Integrated analysis of risks of coastal flooding and cliff erosion under scenarios of long term change   总被引：2，自引：1，他引：1  

R. J. Dawson  M. E. Dickson  R. J. Nicholls  J. W. Hall  M. J. A. Walkden  P. K. Stansby  M. Mokrech  J. Richards  J. Zhou  J. Milligan  A. Jordan  S. Pearson  J. Rees  P. D. Bates  S. Koukoulas  A. R. Watkinson 《Climatic change》2009,95(1-2):249-288

The risks to human populations in coastal areas are changing due to climate and socio-economic changes, and these trends are predicted to accelerate during the twenty-first century. To understand these changing risks, and the resulting choices and pathways to successful management and adaptation, broad-scale integrated assessment is essential. Due to their complexity the two risks of flooding and erosion are usually managed independently, yet frequently they are interconnected by longshore exchange of sediments and the resulting broad scale morphological system behaviour. In order to generate new insights into the effects of climate change and coastal management practises on coastal erosion and flood risk, we present an integrated assessment of 72 km of shoreline over the twenty-first century on the East Anglian coast of England which is a site of significant controversy about how to manage coastal flood and erosion risks over the twenty-first century. A coupled system of hydrodynamic, morphological, reliability and socio-economic models has been developed for the analysis, implemented under scenarios of coastal management, climate and socio-economic change. The study is unique in coastal management terms because of the large spatial scale and extended temporal scale over which the analysis is quantified. This study for the first time quantifies what has for some years been argued qualitatively: the role of sediments released from cliff erosion in protecting neighbouring low-lying land from flooding. The losses and benefits are expressed using the common currency of economic risk. The analysis demonstrates that over the twenty-first century, flood risk in the study area is expected to be an order of magnitude greater than erosion risk. Climate and socio-economic change and coastal management policy have a significant influence on flood risk. This study demonstrates that the choices concerning coastal management are profound, and there are clear tradeoffs between erosion and flood impacts.  相似文献   

Paleomagnetic dating of ironstone nodules (‘nuts’) from the Yowah opal field,central southern Queensland     

P. W. Schmidt  B. L. Dickson 《Australian Journal of Earth Sciences》2017,64(6):743-752

To constrain the age of Australian opal formation, we have undertaken a paleomagnetic study of oxidised ironstone ‘nuts’ from Yowah, Queensland. Following standard methods, we have calculated a mean direction of declination D = 191.4°, inclination I = 61.7° (α₉₅ = 4.0°), indicating a paleomagnetic pole position at latitude λ_p = 71.3°S, longitude ?_p = 119.4°E (A₉₅ = 5.3°). The direction comprises both normal and reverse polarities that fail a reversal test most probably owing to contamination by small recent/present-day components. The mean direction should not be significantly affected. A chi-square comparison with paleomagnetic poles for dated Cenozoic rocks in eastern Australia, poles derived from the Global Moving Hotspot Reference Frame and the Cenozoic pole path for North America, appropriately transferred to Australian coordinates, yields a mean age estimate of 35 ± 7 Ma, i.e. late Eocene to early Oligocene. This is interpreted as the age of the ironstone formation, which places a maximum age for the formation of precious Yowah opal. This result confirms and tightens the age for the nearby Canaway weathered profile.  相似文献   

Surficial Sediments along the Inner Continental Shelf of Maine     

Joseph T. Kelley  Stephen M. Dickson 《Marine Georesources & Geotechnology》2013,31(2-3)

Through 10 years of support from the Minerals Management Service Association of American State Geologists' Continental Margins Program we have mapped along the Maine coast, seaward to the 100 m isobath. In all, 1,773 bottom sample stations were occupied, 3,358 km of side-scan sonar and 5,011 km of seismic reflection profiles were gathered. On the basis of these data, a surficial sediment map was created for the Maine inner continental shelf during the Year 8 project, and cores and seismic data were collected to evaluate sand thickness during Years 9 and 10. Sand covers only 8 % of the Maine shelf, and is concentrated seaward of beaches off southern Maine in water depths less than 60 m. Sand occurs in three depositional settings: (1) in shoreface deposits connected dynamically to contemporary beaches; (2) in submerged deltas associated with lower sea-level positions; and (3) in submerged lowstand shoreline positions between 50 and 60 m. Seismic profiles over the shoreface off Saco Bay, Wells Embayment, and off the Kennebec River mouth each imaged a wedge-shaped acoustic unit which tapered off between 20 and 30 m. Cores determined that this was sand that was underlain by a variable but thin (commonly 1 m) deposit of estuarine muddy sand and a thick deposit of glacial-marine mud. Off Saco Bay, more than 55 million m3 of sand exists in the shoreface, compared with about 22 million m3 on the adjacent beach and dunes. Seaward of the Kennebec River, a large delta deposited between 13 ka and the present time holds more than 300 million m3 of sand and gravel. The best sorted sand is on the surface nearshore, with increasing amounts of gravel offshore and mud beneath the surficial sand sheet. Bedforms indicate that the surficial sand is moved by waves to at least 55 m depth. Seaward of the Penobscot River, no significant sand or gravel was encountered. Muddy estuarine sediments overlie muddy glacial-marine sediment throughout the area offshore area of this river. No satisfactory explanation is offered for lack of a sandy delta seaward of Maine's largest river. Lowstand-shoreline deposits were cored in many places in Saco Bay and off the Kennebec River mouth. Datable materials from cores indicated that the lowstand occurred around 10.5 ka off the Kennebec. Cores did not penetrate glacial-marine sediment in the lowstand deposits, and seismic profiles were ambiguous about the vertical extent of sand in these units. For these reasons, no total thickness of sand was determined from the lowstand deposits, but given the area of the surficial sand, the volume is probably in the hundreds of millions of cubic meters.  相似文献   

