Kevin Parnell

Geological effects of tsunami on mid-ocean atoll islands: The Maldives before and after the Sumatran tsunami

Low-lying coral islands are fragile landforms susceptible to long-term sea-level rise and extreme events, such as hurricanes and tsunamis. The Sumatran earthquake of 26 December 2004 generated waves that reached the Maldives 2500 km away. Observations of the effects of the tsunami are presented here, based on pre- and post-tsunami topographic and planform surveys of 13 uninhabited Maldivian islands. The surveys showed there was no substantial island erosion and no significant reduction in island area. Rather, the tsunami accentuated predictable seasonal oscillations in shoreline change, including localized retreat of exposed island scarps by up to 6 m, deposition of cuspate spits to leeward, and vertical island building through overwash deposition of sand sheets up to 0.3 m thick, covering up to 17% of island area. These results have implications for island stability indicating that low-lying reef islands are physically robust and the geological signature of tsunamis on atoll island development is minor.

Wakes from Large High-Speed Ferries in Confined Coastal Waters: Management Approaches with Examples from New Zealand and Denmark

Large high-speed craft carrying passengers and vehicles produce wake waves that are different from both conventional vessels and smaller fast vessels. Wakes from these high-speed craft can cause environmental problems (such as beach change, ecological disturbance, and damage to structures and archaeological sites) and safety problems (for navigation and for users of the beach and nearshore) in confined waters. As a consequence of the higher speed, the vessel wakes also have a longer period than wakes caused by conventional ships and may lead to substantial wave action in shallow water environments. In both New Zealand and Denmark, issues relating to high-speed craft wakes were not addressed until after the vessels had begun operation, and complex coastal management issues with possibly broader application have had to be addressed. Emerging management strategies have involved regulation using speed and wave height criteria.Large high-speed craft carrying passengers and vehicles produce wake waves that are different from both conventional vessels and smaller fast vessels. Wakes from these high-speed craft can cause environmental problems (such as beach change, ecological disturbance, and damage to structures and archaeological sites) and safety problems (for navigation and for users of the beach and nearshore) in confined waters. As a consequence of the higher speed, the vessel wakes also have a longer period than wakes caused by conventional ships and may lead to substantial wave action in shallow water environments. In both New Zealand and Denmark, issues relating to high-speed craft wakes were not addressed until after the vessels had begun operation, and complex coastal management issues with possibly broader application have had to be addressed. Emerging management strategies have involved regulation using speed and wave height criteria.

Fringing and nearshore coral reefs of the Great Barrier Reef:episodic Holocene development and future prospects

Abstract The Holocene growth of fringing and nearshore reefs on the GBR is examined. A review of data from 21 reefs indicates that most grow upon Pleistocene reef, boulder, and gravel, or sand and clay substrates, with no cored examples growing directly over rocky headlands or shores. Dated microatolls and material from shallow reef-flat cores indicate that fringing and nearshore reefs have experienced several critical growth phases since the mid-Holocene: (1) from initiation to 5500 YBP, optimum conditions for reef and reef-flat growth prevailed; (2) from 5500–4800 YBP, reef-flat progradation stalls in almost 50% of the reefs examined; (3) of reefs prograding post-4800 YBP, approximately half ceased active progradation around 3000–2500 YBP; (4) reefs prograding to present do so at rates well below mid-Holocene rates; (5) a group of nearshore reefs has established since 3000 YBP, in conditions traditionally considered poor for reef establishment and growth. Importantly, many of the reefs that appear to have grown little for several millennia are veneered by well-developed coral communities. Although local conditions no doubt exert some influence over these growth patterns, the apparent synchronicity of these growth and quiescent phases over wide geographical areas suggests the involvement of broader scale influences, such as climate and sea-level change. Recognition and understanding these phases of active and moribund reef growth provides a useful longer term context in which to evaluate reported current declines in fringing and nearshore reef condition.

Oceanographic processes and sediment mixing on a sand flat in an enclosed sea, Manukau Harbour, New Zealand

Abstract Studies of oceanographic and sedimentary processes on intertidal sand flats in an enclosed sea were undertaken to gain a better understanding of the factors controlling the mixing and dispersal of sediment bound contaminants. Field investigations included a 90 day process experiment during which wind, waves, tidal currents, tides, depth of disturbance and sand flat morphology were measured, and 27 months of sand flat profile monitoring. Sediment entrainment by strong spring tidal currents is restricted to the middle and lower regions of the sand flat which are inundated during the peak tidal flows. The upper 2–3 cm of sediment is re-worked across the middle and upper sand flat by mild storm wave events ( H s = 70 cm ), which occurred four times during the 90 day experiment. Numerous ridges and runnels in the upper sand flats are wave-formed features and are maintained by the lack of currents of sufficient magnitude to re-work the features. The ridge and runnel morphology is testimony to large infrequent storm events which re-work the sediment to depths of 20 cm. Such storms are an important mechanism for the release of contaminants and were recorded on 3 occasions in the 27 month profile record.

