pinecone/core-2020-05-10-deduplication huggingface dataset:
Dynamics of suspended sediment transport and yield in a large agricultural catchment, southwest France

The dynamics of suspended sediment transport were monitored continuously in a large agricultural catchment in southwest France from January 2007 to March 2009. The objective of this paper is to analyse the temporal variability in suspended sediment transport and yield in that catchment. Analyses were also undertaken to assess the relationships between precipitation, discharge and suspended sediment transport, and to interpret sediment delivery processes using suspended sediment-discharge hysteresis patterns. During the study period, we analysed 17 fl ood events, with high resolution suspended sediment data derived from continuous turbidity and automatic sampling. The results revealed strong seasonal, annual and inter-annual variability in suspended sediment transport. Sediment was strongly transported during spring, when frequent fl ood events of high magnitude and intensity occurred. Annual sediment transport in 2007 yielded 16 614 tonnes, representing 15 t km−2 (85% of annual load transport during fl oods for 16% of annual duration), while the 2008 sediment yield was 77 960 tonnes, representing 70 t km−2 (95% of annual load transport during fl oods for 20% of annual duration). Analysis of the relationships between precipitation, discharge and suspended sediment transport showed that there were signifi cant correlations between total precipitation, peak discharge, total water yield, fl ood intensity and sediment variables during the fl ood events, but no relationship with antecedent conditions. Flood events were classifi ed in relation to suspended sediment concentration (SSC)–discharge hysteretic loops, complemented with temporal dynamics of SSC–discharge ranges during rising and falling fl ow. The hysteretic shapes obtained for all flood events refl ected the distribution of probable sediment sources throughout the catchment. Regarding the sediment transport during all fl ood events, clockwise hysteretic loops represented 68% from river deposited sediments and nearby source areas, anticlockwise 29% from distant source areas, and simultaneity of SSC and discharge 3%
Landscape-scale controls on the spatial distribution of caesium 137: a study based on an airborne geophysical survey across Northern Ireland

The spatial distribution of 137Cs across the landscape and the processes controlling its redistribution are of interest because (i) 137Cs has been widely used to quantify the movement of soil and sediments and (ii) substantial fallout of 137Cs after the Chernobyl accident has led to contamination of foodstuffs in some places. A high-resolution airborne geophysical radiometric survey of Northern Ireland has provided an opportunity to study the distribution and possible redistribution of 137Cs.\ud
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The 137Cs activity (recorded at 1·2 million points) is distributed in a series of bands oriented approximately 160° and 115° clockwise from north. Geostatistical analysis of the data shows a strong, short-range structure (correlation ranges between 0·6 and 8 km) in 137Cs activity across the vast majority of the region; the spatial distribution shows association with a published, coarse-scale depositional pattern of 137Cs from Chernobyl. Two indices of land form derived from a digital elevation model, namely compound topographic index and the length–slope factor of the Revised Universal Soil Loss Equation, account for only 3% of the variance in 137Cs activity. In contrast, soil type and land cover in combination (including their interaction) account for 20% of the variance. In areas that received moderate fallout from Chernobyl, soil type alone accounts for a substantial proportion of the spatially correlated 137Cs activity. We attribute this to each soil type having a fairly uniform radiocaesium interception potential that differs from those of other soil types and that this potential controls the vertical migration of 137Cs. Over the granitic Mourne Mountains there is a strong spatial cross-correlation between 137Cs activity and airborne estimates of soil potassium, suggesting that the latter provides a measure of the soil's radiocaesium interception potential; this is probably dominated by the quantity of the mineral illite\u
Turbulent shear stresses in hydraulic jumps, bores and decelerating surges

