bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of forest land management on erosion and revegetation after the eruption of Mount St. Helens
Authors: Collins Brian D. , Dunne Thomas
Published: February 2007

The 1980 eruption of Mount St. Helens covered soils with a tephra blanket and killed the forest tree cover in a 550 km2 area. After the eruption, rates of sheetwash and rill erosion, and plant cover were measured on tephra‐covered hillslopes which had been subject to three land‐management practices: grass seeding; scarification, and salvage logging. On rapidly‐eroding hillslopes subject to grass seeding, limited plant covers were established only after erosion had declined sharply. Logging of trees downed by the eruption and scarification of previously logged surfaces slowed erosion, although the effect was small because erosion rates had already slowed substantially by the time these two practices were implemented. The factors controlling erosion, revegetation, and their relative timing at Mount St. Helens are similar to those following explosive volcanic eruptions elsewhere, suggesting that grass seeding is not likely to be effective at slowing erosion following most tephra eruptions, and that early mechanical disturbance could be an effective erosion‐control measure. The results also indicate that even without deliberate conservation measures, processes which mechanically disturb a surface layer of low hydraulic conductivity (such as frost‐action or trampling) can radically reduce runoff and erosion before revegetation has an important effect.
Threshold relations for the transport of sediment by overland flow on desert hillslopes
Authors: Abrahams Athol D. , Luk Shiu‐Hung , Parsons Anthony J.
Published: February 2007

Although the Shields relation was developed for rivers, it has been applied to sediment transport by overland flow. According to the Shields relation, where the critical boundary Reynolds number Re*c exceeds 40, the critical Shields number F*c is independent of both Re*c and the ratio of the critical flow depth to particle diameter dc/D. Analyses of data collected from runoff plots in southern Arizona reveal that F*c is positively correlated with both Re*c and dc/D. Thus the Shields relation does not apply to overland flow on debris‐covered desert hillslopes.

Multiple regression analysis is employed to develop alternative threshold relations in which critical boundary shear stress τc is related to D and dc/D (R2 = 0.782) and to D and Sc (critical gradient) (R2 = 0.625). The computed R2 values derive in large part from the spurious correlations of dc/D and Sc with τc. Nevertheless, the relations may be utilized to predict τc. In this regard, the latter relation is likely to prove more useful than the former because Sc is generally known, whereas dc is not.

An investigation of the functional relation between τc and D reveals that τc varies approximately with D2 for overland flow on the desert hillslopes under study, whereas the Shields relation predicts a linear relation (i.e. a D exponent of 1). This result is consistent with Cheng's data which show that F*c varies with (dc/D)−1 where 0.4 < dc/D < 2 and may be explained in terms of increased energy dissipation both in separation zones downslope of particles and in distortion of the water surface as dc/D decreases. Consequently, larger values of τc, and hence F*c, are required to initiate the transport of particles of a given size D as dc decreases.
Dimension and entropy in the soil‐covered landscape
Authors: Culling W. E. H.
Published: February 2007

Both the Hausdorff dimension and the K‐entropy supply a measure of the irregularity of the landspace surface. The relationship between the two measures is investigated over a variety of terrains in Britain and a method of calculating the entropy is checked against an independent estimate of the dimension with reasonable agreement. The calculation of the K‐entropy requires that the landscape surface be represented by an homogenous ergodic random field. This condition is satisfied by the tendency of soil‐covered terrains to progressively approximate to a form well represented by a Gaussian field.

Gaussian random fields can either be very smooth, possessing derivatives of all orders at every point or they are highly irregular and non‐differentiable everywhere. Within the regular conceptualization the Rice‐Kac theory is used to predict the numbers of crossing points and the extent of excursion sets. These predictions are tested against an example terrain from the High Weald of East Sussex with very good agreement, apart from predictions of local maxima. A worked example of the calculation of the K‐entropy is given as an appendix.

The potential role of information theory in geomorphology extends beyond the use made of entropy in this investigation. In particular ergodic theory has important practical and theoretical implications.
Failure and flow on a 35° slope: Causes and three‐dimensional observations
Authors: Dowdeswell Julian A. , Lamb Henry F. , Lewin John
Published: February 2007

A well‐vegetated 35° slope in upland Wales, U.K., failed during a winter flood event. Failure was linked to high magnitude rainfall and diversion of flowing water onto the slope. Mass movement began with gravitational slumping, which was transformed rapidly into a debris flow. Three‐dimensional characteristics of the active debris flow are reconstructed from mudlines on 58 trees still standing in the flow path. Mudline formation only on the up‐flow side of trees indicates the relatively high viscosity of the debris flow. Mudline height is a function of the maximum thickness and velocity of the flow at any tree.
Mechanisms associated with the erosion of sand dune cliffs, Magilligan, Northern Ireland
Authors: Carter R. W. G. , Stone Gregory W.
Published: February 2007

