bluuebunny/crossref_metadata_2025 huggingface dataset:
On using the effective contact angle and the water drop penetration time for classification of water repellency in dune soils
Authors: Wessel A. T.
Published: February 2007

Sandy soils are often water repellent when dry. In sloping areas this may result in surface runoff and erosion. Water repellency in soils can be classified with the solid‐liquid contact angle which is difficult to determine. Another method is the water drop penetration time. This method is not only easier to apply but provides a more useful scale for classifying water repellent soils. Moreover, it is directly related to erosion hazard because runoff depends on the time required for the infiltration of rain drops. A close relationship was found between the contact angle and the water drop penetration time in dune soils along the coast of the Netherlands.
Contour scaling of a sandstone by salt weathering under simulated hot desert conditions
Authors: Smith B. J. , McGreevy J. P.
Published: February 2007

A laboratory study has been used to investigate relationships between salts and contour scaling—a weathering feature commonly observed on rock surfaces in salt‐rich environments. Surface disaggregation and essentially surface‐parallel cracks were produced in sandstone blocks using 10 per cent solutions of sodium sulphate and magnesium sulphate applied daily to single exposed surfaces for sixty days. A control block soaked once in saturated magnesium sulphate and subsequently wetted daily with distilled water showed extensive surface disaggregation, but no cracking. Both surface disaggregation and subsurface cracking were associated with relative concentrations of microcrystalline salt. A tentative model of contour scaling is proposed, which involves linking together potential cracks by salt‐induced fracturing of intervening, crack‐stopping grains. Further control blocks treated respectively with 10 per cent and saturated sodium chloride showed no evidence of subsurface cracking and only limited surface disaggregation of the ‘saturated’ block.
A model of channel response in disturbed alluvial channels
Authors: Simon Andrew
Published: February 2007

Dredging and straightening of alluvial channels between 1959 and 1978 in West Tennessee caused a series of morphologic changes along modified reaches and tributary streams. Degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed‐levels by as much as 6·1 m. Following degradation, reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction. Aggradation downstream of the area of maximum disturbance reached 0·12 m per year with the greatest rates occurring near the stream mouths.

The adjustment of channel geometry and phases of channel evolution are characterized by six process‐oriented stages of morphologic development—premodified, constructed, degradation, threshold, aggradation, and restabilization. Down‐cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded (threshold stage). Channel widening continues through the aggradation stage as the ‘slough line’ develops as an initial site of lower‐bank stability. The bank profile develops three dynamic elements (1) vertical face (70° to 90°), (2) upper bank (25° to 50°), and (3) slough line (20° to 25°). Alternate channel bars form during the restabilization stage and represent incipient meandering of the channel.
Evolution of salt‐marsh cliffs in muddy and sandy systems: A qualitative comparison of British West‐Coast estuaries
Authors: Allen J. R. L.
Published: February 2007

Salt‐marsh cliffs in the muddy Severn Estuary are mostly strong and tall. They are retreating in response to the erosive attack of wave and tidal currents chiefly through toppling failures and rotational slips. In the sandy Solway Firth and Morecambe Bay systems, marsh cliffs are strong only in their upper parts, where a dense root‐mat of marsh grasses binds the sediments. Here cantilever and toppling failures are the main response of the cliffs to tidal and wave erosion The differences between the three estuarine systems in the mechanisms of marsh‐cliff erosion are partly reflected in the mode of preservation of the cliffs on the restoration of the conditions leading to renewal of marsh growth.
Structure and stability of the former subglacial drainage system of the glacier De Tsanfleuron, Switzerland
Authors: Sharp Martin , Gemmell J. Campbell , Tison Jean‐Louis
Published: February 2007

A well‐developed subglacial drainage system consisting of large cavities developed in the lee of bedrock steps connected together by a network of Nye channels is exposed on an area of recently deglaciated limestone bedrock in front of Glacier de Tsanfleuron, Switzerland. This system covers some 51 per cent of the bedrock surface area, and is believed to have transported the bulk of supraglacially‐derived meltwaters through the glacier. Using the cavity hydraulics model of Kamb (1987), it is shown that the geometry of the system rendered it stable against collapse by meltback of channel roofs into a tunnel‐dominated system. For likely combinations of glacier geometry and meltwater discharge, the steady state water pressure in this system would have been only a small fraction of that required for flotation, and for discharges of less than about 0·5–5 m3 s−1 water would have flowed at atmospheric pressure. The system appears to have adjusted to varying discharges by a combination of varying water pressure and changing the total cross‐sectional area of flow by altering the number of active channels connecting cavities. Glacier sliding velocity would have been independent of meltwater discharge for discharges at which water flowed at atmospheric pressure, but would have risen with increasing discharge for higher flows. Velocities on the order of 0·1 m d−1 are predicted for a realistic range of discharges and effective pressures, and these are believed to be plausible. Episodes of enhanced sliding in glaciers with similar drainage systems could be triggered by a rise in meltwater discharge across the threshold between flows at atmospheric pressure and flow under pressure from the glacier.
Temporal variations in bedload transport rates associated with the migration of bedforms
Authors: Gomez Basil , Naff Richard L. , Hubbell David W.
Published: February 2007