In an open channel, a sudden rise in water level induces a positive surge, or bore, that may develop as a hydraulic jump in translation. When the surge propagates against an adverse slope, it decelerates until it becomes a stationary hydraulic jump. Both hydraulic jumps and decelerating surges induce some intense turbulent mixing and have some major impact on the sediment transport in natural systems. Herein, a physical investigation was conducted in a relatively large rectangular channel. Hydraulic jumps and surges were generated by the rapid closure of a gate at the channel downstream end. The turbulent shear stresses were measured with high temporal and spatial resolution (200 Hz sampling rate) in the jump flow. A comparison between the stationary hydraulic jump, hydraulic jump in translation and decelerating surge measurements showed some marked differences in terms of turbulent mixing. The results highlighted some intense mixing beneath the jump front and roller for all configurations. The levels of turbulent stresses were one to two orders of magnitude larger than a critical threshold for sediment motion. The findings provide some insights into the hydraulic jump migration processes in mobile bed channels, and the complex transformation from a moving jump into a stationary jump. Copyright (C) 2010 John Wiley & Sons, Ltd
Evolution of vegetation activity on vegetated, eroded, and erosion risk areas in the central Spanish Pyrenees, using multitemporal Landsat imagery

11 páginas, 4 tablas, 4 figuras.-- El Pdf es la versión pre-print.The temporal evolution of vegetation activity on various land cover classes in the Spanish Pyrenees was analyzed. Two time series of the normalized difference vegetation index (NDVI) were used, corresponding to March (early spring) and August (the end of summer). The series were generated from Landsat TM and Landsat ETM+ images for the period 1984–2007. An increase in the NDVI in March was found for vegetated areas, and the opposite trend was found in both March and August for degraded areas (badlands and erosion risk areas). The rise in minimum temperature and the time variation of the cloud cover during the study period appears to be the most important factors explaining increased NDVI in the vegetated areas. In degraded areas, no climatic or topographic variable was associated with the negative NDVI trend, which may be related to erosion processes taking place in these regions.This research was supported by the projects CGL2006-11619/HID, CGL2008-\ud
00831/BTE and CGL2008-01189/BTE (Spanish Commission of Science and Technology\ud
and FEDER), ACQWA (FP7-ENV-2007-1- 212250; VII Framework Program of the\ud
European Commission), ‘Las sequías climáticas en la cuenca del Ebro y su respuesta\ud
hidrológica’ (‘Obra Social La Caixa’ and the Aragón Government), and ‘Programa de\ud
grupos de investigación consolidados’ (Aragón Government). The first author was\ud
supported by a scholarship from The National Council for Science and Technology of\ud
Mexico (CONACYT).Peer reviewe
Thresholds for morphological changes on an exposed sandy beach as a function of wave height

A sandy beach in the south of Portugal (Faro beach, Ria Formosa) was surveyed from the dune crest seaward to 15 m
depth 20 times over a period of 26 months.Wave time-series between surveys were analysed to obtain relationships between wave
height and vertical profile variations and to define wave thresholds for important morphological changes. Results show that the
active zone of the profile lies between 5 m above and 10·4 m below mean sea level, and that there are clear cross-shore differences
in the vertical variability of the profile. Based on the pattern of vertical variability, the profile was divided into four cross-shore
sectors: A (berm), 20–80 m from the profile origin; B (sub-tidal terrace), 80–170 m; C (long-shore bar), 170–360 m; and D,
360–700 m. The relationship between the modulus of the maximum vertical change in each sector and the 99th percentile of
significant wave height between surveys was always significant. Calculated thresholds for significant wave height generating
important morphological changes were 2·3 m in sector A, 3·2 m in sectors B and C, and 4·1 m in sector D.info:eu-repo/semantics/publishedVersio
The spatial variation of weathering and soil depth across a Triassic sandstone outcrop