A fifteen year history of coastal dune recession at Magilligan, Northern Ireland has revealed both time and space contrasts in processes and morphology. Since 1968 ‘storm’ frequency has increased, while dune retreat reached a peak (5·4 m) in 1978–1979. Three types of dune eroding events are noted, resulting from particular wave/wind/tide combinations. The spatial variability in dune scarping is associated with vegetation and soil development, and slope failures range from granular avalanches to retrogressive rotational slumps.
A comment on ‘a note on the characteristics and possible origins of desert varnishes from Southeast Morocco’ by Drs. Smith and Whalley
Authors: Dorn Ronald I.
Published: February 2007

This note queries the discussion of the origins of ‘desert varnishes’ (Smith and Whalley, 1988), with particular reference to manganese‐rich conditions. The case for a biotic model of varnish development is proposed and illustrated as opposed to the abiotic model put forward by Smith and Whalley.
A note on the characteristics and possible origins of desert varnishes from Southeast Morocco. A reply to comments by R. I. Dorn
Authors: Smith B. J. , Whalley W. B.
Published: February 2007

This reply to Dorn (1989) argues that a biotic origin is not the only way in which desert varnishes may be formed. It is suggested that a variety of initial conditions may result in similar end products. It is agreed that the dissimilar views of the authors may result from their different philosophies concerning the classification of Mn/Fe varnishes.
Aeolian sand drift from the intertidal zone on a temperate beach: Potential and actual rates
Authors: Sarre Robert D.
Published: February 2007

This paper compares the amount of sand that is potentially moved into a coastal dune system from a beach using estimates based solely on the wind force, with actual measured amounts. The actual sand inputs are determined by measuring sand level changes each month over a period of eighteen months, along a 1760‐m section of foredune on Braunton Burrows, Southwest England. The calculation procedure used to estimate the potential rates of sand drift is based on the capacity of the wind force to transport sand using a published transport equation (White, 1979). The results show that the actual movement rates are markedly smaller than the potential rates for all months except in the summer. Meteorological variables and the watertable level in the adjacent dune system are used in an empirically derived regression equation in an attempt to explain the large discrepancy between the potential and actual movement rates. The resulting corrected potential movement rates are a closer estimate to the actual rates, but there remains much unexplained variance.
Fractal techniques and the surface roughness of talus slopes: Reply
Authors: Andrle Robert , Abrahams Athol D.
Published: February 2007

There is discussion of the role of the self similar fractal model (SSFM) as a dominant paradigm in geomorphology; and how it may be applied appropriately. There is also a difference in the interpretation of curvature in logarithmic plots of step length vs total number of steps. Thirdly there is disagreement about interpreting application of the model to the talus clast transects; and finally on the significance of the dimensions obtained (D < 1·27) along the transects.
Hillslope erosion by rainstorms–a magnitude‐frequency analysis
Authors: De Ploey Jan , Kirkby Michael J. , Ahnert Frank
Published: February 2007

Daily rainfall data for four stations in Europe and east Africa are used to obtain, by means of magnitude‐frequency analysis, a measure of the Cumulative Erosion Potential (CEP) that takes into account rainfall characteristics, soil water storage, and granulometric properties of soils. The CEP has the advantage of being calculated from generally available published rainfall data, so that wide regional coverage is possible. Together with additional data on the surface configuration and on seasonal variations of rainfall and plant cover, the CEP can provide a basis for estimating hillslope erosion by overland flow.
Rock resistance to erosion: Some further considerations
Authors: Augustinus Paul C.
Published: February 2007

Rock resistance to erosion is an often described factor in geomorphic studies, and is generally considered to strongly influence the shape of erosional landforms. However, the property of the rock mass that enables it to resist erosion is rarely considered, and its measurement is rarely justified and assessed adequately. Allison (1988, 1990) examined the intact strength properties of several types of carbonate rocks and considered that dynamic Young's modulus is a good indicator of rock material strength for geomorphic purposes, and cast doubts on the reliability of Schmidt hammer tests for this purpose. Alternative approaches to rock characterization from the view point of evaluating rock intact strength are considered.
Test of Hack's slope to bed material relationship in the Southern Eifel Uplands, Germany
Authors: Schröuder Rolf
Published: February 2007

The local reach gradient of small gravel bed rivers (drainage area 0‐8‐110 km2) in the Eifel, West Germany, is adjusted to transport the river bed sediments. Transport of gravel becomes possible under high flow conditions (Shields entrainment factor ≈‐03).

Mean bed material size for riffle sections increases with distance downstream. For small drainage areas channel slope is a negative exponential function of drainage area, while for the larger region the additional influence of bedload size has to be considered.

