bluuebunny/crossref_metadata_2025 huggingface dataset:
River adjustment to changes in sediment load: The effects of tin mining on the Ringarooma River, Tasmania, 1875–1984
Authors: Knighton A. D.
Published: February 2007

The mining of alluvial tin in the Ringarooma basin began in 1875, reached a peak in 1900–20, and had virtually ceased by 1982. During that time 40 million m3 of mining waste were supplied to the main river, quickly replacing the natural bed material and requiring major adjustments to the channel.

Based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load, the river's transport history is reconstructed using a mass‐conservation model. Because of the lengthy time period (110 years) and river distance (75 km) involved, the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream. Peak storage is predicted in that part of the river where braiding and anastomosis are best developed.

Aggradation was most rapid in the upper reaches close to major supply points, becoming slower and later with distance downstream. Channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common. Bridges had frequently to be replaced. While bed levels were still rising in lower reaches, degradation began in upper ones, notably after 1950, and by 1984 had progressed downriver over 30 km. Rates of incision reached 0·5 m yr−1, especially in the early 1970s when record high flows occurred. As a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions. Also a narrower unbraided channel has developed. The river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris.
The effects of fire on the surface properties and seed germination in two shallow monoliths from a rangeland soil subjected to simulated raindrop impact and water erosion
Authors: Chartres C. J. , Mücher H. J.
Published: February 2007

This paper describes the methods used and some preliminary results of simulated erosion studies on soils with cryptogamic crusts from a semiarid rangeland environment. Two 0·3 m2 shallow monoliths were collected from the upper 20 cm of a Typic Haplargid from the semiarid Australian rangelands and subjected to a range of rainfall intensities and durations representing potentially erosive summer and winter rainfall events. One of the monoliths was cleared of vegetation by a simulated low intensity bushfire. Macro‐ and micromorphological properties of the surface, as well as runoff and erosion losses, were measured during the experiment. Runoff and erosion losses were, as expected, greater for all conditions on the burned than on the unburned monolith. Intensive rainfall damaged the cryptogamic crust unprotected by vegetation by widening and deepening desiccation cracks around the cryptogams, and breaking away and dispersing larger soil fragments from the crack margins. The burned and eroded surfaces provided a much poorer environment for seed entrapment, germination, and growth than did the unburned surface.
Physical and chemical characteristics of a metal‐contaminated overbank deposit, west‐central South Dakota, U.S.A.
Authors: Marron Donna C.
Published: February 2007

A metal‐contaminated overbank deposit in west‐central South Dakota resulted from the discharge of a large volume of mine tailings into a river system between the late 1800s and 1977. The deposit along the Belle Fourche River is typically up to 2 m thick and extends about 90 m away from the channel along the insides of meander bends. The sediments contain above‐background levels of copper, iron, manganese, zinc, and particularly arsenic, which is commonly two orders of magnitude above background level in the contaminated sediments. Carbonate minerals in the deposit limit the desorption of arsenic by preventing acid formation. Arsenic concentrations provide a measure of the dilution of mine tailings by uncontaminated sediment.

The arsenic appears to have been transported and deposited as arsenopyrite, but is now at least partially associated with iron oxides and hydroxides. Within individual samples, arsenic concentration has an inverse relation with grain size that results from the more efficient accumulation of arsenic on the greater surface area of the smaller particles. Arsenic concentration is inversely related to the sample weight percent finer than 16 μm, however, as a consequence of the dilution of the contaminated sediments by uncontaminated sediment with a finer grain‐size distribution. Dilution by uncontaminated sediment from tributaries cause arsenic concentrations to decrease by a factor of 3 along 100 km of floodplain. An influx at high streamflow of uncontaminated sediment from terraces and the premining floodplain as well as from tributaries causes arsenic concentrations in parts of the contaminated deposit that are farthest away from the channel to be two to three times less than arsenic concentrations in overbank sediment that is immediately adjacent to the channel.
Superwaves and superfloods: The bombardment hypothesis and geomorphology
Authors: Huggett R. J.
Published: February 2007

The bombardment of the oceans by asteroids and comets leads to the propagation of very large waves—superwaves. On approaching continental margins, superwaves may grow to heights large enough to spill on to the land, flooding extensive areas of continental lowland. The waters from these superfloods, in running back to the sea, would be capable of carrying out enormous amounts of work, possibly diverting rivers, cutting gorges, forming valley meanders, and leading to the widespread aggradation of coarse deposits produced by incoming superwaves stripping the soil and regolith cover and denuding weathered bedrock. Calculations of the magnitude and frequency of superfloods, based on current asteroidal impact rates, indicate that the superflooding of continental margins, including the British Isles, could have occurred several times since the start of the Pliocene. Thus, there seems to be a case for reviving some of the views of the old diluvialists, and exploring the worth of neodiluvialism as a system of Earth surface history.
Collisions of quartz grains with a sand bed: The influence of incident angle
Authors: Willetts B. B. , Rice M. A.
Published: February 2007

The velocities with which grains were observed to emerge from a sand bed after an intersaltation collision at u* = 40 cm s−1 are reported for four bed attitudes, from horizontal bed to adverse bed slope 15°. The principal effect of bed angle is to alter the magnitude and direction of the ricochet velocity. However, emergent velocities of dislodged grains are consistent with reptation path lengths comparable to the length of the upwind face of ripples in the corresponding wind.

