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11.
The structure and development of foredunes on a locally prograding coast: insights from ground-penetrating radar surveys, Norfolk, UK 总被引：5，自引：0，他引：5
The internal structure of coastal foredunes from three sites along the north Norfolk coast has been investigated using ground‐penetrating radar (GPR), which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non‐destructive or geophysical technique. Combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution. The radar profiles show the internal structures, which include foreslope accretion, trough cut and fill, roll‐over and beach deposits. Foredune ridges contain large sets of low‐angle cross‐stratification from dune foreslope accretion with trough‐shaped structures from cut and fill on the crest and rearslope. Foreslope accretion indicates sand supply from the beach to the foreslope, while troughs on the dune crest and rearslope are attributed to reworking by offshore winds. Bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement. Radar sequence boundaries within dunes have been traced below the water‐table passing into beach erosion surfaces. These are believed to result from storm activity, which erodes the upper beach and dunes. In one example, at Brancaster, a dune scarp and erosion surface may be correlated with erosion in the 1950s, possibly the 1953 storm. Results suggest that dune ridge development is intimately linked to changes in the shoreline, with dune development associated with coastal progradation while dunes are eroded during storms and, where beaches are eroding, a stable coast provides more time for dune development, resulting in higher foredune ridges. A model for coastal dune evolution is presented, which illustrates stages of dune development in response to beach evolution and sand supply. In contrast to many other coastal dune fields where the prevailing wind is onshore, on the north Norfolk coast, the prevailing wind is directed along the coast and offshore, which reduces the landward migration of sand dunes. 相似文献
12.
D. W. T. Jackson J. H. M. Beyers K. Lynch J. A. G. Cooper A. C. W. Baas I. Delgado‐Fernandez I 《地球表面变化过程与地形》2011,36(8):1113-1124
The behaviour of offshore‐directed winds over coastal dune and beach morphology was examined using a combination of modelling (3‐D computational fluid dynamics (CFD)) and field measurement. Both model simulations and field measurements showed reversal of offshore flows at the back beach and creation of an onshore sediment transport potential. The influence of flow reversals on the beach‐dune transport system and foredune growth patterns has previously received little attention. Detailed wind flow measurements were made using an extensive array of mast‐mounted, 3‐D ultrasonic anemometers (50 Hz), arranged parallel to the dominant incident wind direction. Large eddy simulation (LES) of the offshore wind flow over the dune was conducted using the open‐source CFD tool openFOAM. The computational domain included a terrain model obtained by airborne LiDAR and detailed ground DGPS measurements. The computational grid (~22 million cells) included localized mesh refinement near the complex foredune terrain to capture finer details of the dune morphology that might affect wind flows on the adjacent beach. Measured and simulated wind flow are presented and discussed. The CFD simulations offer new insights into the flow mechanics associated with offshore winds and how the terrain steering of wind flow impacts on the geomorphological behaviour of the dune system. Simulation of 3‐D wind flows over complex terrain such as dune systems, presents a valuable new tool for geomorphological research, as it enables new insights into the relationship between the wind field and the underlying topography. The results show that offshore and obliquely offshore winds result in flow reversal and onshore directed winds at distances of up to 20 m from the embryo dune toe. The potential geomorphological significance of the findings are discussed and simple calculations show that incoming offshore and obliquely offshore winds with mean velocities over 13 m s?1 and 7 m s?1, respectively, have the potential to create onshore‐directed winds at the back beach with mean velocities above 3.3 m s?1. These are above the threshold of movement for dry sand and support previous conclusions about the significance of offshore winds in dune and beach budget calculations. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
13.
Ecosystem-based marine spatial management: Review of concepts, policies, tools, and critical issues 总被引：1，自引：0，他引：1
Stelios Katsanevakis Vanessa Stelzenmüller Andy South Thomas Kirk Sørensen Peter J.S. Jones Sandy Kerr Fabio Badalamenti Christos Anagnostou Patricia Breen Guillem Chust Giovanni D’Anna Mike Duijn Tatiana Filatova Fabio Fiorentino Helena Hulsman Kate Johnson Aristomenis P. Karageorgis Ingrid Kröncke Simone Mirto Carlo Pipitone Susan Portelli Wanfei Qiu Henning Reiss Dimitris Sakellariou Maria Salomidi Luc van Hoof Vassiliki Vassilopoulou Tomás Vega Fernández Sandra Vöge Anke Weber Argyro Zenetos Remment ter Hofstede 《Ocean & Coastal Management》2011,54(11):807-820
Conventional sectoral management and piecemeal governance are considered less and less appropriate in pursuit of sustainable development. Ecosystem based marine spatial management (EB-MSM) is an approach that recognizes the full array of interactions within an ecosystem, including human uses, rather than considering single issues, species, or ecosystem services in isolation. Marine spatial planning and ocean zoning are emerging concepts that can support EB-MSM. EB-MSM is driven by high-level goals that managers aim to achieve through the implementation of measures. High-level goals and objectives need to be translated into more operational objectives before specific targets, limits and measures can be elaborated.Monitoring, evaluation and adaptation are necessary to ensure that marine management measures are both effective and efficient. Solid monitoring frameworks are the foundation of adaptive management, as they provide the necessary information to evaluate performance and the effectiveness of management actions. Marine protected areas (MPAs) - possibly set up in networks - constitute a key component in EB-MSM policies and practises and have been applied as a cornerstone in conservation of marine biodiversity, management of fish populations, development of coastal tourism, etc. Moreover, MPA experiences have provided methods and concepts (such as zoning) to a wider EB-MSM context. The assignment of values to biophysical features of the marine environment allows the direct assessment of related management choices and may assist EB-MSM.A range of monetary valuation techniques have been proposed to reduce attributes of goods and services to a single metric. However, in the marine environment such an approach is often over simplistic, and thus less reductive techniques may be necessary. Rather than producing a single metric, the results of non-monetary assessments guide policy allowing weight to be given as necessary to potential areas of conflict and consensus.Strategies to take into account climate change effects and geohazard risks in EB-MSM have been applied or proposed worldwide. EB-MSM regimes must be alert to such risks and flexible to account for changes. 相似文献
14.
