bluuebunny/crossref_metadata_2025 huggingface dataset:
Timescales and the role of inheritance in long‐term landscape evolution, northern New England, Australia
Authors: Fried Alan W. , Smith Nicola
Published: February 2007

Landscape evolution in northern New England is characterized by the persistence of landforms over long time periods. The topography in the study area was initiated by Paleozoic diapiric intrusion of granitic rocks as highs within metasedimentary and volcanic rocks. This framework was probably reinforced by differences in the resistance of the massive igneous and the fractured metasedimentary rocks to erosion. As a result, both the Tertiary and present‐day relief of the area consists of uplands developed on granitic rocks partly overlain by Paleozoic volcanic rocks, and lowlands developed on Paleozoic metasediments. Extensive volcanism in the Tertiary had only a minimal effect on this relationship. A significant impact of Tertiary volcanism, however, was the diversion of major streams across topographic highs. Despite 19‐35 Ma of incision, these streams are still far from establishing equilibrium profiles and dissecting the highs.

The persistence of topography for a timescale of the same order of magnitude as that conventionally thought to be required for planation is due to reduced denudation rates in a passive tectonic setting and the presence of erosion‐resistant Paleozoic igneous units. The latter influence is indicated by knickpoint persistence for 19‐35 Ma on streams diverted across these rocks. Since it is generally considered that such disequilibria are short‐lived features formed by Quaternary or ongoing deformation, this knickpoint persistence has important implications for landscape analyses that use disequilibria to assess recent tectonism in a landscape.
Design and installation of a novel automatic erosion monitoring system
Authors: Lawler D. M.
Published: February 2007

Process inference in geomorphology is hindered by a lack of information on the true temporal distribution of contemporary erosional and depositional activity. To tackle this problem a low‐cost, automatic monitoring system based on the photo‐electronic erosion pin (PEEP) sensor has been developed. The PEEP is essentially an array of photosensitive cells enclosed within a transparent tube and connected by cable to a datalogger. When inserted into an eroding landform, subsequent retreat of the face exposes more photosensitive cells to light which increases PEEP voltage output. Deposition decreases sensor outputs. The logged signals thus reveal the magnitude, timing and frequency of erosion and deposition events with much greater precision than has hitherto been possible. Measurement principles, electronic and physical design, calibration, field installation, problems and prospects and pilot results from a river bank erosion site are discussed. The PEEP system appears to have great potential for disentangling competing hypotheses in geomorphological process studies, and in building and testing erosion and sediment transport models of high temporal resolution.
On the mathematical description of glaciated valley cross sections
Authors: Harbor Jonathan M. , Wheeler Dennis A.
Published: February 2007

Morphometric analyses of glaciated valleys typically involve attempts to fit empirical data from valley cross‐profiles to quadratic (parabolic) or power‐law equations, with the choice of equation depending on the goal of the analysis. In assessing the relative merits of these two types of equations, some confusion has arisen because of apparent variations in coordinate system datums between studies which have made use of the power‐law equation. However, we show that this confusion relates to a simple mathematical error, rather than any true difference in methodology. Of more significance, however, is the fact that in fitting a power‐law equation to observed profiles, significant bias is introduced by the use of a logarithmic data transformation. Because of this implicit bias, power‐law equation parameters are influenced most strongly by data points close in elevation to the centre of the valley, and so failure to account for the depositional elements which frequently occur in these areas can lead to significant errors if the aim of the analysis is to characterize the form of the erosional profile.
A 3‐d model of quaternary terrace development, simulations of terrace stratigraphy and valley asymmetry: A case study for the allier terraces (limagne, France)
Authors: Veldkamp A.
Published: February 2007

The combined effects of climate and tectonism on general terrace stratigraphy and valley asymmetry during the last half million years in the Allier system (France) are simulated by a 3‐D conceptual model (LIMTER). This model allows the formulation and evaluation of long term terrace formation scenarios for the Allier system. Simulation results suggest that terrace stratigraphy in the study area is mainly the result of internal dynamics and climatic change. Local tectonism contributed to the development of unpaired terraces while the general regional uplift played a dominant role in determining terrace formation and preservation in general.
The influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers: A reply
Authors: Reid Ian , Hassan Marwan A.
Published: February 2007