Which water formed Australian sediment-hosted precious and potch opal?     

B. L. Dickson 《Australian Journal of Earth Sciences》2019,66(5):645-655

The means and timing of the formation of Australian sediment-hosted precious opal remain a subject of continuing debate. In this study, the question of which water formed the opal is addressed by examination of rare earth element data for opals and host rocks. The available data, mainly for Lightning Ridge, NSW, suggest a positive Eu anomaly, relative to the neighbouring Sm and Dy, occurs in opals whereas no such anomaly was found for the weathered Cretaceous sediments hosting the opal. Such anomalies may be inherited from the source rock with a similar positive Eu anomaly or generated in situ by severe reduction. There is no indication of major reduction processes during the opal formation that could have led to such a Eu anomaly so this is likely inherited from a source rock. As the opal host rocks did not show this anomaly, the source rocks must be external to the opal fields. Calcite cements within rocks hosting the aquifers of the Eromanga and Surat basins of the Great Artesian Basin have been reported to have a positive Eu anomaly, which strongly suggests that opal was formed by upwelling Great Artesian Basin artesian waters. This work has also highlighted variations in trace-element concentrations in opals, which indicate significant variation in the source water composition during opal formation or different water sources were involved. Either of these is indicative of the source for the opal with its trace elements derived from external sources. These conclusions have significant implications to considerations of how opal formed, and hence, for the exploration for other deposits and to the chemistry and timing that led to the formation of opal.  相似文献   

The distribution of short-chain halogenated aliphatic hydrocarbons in some marine organisms     

A.G. Dickson  J.P. Riley 《Marine pollution bulletin》1976,7(9):167-169

A number of halogenated aliphatic hydrocarbons have been determined in the various organs of three species of molluscs and five species of fish. In general, the compounds were only slightly enriched (2–25 times) on a dry weight basis relative to their seawater concentrations. The usual order of enrichment was found to be brain > gill > liver > muscle. Methyl iodide was found to be the compound most strongly concentrated.  相似文献   

Effects of marsh management on fisheries organisms: The compensatory adjustment hypothesis     

H. Dickson Hoese  Mark Konikoff 《Estuaries and Coasts》1995,18(1):180-197

An overview of data including numbers of species, numbers of individuals, biomass, and average weight per individual from three studies of differing marsh management systems in southwestern Louisiana indicate that populations of managed systems are generally maintained despite partial restrictions on organism movements due to water control structures. At some high level of restriction, perhaps in systems completely leveed and managed for specific target organisms, recruitment and subsequent export may be drastically reduced. However, we suggest that below a critical level of restriction, recruitment, growth, and eventual export approach normal levels. Restrictions may select for or against certain species, but the replacement of those selected against may maintain the overall fishery productivity of the system. *** DIRECT SUPPORT *** A01BY069 00014  相似文献   

pH scales and proton-transfer reactions in saline media such as sea water     

A.G Dickson 《Geochimica et cosmochimica acta》1984,48(11):2299-2308

The three approaches to defining pH scales for use in sea water: the N.B.S. scale, the pH(SWS) or ‘total’ hydrogen ion concentration scale and the ‘free’ hydrogen ion concentration scale are described, and it is shown how these arise as a direct consequence of alternative experimental procedures for determining practical acidity constants. The advantages of conceptual simplicity and of experimental precision inherent in the use of concentration products to describe proton-transfer reactions in saline media are emphasised. In addition, the problems of theoretical interpretation and of reproducibility which result from the conventional nature of the N.B.S. pH scale are described, and the effect on the corresponding ‘apparent’ constants outlined. Insofar as it is concentration products rather than ‘apparent’ constants that are amenable to prediction using models for activity coefficients, the deliberate use of a ‘free’ hydrogen ion concentration scale should be applicable to many areas of aqueous geochemistry in addition to marine chemistry.  相似文献   