Calculations of the loss of forward momentum at collision, using the data for the range of bed attitudes studied suggest that creep is most vigorous on the sloping upwind face of the ripple and diminishes at the crest. As a result, the crest would be expected to accumulate the coarse material which moves predominantly by creep.

The saltations originating in ricochet from the sloping back of the ripple are more vigorous and more concentrated in plan than are those originating at the crest. However, the saltation path length is at least an order of magnitude greater than the ripple wavelength and the probability distribution of path lengths is quite dispersed. Consequently it is very unlikely that these spatial patterns of ricochet are preserved sufficiently distinctly in the saltation cloud and subsequent collision distribution to be the agent of ripple development.

This study therefore supports a view of moving grain interaction with the bed in which saltation provides the power to mobilize grains but ripple growth is associated with reptation and particularly with a pattern of impact which develops with the bed relief. Creep is more active on upwind facing slopes than at the crest, which therefore is a zone of net creep grain deposition.
Lateral migration of linear dunes in the Strzelecki desert, Australia
Authors: Rubin David M.
Published: February 2007

Linear dunes in the Strzelecki Desert trend roughly south‐north. Sand transport, which is toward the NNE, has caused the dunes to migrate eastward while they extend or migrate northward. Eastward lateral migration is evidenced by: (1) asymmetrical shape of the dunes; east‐facing slopes are several times as steep as west‐facing slopes; (2) asymmetrical accumulation of loose recently transported sand (relatively abundant on east‐facing slopes); (3) asymmetrical outcropping of older semiconsolidated aeolian sand on the dune surface (more abundant on west‐facing slopes); and (4) east‐dipping foreset beds that underly the west‐facing flanks of some dunes. Dunes in the Strzelecki Desert are still active in the sense that sand is transported along and across many dune crests. However, the dunes are composed primarily of Pleistocene strata, indicating that the trend of the dunes was established before the Holocene.

The obliquity of the dunes to the transport direction is not merely an aberration of the wind regime of the last few decades. Preferential accumulation of sand on east‐facing flanks indicates that the dunes migrated eastward several metres during the Holocene. Moreover, the west‐facing flanks of some dunes have experienced a minimum of tens of metres of erosion. This asymmetric erosion and deposition were caused by dune obliquity and lateral migration that may have begun as early as the Pleistocene.

Dunes in the Strzelecki Desert and in the adjacent Simpson Desert display a variety of grossly different internal structures. Computer graphics experiments demonstrate that many of these differences in structure can be explained by different angles of climb of the dunes.
An experimental study of complex response in river channel adjustment downstream from a reservoir
Authors: Jiongxin Xu
Published: February 2007

An experimental study is described which attempts to reveal the complex response process of river channel adjustment downstream from a reservoir. A descriptive model has been established which identifies three adjustment stages. In stage I following the change of water and sediment input, the width‐depth ratio of river channel (w/d) and the river channel gradient (s) both decrease, but the river channel sinuosity (r) increases. In stage II, because of feedback from the changing boundary conditions, w/d starts to increase, r decreases, and the rate of gradient decrease becomes very slow. In stage III, equilibrium is reestablished, w/d, r, and s tend to constant values, and the system recovers its stable state.
Autogenic and allogenic denudation in carbonate karst by the multiple basin method: An example from Svartisen, North Norway
Authors: Lauritzen Stein‐Erik
Published: February 2007

In carbonate karst basins, adequate denudation rates are difficult to estimate when there are allogenic inputs. It is shown that the common practice of correcting for allogenic input by Corbel's modified formula leads to erroneous results unless the karst ratio is very high. When choosing small basins that are subsets of each other, assumptions of hydrologic and lithologic uniformity may be satisfied. Then the autogenic and allogenic components of the denudation may be calculated by a linear model of uniform mixing. The model was tested in a subarctic stripe karst in North Norway, yielding an autogenic denudation rate of 32.5 ± 10.2 mm ka−1. The mean annual runoff is 2600 mm. The result is supported by independent denudation rates from comparable areas, micro‐erosion meter data as well as the total post‐glacial corrosion deduced from pedestal and vein heights.
A discussion of hirano and Aniya's (1988, 1989) explanation of glacial‐valley cross profile development
Authors: Harbor Jonathan M.
Published: February 2007

In A rational explanation of cross‐profile morphology for glacial valleys and of glacial valley development, Hirano and Aniya (1988) present an explanation for the apparent catenary form of glaciated‐valley cross profiles based on the assumption that glacial erosion works towards minimizing friction between a glacier and its channel. However, as there is as yet no convincing justification for the application of such extremum principles to this problem, it is not clear how useful this type of analysis might be. In more detail, Hirano and Aniya's analysis includes assumptions about patterns of basal water pressures and the controls on friction inconsistent with other work in this area. Furthermore, as Hirano and Aniya (1989) point out, the catenary solution they derive is the maximum rather than the minimum friction solution. The underlying reason for this surprising result is that the variational principle Hirano and Aniya use is inappropriately structured for the problem being addressed, as it does not involve a cross‐section area, i.e. ice discharge, constraint.