Clifford et al. (1992) argue that differences in hydraulic conditions at the moment of sediment entrainment in Turkey Brook, flood by flood, are attributable to variations in the form drag that arises from cluster microforms. While not denying the possibility of variable cluster concentration, we show that the time‐dependent bed consolidation and cementation that arises as a function of interstitial matrix development can also account for variation in the traction threshold. Clifford et al. further postulate that the growth of pebble clusters just prior to bedload entrainment is a cause of the observed differences in traction thresholds at the start and finish of bedload during a flood event. This merits further examination. However, we point out that clusters are not only observed at low flow and, therefore, already present and able to contribute significant form drag as the next bedload generating flood waxes, but that they are known both to survive more or less intact and to entrap mobile particles during bed disturbing events. The revelation by Clifford et al. that flow structure in the River Quarme reflects differences in bed rugosity between riffles and pools and that it relates in scale to bed roughness elements (perhaps clusters) is not surprising. There is, however, some difficulty in distinguishing the precedence of chicken and egg when using this data set to elucidate the cause of cluster spacing. Nevertheless, the inference that flow and form are dynamically linked is in sympathy with our own conclusions that cluster spacing is an equilibrium condition governed by the interplay of flow resistance and sediment transport.
Differential bedload transport rates in a gravel‐bed stream: A grain‐size distribution approach
Authors: Diplas Panayiotis
Published: February 2007

Two methods that were recently proposed for calculating fractional bedload transport rates in gravel‐bed streams are examined closely. Both of them employ the Oak Creek bedload data. The Diplas (PD) method is guided by dimensional analysis and, therefore, can be used to predict bedload transport in different gravel rivers. The only requirement for using this method is the knowledge of the subsurface material size distribution of the stream of interest. The expression for the fractional bedload transport obtained by the Shih and Komar (SK) method for Oak Creek cannot be used for other streams. Its use for a given stream requires information that is rarely available. For the Oak Creek case both methods demonstrate similar predictive ability.
A reply to [a discussion of shih and Komar's (1990) analysis of differential bedload transport rates in a gravel‐bed stream: A grain‐size distribution approach] by P. Diplas
Authors: Komar Paul D. , Shih Shyuer‐Ming
Published: February 2007

Several points have been raised by Diplas concerning our analyses in Shih and Komar (1990) of bedload transport in gravel‐bed streams, and our comparisons with the approach developed by Diplas (1987) as a modification of the dimensional analysis first undertaken by Parker et al. (1982). We disagree with Diplas' assessment that our approach [cannot be used for other streams] and that dimensional analysis necessarily expands the range of application of his analysis approach. We argue here that the dimensional analysis of Diplas obscures the relationship between the transport rate and grain size, and in fact leads to a complex and implausible dependence. In contrast, our approach allows one to better focus on the changing grain‐size distributions as the flow discharge and mean bottom stress increase.
Relationships between deflation and near surface wind velocity in a coastal dune blowout
Authors: Pluis J. L. A.
Published: February 2007

Detailed field measurements were made of the degree of surface level change in a blowout, situated in the coastal dune area of Meijendel, The Netherlands. A formula was established to express the erosivity of the wind for the corresponding 34 measurement intervals, over a period of about 3 years. Having established, for 12 wind sectors, the relationship between wind velocity at the nearest standard weather station and at five locations in the blowout, correlations were derived between the deflation rate in the blowout and the wind erosivity using standard hourly wind data.

The winter season, although the most windy, is by far the least effective season: the threshold shear wind velocity is disproportionally increased because the moisture content of the surface sand is high. The soil moisture conditions are described as a function of the daily precipitation and evaporation rate. The two most relevant upper and lower threshold shear wind velocities are determined empirically. During the summer season, deflation rate is even higher than indicated by the net surface level change because deflation is partly compensated by deposition of sand transported by rainwash from the blowout margin.

