- Southampton, Southampton, United Kingdom
David Sear
University of Southampton, Geography and Environment, Faculty Member
Sear, DA, Thorne, CR and Newson, MD (2004) Guidebook of applied fluvial geomorphology : Defra/Environment Agency Flood and Coastal Defence R&D Programme, London, Defra Flood Management Division, 256pp. (R&D Technical Report FD1914). ...... more
Sear, DA, Thorne, CR and Newson, MD (2004) Guidebook of applied fluvial geomorphology : Defra/Environment Agency Flood and Coastal Defence R&D Programme, London, Defra Flood Management Division, 256pp. (R&D Technical Report FD1914). ... Full text not available from this repository. ... Official URL: http://www.defra.gov.uk/science/project_data/Docum... ... RDF+N-Triples, RDF+N3, RDF+XML, Browse.
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Small island developing States, such as those in the Pacific, are often prone to multiple hazards that have potential to result in disaster and / or restrict development. Hazard data can be limited in resolution or omitted in or near... more
Small island developing States, such as those in the Pacific, are often prone to multiple hazards that have potential to result in disaster and / or restrict development. Hazard data can be limited in resolution or omitted in or near SIDS’ coasts, but a growing and improved range of datasets are becoming available. Through an analysis of approximately 100 policy documents on hazards and disaster risk management in Pacific island nations, we found: limited information on hazards and how they manifest to disasters at local levels, thus not fully connecting drivers and subsequent risk; at times a non-specific multi-hazard approach prompting the need to address more specific hazards; and restricted temporal and spatial scales of analysis that potentially limit continuity of actions where mitigation methods evolve. These limitations suggest that appropriate and timely high resolution hazard data is needed from the top-down to underpin the design and development of local disaster risk man...
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Historical salmon catch records suggest that climatic variability, and more recently human exploitation, control patterns of abundance in Atlantic salmon populations. We present the first long-term (2000-year) reconstruction of Atlantic... more
Historical salmon catch records suggest that climatic variability, and more recently human exploitation, control patterns of abundance in Atlantic salmon populations. We present the first long-term (2000-year) reconstruction of Atlantic Salmon population variations based on a Marine Derived Nutrient (MDN) lake sediment record. Our record is constructed from nitrogen isotopes (δ15N) measured from a lake sediment core, which we compare with an escapement index (EI) derived from historic net catch data on major Scottish salmon rivers. We used an isotope mixing model to demonstrate that the N isotope values are likely enriched with MDN and demonstrate that Loch Insh sediments are enriched compared with a control site (Loch Vaa) that has never had exposure to salmon. We demonstrate that current adult spawner returns are around half that of historic values prior to major human exploitation. Before the onset of widespread human exploitation and habitat degradation, large fluctuations in sa...
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" At sites where dense concentrations of palaeoliths are found within river gravels, such as many of the sites in the Solent area... it can be assumed that they have not travelled far from their place of discard."(Wessex... more
" At sites where dense concentrations of palaeoliths are found within river gravels, such as many of the sites in the Solent area... it can be assumed that they have not travelled far from their place of discard."(Wessex Archaeology 1992: 12) " Despite the recognition and importance of abrasion very little work has been presented to establish both how it occurs and the rate of its occurrence. Similarly, the dispersal of artefactual material and its behaviour within a river has received little attention."(Rarding et al. 1987: 115)
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Summary Detrimental impacts of excessive fine‐grained sediment inputs to streams and rivers are well established. What is less well understood is the susceptibility of different elements of the freshwater biota to such perturbations and... more
Summary Detrimental impacts of excessive fine‐grained sediment inputs to streams and rivers are well established. What is less well understood is the susceptibility of different elements of the freshwater biota to such perturbations and how such knowledge of their susceptibility could aid in identifying where excessive fine‐grained sediment is impairing ecological condition. Following the collection of biological and sediment data from 179 streams across England and Wales, representative of a range of river types over a gradient of fine sediment loading, objective statistical approaches were applied to establish relationships between the macroinvertebrate assemblage and fine‐grained sediment inputs to river channels. Having factored out that portion of the biological variation associated with natural environmental gradients, a model comprising mass of organic sediment in erosional areas of the stream bed [predominantly associated with the first axis of the partial canonical correspo...