GPR stratigraphy of a large active dune on Parengarenga Sandspit, New Zealand

The Parengarenga Sandspit (Figure 1) is New Zealands only coastal source of silica sand for glass manufacturing. Concerns about the environmental effects of sand extraction from the harbor mouth in the last two decades led the extraction companies to instigate a monitoring program. The Parengarenga beach-dune-monitoring program started in 1982; since that time cross-profiles have been surveyed twice a year from below chart datum (CD) to landward of the sparsely vegetated foredune system. This is the longest continuous record of beach profile measurement in New Zealand, and provides important information on the behavior of this coastal spit system (Parnell, 1997). The sedimentary material in Parengarenga Sandspit consists of 93.5% quartz and has a very uniform fine, sandy grain size (median 193 microns) from near shore to the beach and in the dunes.

Coastal resource management conflicts and community action at Mangawhai, New Zealand

Abstract Whereas public participation and social impact assessment have become central themes in the resource management literature, direct action strategies by local communities have received much less attention. Direct action is likely to result when communities are affected by changes in their environment, whether these are human induced or the result of natural processes, and when agencies of the state fail to respond to the demands of the affected public in respect of such changes. Under these circumstances the local community might take action. This paper describes and analyzes community response to change in the coastal environment. Mangawhai Harbour in northern New Zealand has been subject to problems relating to the management of the coastal environment since the development of a dual inlet configuration in July 1978. By the early 1990s, conditions in the harbor had deteriorated in several important respects. On the basis of evidence indicating that restoration work may not be successful, governm...

Fast Shoreline Erosion Induced by Ship Wakes in a Coastal Lagoon: Field Evidence and Remote Sensing Analysis

An investigation based on in-situ surveys combined with remote sensing and GIS analysis revealed fast shoreline retreat on the side of a major waterway, the Malamocco Marghera Channel, in the Lagoon of Venice, Italy. Monthly and long-term regression rates caused by ship wakes in a reclaimed industrial area were considered. The short-term analysis, based on field surveys carried out between April 2014 and January 2015, revealed that the speed of shoreline regression was insignificantly dependent on the distance from the navigation channel, but was not constant through time. Periods of high water levels due to tidal forcing or storm surges, more common in the winter season, are characterized by faster regression rates. The retreat is a discontinuous process in time and space depending on the morpho-stratigraphy and the vegetation cover of the artificial deposits. A GIS analysis performed with the available imagery shows an average retreat of 3˗4 m/yr in the period between 1974 and 2015. Digitization of historical maps and bathymetric surveys made in April 2015 enabled the construction of two digital terrain models for both past and present situations. The two models have been used to calculate the total volume of sediment lost during the period 1968˗2015 (1.19×106 m3). The results show that in the presence of heavy ship traffic, ship-channel interactions can dominate the morphodynamics of a waterway and its margins. The analysis enables a better understanding of how shallow-water systems react to the human activities in the post-industrial period. An adequate evaluation of the temporal and spatial variation of shoreline position is also crucial for the development of future scenarios and for the sustainable management port traffic worldwide.

Depression Waves Generated by Large Ships in the Venice Lagoon

ABSTRACT Parnell, K.E.; Zaggia, L.; Soomere, T.; Lorenzetti, G., and Scarpa, G-M. 2016. Depression waves generated by large ships in the Venice Lagoon. 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. 907–911. Coconut Creek (Florida), ISSN 0749-0208. At present cruise ships use the Lido and Giudecca channels to berth at the Port of Venice, and cargo vessels use the Malamocco–Marghera channel to berth at the Marghera industrial area. Following a government decree to restrict large ship access to the Port of Venice through the Lido and Giudecca channels, the Port authority has been investigating the construction of a new channel between Marghera and the cruise terminal, to re-route all large vessels through the Malamocco lagoon entrance. Ships in the Venice Lagoon travel at low speeds with associated low depth-based Froude numbers (<0.5), and classical Kelvin wave effects are minimal. However, under certain channel geometries, depression waves (also known as Bernoulli wake) can be substantial with significant far-field effects. In the Malamocco–Marghera Channel, depression waves up to 2.5 m, with high (∼1.5 m/s) near bed water speeds, transform into asymmetric Riemann waves, able to propagate large distances from the navigation channel into the shallow lagoon. By contrast, depression waves associated with large ships in the Lido and Giudecca channels are much smaller (∼0.3–0.4 m). Rerouting large cruise ships entering the Port of Venice through the Malamocco–Marghera channel and a newly constructed channel will have adverse effects on the Venice lagoon with increased water velocities and sediment resuspension associated with the nonlinear Riemann waves. It is therefore essential that the potential effects be thoroughly evaluated using an appropriate methodology before the development of a new lagoon channel.