Hirano and Aniya also discuss the progressive development of glacial‐valley cross profiles, but their analysis is hindered by the fact that most of the data they present are purely morphological, and thus cannot be used to assess form development as a function of either time or extent of glacial erosion. The only possible exceptions are Graf's (1970) data, which give morphological parameters as a function of valley order, but these do not unequivocally support Hirano and Aniya's conclusions, and are used with implicit assumptions about the relationship between valley order and time of glacial occupation or magnitude of glacial erosion that are incorrect or uncorroborated, respectively. However, if we accept the common assumption that glacial erosion results in a progression from initial V‐shaped to broadly U‐shaped (parabolic or catenary) forms, Hirano and Aniya's argument that there are two distinct types of form development (incision in alpine situations versus valley widening under ice sheets) is justified, and is an important observation that needs to be addressed in future models of glacial‐valley development.
The influence of debris flows on channels and valley floors in the Oregon Coast Range, U.S.A.
Authors: Benda Lee
Published: February 2007

Debris flows are one of the most important processes which influence the morphology of channels and valley floors in the Oregon Coast Range. Debris flows that initiate in bedrock hollows at heads of first‐order basins erode the long‐accumulated sediment and organic debris from the floors of headwater, first‐ and second‐order channels. This material is deposited on valley floors in the form of fans, levees, and terraces. In channels, deposits of debris flows control the distribution of boulders. The stochastic nature of sediment supply to alluvial channels by debris flows promotes cycling between channel aggradation which results in a gravel‐bed morphology, and channel degradation which results in a mixed bedrock‐ and boulder‐bed morphology. Temporal and spatial variability of channel‐bed morphology is expected in other landscapes where debris flows are an important process.
Temperature correction of electrical conductivity values
Authors: Calles Bengt , Calles Ulla Maria
Published: February 2007

For a number of applications in geoscience, electrical conductivity of water is often used as a collective measure of the concentration of dissolved solids. A method for temperature correction of electrical conductivity data based on regression analysis of the actual temperature/conductivity relationship of a number of water samples from natural streams is presented. It is shown that the generally used formulae for temperature correction give corrected results that deviate considerably from the values determined by actual measurements. The error increases with decreasing water temperature and may result in data that deviate by as much as 20 per cent from the true values. The implications are thus especially important for measurements of solute loads and concentrations during periods of low stream water tetaperatures e.g. during snowmelt.
Simulation of the size distribution and erosivity of raindrops and throughfall drops
Authors: Brandt C. Jane
Published: February 2007

This paper presents a model that simulates the size distribution and erosivity of raindrops and throughfall drops. It utilizes existing models of rainfall drop size distribution and fall velocity and combines them with newly collated evidence of throughfall drop size distributions. A sensitivity analysis reveals that the model is sensitive to parameters that are easily measured or estimated: rainfall intensity, the mean volume drop diameter of the intercepted throughfall, canopy cover, and canopy height.

The results of the model may be used at two levels. Firstly, to calculate specifically the size and fall velocity of individual drops, parameters that are needed in studies examining the response of soil surfaces to forces applied by rainfall. Secondly, to produce erosivity indices, based on rainfall intensity but which take account of the effects of a vegetation canopy. The paper shows that while the kinetic energy of rainfall (E(0), J mm−1 m−2) may be calculated from an equation of the familiar form:

the kinetic energy of throughfall under any canopy may be calculated by combining this equation with another that relates the energy of drops under a 100 per cent canopy cover (E(100)) and the canopy height:

.
The chronology and stratigraphy of the alluvial terraces of the river Dane Valley, Cheshire, N.W. England
Authors: Hooke J. M. , Harvey A. M. , Miller S. Y. , Redmond C. E.
Published: February 2007

