, J.J. Marra, and R.A. Beach (2001) Wave runup, extreme water levels and the erosion of properties backing beaches. Journal of Coastal Research, 17(2), Stockdon, H.F., R.A. Holman, P.A. Howd, and A.H. Sallenger (2006) Empirical parameterization of setup, swash, and runup. Coastal Engineering, 53, Tonkin & Taylor (2003) Hawke's Bay Nearshore Wave Climate. Report to the Hawke's Bay Regional Council, 13 pp + Appendices. Tonkin & Taylor (2005) Shoreline Modelling Report: Report to the Hawke's Bay Regional Council. Young, I. R., S. Zieger and A.V. Babanin (2011) Global trends in wind speed and wave height. Science, 332,