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Page 1. 1-Introduction A critical issue in fluvial engineering is the prediction of flow resistance associated with vegetation. One type of vegetation which has a significant impact upon flow resistance is Large Woody Debris (LWD ...
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<p>Bedload transport is a fundamental process by which coarse sediment is transferred through landscapes by river networks and is characterized by cyclic sequences of particle motion and rest. Bedload transport has... more
<p>Bedload transport is a fundamental process by which coarse sediment is transferred through landscapes by river networks and is characterized by cyclic sequences of particle motion and rest. Bedload transport has many complex physical controls but may be well described stochastically by distributions of grain step length and rest time obtained through tracer studies. To date, none of these published tracer studies have specifically investigated the influence of large wood on distributions of step length or rest time, limiting the applicability of stochastic sediment transport models in these settings. Large wood is a major component of many forested rivers and is increasing because of disturbances such as wildfire and insect infestations as well as its use in rivers as part of ‘Natural Food Management’ (NFM) practice. This study aims to investigate and model the influence of large wood on grain-scale bedload transport. </p><p>St Louis Creek, an alpine stream in the Fraser Experimental Forest, Colorado, is experiencing increased wood loading resulting from the infestation of the mountain pine beetle in the past decades. We inserted 957 Passive Integrative Transponders (PIT) tagged cobbles in 2016 upstream of a wood loaded reach and measured and tagged > 20 pieces of large wood in the channel. We resurveyed the cobbles and wood on an annual basis after snowmelt, building distributions of rock-step lengths as well as observing any changes and transport of large wood. Additionally, a novel modelling approach based on linear mixed modelling (LMM) statistical approaches is implemented to establish the significance of wood and other factors on probability of particle entrainment, deposition and step length.</p><p>Tracer sediments accumulated both up and downstream of large wood pieces, with LMM analysis confirming a reduction in the probability of entrainment of tracers closer to wood. In addition, when tracers were remobilised, their subsequent step lengths were shorter the closer they were deposited to large wood. In 2019, large wood significantly reduced the step lengths of tracer particles, forcing premature deposition of tracers. This study demonstrates the role of large wood in influencing bedload transport in alpine stream environments, with implications for both natural and anthropogenic addition of wood debris in fluvial environments.</p>
Research Interests: Geology, Forest road, Sediment transport, Sediment, Bed load, and 4 moreFluvial, Sediment Transport, Bed Load, and EGU
<p>Natural Flood Management (NFM) is a nature-based solution for reducing flood risk whilst delivering multiple benefits such as water quality improvements through the mitigation of diffuse pollution (e.g. from soil... more
<p>Natural Flood Management (NFM) is a nature-based solution for reducing flood risk whilst delivering multiple benefits such as water quality improvements through the mitigation of diffuse pollution (e.g. from soil erosion). This study aimed to assess the ability of NFM storage features to trap potential pollutants in run-off from two small (3.4 km<sup>2</sup>) agricultural catchments. The masses of sediment, total phosphorus and organic carbon trapped by 14 NFM features (since construction 2 to 3 years previously) were quantified through sediment surveying and sampling. Streamflow and suspended sediment monitoring downstream of the features enabled catchment fluxes to be calculated. The features trapped a total of 83 tonnes sediment, 122 kg phosphorus, and 4.3 tonnes organic carbon over 2 to 3 years of functioning. Although the footprint of the features was <1% of the catchment area, they drained 44% of the total land area and were able to capture the equivalent of 25% of the total suspended sediment flux (22% of