Three groups of alluvial terraces together with the modern floodplain mark the Postglacial development of the middle part of the Dane Valley, Cheshire. These are a High terrace group of late Pleistocene age, a Middle terrace group of late Pleistocene to early Holocene age, a Low terrace of mid–late Holocene age, and a modern (post ca. 1840 AD) floodplain. A chronology of erosion, deposition, and landform development since mid‐Holocene times is established in this paper on the basis of terrace morphology, stratigraphy, sedimentology, soil analysis, magnetic mineral analysis, and four radiocarbon dates. After dissection of the Middle terrace during the early to mid‐Holocene, a long period of lateral activity by the river was followed by a major aggradation phase, which formed the Low terrace surface. This was followed by dissection during the last ca. 300 years and the development of the modern floodplain since ca. 1840 AD. Various explanations for the changes during the Holocene are considered; the Low terrace aggradation appears to be related to a major phase of mediaeval soil erosion.
The influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers
Authors: Hassan Marwan A. , Reid Ian
Published: February 2007

Pebble clusters are reported widely as characteristic of gravel river beds and are known to influence the initial entrainment of bedload. A field assessment suggests that their distribution is not ubiquitous, favouring channel bars, but also reveals a tendency towards a preferred stream wise spacing. A series of laboratory flume experiments shows that flow resistance rises to, and falls from, a peak value as the longitudinal spacing of pebble clusters decreases, in a manner similar to that shown by others for strip roughness, isolated blocks, and simulated ripples and dunes. The experiments also reveal a strong inverse relationship between bedload flux rates and the flow resistance induced by the concentration of pebble clusters. It is concluded that pebble cluster spacing tends towards an equilibrium that is regulated by a feedback process involving sediment transport rates and that the spatial concentration of these microforms will adjust to the point where they induce maximum flow resistance.
An appraisal of the velocity‐reversal hypothesis for stable pool‐riffle sequences in the river severn, England
Authors: Carling P. A.
Published: February 2007

The ‘velocity‐reversal hypothesis’ is the linchpin for a number of recent conceptual models pertaining to sediment sorting and the maintenance of pool‐riffle sequences in gravel‐bedded streams. The literature in support of the hypothesis together with published adverse criticism is reviewed. It is concluded that convincing evidence for the ubiquitous occurrence of such a reversal in a range of channel geometries is currently unavailable. Continuity considerations indicate that riffles need to be considerably wider than pools for a reversal in the mean velocity to occur under conditions of subcritical flow, high stage, and stable morphology. These observations are substantiated by a detailed study of the hydraulic geometry of stable pool‐riffle sequences in the River Severn, England. Neither the sectionally‐averaged velocity nor the near‐bed shear velocity is sensibly greater in the pools than over the riffles during bankfull or near bankfull flow. Instead a tendency towards equalization of the values of average hydraulic variables is noted as discharge increases. A detailed investigation of the three‐dimensional character of the flow is required to demonstrate whether the entrainment forces within pools can locally exceed those over neighbouring riffles. Unusual behaviour of the energy gradient over riffles during moderate discharges is related to backwater effects as mediated by the spacing of the riffles. The hydraulic data are used to comment on the stability of the test reaches in the context of the development of the River Severn in the vicinity of Shrewsbury.
Automated recognition of valley heads from digital elevation models
Authors: Tribe Andrea
Published: February 2007

Applications of landform recognition in map‐making, geographical information systems, and in improving the storage and representation of earth surface information are described. Reasons are given for the use of digital elevation models for landform recognition: increasing availability of data, easier data integration, and automation of landform recognition.

An automated technique for recognizing valley heads from digital elevation models is presented. The technique has been developed for valley head recognition because valley heads are known locations of geomorphological activity and because areal features have been largely ignored in the automated landform recognition literature. The problem of valley head recognition is divided into valley head location and valley head delineation, and the technique is developed using a DEM representing a simple artificial landscape.

Two methods are given for valley head location. In the first, valley heads are located at valley ends. In the second, valley heads are located at cells which would have water flowing into them from many directions if water was flowing over the terrain. The latter method locates all the valley heads on the artificial landscape. The cells locating valley heads are iteratively ‘grown’ to adjacent cells that are concave in plan and not flat, to delineate the valley head. At best, 82 per cent valley head cells on the artificial landscape are correctly recognized with a 43 per cent commission error.

The method is tested on real data where it is less successful because of the variability of real landscapes and the inadequacy of the methods chosen for valley network delineation. Machine learning of thresholds and a method involving inspection of profiles across a DEM cell are suggested as methods to improve the automated valley head recognition technique.
Patterns of development of lavaka, Madagascar's unusual gullies
Authors: Wells Neil A. , Andriamihaja Benjamin , Rakotovololona H. F. Solo
Published: February 2007

Lavaka (Madagascar's abundant gullies) show a complex pattern of development. Fourteen independent measures of size and shape in 93 lavaka were investigated by principal components analysis and discriminant function analysis. Typical lavaka start either as wounds and raw patches on mid‐hillside that develop step‐like head scarps, or as toe slopes collapsed by seepage, slumping, or undercutting. They become deep, raw, vertical‐sided, teardrop‐ to heart‐shaped gashes that may be deepest and broadest uphill. As the walls retreat, slump, and become overgrown, lavaka become longer, broader, gentler, and partly filled concavities. They can grow to reach from the valley floor to the hill crest (or even beyond the crest) before healing over. Unless excessive erosion creates tors and inselbergs, they heal over and end up as unremarkable hillside reentrants and side‐valleys.
High flow events and sediment transport in small streams in the ‘tertiary basin’ area in piedmont (Northwest Italy)
Authors: Tropeano Domenico
Published: February 2007

Rainfall, peak discharges, and suspended sediment transport were surveyed for 280 events in three small (0.8 to 10 km2) catchments in a hilly area derived from Neogene marls, silts, and sands.

