bluuebunny/crossref_metadata_2025_split huggingface dataset:
Results from a new model of river basin evolution
Authors: Willgoose Garry , Bras Rafael L. , Rodriguez‐Iturbe Ignacio 
Published: February 2007

AbstractThis 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

AbstractThe 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

AbstractSediments 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

AbstractFew 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

AbstractBedload 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

AbstractA 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

AbstractSilcretes 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

AbstractThe 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

AbstractDuring 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

AbstractEstimates 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

AbstractA 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

AbstractX‐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

AbstractA 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

AbstractTopographic 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

AbstractThe 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

AbstractEffects 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

AbstractAn 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.