Temporal variations in bedload transport rates that occur at a variety of timescales, even under steady flow conditions, are accepted as an inherent component of the bedload transport process. Rarely, however, has the cause of such variations been explained clearly. We consider three data sets, obtained from laboratory experiments, that refer to measurements of bedload transport made with continuously recording bedload traps. Each data set is characterized by a predominant low‐frequency oscillation, on which additional higher‐frequency oscillations generally are superimposed. The period of these oscillations, as isolated through the use of spectral analysts, ranged between 0·47 and 168 minutes, and was associated unequivocally with the migration of bedforms such as ripples, dunes, and bars. The extent to which such oscillatory behaviour may be recognized in a data set depends on the duration of sampling and the length of the sampling time, with respect to the period of a given bedform.

Several theoretical probability distribution functions have been developed to describe the frequency distributions of (relative) bedload transport rates that are associated with the migration of bedforms (Einstein, 1937b; Hamamori, 1962; Carey and Hubbell, 1986). These distribution functions were derived without reference to a sampling interval. We present a modification of Hamamori's (1962) probability distribution function, generated by Monte Carlo simulation, which permits one to specify the sampling interval, in relation to the length of a bedform. Comparisons between the simulated and observed frequency distributions, that were undertaken on the basis of the data described herein, are good (significant at the 90 per cent confidence level). Finally, the implications that temporal variability, which is associated with the migration of bedforms, have for the accurate determination of bedload transport rates are considered.
Laboratory experiments on the influence of slope length on runoff, percolation and rill development
Authors: Bryan R. B. , Poesen J.
Published: February 2007

Experiments to test relationships between slope length, percolation, and runoff were carried out in a laboratory flume under simulated rainfall at intensities from 24·2‐26 mm h−1. A composite soil subject to sealing was mixed from a clay and a sand and tested on 2·39 m, 7·18 m, and 17 m slopes for a minimum of 200 min. Runoff discharge is not a simple function of rainfall excess and slope length but shows a complex pattern dominated by surface sealing, rill development and headcut incision. Rill development by concentrated surface wash conformed to established threshold hydraulic conditions, but subsequent headcut incision was necessary to breach the seal and significantly affect percolation/runoff ratios. Headcut evolution is complex, apparently reflecting hydraulic instability and possibly different stages in seal development. Headcut and rill incision shows a cyclic pattern interspersed with broad areas of sheetwash and colluvial deposition where percolation rates are very low.
Sediment transfer and transformation of an alluvial valley floor: The river South Tyne, Northumbria, U.K.
Authors: Macklin Mark G. , Lewin John
Published: February 2007

The amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the River South Tyne, northern England. Analysis of lateral and vertical channel change over this period, the extent of actively reworked gravels, and identification of metals in alluvial units, show five ‘sedimentation zones’ separated by more stable reaches. Aggradation in the late nineteenth century was followed by a period of storage and local reworking, and then incision. Some reaches show short‐term storage of sediment injected from tributaries which may be dispersed by floods. There is some evidence of transfer of sediment bodies downvalley within sedimentation zones, and of a sediment ‘wave’ movement between zones in lower parts of the South Tyne investigated. Present‐day incision, the variation in the area of actively reworked gravel spreads, and the widespread dispersal of fine‐grained toxic metal mining wastes all have practical implications. The intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave.
Morphology of Red Creek, Wyoming, an arid‐region anastomosing channel system
Authors: Schumann R. Randall
Published: February 2007

Red Creek, in the Red Desert area of the Great Divide Basin, Wyoming, is an arid‐region anastomosing stream. The narrow, deep, and sinuous main channel is flanked by anastomosing flood channels, or anabranches. Most anabranches are initiated at meander bends. The primary mechanism of anabranch initiation is avulsion during overbank floods. Anabranch enlargement occurs by headward erosion. Anabranches act as distributary channels during floods, when water and sediment from overbank flows are transported to and deposited on the floodplain via the anabranches. During periods of low discharges, the anabranches act as tributaries to the main channel, transporting runoff from the floodplain and surrounding hillslopes to the main channel of Red Creek.