Under similar hydrological input conditions, stream flow behaviour and sediment delivery differed considerably from one catchment to another, depending on topography, lithology, land use, and especially sediment availability. Analytical treatment of data showed a good fit between sediment yield and peak flow discharge. Less good, although still significant, was the correlation between sediment concentration and discharge values for different flow stages. Rainfall peak/basin lag time and rainfall/discharge showed poor or no correlation, mainly due to strong variations in rainfall distribution.

Sediment concentration in the catchments varied enormously according to season, from zero up to 334 g 1−1; sediment yield was 160‐900 tonnes km−2 yr−1 in the two major catchments, and over 5200 tonnes km−2 yr−1 in the headwater catchment, stressing the importance of small tributaries not only in inducing floods in downstream channels, but also in sediment supply.
Formation of stationary alternate bars in a steep channel with mixed‐size sediment: A flume experiment
Authors: Lisle Thomas E. , Ikeda Hiroshi , Iseya Fujiko
Published: February 2007

Alternate bars were formed by sediment transport in a flume with Froude‐modelled flow and relative roughness characteristic of gravel‐boulder channels with steep slopes. The flume (0.3 m wide × 7.5 m long) was filled with a sand‐gravel mixture, which was also fed into the top of the flume at a constant rate under constant discharge. Channel slope was set at 0.03. Initially, coarse particles accumulated on incipient bar heads near one side of the flume and diverted flow and bedload transport across the flume toward a pool scoured against the opposite flume wall downstream. Sorting in the pool directed coarse particles onto the next bar head downstream. Alternate sequences of pools and coarse bar heads were thereby linked down the entire flume by interactions of sediment sorting, flow, and channel morphology. During episodes of bar construction, unsorted bedload invaded interior bar surfaces and was deposited. Persistent deposition of coarse particles on bar heads prevented downstream migration of bars by inhibiting bar‐head erosion and bedload transport over bars. Likely factors leading to bar‐head stabilization in modelled gravel‐bed channels are coarse mixed‐size sediment, steep channel gradients, and shallow depths.
Empirical relations for the sediment transport capacity of interrill flow
Authors: Everaert Wilfried
Published: February 2007

Experiments were carried out in order to measure the sediment transport capacity of interrill flow with and without rainfall and to relate the transport capacity to selected hydraulic parameters, such as effective stream power and shear velocity. Different sediments were used in order to study the effect of grain size. The proposed relationships show considerable variations with grain size and there is only a minor effect of rainfall on the transport capacity which also seems to be grain size dependent.

The proposed relationships can be used to predict sediment transport capacity of interrill flow and can therefore contribute to the development of physically based erosion models.
Summer and winter regimes of runoff generation and soil erosion on cultivated loess soils (The Netherlands)
Authors: Kwaad F. J. P. M.
Published: February 2007

Monthly runoff and soil loss data of three fallow experimental plots are presented, comprising a summer and following winter season. The fallow plots were only tilled once, at the end of April. Summer runoff appeared to be controlled by rainfall intensity and conforms to the Horton model of overland flow generation. Winter runoff was primarily controlled by rainfall amount and conforms to the saturation or storage control model of runoff generation. Summer runoff volume was one fourth of winter runoff volume. Summer soil loss was twice as high as winter soil loss and was caused by high intensity, high energy rainfall. Winter soil loss was due to detachment limited erosion, caused by low intensity, low energy rainfall. Mean sediment concentration of winter runoff was one seventh of that of summer runoff. Implications for runoff and erosion of climatic change, involving increased rainfall amounts or intensities in summer or winter, are given.
Estimation of flow resistance in gravel‐bedded rivers: A physical explanation of the multiplier of roughness length
Authors: Clifford N. J. , Robert A. , Richards K. S.
Published: February 2007