Good agreement with Hack's data (1957) for Virginia and Maryland, U.S.A., is achieved (S = 0.0066 (D50/A)‐ 40., r = 0.67).
The evolution of tidal creek networks, mary river, northern Australia
Authors: Knighton A. David , Woodroffe Colin D. , Mills Kevin
Published: February 2007

Tidal creek networks have in 50 years extended over 30 km inland across the coastal plains of the Mary River in northern Australia, invading freshwater wetlands and destroying the associated vegetation. The networks have grown at an exponential rate through a combination of main channel extension and tributary development, with concomitant widening of the creeks. A large tidal range, very small elevational differences over the plains, and the availability of preexisting channel lines (notably in the form of palaeochannels) have been major factors contributing to the rapid rate of expansion.

Close parallels exist between these networks and terrestrial networks as regards modes of growth and planimetric properties. A channel is initiated when the diffuse flow of a seepage zone becomes concentrated through localized scour. Subsequent development is characterized by the rapid extension of long first‐order channels, with most tributary addition occurring later. Model tests suggest that branching was more likely on exterior links in the early stages but that exterior and interior link branching became more equally likely through time. Although the headward limits of the main creeks seem to have been reached, tributary infilling will continue to progress upstream. Only in the most downstream parts is a stable drainage density being approached.

The networks not only satisfy the laws of drainage network composition and the basic postulates of the random model but also depart from topologic randomness in similar ways to terrestrial networks. Both topologic and length properties have changed during evolution but largely at the link rather than network scale. The close correspondence with terrestrial networks may be due to the low relief and the relatively unconstrained nature of growth in which availability of space was the main determining factor.
Burst‐like sediment suspension events in a sand bed river
Authors: Lapointe Michel
Published: February 2007

In a much quoted paper, Jackson (1976) hypothesized that turbulent [bursting] motions such as those documented in laboratory boundary layers play a major role in alluvial sediment suspension. To date, the hypothesis remained largely untested, due to difficulties in monitoring turbulent suspension in rivers. This study provides field data documenting burst‐like turbulent motions over a sandy bed channel and quantifying the role of these motions in sand suspension. The data were collected in a 10 m deep channel of the Fraser River near Mission, British Columbia, Canada. Turbulent fluctuations of both flow components, downstream and normal to the bed, along with the output of an optical suspended sediment sensor, were monitored 1 m above the river bed. Typical flow velocities averaged 0·9 ms−1 at the sensors, where mean suspended sediment concentrations were 500 mgl−1; decimetre height small dunes on the backs of larger, half‐metre amplitude dunes covered the channel bed in the area.

Brief but intense, burst‐like [ejection and inrush] events were identified in the flow records, where they are responsible for a high degree of [intermittency] in shear stress over the dunes: 80 per cent of the turbulent momentum exchange across the 1 m level can be ascribed to such brief (3‐8 s duration) events, active under 12 per cent of the time. In addition, the record of fluctuating sediment concentrations reveals these burst‐like motions to be highly effective in vertically mixing suspended sediment and thus, ultimately, in maintaining suspended sediment transport above the dune bed. The bulk (60 and 90 per cent in two deployments) of the vertical sediment mixing was accomplished by intense events active some 10 per cent of the time.

No discrete recurrence timescale for these ‘burst‐like’ mixing events is evident, however. Rather, a continuous variation of return periods was observed as a function of the magnitude of vertical mixing event considered. To that extent, conceptual models of sediment transport in terms of burst events with a predictable recurrence such as proposed by Jackson (1976) may be misleading.
Secondary flow in anabranch confluences of a braided, gravel‐bed stream
Authors: Ashmore P. E. , Ferguson R. I. , Prestegaard K. L. , Ashworth P. J. , Paola C.
Published: February 2007

Measurements of the primary and secondary velocity components were máde in two, active, braided river anabranch confluences with a simple Y‐shaped plan form, in the gravelly Sunwapta River (D50 of approximately 30 mm). Flow velocity was measured at regularly‐spaced intervals using a bidirectional electromagnetic current meter and the measured downstream and cross‐stream velocities were converted to primary and secondary velocities to yield the secondary circulation. The primary (downstream) velocity field shows two high velocity streams from the two tributaries which merge (and, in some cases, accelerate) into a single high velocity core over the thalweg. Primary flow velocity declines as the flow expands and diverges at the downstream end of the confluence.