Aggradation is occurring in the main channel and on the floodplain throughout the study reach. Infilling of the main channel occurs primarily by lateral accretion, while the floodplain accretes vertically through deposition of overbank sediment from the main channel and anabranches. Infilling of the main channel may cause avulsion of the main channel into an anabranch. The abandoned main channel segment may then fill completely or act as an anabranch. Because lateral migration of channels is inhibited by the high cohesion of the silt and clay channel sediment, periodic avulsion is the primary form of lateral mobility in the system.
Enhanced boulder weathering under late‐lying snowpatches
Authors: Ballantyne Colin K. , Black Nicola M. , Finlay Donna P.
Published: February 2007

A Schmidt test hammer was employed to assess the aggregate surface hardness of samples of boulders dug out from under late‐lying snowpatches at sites in Switzerland, Scotland and Norway. The results were compared with an equivalent set of readings made on boulders at nearby snow‐free control sites. The results in every case reveal that the aggregate surface hardness of boulders buried by late‐lying snow is significantly less (at the 0·001 level) than that of boulders at the corresponding control sites. This result indicates that late‐lying snow significantly enhances rock weathering, probably because boulder and rock surfaces are exposed to prolonged wetting by percolating meltwater under late‐lying snowbeds.
Channel sediment variability along a river: A case study of the Siret River (Romania)
Authors: Ichim I. , Radoane M.
Published: February 2007

The Siret River has the largest drainage basin (42 274 km2) in Romania. It gathers all the rivers from the eastern part of the Eastern Carpathians, a fact that causes marked asymmetry of the basin. This study is principally concerned with changes in the form of the longitudinal profile and the grain size variability introduced by the Carpathian tributaries. Channel sediment analyses considered the petrography, granulometry, and morphometry of the pebbles, relating these to the river bed and floodplain geometry and to some properties of the drainage basin.

The following conclusions arise. The Siret River undergoes an intense regrading of its longitudinal profile, with marked aggradation between transects 24 and 26 (see Figures 1 and 2). This reflects selective accumulation of coarse material due to the massive contribution of the Carpathian tributaries. This phenomenon has been continuous throughout the Holocene, resulting in the gravel sheet formation of the Pericarpathian piedmont.
Solution‐collapse depressions and suspensates in the limnocrenic lake of banyoles (ne Spain)
Authors: Canals M. , Got H. , Julia R. , Serra J.
Published: February 2007

A high resolution seismic reflection survey in the Banyoles limnocrenic solution lake allowed penetration of dense suspensates occupying cone‐like bottom depressions of different size. The depressions result from the dissolution and collapse of underlying Eocene calcareous and gypsiferous materials over which lacustrine sediments of varying thicknesses have accumulated.

The suspensates occupying the depressions present three main types of seismic signatures: stratified, semistratified, and transparent. The densities of the suspensates and the water depths of their tops, which fluctuate continuously, vary from one depression to another. The maximum seismically recorded suspensate thickness is 44 m.

Morphological and structural features, seismic characters, and variable degrees of hydraulic activity, point to the existence of different stages of maturity in the lake bottom depressions. This work brings new insight on the dynamics and evolution of limnocrenic solution lakes.
Some mudslide movement patterns
Authors: Allison Robert J. , Brunsden Denys
Published: February 2007

A study has been made of the mechanisms of movement in a mudslide and the interrelationships between the controlling variables. Detailed monitoring has been conducted on a mudslide developed in the Wealden Beds, a Cretaceous mudrock. The parameters which govern mudslide instability have been continuously monitored using electronic datalogging techniques. Slip can be divided into four components: small ‘multiple’ (stick slip) movements which are grouped temporally; gradual or ‘graded’ slip within defined temporal limits; rapid ‘surge’ events which occur over a short time interval and involve large displacements and unexplained ‘random’ movements. Each of these four components occurs with varying frequency and at different times in the seasonal record. Slip is usually separated by periods of little or no change. Each component of mudslide movement displays characteristic patterns of pore water pressure change.
Scour, fill, and burial depth of coarse material in gravel bed streams
Authors: Hassan Marwan A.
Published: February 2007

Scour, fill, and burial depths of coarse particles were examined in two ephemeral streams using magnetically‐tagged particles and scour chains. The burial depth varied within a bedform and from one bedform to another. The maximum burial depth was recorded in bars, but differences in the mean burial depth in the pools, bar, and thalweg were insignificant. Mean burial depth was three to six times the median size of material on bar surfaces and ten to thirty times that in the pools and thalweg. More than eighty per cent of the tagged particles which were located on, or close to, the bed surface moved in each event. Although previously buried particles were moved by flood events, others which were initially exposed remained stationary on the surface or were buried in situ. The data indicate that the mean burial depth was intermediate between the mean depths of scour and fill. Deeply buried particles probably reflect the development of scour holes during flood flows. Aggradation and degradation changed the recorded burial depth, relative to the local bed surface, of stationary tracer particles. These observations indicate that scour and fill processes during a flow event are sporadic and change with water discharge.
Large‐scale floodplain modelling
Authors: Gee D. Michael , Anderson Malcolm G. , Baird Laura
Published: February 2007