The need to estimate velocity and discharge indirectly in gravel‐bedded rivers is a commonly‐encountered problem. Semilogarithmic friction equations are used to estimate mean velocity using a friction factor obtained from depth and grain size information. Although such equations have a semi‐theoretical basis, in natural gravel‐bed channels, an empirical constant (6.8 or 3.5) has to be introduced to scale‐up the characteristic grain size (D50 or D84) to represent the effective roughness length. In this paper, two contrasting approaches are used to suggest that the multiplier of characteristic grain size is attributable to the effect of small‐scale form resistance, reflecting the occurrence of microtopographic bedforms in gravel‐bedded environments. First, spatial elevation dependence in short, detailed bed profiles from a single gravel‐bedded river is investigated using semivariogram and zero‐crossing analyses. This leads to objective identification of two discrete scales of bed roughness, associated with grain and microtopographic roughness elements. Second, the autocorrelation structure of the three‐dimensional near‐bed velocity field is examined to identify regularities associated with eddy shedding and energy losses from larger grains and microtopographic bedforms. Apart from improving the capacity to determine friction factors for velocity and discharge estimation, the findings have implications in general for the initial motion of gravelly bed material.
Bedload entrainment, travel lengths, step lengths, rest periods—studied with passive (iron, magnetic) and active (radio) tracer techniques
Authors: Schmidt Karl‐Heinz , Ergenzinger Peter
Published: February 2007

This paper reports results from bedload transport investigations with active (radio) and passive (iron, magnetic) tracers in the Lainbach, a step‐pool mountain river, in Bavaria, Southern Germany. The spatial distributions of the iron tracers after flood events can be best described by exponential or Gamma distributions. There is some indication of a tendency of size‐selective transport of the iron tracers, but there is also a considerable amount of scatter in the correlations between weight (size) and travel length owing to the masking influence of other variables, such as the shape of the particles and different positions in the river bed. The experiments with artificial magnetic tracers showed that elongated pebbles (rods) had the longest mean transport distance, platy ones (discs) remained relatively close to the starting points. The particles from the pool showed the greatest transport lengths and a 100 per cent chance of being eroded.

The Pebble Transmitter System (PETSY) consists of transmitters implanted into individual pebbles, a computerized receiver, a stationary antenna system with an antenna switchboard, and a data logging system. The particles do not move continuously but in a series of transport steps and non‐movement intervals. A single value for a given size‐class is not adequate to describe the critical conditions of entrainment under natural circumstances. A probability approach is much more suitable. The critical unit discharges (total discharge divided by active channel width) along the measuring reach are dependent on river bed morphology. In the steps bedload needs higher unit discharges to be entrained. Once entrained, the transport of bedload is stochastic in nature and the single particle transport is controlled by the step lengths and the duration of rest periods. The distributions of both parameters can be approximated by exponential functions. Applying the stochastic concept proposed by Einstein the mean values of the random variables [step length] and [duration of rest period] measured with the PETSY technique were used for the simulation of spatial distributions of bedload particles from point sources. More field and laboratory data are needed to include varying flow and roughness conditions with tracers representing different particle characteristics.
Bed load transport during rising and falling stages on two small streams
Authors: Kuhnle Roger A.
Published: February 2007

Bed load transport rates were measured with continuously recording pit samplers on two small gravel‐bed streams in the Goodwin Creek Research Watershed, northern Mississippi, U.S.A. When transport samples were grouped according to whether the stage was rising or falling, significant differences in mean bed load transport rates were found at nearly all flow strengths. At higher flow strengths, mean bed load transport rates were greater during rising stages than during falling stages. The greater transport rates measured during rising stages may be caused by a lag in the formation and destruction of bed roughness elements. One of the streams also showed evidence for greater transport rates for low flows as the stage declined. This may be caused by differences in the stability of the bed material at the beginning and at the end of a transport event.
The fractal properties of topography: A comparison of methods
Authors: Klinkenberg B. , Goodchild M. F.
Published: February 2007

In this study the fractal characteristics of fifty‐five digital elevation models from seven different United States physiographic provinces are determined using seven methods. The self‐similar fractal model tested in this analysis is found to provide a very good fit for some landscapes, but an imperfect fit for others. Thus, outright rejection of this model does not appear to be warranted, but neither does a blind application.

The three implementations of the dividers methods considered in this study consistently produce lower dimensions than those produced by the other methods, and those dimensions consistently do not vary much between surfaces. Although the dimensions produced by the cell counting method (applied to the digital elevation model itself) display consistent intersurface variation, the dimensions are generally lower than those produced by the variogram‐based methods. Among the variogram‐based methods, the dimensions of the quarter‐sections of the digital elevation models are generally greater than the dimensions obtained from the other variogram‐based methods. The dimensions produced by the variogram method which considered the surfaces on a directional basis are very similar, on average, to the dimensions produced by the entire‐surface variogram.
Continental rifting and drainage reversal: The clarence river of Eastern Australia
Authors: Haworth R. J. , Ollier C. D.
Published: February 2007

The Clarence River on Australia's east coast has an anomalous drainage pattern. Its right‐bank tributaries are markedly barbed, suggesting reversal, whereas Tertiary volcanism has disrupted its left‐bank drainage. The southeast‐flowing Clarence is closely aligned with the northwest‐flowing Condamine River just across the Continental Divide. The Condamine‐Clarence alignment is continued by a large southern tributary, the Orara River, which flows northwest, away from the sea, to meet the southeast‐flowing Clarence. A broad river with a quite different character flows east from near the Orara‐Clarence junction to the sea. This is essentially an overflow channel.