The secondary circulation is dominated by two helical cells, back‐to‐back, plunging over the thalweg and diverging at the bed. This is the first confirmation of this flow structure in confluences, based on field measurements. The strength of the secondary cells declines downstream through each confluence, and laterally away from the thalweg area in cross‐section. There is also a tendency for one cell, from the larger of the tributaries, to override the other. The secondary and primary flow structure and strength differs slightly between the two confluences and this is reflected in differences in scour hole form.
The West Victorian Uplands of Southeastern Australia: Origin and history
Authors: Joyce E. B.
Published: February 2007

The West Victorian Uplands is a region of low relief, gentle gradients, young volcanicity and local domal uplift. These characteristics distinguish it from the rest of the Eastern Highlands of Australia. The origin of the West Victorian Uplands dates back to uplift in the Cretaceous, but elevation and relief have always remained low. Further uplift, extending westwards from central Victoria, may have begun raising the West Victorian Uplands in Middle Tertiary times. Doming, fault activity, earthquakes and volcanism are extending progressively westwards. Not only may the Eastern Highlands of Victoria have grown in this way in the past, but the area may also provide a view of the early evolution of the Eastern Highlands of Australia.
An experimental study of sapped drainage network development
Authors: Gomez Basil , Mullen Victor T.
Published: February 2007

In a basin developed on a stream table, effluent subsurface flow supported a channel network that evolved by a combination of headward growth, lateral widening and divide decay. The area occupied by the developing network increased with time. Circularity was used to characterize network evolution which occurred in three phases (initiation, extension and abstraction). Basin sediment discharge declined exponentially with time. Pronounced quasi‐cyclic variability was superimposed upon this general trend. Some of the variability was directly linked to changes in the amount of sediment supplied to the channel. The variation of mean network sediment yield (mean sediment discharge scaled by network area) with time adequately described the general decline in sediment discharge as the network evolved.
The variation of soil erodibility with slope position in a cultivated canadian prairie landscape
Authors: Martz Lawrence W.
Published: February 2007

This study examined the variation in soil erodibility along hillslopes in a Prairie landscape. The soil loss produced by simulated rainfall on undisturbed soils was used as an index of relative soil erodibility. Relative erodibility, and several soil properties, were measured at the summit, shoulder, midslope footslope and toeslope of 11 slope transects in an area of cultivated grassland soils on hummocky glacial till. The variation of erodibility with slope position was statistically significant, and slope position explained about 40 per cent of the variation in the erodibility measurements. Erodibility was 14 per cent higher on the shoulder and midslope, and 21 per cent lower on the toeslope, than on the summit and footslope. Local variation in erodibility along slopes was considered to be an important control on patterns of soil erosion in the landscape. The variation of erodibility along the slopes reflected soil property trends. The greatest erodibility was associated with upper slope positions where soils tended to be shallow, coarse, poorly leached and low in organic matter, while lower erodibility was found at lower slope positions with deep, organic‐rich and leached soils. Of the individual soil properties considered, silt and sand content were the most highly correlated with erodibility. The results, together with results from other studies, also suggest that net erosion and erodibility are positively related.
Mobilization of aluminium in the wathering profiles of the African surface in Malawi
Authors: McFarlane M. J. , Bowden D. J.
Published: February 2007

Leaching of aluminium from the weathering profile of the African surface in Malawi was deduced from the chemistry of a vadose profile. Its loss occurs where congruent kaolinite dissolution results in saprolite collapse, leaving a weakly lateritized, sandy residual mantle. This leaching is a contemporary process, as shown by the precipitation of aluminosilicate evaporites in the dambos (seasonally waterlogged bottomlands). This paper presents the results of determinations, by ICP‐OES and AAS‐graphite furnace, of aluminium levels in groundwaters, examining the effects of a variety of pretreatments. Filtration (0.45 μm) substantially reduces the levels of total aluminium, showing it to be in particulate form. Subsequent acidification causes precipitation of < 0.45 μm forms of aluminium, further reducing the apparent levels to below ICP‐OES detection limit. This is consistent with mobilization in organically bound forms which are destabilized at low pH, and accords with earlier work which showed that indigenous micro‐organisms can cause dissolution of kaolinite. Organically bound mobilization provides an explanation for aluminium leaching at near‐neutral pH in conjunction with the presence of silica in solution.

The identification of this mechanism of kaolinite dissolution and aluminium evacuation from vadose profiles provides a realistic process for the levelling of extensive planation surfaces; the contingent collapse of the kaolinized saprolite would lower the interfluves, progressively narrowing the vadose zone until the landsurface approaches the planar form of the stable, regional water‐table.
Analysis and interpretation of patterns within and between hydroclimatological time series in an alpine glacier basin
Authors: Gurnell A. M. , Clark M. J. , Hill C. T.
Published: February 2007

This paper explores patterns within and between climatological and hydrological time series from an alpine glacier basin. Time series recorded in the basin of the Haut Glacier d'Arolla over the 1989 ablation season are subdivided into five subperiods. Box‐Jenkins ARIMA (AutoRegressive Integrated Moving Average) and TFN (Transfer Function‐Noise) models are estimated for each of the five subperiods and differences between the models are interpreted in the context of changing glacier hydrology, particularly the changing nature and extent of the glacier drainage network.
Fan and playa areas in southern California and adjacent parts of Nevada
Authors: Jansson Peter , Jacobson Douglas , Le Hooke Roger B.
Published: February 2007

In bolsons in the desert regions of southern California and adjacent parts of Nevada, the area underlain by alluvial fan gravels and playa sediments is generally ˜1·2 times the area being eroded to produce those sediments. In certain larger basins in the vicinity of Death Valley, however, the depositional area is only about half the size of the erosional area. This reflects the more active tectonic environment in these bolsons.