A two‐dimensional horizontal finite element numerical model (RMA‐2) was applied to a 24 km river channel‐floodplain reach in West Germany. Initial results indicate that finite element schemes may successfully estimate inundation in large‐scale floodplain applications. Potentially, the resulting detailed velocity vector distributions and identification of inundation zones throughout storm events could provide an insight into the present day sedimentary environment on the floodplain.
Runoff generation in a sandy area—the nizzana sands, Western Negev, Israel
Authors: Yair A.
Published: February 2007

This paper presents the results of sprinkling experiments conducted over the lower part of vegetated and crusted linear dunes as well as over flat playa surfaces that appear in the interdune corridors. Data obtained show that these two surface units respond quickly to rainstorms. Runoff generation can be expected for any storm exceeding 2‐3 mm and runoff coefficients are high. When the topsoil algal crust, 1 to 2 mm thick, is removed from the surface of the dune, infiltration increases drastically and eliminates any possibility of runoff generation under present‐day rainfall conditions. This data may be of great help in the understanding of the geomorphology and sedimentary sequence of the corridors separting linear dunes.
Experimental frost and salt weathering of chalk—I
Authors: Jerwood L. C. , Robinson D. A. , Williams R. B. G.
Published: February 2007

To try to resolve the conflicts surrounding the influence of salts on frost weathering, chalk cubes were immersed, separately, in solutions of sodium chloride, sodium sulphate, and magnesium sulphate at concentrations of 5·5 per cent and 12·5 per cent, in a mixed solution of sodium chloride and sodium sulphate, and in distilled water. The cubes were subjected to six freeze‐thaw cycles with temperatures ranging from either +15 to — 10°C or + 15 to — 30°C. The results confirm that frost weathering can be enhanced by the presence of certain salts, but the degree of enhancement depends both on the concentration and type of salt and on the intensity of the freeze‐thaw regime. Some, but not all, of the results can be explained by the phase changes that occur during the freezing of the salt solutions.
Slope‐induced changes in channel character along a gravel‐bed stream: The Allt Dubhaig, Scotland
Authors: Ferguson Rob , Ashworth Phil
Published: February 2007

Changes in channel character along a small river in the Scottish Highlands are described using measurements in seven reaches over a 3 km length with no significant tributaries but a decline in slope from 0.02 to 0.00015 because of local baselevel control. This decline in slope is associated with rapid downstream fining of the gravel bed followed by an abrupt transition to a sand bed. The channel pattern alters progressively rather than abruptly, in the sequence (1) near‐braided, (2) meandering with active point‐bar chutes, (3) meandering with active outer‐bank talweg, (4) stable equiwidth sinuous. The changes in channel pattern and hydraulic geometry are predicted better by rational approaches based on critical shear stress or other physical concepts than by purely empirical discriminant or trend equations. Measurements in five reaches confirm a downstream decrease in shear stress and the amount and calibre of bedload. It is argued that the downstream changes in channel character in this stream are induced by profile concavity inherited from deglacial conditions, are typical of many streams in mountainous areas and can be understood in terms of slope‐induced changes in hydraulic properties.
Neotectonic effects on sinuosity and channel migration, Belle Fourche River, Western South Dakota
Authors: Gomez Basil , Marron Donna C.
Published: February 2007

Short‐term instability in the behaviour of a small, meandering alluvial channel is identified from the relation between sinuosity and either floodplain slope or channel slope within 17 reaches along an 81‐kilometre section of the Belle Fourche River in western South Dakota. In reaches 1 to 4 and 11 to 17 the channel is relatively stable and sinuosity varies inversely with channel slope. In reaches 5 to 10, sinuosity is positively related to floodplain slope. Sinuosity increases markedly in reaches 5, 6, and 7 (which are immediately downstream from a discontinuity in the long profile of the floodplain) in association with an increase in floodplain slope. Immediately upstream from the discontinuity, bankfull channel depth and sinuosity decrease and the area of the floodplain reworked by meander migration between 1939 and 1981 increases, in association with a decrease in floodplain slope. Channel behaviour in reaches 5 to 10 is best explained as a consequence of neotectonic activity, as indicated by changes in elevation recorded along geodetic survey lines that cross lineaments that may delimit the eastern boundary of the Black Hills uplift. Sinuosity acts as a barometer of the effects of neotectonic activity on alluvial channels. Initial indications of channel and floodplain instability due to neotectonic activity may be derived from evidence of anomalously active channel migration, as documented from photographic or topographic sources.
Results from a new model of river basin evolution
Authors: Willgoose Garry , Bras Rafael L. , Rodriguez‐Iturbe Ignacio
Published: February 2007

This paper briefly describes a model of the erosional development of catchments and their channel networks. The model differentiates between the dominant transport processes in hillslope and channels. The development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms. The growth of a river basin is qualitatively described.

The model concepts are used to study the basin during periods of growth (transient periods), as well as during dynamic equilibrium. This leads to hypotheses about the relationship between slopes, relief, tectonic uplift, erodability, runoff, and catchment area.