the fine (silt and clay) sediment flux), 14% of the total phosphorus flux, and 13% of the particulate organic carbon flux during the monitored period. Results show how accumulation rates were influenced by hydrological connectivity, with greater accumulation in features constructed directly on streams (online features), and offline features which filled from streamflow diverted by instream woody dams. Compared with the topsoil in each contributing area, trapped sediment was enriched in phosphorus and carbon in the majority of features, having on average 50% higher phosphorus and 17% higher organic carbon concentrations than surrounding arable soils, highlighting its potential value for redistribution on farmland. The results of this monitoring demonstrate the potential of NFM interventions to provide additional value by mitigating diffuse pollution in lowland catchments.</p>
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<p>Bedload transport is a fundamental process by which coarse sediment is transferred through landscapes by river networks and may be well described stochastically by distributions of grain step length and rest time... more
<p>Bedload transport is a fundamental process by which coarse sediment is transferred through landscapes by river networks and may be well described stochastically by distributions of grain step length and rest time obtained through tracer studies. To date, none of these published tracer studies have specifically investigated the influence of large wood in the river channel on distributions of step length or rest time, limiting the applicability of stochastic sediment transport models in these settings. Large wood is a major component of many forested rivers and is increasing due to anthropogenic ‘Natural Flood Management’ (NFM) practices. This study aims to investigate and model the influence of large wood on grain-scale bedload transport. </p><p>We tagged 957 cobble – pebble sized particles (D<sub>50 </sub>= 73 mm) and 28 pieces of large wood (> 1 m in length) with RFID tracers in an alpine mountain stream. We monitored the transport distance of tracers annually over three years, building distributions of tracer transport distances. Empirical data was used in linear mixed modelling (LMM) statistical analysis, determining the relative influence proximity to wood had on likelihood of entrainment, deposition, and the transport distances of sediments. </p><p>Tracer sediments accumulated both up and downstream of large wood pieces, with LMM analysis confirming a reduction in the probability of entrainment of tracers closer to wood in all three years. Upon remobilisation, tracers entrained from positions closer to large wood had shorter subsequent transport distances in each year. In 2019, large wood also had a trapping effect, significantly reducing the transport distances of tracer particles entrained from upstream, i.e. forcing premature deposition of tracers. This study demonstrates the role of large wood in influencing bedload transport in alpine stream environments, with implications for both natural and anthropogenic addition of wood debris in fluvial environments.</p>
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Research Interests: Zoology, Biology, Ecology, Habitat, Fisheries Sciences, and 4 moreFishery, Brood, Oncorhynchus, and Limiting
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Abstract Eutrophication and sedimentation are affecting global Marine Protected Area (MPA) ecosystems, such as estuaries, as catchments are developed and sea levels rise. Managers are often faced with short term datasets and modelling... more
Abstract Eutrophication and sedimentation are affecting global Marine Protected Area (MPA) ecosystems, such as estuaries, as catchments are developed and sea levels rise. Managers are often faced with short term datasets and modelling evidence with which to undertake management of these complex open systems. Longer term datasets which monitor environmental change can be used to improve understanding of estuary biogeochemistry and the resulting ecological response. In this paper we use the case study of Holes Bay, Poole Harbour to explore how palaeoenvironmental archives can be used to extend the evidence base for sediment, nutrient and ecological management within a coastal MPA.