This perspective piece makes a case for a more rigorous treatment of managed retreat as a politically, legally, and economically distinct type of relocation that is separate from climate migration. We argue that the use of both concepts interchangeably obfuscates the problems around climate-induced mobilities and contributes to the inconsistencies in policy, plans, and actions taken by governments and organizations tasked with addressing them. This call for a disentanglement is not solely an academic exercise aimed at conceptual clarity, but an effort targeted at incentivizing researchers, practitioners, journalists, and advocates working on both issues to better serve their constituencies through alliance formation, resource mobilization, and the establishment of institutional pathways to climate justice. We offer a critical understanding of the distinctions between climate migration and managed retreat grounded in six orienting propositions. They include differential: causal mechanisms, legal protections, rights regimes and funding structures, discursive effects, implications for land use, and exposure to risks. We provide empirical examples from existing literature to contextualize our propositions while calling for a transformative justice approach to addressing both issues. 相似文献
15.
Physical and biological development of a newly breached managed realignment site, Humber estuary, UK 总被引：1，自引：0，他引：1
As part of the Humber flood defence upgrade works (Urgent works) undertaken by the Environment Agency, the Paull Holme Strays site was identified as one of twelve potential managed realignment sites within the Humber catchment. The site was breached in September 2003, creating 80 hectares of new intertidal habitat. Initial accretion monitoring commenced in December 2003 with annual surveys of invertebrate colonisation commencing in October 2004. The present study gives details of the physical development of the newly created mudflat within the site, together with invertebrate colonisation and benthic community change over time. Comparisons between the newly created habitat and the existing mudflat outside the old sea wall are made. The macrofaunal communities found within the area as a whole are considered to be characteristic of the area with low species diversity, high abundance and small body size. The community within the managed realignment site is still in an early successional stage with low abundance and diversity in comparison with other sites within this part of the Humber. However the community biomass increased considerably between 2004 and 2005. Colonisation within the managed realignment site is still primarily concentrated in the areas around the two breach sites and is thought to be restricted in other areas due to infrequent tidal inundation. 相似文献
16.
Karl F. Nordstrom Nancy L. Jackson Katherine H. Korotky Jack A. Puleo 《地球表面变化过程与地形》2011,36(6):779-789
Wind characteristics and aeolian transport were measured on a naturally evolving beach and dune and a nearby site where the beach is raked and sand‐trapping fences are deployed. The beaches were composed of moderately well sorted to very well sorted fine to medium sand. The backshore at the raked site was wider and the foredune was more densely vegetated and about 1 m higher than at the unraked site. Wind speeds were monitored using anemometers placed at 1 m elevation and sand transport was monitored using vertical traps during oblique onshore, alongshore and offshore winds occurring in March and April 2009. Inundation of the low backshore through isolated swash channels prevented formation of a continuously decreasing cross‐shore moisture gradient. The surface of the berm crest was dryer than the backshore, making the berm crest the greatest source of offshore losses during offshore winds. The lack of storm wrack on the raked beach reduced the potential for sediment accumulation seaward of the dune crest during onshore winds, and the higher dune crest reduced wind speeds and sediment transport from the dune to the backshore during offshore winds. Accretion at wrack seaward of the dune toe on the unraked beach resulted in a wider dune field and higher, narrower backshore. Although fresh wrack is an effective local trap for aeolian transport, wrack that becomes buried appears to have little effect as a barrier and can supply dry sand for subsequent transport. Aeolian transport rates were greater on the narrower but dryer backshore of the unraked site. Vegetation growth may be necessary to trap sand within zones of buried wrack in order to allow new incipient foredunes to evolve. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
17.
