Climate change is increasing the threat of erosion and flooding along coastlines globally. Engineering solutions (e.g. seawalls and breakwaters) in response to protecting coastal communities and ...associated infrastructure are increasingly becoming economically and ecologically unsustainable. This has led to recommendations to create or restore natural habitats, such as sand dunes, saltmarsh, mangroves, seagrass and kelp beds, and coral and shellfish reefs, to provide coastal protection in place of (or to complement) artificial structures. Coastal managers are frequently faced with the problem of an eroding coastline, which requires a decision on what mitigation options are most appropriate to implement. A barrier to uptake of nature‐based coastal defence is stringent evaluation of the effectiveness in comparison to artificial protection structures. Here, we assess the current evidence for the efficacy of nature‐based vs. artificial coastal protection and discuss future research needs. Future projects should evaluate habitats created or restored for coastal defence for cost‐effectiveness in comparison to an artificial structure under the same environmental conditions. Cost‐benefit analyses should take into consideration all ecosystem services provided by nature‐based or artificial structures in addition to coastal protection. Interdisciplinary research among scientists, coastal managers and engineers is required to facilitate the experimental trials needed to test the value of these shoreline protection schemes, in order to support their use as alternatives to artificial structures. This research needs to happen now as our rapidly changing climate requires new and innovative solutions to reduce the vulnerability of coastal communities to an increasingly uncertain future.
Coastal managers are frequently faced with the problem of an eroding coastline, which requires a decision on what mitigation options are most appropriate to implement. A barrier to uptake of nature‐based coastal defence is stringent evaluation of the effectiveness in comparison to artificial protection structures. Here, we assess the current evidence for the efficacy of nature‐based vs. artificial coastal protection and discuss future research needs. Future projects should evaluate habitats created or restored for coastal defence for cost‐effectiveness in comparison to an artificial structure under the same environmental conditions, in order to support their use as alternatives to artificial structures.
The mobility of coastal dunes is characterised by bio-geomorphological responses related to change in boundary conditions, particularly sediment supply, wind and vegetation cover, as well as human ...activities. There remains uncertainty regarding the relative importance of these drivers on dune mobility at a global scale. In this study, trends and dominant drivers of coastal dune mobility are synthesised through the literature review focusing on shifts in dune mobility over the last century (1870–2018). In total, 176 individual dunes, with 55 dunes from the Europe-Mediterranean area, 23 from Africa, 30 from North America, 23 from South America, 20 from Oceania and 23 from Asia, are reviewed in this work. The results show that there is a worldwide trend of dune stabilisation, with 93% (164 out of 176) of the reviewed sites showing a loss of bare sand area due to an increase in vegetation cover and urbanisation expansion. Multiple factors have contributed to the stabilisation process, including (a) land-use change such as the change of traditional farming practises, coastal urbanisation and tourism development; (b) dune stabilisation projects; (c) sediment decline caused by the riverine and coastal constructions; and (d) change in climate (i.e. the decrease in windiness, and the increase in temperature and rainfall) and storms. Our results suggest human intervention played a dominant role in altering dune mobility for most dunes during the past century, while climate and storms are also important drivers, especially for dune sites with limited human activities.
Changes in vegetation cover and dune mobility of Woolamai dune fields on the southeast coast of Australia were quantified based on a time series of aerial imagery (1939 to 2020). Results showed that ...the dune fields have shifted from nearly all bare sand (with <5% vegetation cover) to a new quasi‐equilibrium state, being almost fully stabilized by vegetation (>80%) from 1939 to 2020. Three temporal stages of vegetation change were identified, namely: (I) early expansion over 1939–1975; (II) rapid growth from 1976 to 2010; and (III) recent ‘quasi‐equilibrium’ state in 2010–2020. In stage I, complex impacts of climate and human activities co‐existed with uncertainty of the dominant factor. In this early stage, vegetation growth was constrained to the low and sheltered areas, indicating the influence of topography. Rapid vegetation growth took place in 1976–2010 (stage II), during which a re‐vegetation programme combined with favourable climate conditions promoted vegetation growth. In the last decade (stage III), vegetation might have reached a new quasi‐equilibrium when the vegetation almost reached a maximum. The slight loss of vegetation could be attributed to weed control and an unfavourable climate for growth (drier and windier) in Woolamai dune fields.
This study showed that variations in vegetation cover and dune mobility through time are not simply linked to a single factor but depend on the occurrence of multiple factors (e.g. topography, climate and human activities) that promote stability, or alternatively, mobility of the dune system. This research contributes to expanding our understanding of the complexity of the bio‐geomorphologic dynamics in dune fields. It also provides detailed observational evidence for the historical trajectory of vegetation expansion from the bare dune fields to a fully stabilized state, which can be used to verify and refine models for other similar dune sites.
