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The sedimentary sequences found within estuaries in the north west Nelson region of central New Zealand are investigated in order to quantify the timing of the end of the Post Glacial Marine Transgression. This region has been identified as being relatively stable in terms of vertical tectonic movement during the Holocene, but is yet to yield any reconstructions of eustatic sea level. In this study, we investigate the Holocene infill of a barrier estuary (Parapara Inlet) through sedimentological analysis and radiocarbon dating of 18 vibracores up to 4.2 m in length. It is found that the estuary infilled through a combination of lateral flood tide and fluvial delta progradation as well as vertical central basin infill. The central basin infilled at a consistent rate of 0.4 mm/year in both the mid (7.0–6.0 ka) and late-Holocene (2.5–1.5 ka). By the time of early human (Maori) settlement (c. 1 ka), the estuary surface was at low intertidal elevations with sediment being transported from the fluvial to tidal delta. A discernible change in sedimentation rates could not be associated with Maori settlement; however, infill rates increased to at least 12.5 mm/year in the past 150 years due hydraulic sluicing associated with mining. The sedimentary history of Parapara Inlet is compared to nearby Whanganui Inlet, d’Urville Island and Nelson to establish the character of regional Holocene sea level movement. It is found that relative sea level reached modern elevations between 8 and 7 ka in the region. The similarity between sea level curves for the end of the post glacial marine transgression (PMT) to other tectonically stable sites in northern New Zealand suggests that this curve can now be considered a true eustatic signal for the New Zealand archipelago.

Shoreline erosion is predicted to increase as the result of climate change, yet the effects on foredune-building species and associated dune processes remain poorly understood. To predict the response of foredune plant communities to increased erosion we examined the abundance of six early colonising dune-building species across 71 beach-foredune sites in south-east Australia. The assumption being that those species better adapted to shoreline retreat will be more frequent and have increased abundance on erosional coasts than species lacking the capacity to withstand or re-establish following periods of storm-induced erosion. All species were frequently recorded regardless of the rate of shoreline progradation or erosion, which ranged 3.8 to −2.2 m year−1. Species presence was not related to erosion rates; however, there was a significant association between the rate of shoreline change and abundance for some of the studied species. Variation in traits related to tolerance to salinity and burial and the ability to establish following erosion appear to correspond to the observed patterns of species abundance. While this study examined only six species, it appears that species that are restricted to zones closer to the spring-tide level, that have a persistent rather than opportunistic growth-history or that are limited in their ability to recolonise following erosion, are more likely to be negatively impacted by increased rates of coastal erosion. Given the association between vegetation and foredune morphology these findings have important implications for the management of sandy coasts.

Large boulder-size clasts can represent important archives of high energy erosional wave activity at the coast. From tropical coral reefs to high-latitude eroding cliffs, boulders have been used to hindcast the frequency and magnitude (height) of waves produced by both storms and tsunami. Such reconstructions are based on the balance between the hydrodynamic forces acting on individual boulders and the counteracting resistive forces of friction and gravity. We test published models on over 900 intertidal boulders on the coast at Staithes in North Yorkshire, U.K., using repeat high-resolution topographic survey data. We quantified the predicted versus actual rates of boulder movement in the field over a 7-year period (2007–2014). We assessed the degree to which local geomorphology and biology may affect the resistive forces inhibiting transport. We found that 84% of intertidal boulders predicted to be mobile remained stationary over 7 years, suggesting that in some contexts boulder movement may be significantly less than predicted, regardless of boulder volume, shape or location. In situ cementation of boulders to the substrate by marine organisms appears to play a key role in retarding or preventing boulder transport. The implication is that boulder characteristics may not always provide a reliable estimation of wave height on the coast and reliance solely on hindcasting relationships may result in under prediction of the frequency and magnitude of past storm wave activity. We suggest here that more field studies that consider boulder movement are needed, set within specific site contexts, and that these data are used to improve the applicability and robustness of boulder transport models.

Coarse woody debris (CWD) is an important component of fluvial systems affecting in-channel hydrology and sediment storage which in turn controls channel geometry and evolution. The role of coarse woody debris in coastal geomorphology is an emerging research field and this study investigates its role on mixed sand and gravel beach systems. A case-study approach is used whereby two field areas in Wellington, New Zealand, each with two distinct beaches with differing wood accumulations, were investigated through field surveying. It is found that on gravel beaches CWD is most important during storm events where it causes the berm crests to be 0.5–1.0 m higher than on unwooded beaches, as well as making the beachface twice as steep. During calm periods the berm appears to be inactive as non-storm waves can only rework the lower beachface. A review of the literature indicates that on sandy beaches CWD is most important in the post-storm recovery of beach systems. The same wave event that causes beach erosion also deposits the CWD. During calm periods the woody material is a trap for sand being transported along the beachface and therefore aids in re-establishing foredune systems. The differing sediment composition between sandy and gravelly beaches drives their morphological response to storm events and in turn determines how CWD interacts with the beach profile.

Niue is an uplifted limestone island, which preserves an atoll morphology with a sequence of terraces around its outer margin. A modern terrace fringes much of the island and this paper examines the extent to which this terrace can be considered accretionary and constructed by coral and coralline algae, or erosional and truncated by those processes that form shore platforms. The occurrence of Pleistocene limestone outcropping across this terrace and the continuation of caves and other karst features, dissecting the sub-aerial limestones, onto the forereef indicate the overall significance of erosion. At present live coral cover is restricted to isolated colonies growing in grooves, potholes and karstic channels eroded into the modern terrace surface. Coralline algae coat the outer margin of this terrace, and also veneer prominent surf benches that occur on the windward shore, 1–2 m above the terrace surface. Terrace evolution on Niue therefore appears to be primarily erosional in origin. There is little accommodation space for reef growth and, as a result, accretional fringing reefs are absent around most of the island. Erosional processes have also dominated landscape evolution for at least the past few eustatic cycles. Fringing reef growth is absent or severely restricted during the last interglacial and occurs as sporadic small reefs on the seaward margin of an erosional terrace during the penultimate interglacial. The development of terrace features in uplifting reef settings does not necessarily originate through accretional reef processes and may in fact be entirely erosional. Although reef terraces are frequently depositional in other settings, those present on Niue indicate a predominance of erosion, indicating the need to discriminate emergent terraces in terms of the extent to which they are erosional or accretionary when using such features to reconstruct island palaeoenvironments.

Concern about coastal sedimentation in New Zealand is widespread. As a result, many regional councils now undertake monitoring programmes to understand the rate of change that is occurring within estuarine environments. A variety of techniques are used to understand estuarine infill from short-term (fixed rods, marker layers, laser surveying) to long-term studies (coring). Short-term studies provide detailed but temporally restricted data sets, while coring studies provide long-term generalised data. This paper reviews the common methods used within New Zealand and suggests that a combination of both methods is the ideal for understanding sediment infill.