Although dunes fronted by sandy beaches constitute approximately 80 per cent of South Africa's coastline, few studies have addressed the formation and life cycle of coastal foredunes, the small, ephemeral shore‐parallel dune ridges typically less than 5 m high and 20 m wide, which form seaward of the storm line. This study used regular, detailed topographic surveys of embryo and foredunes at Tugela mouth, an aggrading stretch of shoreline on the subtropical east coast of South Africa, over a 32‐month period, to gain insight into the formation and motion of these highly mobile landforms over the short term. Average wind drift potential at Tugela mouth during the study period, at 2·35 m s?1, was an order of magnitude lower than that typical of most parts of the eastern South African coast. The dominant sand‐moving wind for the region was from the southwest to west‐southwest at 10·7 to 13·8 m s?1, with a secondary vector from north to north‐northeast at 10·8 to 13·8 m s?1. Signi?cant shoreline retreat, a result of the low sediment yield of the Tugela River during the study period, was one of the main results. This provided the context for redistribution of sand from the inland to the seaward side of the study area, a consequence of the dominant wind direction, and for frequent creation and destruction of short‐lived embryo dunes. Those foredunes which survived the whole study period tended to increase in height, but there was no consistent directional trend in foredune crest movement throughout the 32 months. The study results generally supported Psuty's model of foredune development, but could not con?rm his contention of landward retreat of dune forms under conditions of shoreline erosion. This may be due to the relatively short duration of the study, or possibly to low wind drift potential at the site. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
18.
Due to a growing world population and the effects of anthropogenic climate change, access to clean water is a growing global concern. Managed aquifer recharge (MAR) is a method that can help society's response to this increasing demand for pure water. In MAR, the groundwater resources are replenished and the quality of the recharged surface water is improved through effects such as the removal of organic matter. This removal occurs through mechanisms such as microbial decomposition, which can be monitored by studying the isotopic composition of dissolved inorganic carbon (DIC). Nevertheless, the monitoring can be difficult when there are other factors, like dissolving calcite, affecting the isotopic composition of DIC.The aims of this study were to establish a method for monitoring the decomposition of organic matter (dissolved organic carbon – DOC) in cases where calcite dissolution adds another component to the DIC pool, and to use this method to monitor the beginning and amount of DOC decomposition on a MAR site at Virttaankangas, southwestern Finland. To achieve this, we calculated the mean residence times of infiltrated water in the aquifer and the fractions of this water reaching observation wells. We conducted geochemical modelling, using PHREEQC, to estimate the amount of DOC decomposition and the mineral reactions affecting the quality of the water. 相似文献
19.
Elsemarie Mullins Laura J. Moore Evan B. Goldstein Theo Jass John Bruno Orencio Durán Vinent 《地球表面变化过程与地形》2019,44(9):1734-1747
Coastal foredunes provide the first line of defense against rising sea levels and storm surge and for this reason there is increasing interest in understanding and modeling foredune formation and post-storm recovery. However, there is limited observational data available to provide empirical guidance for the development of model parameterizations. To provide guidance for improved representation of dune grass growth in models, we conducted a two-year multi-species transplant experiment on Hog Island, VA, U.S.A. and measured the dependence of plant growth on elevation and distance from the shoreline, as well as the relationship between plant growth and sand accumulation. We tracked total leaf growth (length) and aboveground leaf length and found that Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats) grew more than Spartina patens (saltmeadow cordgrass) by a factor of 15% (though not statistically significant) and 45%, respectively. Our results also suggest a range of basal/frontal area ratios (an important model parameter) from 0.5-1 and a strong correlation between transplant growth and total sand deposition for all species at the scale of two years, but not over shorter temporal scales. Distance from the shoreline and elevation had no effect on transplant growth rate but did have an effect on survival. Based on transplant survival, the seaward limit of vegetation at the end of the experiment was approximately 30 m from the MHWL and at an elevation of 1.43 m, corresponding to inundation less than 7.5% of the time according to total water level calculations. Results from this experiment provide evidence for the dune-building capacity of all three species, suggesting S. patens is not a maintainer species, as previously thought, but rather a moderate dune builder even though its growth is less stimulated by sand deposition than A. breviligulata and U. paniculata. © 2019 John Wiley & Sons, Ltd. 相似文献
20.
Fast population growth and rapid industrialization, on one hand, and lack of sewerage network and poor living condition, on
the other, have led to the deterioration of surface and ground water quality in the city of Addis Ababa. The urban wastewater
is discharged largely into streams that drain the city. Only less than 3% join the wastewater treatment facilities. Due to
sporadic rainfall that causes shortage in groundwater recharge, managed aquifer recharge (MAR) experiment was tested on soil
column collected from Akaki Well Field which is located in the southern part of the city using water from the Big Akaki River
that crosses the same well field and effluent from Kaliti Wastewater Treatment Plant. Water quality analysis for 17 different
parameters was done for both the inflow and outflow water samples and soils were tested for electrical conductivity and cation
exchange capacity. The results indicate improved water quality as a result of higher attenuation/filtration capacity of the
vadose zone in the well field due to the presence of vertisols. The main geochemical processes that have acted in the soil
column could be cation exchange, dissolution, precipitation, oxidation, nitrification, die off etc. that are responsible for
the effectiveness of vadose zone for MAR. 相似文献