Of the areas underlain by recent sediments in these bolsons, playas make up 2–6 per cent. Smaller playas are found in the Mojave region, and seem to be associated with sedimentary terranes. Conversely, igneous terranes support larger playas. Larger deviations of playa area from these averages are attributable to incorrect identification of bolson boundaries. Fine sediment is either able to pass through the bolson to the next down stream, or is being collected from areas upstream that were not considered to be part of the system. For example, the playa in Death Valley is unusually large. This is in part because the Death Valley playa has been deformed tectonically so parts of it are now eroding, and in part because the outlet of Lake Tecopa was downcut in the geologically recent past, so sediment once trapped there now reaches Death Valley. The size of the playa in Death Valley is still adjusting to these changes.
Physical modelling of gelifluction and frost creep: Some results of a large‐scale laboratory experiment
Authors: Harris Charles , Gallop Michael , Coutard Jean‐Pierre
Published: February 2007

An experimental slope was constructed in a 5 m × 5 m square refrigerated tank. The slope was formed of four sections, each consisting of regolith (soil) collected from a distinct bedrock lithology. The four lithologies utilized were granite, limestone, mudstone and slate. The slope was subjected to freezing and thawing from the surface downwards. Water was supplied at the base of the soil during freezing. Frost heaving and surface downslope soil movement were determined after each of 15 freezing cycles, and the profiles of soil movement with depth for each soil type were measured at the end of the 15th cycle. The experimental soils were non‐cohesive; those derived from granite and limestone were respectively sandy and gravelly in texture, while those derived from mudstone and slate were silt‐rich. Mass movement in the granite and limestone soils was due mainly to frost creep and was associated with the growth of needle ice. In the mudstone and slate soils, gelifluction was dominant as a result of high moisture contents caused by the melting of segregation ice. Mean per cycle rates of downslope soil transport for the granite, limestone, mudstone and slate soils were 5·8 cm3 cm−1, 6·9 cm3 cm−1, 21·2 cm3 cm−1 and 31·2 cm3 cm−1 respectively, units referring to the volume of soil passing a unit width of slope per cycle. Mass movement rates were shown to be strongly related to the silt content of the soils.
Discussion. Denudational isostatic rebound of intraplate highlands: The Lachlan river valley, Australia
Authors: Fabel Derek , Webb John , Finlayson Brian
Published: February 2007

Episodic terrace cutting cannot be a complex response to the steady isostatic rebound forecast by an elastic flexure model because three terraces match epiphreatic passage levels in nearby caves. There is also some doubt about how fluvial incision rates should be extrapolated to catchment‐wide rates. At the local scale of the Lachlan River highlands, active tectonic compression may be more important than flexure, which is more important at a regional scale.
Erosion rather than plant dieback as the mechanism of marsh loss in an estuarine marsh
Authors: Nyman J. A. , Carloss M. , Delaune R. D. , Patrick W. H.
Published: February 2007

Coastal marsh loss in Louisiana is attributed to plane dieback caused by processes that stress vegetation, and a common landscape pattern is broken marsh that expands at the expense of surrounding unbroken marsh. We tested the hypothesis that vegetation is more stressed in broken marsh than in adjacent unbroken marsh, as indicated by vegetation aboveground biomass, species diversity and soil Eh, on transects that extended from broken marsh to unbroken marsh at Marsh Island, Louisiana. Soil Eh, vegetation above‐ground biomass and species diversity did not differ between broken marsh and unbroken marsh, and above‐ground biomass was similar to that reported from other marshes. Thus, we rejected the hypothesis that marsh loss is related to vegetation stress. Two factors were related to vegetation vigour: soil drainage and soil bulk density. Surprisingly, significant soil drainage occurred in broken marsh but not in unbroken marsh. Above‐ground biomass of the dominant plant, Spartina patens (Aiton) Muhl., was lowest where soil bulk density was less than 0‐08 gcm−3, which illustrated the importance of mineral matter accumulation in submerging coastal marshes. The mechanism of marsh loss appeared to be erosion below the living root zone, as indicated by the vertical and often undercut marsh‐water interface, and by the separation of sod clasts. This is different from more rapid marsh loss associated with plant stress which we observed in other Louisiana marshes only 135 km away, indicating that marsh loss mechanisms can vary spatially even within a relatively small region.
Gravel transport and morphological change in braided sunwapta river, Alberta, Canada
Authors: Goff James R. , Ashmore Peter
Published: February 2007