Rare studies of changes in coastal dune mobility have been done on the southeast Australian coast. Study of the Woolamai dune field, Victoria showed dramatic shifts of vegetation cover from nearly bare to almost fully vegetated over 1939–2020. Three stages of vegetation and dune mobility changes were identified which are linked to multiple factors, including the dune field topography, local climate and human activities, which promoted stability or alternatively mobility of the dune system in the field.
Living shorelines aim to enhance the resilience of coastlines to hazards while simultaneously delivering co-benefits such as carbon sequestration. Despite the potential ecological and socio-economic ...benefits of living shorelines over conventional engineered coastal protection structures, application is limited globally. Australia has a long and diverse coastline that provides prime opportunities for living shorelines using beaches and dunes, vegetation, and biogenic reefs, which may be either natural (‘soft’ approach) or with an engineered structural component (‘hybrid’ approach). Published scientific studies, however, have indicated limited use of living shorelines for coastal protection in Australia. In response, we combined a national survey and interviews of coastal practitioners and a grey and peer-reviewed literature search to (1) identify barriers to living shoreline implementation; and (2) create a database of living shoreline projects in Australia based on sources other than scientific literature. Projects included were those that had either a primary or secondary goal of protection of coastal assets from erosion and/or flooding. We identified 138 living shoreline projects in Australia through the means sampled starting in 1970; with the number of projects increasing through time particularly since 2000. Over half of the total projects (59 %) were considered to be successful according to their initial stated objective (i.e., reducing hazard risk) and 18 % of projects could not be assessed for their success based on the information available. Seventy percent of projects received formal or informal monitoring. Even in the absence of peer-reviewed support for living shoreline construction in Australia, we discovered local and regional increases in their use. This suggests that coastal practitioners are learning on-the-ground, however more generally it was stated that few examples of living shorelines are being made available, suggesting a barrier in information sharing among agencies at a broader scale. A database of living shoreline projects can increase knowledge among practitioners globally to develop best practice that informs technical guidelines for different approaches and helps focus attention on areas for further research.
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•The application of living shorelines is not well-captured in scientific literature.•Projects were extracted from a survey and interviews with coastal practitioners.•At least 178 linear kms of living shorelines through 138 projects have been installed.•The database contributes to knowledge sharing globally to develop best practice.
The dispersal of rhizomes by waves and ocean currents allows invasive coastal plants to spread rapidly over long distances. Long-term management of these species should recognise the potential for ...regeneration from rhizome fragments and the likelihood of invasion or reinvasion of dunes. Here, we assess the sprouting ability of Ammophila arenaria (marram grass), an invasive weed of temperate dune systems, which spreads by the marine dispersal of rhizomes. Rhizomes were obtained from four sites in southern New Zealand. Comparative growth trials were conducted to compare the sprouting ability of rhizomes originating from different populations, seasonal restrictions in sprouting potential, and the effects of fragment morphology (length and node number) and rhizome type (vertical or horizontal) on sprouting ability. Overall, the sprouting ability of A. arenaria is high, although we found this ability varied between populations, with season, and in relation to fragment length. Rhizomes formed shoots rapidly when fragmented, indicating a weak or limited innate dormancy. Reduced sprouting appears to be due to variation in the growth reserves stored within the rhizomes at the time of fragmentation. Large numbers of viable rhizomes will be dispersed during events that erode foredunes, and all populations of invasive A. arenaria growing within reach of waves should be considered a potential source of propagules, a conclusion that has implications for management agencies seeking to protect or restore apparently isolated dune systems.
The removal of invasive species is common in restoration projects, yet the long‐term effects of pest management programs are seldom assessed. We present results of a long‐term program to remove the ...invasive species Lupinus arboreus (lupin) from sand dunes in New Zealand. We evaluate the response of plant communities to lupin removal, by comparing total plant cover, the cover of non‐native and native plant species, and species richness between sand dune sites where lupin removal has occurred, not occurred, and where lupin has never been present. Neither lupin presence nor removal had a significant impact on the foredune environment. Following removal, total and other non‐native plant cover remained higher, and the cover of several native sand dune species remained lower compared with uninvaded sites in the deflation and backdune environments. These changes can be attributed to persistent effects associated with the invasion of lupin, but have also developed in response to lupin removal. The results of this study have implications for restoration projects in sand dunes. Pest management alone is unlikely to be sufficient to restore plant communities. Given the difficulties in restoring plant communities once an invasive species has established, managers should prioritize actions to prevent the spread of invasive species into uninvaded areas of sand dunes. Finally, the response to lupin invasion and removal differed between dune habitats. This highlights the importance of tailoring a pest management program to restoration goals by, for example, prioritizing areas in which the impacts of the invading species are greatest.