This series of aligned streams, the Condamine‐Clarence‐Orara, represents the remains of an earlier northwest‐flowing stream that extended the full length of the Clarence‐Moreton Basin, an eastern extension of the Great Artesian Basin. During the Jurassic, the Clarence‐Moreton Basin was filled with sediments from the surrounding highlands, including those to the east of the present coastline. Continental rifting from Late Cretaceous times onwards led to the opening of the Tasman Sea, causing the reversal and beheading of the original northwest‐flowing streams and the formation of the Great Escarpment.

The evolution of the Clarence River does not fit into most conventional geomorphic paradigms such as cycles, climatic geomorphology or steady‐state landforms. It is the result of a succession of unique events on a very long timescale, and as such is a classic example of evolutionary geomorphology.
Virtual rate and mean distance of travel of individual clasts in gravel‐bed channels
Authors: Hassan Marwan A. , Church Michael , Ashworth Philip J.
Published: February 2007

Travel distances in gravel‐bed rivers of tagged particles of various sizes are related to excess stream power estimated for peak discharge. Mean distance of movement, irrespective of grain size, is weakly correlated with stream power, especially near the threshold of movement. There may be several reasons for the weak correlation, including variable effects of bed structure, varying magnitudes of sediment mobilizing events and sampling problems. Grain size itself is of marginal significance. The virtual rate of travel calculated using total time for which the flow is larger than that needed to initiate clast movement also bears a weak relation to the excess stream power over the period. Better results are obtained by relating the virtual rate of travel to the first peak of the flow event only. This implies that the initial seeding of the tagged particles dominates the observations. Nonetheless, an underlying general relation is indicated by the data, which are derived from a wide range of flow regime types.
Delivery of upper‐basin sediment to the lower neuse river, North Carolina, U.S.A.
Authors: Phillips Jonathan D.
Published: February 2007

Extensive storage of upper‐basin Piedmont sediment and apparent low sediment supply to streams in lower‐basin Coastal Plain areas generates questions as to the source of alluvium in lower reaches of rivers of the U.S. Atlantic drainage. This was investigated on the Neuse River, North Carolina, using a mineralogical indicator of sediment source areas. The utility of mica flakes for discriminating between Piedmont and non‐Piedmont sources of sediment in the lower Coastal Plain reaches of the Neuse was established on the basis of an examination of the U.S. National Soils Database and of 26 soil surveys of the North Carolina Coastal Plain. From the Neuse River estuary to 48 km upstream there are no mica flakes in floodplain soils or in river bank and channel shelf sediments. Mica flakes become more common upstream. This suggests that a very small proportion of the sediment eroded in the Piedmont portion of the watershed is delivered to the river mouth. The small amounts which presumably do reach the lower Coastal Plain are so diluted by Coastal Plain‐derived alluvium that no Piedmont origin can be discerned. This demonstrates a dominantly Coastal Plain source and underscores the importance of storage and discontinuous transport in fluvial sediment systems. More importantly, results suggest that upper‐ and lower‐basin sediment dynamics are not only non‐linearly related, but may be virtually decoupled.
Lateral migration, thermoluminescence chronology and colour variation of longitudinal dunes near Birdsville in the Simpson Desert, central Australia
Authors: Nanson G. C. , Chen X. Y. , Price D. M.
Published: February 2007

The longitudinal dunes of the Simpson Desert, in the vicinity of Birdsville, have been reworked largely during the Holocene from dunes deposited up to 80000 years ago or earlier. The widespread asymmetry of these roughly northward‐trending dunes, with steeper eastern faces and more gentle western faces, supports wind‐rose data showing sand‐transporting winds from the southwest obliquely intersecting the dunes. While this suggests a change in the wind pattern since the dune field was oriented, it does not indicate that the dunes are necessarily shifting leeward (eastward) as a consequence. It is hypothesized that the direction of migration is controlled by the extent to which the dunes are vegetated. Relatively well‐vegetated dunes can accrete sand on their gentle stoss slopes and erode on their lee slopes causing them to shift westward and hence obliquely into the wind, a condition that probably prevails in wetter regions and during episodes of relatively humid climate. In contrast, in very dry areas or during arid phases, sand can move unimpeded up a sparsely vegetated stoss face and over the crest to form an avalanche or slip face on the lee side, thereby causing the dunes to shift eastward. Despite evidence that longitudinal dune crests can shift laterally to some extent, the dunes in the western part of the Simpson Desert have not migrated, either westward or eastward, more than 100m or so from their Pleistocene cores. Aeolian transport and partial or complete removal of iron cutans from around quartz grains results in dunes of widely varying colour yet of similar age.
Mega‐scale glacial lineations and cross‐cutting ice‐flow landforms
Authors: Clark Chris D.
Published: February 2007

Landsat images reveal a previously unsuspected large‐scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow. Such a glacial grain can be regarded as a landform assemblage comprised of a number of components. Drumlins and megaflutes form part of the pattern, but in addition there are two previously undocumented ice‐moulded landform elements: streamlined lineations of much greater proportions, referred to as mega‐scale glacial lineations, and a distinctive cross‐cutting topology within the grain.