In this study, we used an archive of borehole logs from the British Geological Survey to collect information on the spatial structure of weathering that extends from the surface to competent bedrock across the Triassic Sherwood Sandstone Group outcrop (750 km2), in the East Midlands, UK. The borehole logs were used to estimate the thickness of the soil (n = 280) and soil and saprolite (S&S) to competent rock (n = 500). The weathering profile of the sandstone consisted of soil (median thickness ∼ 1·5 m) overlying a transition zone of compacted and weakly cemented weathered sandstone saprolite over bedrock. Topographic analysis using a NEXTMAP 5 m × 5 m digital elevation model (DEM) revealed no significant relationships between slope properties (relief, flow length, flow accumulation or slope angle) and soil or S&S thickness. A weak, but statistically significant correlation was found between the thickness of the soil and S&S (rs = 0·25, p < 0·001, n = 192). The variation in soil thickness may be related to changes in current and historic and land-use, variation in sandstone properties and the influence of glacial/peri-glacial processes. The thickness of the saprolite was more variable towards the southern part of the study area, where it increased to a maximum 40 m. We hypothesize and provide evidence that the greater weathering thickness is related to the occurrence of increased faulting in this part of the study region, allowing increased access to meteoric waters. A possible source of increased water supply is meltwater from Quaternary ice sheets; the overburden of ice may have increased sub-glacial pore water pressure, with the fractures and faults acting as a drainage system for the removal of dissolved weathering product
Evaluation of the controls affecting the quality of spatial data derived from historical aerial photographs

This article was published in the journal, Earth Surface Processes and Landforms [© John Wiley & Sons, Ltd.] and the definitive version is available at: http://dx.doi.org/10.1002/esp.2111This paper is concerned with the fundamental controls affecting the quality of data derived from historical aerial photographs typically used in geomorphological studies. A short review is provided of error sources introduced into the photogrammetric workflow. Data-sets from two case-studies provided a variety of source data and hence a good opportunity to evaluate the influence of the quality of archival material on the accuracy of coordinated points. Based on the statistical weights assigned to the measurements, precision of the data was estimated a priori, while residuals of independent checkpoints provided an a posteriori measure of data accuracy. Systematic discrepancies between the two values indicated that the routinely used stochastic model was incorrect and overoptimistic. Optimized weighting factors appeared significantly larger than previously used (and accepted) values. A test of repeat measurements explained the large uncertainties associated with the use of natural objects for ground control. This showed that the random errors not only appeared to be much larger than values accepted for appropriately controlled and targeted photogrammetric networks, but also small undetected gross errors were induced through the ‘misidentification’ of points. It is suggested that the effects of such ‘misidentifications’ should be reflected in the stochastic model through selection of more realistic weighting factors of both image and ground measurements. Using the optimized weighting factors, the accuracy of derived data can now be more truly estimated, allowing the suitability of the imagery to be judged before purchase and processing
Lateral plucking as a mechanism for elongate erosional glacial bedforms : explaining megagrooves in Britain and Canada

Megagrooves are kilometre-scale linear topographic lows carved in bedrock, separated by ridges, typically in areas of largely devoid of till.  They have been reported from several areas covered by Pleistocene glaciations, such as Canadian NW Territories, Michigan and NW Scotland. Here we report two previously undocumented megagroove fields from Ungava, Canada, and northern England, and present new analyses of the megagrooves from NW Scotland.  This paper seeks to determine the nature of the lithological and structural controls on the occurrence and formation of megagrooves.  Analysis of both geomorphological and bedrock properties shows that megagrooves are generally:\ud
a)	confined to well stratified or layered bedrock, such as (meta)sedimentary rocks with closely spaced joints, and tend not to occur on massive rocks such as gneiss or granite, or thick-bedded sedimentary rocks;\ud
b)	subparallel to palaeo-ice flow and the strike of the strata; and tend not to occur where palaeo-ice flow is at high angles to the strike of strata; \ud
c)	produced by significant glacial erosion by sustained unidirectional ice flow.\ud
Detailed analysis of megagrooves in NW Scotland shows that neither glacio-fluvial erosion, nor differential abrasion was the dominant mechanism of formation.   A mechanism, here termed ‘lateral plucking’, is suggested that involves block plucking on rock steps parallel to ice flow.  Removal of joint-bounded blocks from such rock steps involves a component of rotation along a vertical axis. Block removal may be enhanced by a direct component of shear stress onto the vertical stoss sides. The lateral plucking mechanism results in horizontal erosion at right angles to the ice flow, and enhances the groove/ridge topography.  Megagrooves are potentially useful as palaeo-ice flow indicators in areas devoid of till, and can thus complement the palaeo-ice stream datasets which are presently largely based on soft-sediment landform studies.  \u
Increase in coarse sediment transport associated with disturbance of gravel river beds by signal crayfish (Pacifastacus leniusculus)