Hydrogeochemical interpretations of apparent anomalies in base metals and radium in groundwater near Lake Maurice in the Great Victoria Desert     

A.M. Giblin  B.L. Dickson 《Journal of Geochemical Exploration》1984,22(1-3)

Apparently anomalous levels of Cu, Pb, Zn (up to 6.1, 26.0 and 10.8 mg 1⁻¹ respectively) and Ra (2000 pg 1⁻¹) have been noted in groundwaters from 28 drill holes within a 20 km × 20 km zone centred about a 10 times background airborne radiometric anomaly near Lake Maurice in the Great Victoria Desert in South Australia. Within 6 km of the anomaly centre the water table depth is generally less than 10 m, increasing to approximately 30 m in the drill holes furthest from the anomaly centre. All waters are very acid (pH 3.6 to 5.8) and deficient in carbonate species (all <0.5 mg 1⁻¹) but saturated with respect to calcium sulphate minerals. XRD traces of drill hole cuttings show the presence of quartz and halite at every sample site, pyrite at 75% of sites, variable amounts of kaolinite and muscovite at all sites, and variable amounts of feldspar, jarosite, calcium sulphate minerals, hydrated iron oxides, siderite, chlorite and calcite at certain locations only. Salinity of waters is very high ranging from that approximating sea water (Ionic strength (I) = 0.93 and Cl⁻ = 19 g 1⁻¹) to approximately six times sea water salinity (I = 4.61 and Cl⁻ = 120 g 1⁻¹).  相似文献   

Shore platform development around Lord Howe Island, southwest Pacific   总被引：1，自引：0，他引：1  

Mark E. Dickson   《Geomorphology》2006,76(3-4):295-315

This paper describes the morphology of near-horizontal basalt and calcarenite shore platforms around Lord Howe Island as well as the lithological and process environment in which they occur. The morphology of platforms around the island is highly varied. For instance, they occur at a wide range of elevations between low-tide level and several metres above the highest tides, and their width ranges between just a few metres to over 100 m. However, common to most platforms is that they have near-horizontal surfaces that terminate abruptly in a steep scarp at their seaward edge. Correlations indicate that the variability in platform elevation and width is attributable to variability in key parameters of erosion, such as rock resistance and shoreline water depth. Whereas wider platforms occur in rocks of lesser resistance, platform elevation is shown to increase both as rock resistance and the depth of water at the shoreline increases. Wave exposure has a significant control on platform width in some instances, but an over-arching relationship was not detected. Most platforms around the island appear to have developed over the Holocene and a conceptual model is proposed to account for the varied morphology of platforms that have developed over this period. Resistant plunging cliffs occur along about 18% of the rocky coastline of Lord Howe Island and represent the starting point for the model. Where cliffs have yielded to wave erosion platforms have been initiated at an elevation controlled predominantly by rock resistance and shoreline water depth. At Lord Howe Island narrow platforms up to about 20 m wide in exposed locations generally occur about 4 to 6 m above high tide level, and have apparently been subject to very infrequent erosion. Shore platforms about 20 to 40 m wide have generally formed in less resistant rocks, are somewhat lower at about 2 to 3 m above high tide level, and have been subject to more frequent erosion over the Holocene. Most basalt platforms around the island fall within these first two categories, but there are some instances of platforms about 50 m wide. These platforms have formed in rocks of comparatively low resistance and are relatively low in elevation occurring close to the level of high tide. An interesting feature of some of these wide platforms is that, unlike the morphology of narrower platforms, raised ramparts sometimes occur on their outer edge.  相似文献   

Systemic impacts of climate change on an eroding coastal region over the twenty-first century   总被引：2，自引：1，他引：2  

Mark E. Dickson  Mike J. A. Walkden  Jim W. Hall 《Climatic change》2007,84(2):141-166

A numerical model detailing the functioning and emergent behaviour of an eroding coastal system is described. Model output from a 50-km study region centred on the soft-rock shore of northeast Norfolk was verified through comparison with cliff recession rates that were extracted from historical maps spanning more than a century. Predictions were then made for the period 2000 to 2100 under combined climatic change and management scenarios. For the scenarios evaluated, the model was relatively insensitive to increases in offshore wave height and moderately sensitive to changes in wave direction, but the most important effects were associated with accelerated sea-level rise (SLR). In contrast to predictions made using a modified version of the Bruun rule, the systems model predicted rather complex responses to SLR. For instance, on some sectors of coast, whereas the Bruun rule predicted increased recession under accelerated SLR, the systems model actually predicted progradation owing to the delivery of sediment from eroding coasts up-drift. By contrast, on coasts where beaches are underlain by shore platforms, both the Bruun rule and the systems model predicted accelerated recession rates. However, explicit consideration of the interaction between beach and shore platform within the systems model indicates that these coasts have a broader range of responses and lower overall vulnerability to SLR than predicted by the Bruun rule.  相似文献