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IntroductionIslands of the Southwest Pacific are exposed to geologic and climate-related disturbances that occur on a range of timescales and which probably affect, to varying degrees, their terrestrial ecosystems. Over the past ∼1100... more
IntroductionIslands of the Southwest Pacific are exposed to geologic and climate-related disturbances that occur on a range of timescales and which probably affect, to varying degrees, their terrestrial ecosystems. Over the past ∼1100 years we know of two major events in the region: the Kuwae eruption which is thought to have occurred ∼500 cal. years BP and a shift to drier conditions which began ∼1100 cal. years BP.MethodsWe investigated terrestrial and lacustrine ecosystem responses to these events and also to a changing fire regime, likely human-caused, using a multi-proxy (C/N, charcoal, chironomids, pollen, and tephra) record from Lake Emaotul, Efate, Vanuatu.ResultsTephra from the Kuwae eruption was found across a 6 cm layer which our age-depth model suggests was deposited 650–510 cal. years BP (95% confidence). Forest and chironomid community turnover increased during the wet-dry shift 1100–1000 cal. years BP; subsequently, chironomid turnover rates decreased again within <...
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Researchers have previously demonstrated correlations between seismic signals and fluvial processes (in particular discharge and bedload transport). This is an attractive finding because it suggests the possibility of an unobtrusive... more
Researchers have previously demonstrated correlations between seismic signals and fluvial processes (in particular discharge and bedload transport). This is an attractive finding because it suggests the possibility of an unobtrusive method to measure bedload transport. However, the range of rivers where this might work, the way in which seismic data might vary with channel type, and the strengths of any correlations between fluvial processes and seismic data are still unknown. We collected three sets of seismic data over 6 months adjacent to two different rivers (Trout Beck, a bedrock‐alluvial channel; and Bury Green Brook, an alluvial channel), along with concurrent discharge and bedload data. Initial analysis of the data suggests that the best correlation between seismic data and fluvial processes occurs in Trout Beck (seismometer TBU), where the seismometer was closely coupled to the bedrock that comprised the river channel. We identify dominant signals at 12 and 21 Hz; however, ...
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Small, 1st and 2nd -order, headwater streams and ponds play essential roles in providing natural flood control, trapping sediments and contaminants, retaining nutrients, and maintaining biological diversity, which extend into downstream... more
Small, 1st and 2nd -order, headwater streams and ponds play essential roles in providing natural flood control, trapping sediments and contaminants, retaining nutrients, and maintaining biological diversity, which extend into downstream reaches, lakes and estuaries. However, the large geographic extent and high connectivity of these small water bodies with the surrounding terrestrial ecosystem makes them particularly vulnerable to growing land-use pressures and environmental change. The greatest pressure on the physical processes in these waters has been their extension and modification for agricultural and forestry drainage, resulting in highly modified discharge and temperature regimes that have implications for flood and drought control further downstream. The extensive length of the small stream network exposes rivers to a wide range of inputs, including nutrients, pesticides, heavy metals, sediment and emerging contaminants. Small water bodies have also been affected by invasio...
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Within forested floodplains geomorphological processes are strongly modified by live and dead vegetation. However, interactions between the vegetation, water and sediments are poorly understood. Observations made along semi-natural rivers... more
Within forested floodplains geomorphological processes are strongly modified by live and dead vegetation. However, interactions between the vegetation, water and sediments are poorly understood. Observations made along semi-natural rivers in the New Forest, UK suggest the presence of particular suites of landforms on the floodplain that owe their formation to such interactions. For example extensive networks of floodplain channels and
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1.1 The Quantifiable Continuum of Uncertainty. Notice that once uncertainties are acknowledged as unquantified uncertainties, increased knowledge about the uncertainties will determine their position on the continuum.. .. .. 11 1.2... more
1.1 The Quantifiable Continuum of Uncertainty. Notice that once uncertainties are acknowledged as unquantified uncertainties, increased knowledge about the uncertainties will determine their position on the continuum.. .. .. 11 1.2 Typology for sources and degree of uncertainty. Adapted from Van Asselt's (2000) proposed typology for uncertainties in integrated assessment.. .. 12 1.3 Some potential relationships between knowledge and uncertainty through time. Contrary to the argument of the positivist, no unique inverse relationship between uncertainty and knowledge exists. See Section ref{TYPOLOGYSEC 15 1.6 Five Philosophical Attitudes Towards Uncertainty. The Venn diagram is meant to illustrate the overlap between contemporary attitudes towards uncertainty. Note that ignoring uncertainty, shares no overlap with contemporary attitudes towards uncertainty.. 1.8 Cope With Uncertainty Strategy. The reductionist view of coping with individual sources of uncertainty. The end result of this strategy is always to cope with uncertainty. In terms of river management and restoration applications, applying the precautionary principle allows decisions to be made in the face of uncertainty and adaptive management allows iterative 2.1 Premise of Reducible Ignorance in Embracing Uncertainty Framework Context. The limited knowledge within the restoration community about uncertainties is highlighted here as reducible ignorance, which could be reduced through further research and education. The grayed out areas are the linkages to the rest of the 'embracing uncertainty' framework (see Figure 1.