This article was submitted for publication in the journal, Earth Surface Processes and Landforms [© John Wiley & Sons, Ltd.] and the definitive version is available at: http://dx.doi.org/10.1002/esp.2192There is growing acknowledgement of the interaction between animals and the river bed on which they live and the implications of biological activity for geomorphic processes. It has been observed that signal crayfish (Pacifastacus leniusculus) disturb gravel substrates, potentially promoting sediment transport and impacting ecological communities. However, the mechanisms involved and the extent of their impact remain poorly understood, especially in relation to other processes that affect grain mobility in gravel-bed rivers. A series of flume experiments, using loose and water-worked gravel beds of narrowly graded grain sizes that were exposed to 6 h of crayfish activity under low-velocity flows, showed a substantial increase in the number of grains entrained by subsequent higher-velocity flows when compared with control runs in which crayfish were never introduced. Crayfish alter the topography of their substrate by constructing pits and mounds, which affect grain protrusion. When walking and foraging, they also alter gravel fabric by reorienting and changing the friction angle of surface grains. In water-worked surfaces, this fabric rearrangement is shown to lead to a statistically significant, partial reversal of the structuring that had been achieved by antecedent flow. For these previously water-worked surfaces, the increase in entrainment arising from disturbance by crayfish was statistically significant, with grain transport nearly twice as great. This suggests that signal crayfish, an increasingly widespread invasive species in temperate latitudes beyond their native NW North America, have the potential to enhance coarse-grained bedload flux by altering the surface structure of gravel river beds and reducing the stability of surface grains. This study illustrates further the importance of acknowledging the impact of mobile organisms in conditioning the river bed when assessing sediment entrainment mechanics in the context of predicting bedload flux
Impact of subsurface rock fragments on runoff and interrill soil loss from cultivated soils

Field and laboratory studies have indicated that rock fragments in the topsoil may have a large impact on soil properties, soil quality, hydraulic, hydrological and erosion processes. In most studies, the investigated rock fragments still remain visible at the soil surface and only properties of these visible rock fragments are used for predicting runoff and soil loss. However, there are indications that rock fragments completely incorporated in the topsoil could also significantly influence the percolation and water distribution in stony soils and therefore, also infiltration, runoff and soil loss rates. Therefore, in this study interrill laboratory experiments with simulated rainfall during 60 min were conducted to assess the influence of subsurface rock fragments, incorporated in a disturbed silt loam soil at different depths below the soil surface (i.e. 0.001, 0.01, 0.05 and 0.10 m), on infiltration, surface runoff and interrill erosion processes for small and large rock fragment sizes (i.e. mean largest diameter equals 0.04 and 0.20 m, respectively). Although only small differences in infiltration rate and runoff volume are observed between the soil without rock fragments (control) and the one with subsurface rock fragments, considerable differences in total interrill soil loss are observed between the control treatment and both contrasting rock fragments sizes. This is explained by a rapid increase in soil moisture in the areas above the rock fragments and therefore a decrease in topsoil cohesion compared to a control soil profile. The observed differences in runoff volume and interrill soil loss between the control plots and those with subsurface rock fragments is largest after a cumulative rainfall (Pcum) of 11 mm and progressively decreases with increasing Pcum. The results highlight the impacts and complexity of subsurface rock fragments on the production of runoff volume and soil loss and calls for attention in process-based runoff and erosion models.Peer reviewe
Morphological change of natural pipe outlets in blanket peat