Fringing reef circulation

The impact of sea level rise on coral reef flats was one of the first considerations raised in relation to climate change and coral reefs. Most publications in the 1980s considered the impact to be a beneficial one. This was especially so in the Indo-Pacific area, where isostatic adjustments had produced a sea level at or above its present position for over 6,000 years. Many reefs are now adjusted to this level with lagoons infilled, sediments dominating the reef flat and living corals limited to shallow pools (Figure 1). Such reef flats are too shallow for at least half the tidal cycle for the transmission of waves with sufficient energy to entrain and transport all but the finest sediments. Many general references on Greenhouse effects emphasized the rejuvenation of reef tops (e.g., Henderson-Sellers and Blong, 1989) whilst others went as far as suggesting reefs could be drowned and many ecosystems eliminated (e.g., Falk and Brownlow, 1989). Some scientific assessments suggested that renewed coral growth would make reef flats aesthetically more pleasing (e.g., Hopley and Kinsey, 1988).[Extract] Estimations of coral reef accretion rates can be undertaken using a number of techniques. Most tedious is the use of growth rates from individual organisms (Chave et al., 1972). More recent methods include the measurement of total reef metabolism and calcification (Kinsey, 1985) or estimates of rates during the Holocene from dated drill cores (Davies, 1983; Davies and Hopley, 1983).[Extract] Because of the complexity of coral reefs and difficulties in ground survey, the reef environment was one of the earliest to take advantage of remote sensing techniques (Hopley, 1978). Both aircraft and balloons (e.g., Rutzler, 1978) formed the initial platforms, usually for vertically mounted cameras using black and white film. On the Great Barrier Reef (GBR), the earliest vertical aerial photography was in 1925, when the Royal Australian Air Force photographed the Low Isles at a scale of 1:2,400 in 1928 for the Yonge Expedition (see Great Barrier Reef Committee). Simultaneously, Umbgrove (1928, 1929) was photographing reefs in Indonesia to aid the extensive work he was carrying out there.Sea level is the local height of the oceans surface, usually measured to a datum referenced to a tidal position established from a record in which high-frequency motions such as wind waves and periodic changes (e.g., due to the tides) have been averaged out. Local sea level fluctuates regularly with tides and irregularly in response to factors including wind and currents, water temperatures and salinities, and atmospheric pressure. Relative sea level is the elevation of the sea surface relative to the land at a given location. Global or eustatic sea-level fluctuations occur as the volume of water in the earths oceans changes when ice caps and glaciers grow or melt, or as large-scale changes in the configuration of ocean basins and continental margins occur through plate tectonics. There are also regional and local isostatic processes that produce spatially different patterns of relative sea-level change, including thermal expansion of surface waters, changes in meltwater load, crustal adjustment of areas directly or indirectly affected by ice on- and offloading (see Glacio-Hydro Isostasy), coastal uplift or subsidence due to tectonic processes (see Earthquakes and Emergence or Submergence of Coral Reefs), and subsidence due to aquifer depletion or sediment compaction. Sea-level indicators are used to determine relative sealevel changes at a location. Locating a sea-level indicator and determining its age and elevation relative to its modern counterpart can establish relative sea-level change. Sea-level indicators on coral reefs include a range of biological, geomorphological, sedimentological, and chemical features that provide information on the position of the sea surface at the time that they lived or were formed. They usually comprise features with a known relationship to a tidal position or datum.The earliest work on geohydrology applicable to coral cays was undertaken separately by Ghyben and Herzberg in the late 1800s and early 1900s, who determined the shape and thickness of a freshwater lens that forms under coral cays once they reach a minimum size. The relationship, which is based on the different densities of freshwater and saltwater, is expressed in the Ghyben–Herzberg equation: z = (ρf/(ρs - ρf))h, where h is the distance above sea level to the water table (phreatic surface), z is the distance below sea level to the freshwater–saltwater interface, and rs and rf are the densities of saltwater and freshwater, respectively. Using densities of 1.00 g cm-3 for freshwater and 1.025 g cm-3 for saltwater gives the often quoted relationship z = 40 h. The Ghyben–Herzberg model makes an assumption of a single layer homogeneous medium, and a system in hydrostatic equilibrium, with