It is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation.
Erosion rates in the southern oregon coast range: Evidence for an equilibrium between hillslope erosion and sediment yield
Authors: Reneau Steven L. , Dietrich William E.
Published: February 2007

The relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes. In landscapes containing hillslopes crenulated by alternating topographic noses and hollows, estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows. Hollows act as local traps for a portion of the colluvium transported down hillslopes, and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area. Analysis of colluvial deposits in nine Oregon Coast Range hollows has yielded average colluvial transport rates into the hollows of about 35cm3cm−1yr−1 and average bedrock lowering rates of about 0.07 mm yr−1 for the last 4000 to 15000 yr. These rates are consistent with maximum bedrock exfoliation rates of about 0.09 mm yr−1 calculated from six of the hollows, supporting the interpretation that exfoliation rates limit erosion rates on these slopes. Sediment yield measurements from nine Coast Range streams provide similar basin‐wide denudation rates of between 0.05 and 0.08mm yr−1, suggesting an approximate steady‐state between sediment production on hillslopes and sediment yield. In addition, modern sediment yields are similar in basins varying in size from 1 to 1500 km2, suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape.
High energy coastal sedimentary deposits; an evaluation of depositional processes in Southwest England
Authors: Foster I. D. L. , Albon A. J. , Bardell K. M. , Fletcher J. L. , Jardine T. C. , Mothers R. J. , Pritchard M. A. , Turner S. E.
Published: February 2007

Sediments left by coastal flooding have been observed worldwide and have been variously ascribed to the action of storm surges and tsunami waves. To date, no study has attempted to unequivocally establish on stratigraphical, sedimentological, and palaeoecological grounds the means by which these two different processes might be distinguished in coastal sedimentary sequences. This paper examines the evidence for historical storm surges and tsunamis and shows that both high magnitude events have been documented over the past 250 years in southwest England. Sand layers of varying thickness are present within Holocene lagoonal and peat sequences of several shallow lakes of the Scilly Isles. Detailed analysis of Big Pool, St Agnes, indicates that the basal peats date from around 1000 BP. Within the basal peats are numerous thin sand layers. Above the basal peat is an extensive sand layer 15 to 40 cm thick. The base of this latter layer probably dates from the early to mid 18th century. Particle size, grain surface morphology, diatom, and mineral magnetic studies are used to try and determine the most likely mode of deposition. The results of all analyses are inconclusive, but the weight of evidence suggests that the increasing frequency of thin sand layers in the upper part of the basal peat may be related to the increasing frequency and intensity of Atlantic storms during the Little Ice Age superimposed upon a rising sea level. The thick sand layer may have been deposited by the tsunami wave generated by the Lisbon earthquake of November 1,1755. Due to the difficulties in distinguishing depositional processes in coastal environments known to have been affected by storm surges and tsunami waves, it is suggested that generally accepted sedimentological techniques are inadequate for discriminating depositional processes in coastal environments.
Impact of flow variability on the morphology of a low‐energy meandering river
Authors: Rhoads Bruce L. , Miller Michael V.
Published: February 2007

Few studies have precisely documented the response of stream channels to short‐term flow variability. This paper examines the impact of sequential flows of various magnitudes on the morphology of a low‐energy river in northeastern Illinois, U.S.A. Between June 1986 and November 1988 channel cross‐sections were surveyed on a semiannual basis at 26 locations along a 7.2 km stretch of the Des Plaines River. During this period an estimated 100‐year flood, several bankfull flows, and an extreme low flow associated with a severe drought occurred. The response of the river channel to each of these events was relatively minor. Mean changes for the reach were generally less than 3 per cent for mean depth and less than 1 per cent for width. Statistical analysis indicates that net changes in width and depth over the entire period were not significantly different from zero. This lack of geomorphic response is attributable to low stream power, low hydrologic variability, fine bed materials, and cohesive banks along this stretch of river. Although dramatic changes in channel morphology did not occur, subtleties in geomorphic response were observed that reflect the temporal ordering of hydrologic events.
Channel morphology and bedload pulses in braided rivers: a laboratory study
Authors: Hoey Trevor B. , Sutherland Alex J.
Published: February 2007

Bedload pulses in gravel‐bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology. Bedload transport and channel morphology were measured in a small‐scale generic model of braided gravel‐bed streams. Two experiments are described in which braided channels developed in a 14 m × 3 m sand tray. Total bedload output from the tray was weighed every 15 minutes. Stream bed geometry was surveyed every four hours. Pulses were observed in the bedload output time series, and were qualitatively related to the channel morphology immediately upstream of the measuring section. The Bagnold (1980) bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading. Underprediction occurred when applied to degrading channels. Aggradation was associated with channel multiplication and bar deposition. Channel pattern simplification occurred when degradation took place, and bars emerged from the water flow. Development of phases of aggradation and degradation is dependent upon the three‐dimensional geometry of the stream beds. Spatial and temporal feedback loops can be identified, enabling links between channel morphology and bedload transport rate to be directly identified.
Bedload transport processes in a braided gravel‐bed river model
Authors: Young W. J. , Davies T. R. H.
Published: February 2007