Hilton, M.J.; Hatcher, S.V.; Wakes, S.J., and Konlechner, T.M., 2016. Flow Deflection and Deceleration Across a Simple Foredune. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. ...(eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 293–297. Coconut Creek (Florida), ISSN 0749-0208. There are few field observations of flow deflection across foredunes in a range of incident wind conditions. This study reports observations of (1) flow deflection across the seaward slope of a foredune during alongshore and oblique onshore incident winds; and (2) associated sand transport. We compare these with modelled results from Hesp et al. (2015). Sonic anemometers and sand traps were deployed along a transect across a simple foredune at St. Kilda Beach, Dunedin, New Zealand. Representative sections of each record were isolated for a range of incident wind directions, and for each section we determined flow deflection and relative change in wind velocity. The incident winds, observed on a 3m mast on the beach, ranged from 228° (35° oblique onshore) to 268° (5° oblique offshore) and 6 – 14 ms−1 mean wind speed (over 5–15 minute intervals). Gusts reached 28 ms−1. Onshore deflection varied between 19° and 23° for incident winds between 228° and 249° and 9–14 ms−1. Our results are only partly consistent with those of Hesp et al. (2015) for a similar foredune and similar strength winds. We also found deflection increases with increasing obliquity, the degree of deflection increases towards the crest, and that topographically-forced flow acceleration is strongly influenced by the angle of approach of the incident winds. In general, however, we measured more flow deflection than was modelled, including significant deflection for highly oblique winds. Relative wind velocity up the profile showed deceleration up-slope for all sections because the anemometers were placed within the vegetation.
Buckley, E.C.B.; Hilton, M.J., Konlechner, T.M., and Lord, J.M., 2016. Downwind sedimentation and habitat development following Ammophila arenaria removal and dune erosion, Mason Bay, New Zealand. ...In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 268–272. Coconut Creek (Florida), ISSN 0749-0208. Since 2002 Ammophila arenaria has been progressively eradicated from a section of the transgressive dune system at Mason Bay, New Zealand to restore dune mobility. This study examines whether sand released from the treatment areas is accumulating in down-wind dune environments, particularly stony deflation surfaces. Deflation surfaces are nationally threatened habitats that contain at-risk native plants and are important flocking sites for endangered shore birds. Sand accumulation in the stonefield may cause a shift in texture and character from deflation lag to sand dunes, potentially reducing habitat for these species. Sediment accumulation was examined over a nine month period within a 200m × 50m plot located immediately downwind of a series of long-walled parabolic dunes, recently destabilised by A. arenaria removal. Sand accumulation was monitored using 500 erosion pins. Digital elevation models were derived from two total station surveys to determine whether sand is accumulating in conjunction with Ficinia spiralis nebkha. Wind speed and direction were measured during wind events to determine whether sand is deposited during these events or whether sand passes through. The surface of the study area accreted 3.22mm, on average, during the study. Accretion and erosion was not strongly correlated with vegetation cover. The intensity of aeolian sedimentation appears to increase with increasing distance inland, because the study site increases in elevation and exposure further inland. Sand pits dug across the area showed medium term sand accumulation aross the study site with most of the accumulation closer to the eroding depositional lobes.
Konlechner, T.M.; Buckley, E.C.B.; Hilton, M.J., and Wakes, S.J., 2016. Downwind dune dynamics following Ammophila arenaria invasion. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, ...R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 298–302. Coconut Creek (Florida), ISSN 0749-0208. The growth of large foredunes following invasion by non-native plants has been linked to changes in beach-dune sediment transfers, and the deflected evolution of transgressive dune systems. These changes have the potential to alter downwind plant communities by modifying habitats. This paper describes changes to a transgressive dune system in southern New Zealand following invasion by Ammophila arenaria and associated foredune development. Landforms were mapped using aerial imagery from 1958, when A. arenaria was present but not dominant, through to 2013. The landscape downwind of the foredune has evolved from a sparsely vegetated, sandy landscape, dominated by nebkha, to a landscape containing well-defined, long-walled parabolic dunes and stony deflation surfaces. These changes are associated with an increase in deflation surface habitat and plant species diversity, and a corresponding loss of habitat for species associated with dunal areas. The area of deflation surface has increased 18% to 31% of the study area while dune areas decreased from 74% to 51%. These results indicate species associated with transgressive dune systems are sensitive to variations in sand supply and changes in this supply may occur over decadal scales. Land managers are now restoring beach-hinterland sand exchange by destabilizing the foredune and adjacent parabolic dunes to encourage sand drift inland.
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