no mixing of fresh and salt water, giving a sharp transition between the freshwater and saltwater. This model is normally implemented with the Dupuit assumption of horizontal flow (Oberdorfer et al., 1990) and is frequently applied in resource assessments of potable water for human use on inhabited coral cay islands. In reality, this model makes assumptions that are clearly not valid inmost coral reef environments. Tidal fluctuations of the water level are assumed to be negligible, watermovement within the lens is assumed to result entirely from recharge-induced changes to the hydraulic head, outflow from the freshwater lens required to maintain mass-balance is assumed to take place at the island margin, and mixing within the framework caused by various water movements and pressure gradients (such as tidal mixing) is not considered. Perhaps most significantly, the assumption of a homogeneous medium rarely holds. In particular, differences in the reef framework above and below the Pleistocene solution unconformity (sometimes called the Thurber discontinuity) typically found 6–25 below the current reef flat level in tectonically stable areas, means that the model is fundamentally flawed. In general, a very broad transition zone between fresh and saltwater can be expected.Fringing reefs have been described as being morphologically simple (Kennedy and Woodroffe, 2002), but variation in important parameters such as the reef morphology, tidal range, and wave energy means that a widely applicable model of fringing reef water circulation does not exist. Fundamental distinctions can be made between fringing reefs with or without an enclosed lagoon, those on the windward shores (with circulation normally driven by waves) or leeward shores (with tidal and other currents dominating), and those enclosed by headlands (where topographically controlled circulation is important) or those that extend along a more or less straight shoreline. Other reef types that could be described as fringing are variously described as either fringing or barrier (e.g., Ningaloo Reef, Australia; Hearn, 1999), bank-fringing (e.g., Great Pond Bay, St Croix, U.S. Virgin Islands; Lugo-Fernandez et al., 1998b), bank-barrier (e.g., Tague Reef, St Croix; Lugo-Fernandez et al., 2004), or coral lagoons (e.g., Kaneohe Bay, Oahu, Hawaii; Hearn, 1999). Other authors have described reefs adjacent to coral cays as fringing (Daly and Brander, 2006).Coral reefs are the largest landforms built by plants and animals. Their study therefore incorporates a wide range of disciplines. This encyclopedia approaches coral reefs from an earth science perspective, concentrating especially on modern reefs. Currently coral reefs are under high stress, most prominently from climate change with changes to water temperature, sea level and ocean acidification particularly damaging. Modern reefs have evolved through the massive environmental changes of the Quaternary with long periods of exposure during glacially lowered sea level periods and short periods of interglacial growth. The entries in this encyclopedia condense the large amount of work carried out since Charles Darwin first attempted to understand reef evolution. Leading authorities from many countries have contributed to the entries covering areas of geology, geography and ecology, providing comprehensive access to the most up-to-date research on the structure, form and processes operating on Quaternary coral reefs.

Developing a framework for integrating local and scientific knowledge in internationally funded environment management projects: case studies from Kien Giang Province, Vietnam

ABSTRACT Local and scientific knowledge, when adequately and properly integrated, produces enormous benefits for natural resource management in comparison to a single knowledge system being used. Adequate and proper integration has major constraints that include ineffective use of the integrated knowledge, thoroughly inclusive processes, and true public participation. A six-stage framework is developed using the results and conclusions of two case studies regarding sustainable management of eroding mangrove-dominated muddy coasts in Vam Ray, Hon Dat district, Kien Giang Province, Vietnam. The framework does not stop with the creation of integrated knowledge, but should undergo a longer process. The new knowledge developed in this framework is the understanding gained and lessons learnt during the testing of products of multiple knowledge systems in a local context rather than products of integrated knowledge systems themselves. The Vam Ray framework promotes a high level of participation, effective use of products of multiple knowledge systems, maximum integration of local and scientific knowledge, local ownership, and sustainability. Therefore, the Vam Ray framework adds a new dimension to the literature in relation to integration of local and scientific knowledge in natural resource management.