The relation between morphological change and patterns of variation in bedload transport rate in braided streams was observed by repeated, daily topographic surveys over a 25 day study period in a 60 m reach of the proglacial Sunwapta River, Alberta, Canada. There are two major periods of morphological change, each lasting several days and each involving the complete destruction and reconstruction of bar complexes. Bar complex destruction was caused by redirection of the flow and by downstream extension of the confluence scour zone upstream. Reconstruction involved accretion of unit bars on bar head, flank and tail and in one case was initiated by disection of a large, lobate unit bar. High rates of sediment movement, measured from net scour and fill of the cross‐sections, coincided with these morphological changes. Sediment was supplied from both bed and bank erosion, and patterns and distances of transfer were highly variable. Rates of transport estimated by matching upstream erosional volumes with downstream deposition were much greater than those estimated from either a step‐length approach or a sediment budget. Measurements of scour and fill and observations of morphological change indicate that step lengths (virtual transport distances) were typically 40–100m during a diurnal discharge cycle. Shorter step lengths occurred when transfer was confined to a single anabranch and longer steps involved channel changes at the scale of the entire reach. Sediment budgeting was used to describe the spatial patterns of sediment transport associated with the morphological changes and to estimate minimum daily reach‐averaged transport rates. Mean bedload transport rates correlate with discharge, but with considerable scatter. The largest deviations from the mean relation can be tied to phases of channel incision, bank erosion, scour hole migration, bar deposition and channel filling apparently controlled by changes and fluctuations in sediment supply from upstream, independent of discharge. These are interpreted as field evidence of ‘autopulses’ or ‘macropulses’ in bedload transport, previously observed only in laboratory models of braided streams.
Comments on richards: The problems of ‘real’ geomorphology
Authors: Bassett K.
Published: February 2007

A number of comments are made as a response to the editorial “Real” geomorphology' (Richards, 1990). The call for more involvement by geomorphologists in current philosophical debate is welcomed and the adoption of a broadly realist scientific approach is supported. Some contentious issues arise from this debate and these are outlined and discussed.
Cave levels and cave development in the mitchell plain following base‐level lowering
Authors: Johnson P. A. , Gomez Basil
Published: February 2007

Multiple levels evolved in Buddha–Christian's Cave and in Donaldson's–Bronson's–Twin Cave in a subtly different manner to that normally associated with the development of multilevel caves adjacent to entrenched river valleys. It is often assumed that lower cave levels are generated by successive phases of valley entrenchment; however, multiple levels may also be induced by progressive adjustments in groundwater flow paths. Such adjustments occur as the effects of a change in base level propagate up‐basin. In the Mitchell Plain much of the late Pleistocene drop in the elevation of the principal drainage (the East Fork of the White River) was accommodated by entrenchment along the lower reaches of tributary valleys. Caves initially developed in the mid‐sections of tributary basins at relatively shallow depths. In the vicinity of the cave exit, the piezometric surface gradually steepened and was eventually lowered through a combination of valley headwall retreat and the incremental concentration of flow through master conduits. Upper‐level passages were abandoned once the original high‐level flow paths were replaced by lower‐level routes.
Automated mapping of land components from digital elevation data
Authors: Dymond J. R. , Derose R. C. , Harmsworth G. R.
Published: February 2007

An algorithm for automating the mapping of land components from digital elevation data is described. Land components are areas of relatively uniform slope and aspect and often correspond with ridge crests, shoulders, head slopes, back slopes or foot slopes. Aspect regions, which generally span from stream to ridge, are first identified by generalizing an aspect map derived from digital elevation data. The aspect regions are then split successively into land components by grouping pixels above or below an automatically determined contour of elevation or ‘distance from stream’. The contour approximates a slope break. The land components mapped in this way give a complete polygonization of a hilly landscape and are a reasonable approximation of manually mapped land components.
A simulation study of the role of raindrop erosion in the formation of desert pavements
Authors: Wainwright John , Parsons Anthony J. , Abrahams Athol D.
Published: February 2007

A simple model of raindrop erosion—the combined effects of the detachment of sediment by raindrops and its transport by splash or by overland flow—is developed to examine the role of this process in the formation of desert pavements. Application of the model to soils in areas of existing pavement initially simulates the formation of pavements, but the changing sediment size distributions lead to the subsequent destruction of these modelled surfaces. An improved model that accounts for the feedback effects of the changing size distributions on infiltration and microtopography is then developed. Incorporating these effects allows simulated pavements to be maintained over longer periods. The model yields desert pavements whose particle size compositions differ in response to differences in initial soil characteristics, slope and rainfall intensity. This model is tested against empirical data from a site where there is intershrub pavement and associated mounds of fines beneath desert shrubs. The results successfully predict the accumulation of fines under shrubs but underestimate the development of the pavement between shrubs. These findings suggest that the raindrop erosion mechanism on its own cannot account for the development of the pavement and that some other mechanism leading to the surface concentration of coarse particles must also be operating.
Design and calibration of a recording bedload trap
Authors: Harris T. , Richards K. S.
Published: February 2007