A 1:50 scale hydraulic model was designed, based on Froude number similarity and using hydrological and sediment data from a small braided gravel‐bed river (the North Branch of the Ashburton River, Canterbury, New Zealand). Eighteen experiments were conducted; seven using steady flows, and eleven using unsteady flows. The experiments were carried out in a 20 m × 3 m tilting flume equipped with a continuous sediment feed and an automated data acquisition and control system. In all experiments water at 30°C was used to reduce viscosity‐related scale effects.

Analyses of the experimental data revealed that bedload transport rates in braided channels are highly variable, with relative variability being inversely related to mean bedload transport rate. Variability was also found to be cyclic with short‐term variations being caused by the migration of bedforms.

Bedload transport was found to be more efficient under steady flow than under unsteady flow, and it was postulated that this is caused by a tendency for channel form to evolve towards a condition which maximizes bedload transport for the occurring flow. Average bedload transport rate was found to vary with channel form, although insufficient measurements were made to define a relationship.
Investigation on age and genesis of silcretes in Queensland (Australia)–Preliminary results
Authors: Radtke Ulrich , Brüuckner Helmut
Published: February 2007

Silcretes from Queensland (Australia) were dated by means of the electron spin resonance dating technique. The results range from 1.5 to 10.8 million years; therefore, these silcretes were formed between the upper Miocene and the early Pleistocene. For a conclusive interpretation of the data geochemical and thin section analyses were also carried out. ESR dating of silcretes for the first time offers a direct approach to a chronostratigraphic framework of the genesis of these duricrusts, and of the palaeoclimatic events attributed to them.
Denudation, isostasy and landscape evolution
Authors: Gilchrist A. R. , Summerfield M. A.
Published: February 2007

The idea that the isostatic response to progressive denudational unloading can be episodic over cyclic timescales is widely cited in the geomorphological literature. We demonstrate, however, that this notion, which has been regarded as a possible mechanism of widespread landscape rejuvenation, is based on a fundamental misunderstanding of the principles of flexural isostasy. Rather than a discontinuous response, in cases where the half‐width of the applied load is greater than a few tens of kilometres the lithosphere experiences a continuous compensation which is dependent upon the wavelength of the applied load rather than upon a lateral, or vertical, threshold of unloading which has to be exceeded before isostatic recovery is initiated. Although a flexural isostatic response cannot account for episodic uplift during a denudational cycle, it can explain the growth and persistence of significant marginal upwarps along passive margins across which there is a marked contrast in denudation rates. Such marginal upwarps, in turn, probably play a critical role in the long‐term evolution of drainage systems and landscapes in adjacent continental hinterlands.
Channel change and the significance of floodplain stratigraphy: 1990 flood event, lower river Tay, Scotland
Authors: Gilvear D. J. , Harrison D. J.
Published: February 2007

During February 1990 a flood event on the River Tay with an estimated recurrence interval of 70 years in its lower reaches caused extensive flooding and geomorphological change. The most extensive area of flooding and dramatic geomorphological change, the erosion of two new channels across the floodplain, was in the vicinity of the village of Caputh, Perthshire. The location of the eroded channels relates to the position of former river courses, identifiable by depressions in the floodplain surface and floodplain stratigraphy. The lower floodplain surface elevation and occurrence of gravel and sand deposits along the line of the former river courses caused the area to be more vulnerable to erosion and controlled the morphology of the eroded channels.
Sediment yields and sources in a welsh upland lake‐catchment during the past 800 years
Authors: Dearing J. A.
Published: February 2007

Estimates of suspended sediment yield over the past 800 years have been derived from a whole‐basin study of lake sediments in Llyn Geirionydd, North Wales. Magnetic and physical sediment properties were used to correlate a suite of cores to a master chronology based on 210Pb and 14C dates. The sources of sediment within the catchment were identified by comparing the magnetic and heavy metal properties of sediments, soils, and stream sediments. Mean suspended sediment yields range from 6 to 18 t km−2 yr−1 with high yields in the periods 1765‐1830 and 1903‐1985 corresponding to mining activities in the catchment. The impact of earlier deforestation, agricultural expansion, or climatic change on sediment yields is low, although there is evidence that agricultural activities increased levels of peak stream discharge. Afforestation in the 20th century does not appear to have significantly increased sediment yield. Sediment sources have remained fairly constant through time; they appear to be widespread and dominated by stream channel sides rather than point sources, except during the mining phases when spoil material has dominated the sediment load. Sediment loads to the lake today are still dominated by sediment derived from unvegetated spoil heaps.
Hydraulic conditions for rill incision under simulated rainfall: A laboratory experiment
Authors: Slattery Michael C. , Bryan Rorke B.
Published: February 2007

A series of controlled laboratory experiments were conducted in order to obtain precise data on the hydraulic and sediment transport conditions during rill formation. Tests were carried out using a crusting‐prone binary mixed soil in a 15 m long flume at an average slope of 0·087 under simulated rainfall. Rainfall intensities varied from 30–35 mm h−1 and developed about 70 per cent of the kinetic energy of natural rainfall of similar intensity.