The ice‐moulded landform assemblage is described and illustrated with reference to examples from Canada. Possible modes of genesis of such landforms are discussed and their glaciological implications outlined. The discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment, and demands a radical re‐interpretation of ice sheet dynamics.
Bagnold's kink: A physical feature of a wind velocity profile modified by blown sand?
Authors: McEwan I. K.
Published: February 2007

Bagnold (1941) made detailed measurements of the wind profile modified by blown sand. He noted that each velocity profile appeared to be kinked and suggested that the position of the kink corresponded to the height at which an average or a characteristic trajectory extracted the bulk of its momentum from the wind. However, Anderson and Haff (1988) have shown that in aeolian sand transport the grain cloud is made up from a distribution of trajectory paths and that it was an over‐simplification to attempt to describe the complex behaviour of the grain cloud in terms of a single representative trajectory. These recent developments leave the nature and even the existence of the kink observed by Bagnold (1941) open to question.

This paper shows that a kink is indeed a physical feature of the modified wind velocity profile and that it is caused, as Bagnold (1941) suggested, by a maximum, occurring at some height above the surface, in the momentum extracted by the grains from the wind. Further comments are made on both the form of the modified wind velocity profile and the fluid shear stress profile in the grain layer. In particular these comments, based upon a theoretical analysis, suggest an experimental means to measure the mean surface fluid shear stress and to gain, from accurately measured wind profiles, a greater insight into the grain cloud which caused the modification.
Rapid uplift, stepped marine terraces and raised shorelines on the Calabrian coast of Messina Strait, Italy
Authors: Dumas B. , Gueremy P. , Lhenaff R. , Raffy J.
Published: February 2007

A series of 26 Quaternary shorelines, stepped between present sea level and 556 m, are studied. They are part of the flight of marine terraces of the Aspromonte region. The shorelines were determined using three geomorphological models: wave‐cut platforms and gravel‐built terraces associated with their sea‐cliff foot, and observations of lateral changes between marine terraces and fluvial terraces. The elevation of the sea‐cliff foot is either measured directly, by exposure in cross‐section, or by estimation from geomorphological patterns. With caution, we connect the different landmarks of the shorelines which are discontinuous because of destruction between interfluves or because they are overlain by torrential deposits.

The results of mapping show that there are few differential movements from one transect to another and mean uplift rate is 98 cm ka−1. This rate is calculated on the basis of a correlation of the area studied with the Ravagnese Tyrrhenian site, 125 m high, whose date is isotopic substage 5e. Middle and Late Quaternary tectonic activity leads to faulting, slight folding and warping but some scarps associated with faults are actually ancient sea cliffs.
Morphology and causes of recent peat slides on Skerry Hill, Co. Antrim, Northern Ireland
Authors: Wilson Peter , Hegarty Carol
Published: February 2007

Two shallow translational slides occurred in blanket peat on Skerry Hill, Co. Antrim, in November 1991 at sites adjacent to slides activated c. 25 years ago. Heavy rainfall, degraded drainage ditches and slope morphology are considered to have been important factors contributing to peat instability. The failure planes are located close to the peat base, at the boundary between less compact fibrous peat above and more compact humified peat below. The preservation of large blocks and rafts of intact peat and the limited amount of liquefied peat in the debris tongues is thought to reflect the degree of peat humification. There is also some evidence to suggest that the peat was probably undersaturated at the time of failure and this may have assisted preservation of intact peat blocks. Tension cracks, resulting from either short‐term desiccation or long‐term slow mass movement, are thought to have facilitated the rapid transfer of heavy rain to the subsurface peat, causing high pore‐water pressures and lubrication of the failure planes. Vegetation recolonization will probably follow a pattern similar to that observed on the adjacent earlier slides.
A process‐based classification system for headwater streams
Authors: Whiting Peter J. , Bradley Jeffrey B.
Published: February 2007

In this paper we develop a classification system for small headwater streams predicated upon an understanding of the dominant physical processes acting in the channel and its basin, and the conditions under which these processes operate. The variables used to build the classification are hillslope gradient, valley width as compared to channel width, channel gradient, channel depth and sediment size. Using physical laws and morphologic relationships, we recognize domains in which various processes dominate. Channels within the same process domain can be expected to behave in a similar manner in transporting sediment and water and responding to and recovering from basin disturbance, therefore we use the domains to recognize distinct channel types. This classification system provides the foundation for building an approach for identifying basins and streams that are comparably sensitive to landuse.