This paper reports design modifications to the recording bedload trap developed by Reid et al. (1980), and rigorous calibration procedures followed both before and after installation. An unexpected temperature dependence of the trap and stage pressure transducer records is identified and corrected. The consequences of this dependence for the interpretation of a bedload‐transport event are discussed.
Problems associated with quantitative magnetic sourcing of sediments of the scarborough to mablethorpe coast, Northeast England, U.K.
Authors: Lees J. A. , Pethick J. S.
Published: February 2007

There are many problems associated with beach tracing and sand provenance in coastal studies over short and long timescales. Here, an attempt has been made to trace the source sediments of the beaches along the Holderness and Humberside coastline of northeast England, between Scarborough and Mablethorpe, using rapid field and laboratory magnetic techniques. The methodology employed involves classification and modelling of sediment sources and mixtures based on their magnetic properties. Focus is given to a strong ferrimagnetic black sand (heavy mineral) which dominates the magnetic signal of the beach mixtures. Delimiting the spatial extent, quantifying and tracing of this mineral may give a good indication of wave energy and sediment movement processes along this coastline. This paper represents results obtained during a short‐time‐scale survey.
Seabed stress determinations using the inertial dissipation method and the turbulent kinetic energy method
Authors: Stapleton K. R. , Huntley D. A.
Published: February 2007

Direct measurements of seabed stress are difficult, especially in field conditions. Several methods for estimating these stresses using current meter data are available. Two of these methods, the Inertial Dissipation Method and the Turbulent Kinetic Energy Method, are described below, and a Matlab program is used to analyse data from a wave‐current environment.
Discrete modeling of the air‐gap field of synchronous machines for computation of torque and radial forces
Authors: Bekemans Marc , Matagne Ernest , Labrique Francis
Published: February 2007

In this paper, we exploit the multiple symmetries and the discrete character of the current distribution to express the torque and the radial forces in a PM synchronous machine. Under some assumptions, the magnetic field can be built with a limited number of discrete functions. These functions can constitute an orthogonal base of a vector space for the representation of the machine magnetic state. The representation of the stator and rotor fields as vectors of this space makes it possible to interpret the torque and the radial forces from the concept of distance between these vectors. The proposed method for torque and radial forces computation is well suited for a real‐time evaluation and can be used for a generalization of the Field‐Oriented Control to machines with non‐sinusoidal flux distribution. Copyright © 2007 John Wiley & Sons, Ltd.
A model of the unsteady response of a backward‐facing compliant step
Authors: Gerber A. G. , Holloway A. G. L. , Ng C.
Published: February 2007

A large number of industrial surface coating and continuous casting operations require a fluid to flow from a reservoir, over a compliant step, onto a moving substrate. The contact line between the compliant step and substrate in such cases generally responds in an unsteady manner, depending on flow conditions, which can have an important influence on the surface quality of the final product. This work describes the development of a computational fluid dynamics (CFD) model for predicting this unsteady response, with a particular emphasis on isolating the natural frequency of the contact line in a backward‐facing step configuration. The compliant step was developed and implemented in the context of a pressure‐based finite‐element/finite‐volume CFD solution, implicit in time, and considers in‐surface forces based on a surface tension coefficient or an elastic membrane. Copyright © 2007 John Wiley & Sons, Ltd.
Inference on haplotype/disease association using parent‐affected‐child data: the projection conditional on parental haplotypes method
Authors: Allen Andrew S. , Satten Glen A.
Published: February 2007

We develop a method that allows inference on parameters in log‐linear models of the relative risk of disease given an individual's haplotypes, that can be used to analyze case‐parent trio data. Our methods are robust to population stratification and can also be used for inference on the effect of interactions between haplotypes and environmental covariates. We compare our results with the family‐based association test (FBAT) of Horvath et al. ([2004] Genet. Epidemiol. 26:61–69), and discuss when marginal tests, such as those available in FBAT, can be misleading. Our approach generalizes previous results of Allen et al. ([2005] Biometrika 92:559–571), allowing for missing genotype data and haplotype × environment interactions. Additional computational simplifications are also discussed. Genet. Epidemiol. 2007. Published 2007 Wiley‐Liss, Inc.
The relationship of the Bowland shales to the pendleside limestone in the Clitheroe, Slaidburn and Sykes Anticlines
Authors: Parkinson D.
Published: February 2007

The Pendleside Limestone is redefined as comprising the B1 (S2) zone and the lower part of the B2 (D1) zone. It is argued that the Bowland Shales, including the basal beds of upper B2 age, transgress the Pendleside Limestone northwards from Clitheroe, following a shallow earth‐movement with axes crossing the Ashnott Anticline, the Slaidburn Anticline and the Sykes Anticline. The Slaidburn Breccia is shown to be of lower B2 age. There is unconformable overlap locally of the Lower Bowland Shales.
The stratigraphy, sedimentology and palaeontology of the Pleistocene Knocknasilloge Member, Co. Wexford. Ireland
Authors: Thomas G. S. P. , Kerr P.
Published: February 2007