Runoff and sediment discharge measured at the downstream weir were strongly influenced by rill forming processes. Essentially, rill incision reduced runoff discharge as a result of increased percolation in rill channels but increased sediment discharge. Secondary entrainment processes, such as bank collapse, also increased sediment discharge at the weir. Knickpoint bifurcation and colluvial deposition, however, decreased sediment discharge. Rills always developed through the formation of a knickpoint. The critical condition for knickpoint initiation was the development of supercritical flow and waves which mould and incise the bed. Prior smoothing of the soil surface by entrainment and redistribution of sediment facilitated supercritical flow. Statistical analysis showed that hydraulic and sediment transport conditions differed significantly in rilled and unrilled flows. The relationship between sediment discharge, rill erosion, and flow hydraulics was found to be nonlinear, conforming to a standard power function in the form y = axb. Rills were also associated with significantly increased sediment transport capacities. However, rill initiation was not clearly defined by any specific hydraulic threshold. Instead, rilled and unrilled flows were separated by zones of transition within which both types of flow occur.
Alluvial sediment sources in a glaciated catchment: The voidomatis basin, Northwest Greece
Authors: Woodward Jamie C. , Lewin John , MacKlin Mark G.
Published: February 2007

X‐ray diffraction (XRD) of the fine matrix component of four alluvial units and modern channel sediments in the Voidomatis River Basin of northwest Greece shows that fine sediment sources have changed considerably during the late Quaternary. The matrix fraction of the modern channel sediments is derived predominantly from erosion of local flysch rocks and soils. During the last glaciation, however, the fine sediment load of the Voidomatis River was dominated by glacially‐ground, finely comminuted limestone materials. Limestone‐derived fine sediment is not produced in significant amounts under modern climatic conditions. By combining this XRD work with a detailed programme of clast lithologic 1 analysis we have reconstructed former bedload and fine sediment load composition. The lithological properties of both the coarse (8‐256 mm) and fine (< 63 μm) elements of the sediment load have varied markedly during the late Quaternary. A simple, semiquantitative assessment of fine sediment mineralogy, using diffractogram peak‐height data, has provided a valuable complement to the information gathered from more traditional clast lithological techniques. Together, in favourable geological settings, fine fraction mineralogy and clast lithological analysis can provide a valuable tool for the reconstruction of late Quaternary alluvial environments.
Denudational isostatic rebound of intraplate highlands: The lachlan river valley, Australia
Authors: Bishop Paul , Brown Roderick
Published: February 2007

A range of evidence from the Lachlan valley in the southeast Australian highlands is consistent with Neogene isostatic rebound in response to denudational unloading. This evidence is found along the inland edge of the highlands in the transition zone between the highlands proper and the Lachlan's inland alluviated valley and the intracratonic Murray Basin. The amounts and rates of uplift indicated by offsets of suballuvium bedrock profiles and the long profiles of Tertiary valley‐filling basalts are consistent with modelling of denudational rebound using known rates of highland denudation and basinal sedimentation, and reasonable crustal properties. The modelling shows that weak to moderately strong strong lithosphere (effective elastic thickness, Te = 1‐25 km) and strong lithosphere (Te = 100 km) are all consistent with the observed amounts of rebound. Strong lithosphere must be broken, however, to be consistent with the field data. Even in the Australian setting, which is characterized by very low rates of denudation, isostatic rebound in response to denudational unloading must be a significant factor in maintaining highland elevation and must be incorporated in models of long‐term landscape evolution. It would be expected that denudational isostatic rebound would be an even more significant component of long‐term landscape evolution in areas of higher denudation rates.
Topographic changes associated with coastal dune blowouts at island beach state park, New Jersey
Authors: Gares Paul A.
Published: February 2007

Topographic changes in two blowouts located in Island Beach State Park, New Jersey, USA were monitored over the winter of 1981‐1982. Elevation changes were measured with erosion pins, and sediment traps placed at comparable locations in each blowout monitored the amount of sand moved by the wind. Discrete wind events were identified from regional data, and morphological data for the intervals with the highest onshore and offshore wind speeds are examined in detail.