Peatlands are important carbon stores and many have natural pipes (tunnels) that transport water and carbon. Pipes are often viewed as passive and slowly changing features of peatland landscapes, particularly for sites that are relatively undisturbed by land management. However, there is a lack of data on pipe morphology change over time. This paper presents the first survey of natural pipe outlets in a peatland in which morphological changes in pipe outlets through time were measured. Three surveys of natural pipe outlets between 2007 and 2010 were conducted in a 17.4 ha, relatively undisturbed, blanket-peat-covered catchment in northern England. 27 of the 91 pipe outlets mapped in the first survey had perennial discharge and these outlets were significantly larger and shallower than those from ephemerally-flowing pipes. The cross-sectional area of 85% of pipe outlets changed (increased or decreased) during the study, with 20% of pipe outlet areas changing by more than 50 cm2 (equivalent to a median 207 % change in area for this upper fifth of pipes) up to a maximum of 312cm2 for one pipe outlet. During the study, 18 pipe outlets completely infilled, while four new ones appeared. Mean pipe outlet area increased between August 2007 and July 2009 but decreased from July 2009 to April 2010. The largest changes in pipe morphology occurred between July 2009 and April 2010, which spanned the coldest winter for 31 years in the UK. During this period there was a significant increase in the proportion of vertically-elongated pipes and a decrease in the proportion of circular pipes. Pipe outlet morphology in blanket peat catchments is shown to be dynamic and may respond relatively quickly to changes in flow or extreme events, linked to short-term changes in weather and hence\ud
potentially to longer-term changes in climate or land management
Beach erosion and recovery during consecutive storms at a steep-sloping, meso-tidal beach

This study analyses beach morphological change during six consecutive storms acting on the meso-tidal Faro Beach
(south Portugal) between 15 December 2009 and 7 January 2010. Morphological change of the sub-aerial beach profile was monitored
through frequent topographic surveys across 11 transects. Measurements of the surf/swash zone dimensions, nearshore bar dynamics,
and wave run-up were extracted from time averaged and timestack coastal images, and wave and tidal data were obtained
from offshore stations. All the information combined suggests that during consecutive storm events, the antecedent morphological
state can initially be the dominant controlling factor of beach response; while the hydrodynamic forcing, and especially the tide
and surge levels, become more important during the later stages of a storm period. The dataset also reveals the dynamic nature of
steep-sloping beaches, since sub-aerial beach volume reductions up to 30m3/m were followed by intertidal area recovery (–2<z
3m) with rates reaching ~10m3/m. However, the observed cumulative dune erosion and profile pivoting imply that storms, even
of regular intensity, can have a dramatic impact when they occur in groups. Nearshore bars seemed to respond to temporal scales
more related to storm sequences than to individual events. The formation of a prominent crescentic offshore bar at ~200m from
the shoreline appeared to reverse the previous offshore migration trend of the inner bar, which was gradually shifted close to the seaward
swash zone boundary. The partially understood nearshore bar processes appeared to be critical for storm wave attenuation in
the surf zone; and were considered mainly responsible for the poor interpretation of the observed beach behaviour on the grounds of
standard, non-dimensional, morphological parameters.202798info:eu-repo/semantics/publishedVersio
A simple model for the formation of vegetated dunes

A simple model for the dynamics of dunes associated with vegetation is
proposed. Using the model, formation processes of transverse dunes, parabolic
dunes and elongated parabolic dunes according to two environmental factors:
i)the amount of sand at the source, ii)the wind force, are simulated. The
results have qualitative correspondence to the real counterpart, and the
simplicity of the algorithm and the consequent easiness of the handling of this
model provide us with wide applicability for the investigation of the complex
interplay between vegetation and dunes.Comment: 4 figure