The Pleistocene Knocknasilloge Member, an upward coarsening sequence of massive and laminated muds to cross‐laminated fine sands and silts, was deposited in a series of shallow lacustrine basins formed at the retreating margin of the Late Devensian Irish Sea ice‐sheet. Sedimentary successions mark increased proximity to a sediment input source and a shift from lake floor suspension sedimentation to bottom traction in low‐angled prodelta foresets and distributary barmouth channels. The microfauna contained within the sequence is derived from preexisting climatic stages and there is no evidence to support either an in situ interglacial or glaciomarine origin, as previously proposed.
The occurrence of hydrocarbons in Cambrian sandstones of the Welsh Borderland
Authors: Parnell John
Published: February 2007

Hydrocarbon shows occur in Cambrian sandstones in the Welsh Borderland. In Shropshire, sandstones of the Upper Comley Group in particular contain hydrocarbons infilling residual primary porosity and secondary porosity after leaching of feldspars. In the Malvern Hills, the Hollybush Sandstone is locally black due to an impregnation by hydrocarbons. Evidence from the distribution of hydrocarbons in other Lower Palaeozoic rocks and in Precambrian rocks in Shropshire suggests that they have migrated from hydrocarbon‐bearing Carboniferous sandstones. However, the source of hydrocarbons for the Hollybush Sandstone may be the immediately superjacent Upper Cambrian black shales.
A review of sandstone illite cements and aspects of their significance to hydrocarbon exploration and development
Authors: Macchi L.
Published: February 2007

Current understanding of the origin of illite cements within the pore systems of sandstone reservoirs is at best speculative whilst knowledge of the control of illite morpholoy is, to all practical purposes, non‐existent. This is unfortunate considering the widespread occurrence of illite and the often disastrous decrease in reservoir performance associated with its presence (up to 200‐fold decreases in permeability have been recorded from aeolian sandstones of the U.K. southern North Sea for example). An advanced knowledge of the origin of this clay mineral is thus of considerable importance to the future of the hydrocarbon exploration and production industry. This paper presents an assessment of sandstone illite morphotypes and reviews the mechanisms which have been proposed for their formation.
Strain fields and foliation trajectories around pre‐, syn‐, and post‐tectonic plutons in coaxially deformed terranes
Authors: Mandal Nibir , Chakraborty Chandan
Published: February 2007

This paper determines, using simple mathematical models, maps of strain fields and foliation trajectories in the neighbourhood of plutonic bodies intruded into a region before, during, and after a lateral compression. The analyses reveal contrasting features for the three cases, which may be useful in distinguishing pre‐, syn‐, and post‐tectonic plutons in coaxially deformed terranes.

The theoretically calibrated strain variation curve, along the regional shortening direction, around a pretectonic, rigid plutonic body shows a zone of strain increase (relative to the far‐field strain), whereas that around a syntectonic pluton shows a zone of strain decrease along with a zone of strain increase. The foliations deflect outward from a pretectonic pluton, but they bend towards a syntectonic pluton. The analysis also reveals that syntectonic plutons are likely to be elliptical in plan with axial ratio directly dependent on the ratio of the pluton's stress to the tectonic stress.

Tectonic foliations deflect away from post‐tectonic plutons. However, the foliated area around a post‐tectonic pluton is systematically divided into two sets of zones one characterized by foliations showing compressional features, the other showing extensional features.
A revision of the age of the hen‐dy‐capel ooidal ironstone (ordovician), llanengan, N. Wales
Authors: Young T. P.
Published: February 2007

Pendent didymograptid graptolites are described from mudstones immediately overlying the Hen‐dy‐capel ironstone (St. Tudwal's Peninsula, Lly̌n, North Wales). The graptolites indicate a Llanvirn age for these beds, implying a Llanvirn or Arenig age for the ironstone, in contrast with the previous interpretation of a gracilis Biozone age. The redating of the ironstone horizon suggests that the Pen‐y‐gaer mudstones may be at the base of the local Nant Ffrancon Formation, rather than being equivalent to the lower Caradoc Tyddyn Dicwm beds above the Tremadog ironstone as widely supposed. The ironstones at Trefor, Betws Garmon, and Llandegai, which have been correlated with the Hen‐dy‐capel ironstone on the basis of acritarch assemblages, may also have a similar age. A reinterpretation of the age of these localities as Llanvirn would remove the stratigraphic problems introduced by their previously suggested early gracilis Biozone age. The Hen‐dy‐capel ironstone forms one of a large number of ironstones recorded from close to the Arenig‐Llanvirn boundary in N. Wales, and elsewhere at high southern palaeolatitudes.