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The Hawaiian Islands have a long history of destructive and deadly tsunamis from both distant and local sources. Gaining a more detailed understanding of the historical record of tsunami impacts is a key step in reducing the vulnerability... more
The Hawaiian Islands have a long history of destructive and deadly tsunamis from both distant and local sources. Gaining a more detailed understanding of the historical record of tsunami impacts is a key step in reducing the vulnerability of coastal communities to tsunami inundation. This paper explores the history and prehistory of tsunamis in the Hawaiian archipelago, while proposing methods to narrow the gaps in our current understanding of their impacts. Future strategies to reduce risk and improve resilience to tsunami flooding are also discussed and evaluated.
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This paper introduces a novel method for modelling the influence of likely autonomous sailing craft failure conditions into the route planning algorithm. The accuracy of the original route planning algorithm is quantified using numerical... more
This paper introduces a novel method for modelling the influence of likely autonomous sailing craft failure conditions into the route planning algorithm. The accuracy of the original route planning algorithm is quantified using numerical error estimation techniques. It was found that over the course of a Trans Atlantic voyage a grid size of 36 km produced an error of +/- 2 hours over the course of a $36.5$ day voyage. The implementation of the failure model within the routing algorithm is verified using a control weather scenario. This verification is shown to be significant with respect to the method's numerical error. Future work will involve gathering evidence on failure criteria in order to update the failure model.
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Data contains information on membrane thickness, membrane quotient, membrane porosity and membrane permeability of eggs of 5 populations of Atlantic salmon. Additional data is presented on oxygen requirements derived from the application... more
Data contains information on membrane thickness, membrane quotient, membrane porosity and membrane permeability of eggs of 5 populations of Atlantic salmon. Additional data is presented on oxygen requirements derived from the application of the mass transfer theory.Document contains data relating to below linked thesis and paper entitled: "Variation in egg structure among five populations of Atlantic salmon (Salmo salar) influences their survival in low oxygen conditions" to be published in the journal Royal Society Open Science.Information on method of data collection and calculation is available at: https://eprints.soton.ac.uk/id/eprint/413854
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The critical shear stress (τc) for grain entrainment is a poorly constrained control on bedload transport rates in rivers. Direct calculations of τc have been hindered by the inability to measure the geometry of in situ grains; i.e., the... more
The critical shear stress (τc) for grain entrainment is a poorly constrained control on bedload transport rates in rivers. Direct calculations of τc have been hindered by the inability to measure the geometry of in situ grains; i.e., the shape and location of each grain relative to surrounding grains and the bed surface. We present the first complete suite of three-dimensional (3-D) grain geometry parameters for 1055 water-worked grains, and use these to parameterize a new 3-D grain entrainment model and hence estimate τc. The 3-D data were collected using X-ray computed tomography scanning of sediment samples extracted from a prototype scale flume experiment. We find that (1) parameters including pivot angle and proportional grain exposure do not vary systematically with relative grain size; (2) τc is primarily controlled by grain protrusion, not pivot angle; and (3) larger grains experience larger forces as a result of projecting higher into the flow profile, producing equal mobil...