Vegetation is the primary influence on the development of the two blowouts. Blowout A is characterized by eroding sidewalls, a stable base, and an accreting blowout rim. High rates of sediment transport occur through the blowout throat which results in accretion on the vegetated rim. This blowout is an active sediment transfer system. Vegetation causes a large amount of deposition in the throat of blowout B. As vegetation was buried over the winter, the area of deposition migrated inland. Sidewall erosion also occurred in blowout B. Little change was recorded on the blowout rim. Blowout B is a recovering system where sediment is delivered to the blowout floor from the beach by onshore winds and from the blowout rim by offshore winds where it is stabilized by vegetation.

The development of foredune blowouts is governed largely by vegetation cover on the dune crest and by sidewall erosion during offshore and onshore winds. Blowout recovery depends on vegetation growth and sediment deposition in the throat, and on the role of the sidewalls as sources of sediment which is deposited elsewhere within the system. Foredune blowouts are dynamic systems in which positive feedbacks in sediment availability and vegetation growth lead to a cycle of development and closure.
Historical geomorphology and pedology of the Gandak Megafan, Middle Gangetic Plains, India
Authors: Mohindra R. , Parkash B. , Prasad J.
Published: February 2007

The Gandak megafan of eastern Uttar Pradesh and northwestern Bihar lies in the Middle Gangetic Plains. The Gandak River has shifted about 80 km to the east due to tilting in the last 5000 years. This has created a soil chronoassociation similar to the chronosequences found on some flights of river terraces. This chronoassociation has five members, QGD1‐5. They are distinguished on the basis of profile development, clay mineralogy and calcium carbonate content. Chlorite transforms to vermiculite on a large scale from QGD1 to QGD3 and decreases drastically in member QGD4. Kaolinite and interstratified kaolinite‐smectite are abundant in the older members of the chronoassociation. The youngest soils (QGD1:? < 500 b.p.) are found on the floodplains of the major rivers. QGD2 soils, like those of the Young Gandak Plain, date from? > 500 b.p., while QGD3 soils, like those on the Older Gandak Plain and Old Rapti Plains date back to 2500 b.p. QGD4 soils, like those on the Oldest Gandak Plain, are dated as? 5000 years b.p., whilst the oldest QGD5 soils, as on the Old Ghaghra Plain and Ganga‐Ghaghra Interfluve, date back to 10000 b.p. These soils, which include pedogenic calcite and a? saline epipedon, indicate a dry climatic spell during the period 9000‐11000 b.p. Faults developed on the megafan are not related to the basement structures.
Effects of coarse woody debris on morphology and sediment storage of a mountain stream system in western Oregon
Authors: Nakamura Futoshi , Swanson Frederick J.
Published: February 2007

Effects of coarse woody debris (CWD) on channel morphology and sediment storage were investigated at five sites, representative of first‐order to fifth‐order streams. In the steep and bedrock‐confined stream (first‐second order), interaction between the channel and CWD was limited, except where breakage upon falling produced CWD pieces shorter than channel width. Channel widening, steepening and sediment storage associated with CWD were observed predominantly in third‐ to fifth‐order streams. Variation in channel width and gradient was regulated by CWD. In the fifth‐order stream, most of the CWD pieces derived from the riparian forest interacted directly with the channel without being suspended by sideslopes. In this system CWD promoted lateral channel migration, but sediment storage was temporary, with annual release and capture.
Enhanced bedrock weathering in association with late‐lying snowpatches: Evidence from Livingston Island, Antarctica
Authors: Hall Kevin
Published: February 2007

An indication of the extent of weathering on different aspects of rock outcrops on Livingston Island, Antarctica, was obtained by means of a Schmidt hammer, a cone indenter and measurement of weathering rind thickness. Results show that weathering, particularly chemical weathering, is enhanced on the lee side of outcrops where snow accumulates as a result of prolonged wetting by the melting snow. Rock moisture and temperature data indicate that the south‐facing, snow‐accumulation side of obstacles have high rock moisture levels and maintain relatively high temperatures. Whilst chemical weathering is greater on the leeward side of outcrops, mechanical processes are greater on the windward side. The presence of late‐lying snow thus appears to exert a strong influence on weathering.
The effects of deforestation on slope and channel evolution in the tectonically active Darjeeling Himalaya
Authors: Froehlich Wojciech , Starkel Leszek
Published: February 2007

The main indicators of Quaternary tectonic uplift are the young mountain slopes of the Darjeeling Himalaya, rising straight above the Ganga–Brahmaputra foredeep, fragments of uplifted river terraces and fresh fault scarps. Evidence for the continuation of the uplift includes downcutting of the Tista and other straight rivers in the bedrock, continuing aggradation in the plains and overriding of the metamorphic rocks on the alluvia. Owing to deforestation and extensive land use, the earlier natural tendency of a dominance of channel incision over slope degradation has changed to prevailing aggradation, even in steep valley reaches, caused by intensive slope mass movements and the overloading of the mountain creeks. Aggradation progresses upstream along the rivers dissecting the mountain front.