With regard to spatial variation in the deflation rate within the blowout, it appears that locations with relatively high velocities coincide with higher deflation rates. However, the spatial variation is commonly less than is expected from the horizontal wind velocity distribution. In view of this the role of wind direction, blowout morphology and algal coverage of the soil in the deflation rate is discussed.
An approximation of the sediment budget of the lower mississippi river prior to major human modification
Authors: Kesel Richard H. , Yodis Elaine G. , McCraw David J.
Published: February 2007

A sediment budget is constructed for the Lower Mississippi River prior to the introduction of most human modifications. Components of the budget are derived from historical data including Mississippi River Commission hydrographic survey maps for the period from 1877 to 1924. A quantitative estimate of major sediment sources, sinks and storage locations in the Lower Mississippi Valley suggest that the most important sediment source was from bank caving and that at least 50 per cent more sediment was deposited in short‐term channel storage than in longer‐term overbank storage. The budget indicates that the proportion of sediment transported as bedload was significantly greater than previously estimated. The magnitude and variability of these sediment budget components are discussed. The results of the study suggest that prior to modifications the river was aggrading over much of its length.
Post‐eruption erosion and deposition in the 1980 crater of Mount St Helens, Washington, determined from digital maps
Authors: Mills Hugh H.
Published: February 2007

The crater of Mount St Helens shows one of the world's highest known rates of mass wasting. On many summer days, rockfall is almost continuous, and many large rock and dirty‐snow avalanches have travelled several kilometres from their sources on the crater walls. Since formation of the crater on 18 May 1980, talus cones exceeding 100 m in thickness have formed at the base of the unstable 600 m high crater walls. To estimate rates of erosion and deposition, a series of digitized topographic maps made from aerial photographs taken of the crater in 1980, 1981, 1983, 1986 and 1988 were analysed using a geographic information system. Between 1980 and 1988, 30 × 106 m3 of rock were eroded from the crater wall, representing a mean retreat rate of 2.1 m yr−1. To account for the volume increase that occurs when bedrock is transformed into scree, this volume is multiplied by 4/3; this provides an estimate of the rock‐debris volume supplied to the crater floor of 40 × 106 m3. The actual volume of deposits that accumulated during this 8 year period, however, is 68 × 106 m3. The difference of 28 × 106 m3 is presumably the volume of snow intercalated between insulating layers of rock debris. Similar calculations for each of four time intervals between 1980 and 1988 suggest that wall erosion and thus talus accumulation rates are declining, but that rates will probably remain high for decades to come.
A numerical model for shore‐normal sediment size variation on a macrotidal beach
Authors: Horn Diane P.
Published: February 2007

This paper describes a computer simulation model which is designed to predict the selective shore‐normal sorting of grain sizes in the nearshore environment. The model simulates wave shoaling, wave height attenuation due to frictional losses and breaking, using linear theory up to the break point and a breaker decay model in the surf zone. Peak horizontal orbital velocities at the bed are calculated from Stokes second‐order wave theory. The peak onshore and offshore velocities are used with the threshold expression of Komar and Miller (1975) to generate a spatial pattern of size variation of threshold grain diameter along a profile normal to the shore from deep water to the swash zone. The predicted grain size is used in an hydraulic interpretation of grain size distribution on the intertidal profile, based on the hydrodynamic variations over a tidal cycle on a macrotidal beach. The model is successful in predicting the broad pattern of increasing grain size in the onshore direction which has been observed in nature. Comparisons between measured and predicted grain size distributions indicate that the predictions of the model are better than those of previous models, but the model is more successful at predicting sediment size distributions than at predicting mean sizes on a beach profile.
Post‐deforestation soil loss from steepland hillslopes in Taranaki, New Zealand
Authors: Derose R. C. , Trustrum N. A. , Blaschke P. M.
Published: February 2007

Soil erosion on steepland hillslopes in Taranaki, New Zealand, where landsliding is the dominant erosion form, was investigated by comparing mean regolith depths between first‐order basins that have had their forest cover removed for different periods of time. Regolith depth and slope angle data were collected along 19 profile lines and 30 profile lines from steepland basins that had been deforested for 10 and 85 years, respectively. These profile lines were subdivided into a total of 236 profile segments of relatively linear slope angle and uniform regolith depth, that averaged 17·5 m in length.

The depth of pre‐existing regolith on post‐deforestation landslide sites is estimated from a regression of regolith depth on slope angle for undisturbed (non‐landslide) profile segments. Regolith depletion on landslide sites is in turn estimated by subtracting the depth of regolith on landslide sites from the estimate of pre‐existing regolith depth. Regolith depletion by post‐deforestation landslides, averaged over the entire length of profile lines, gives an estimate of average surface lowering. For the area deforested for 85 years, average surface lowering by post‐deforestation landslides is 0·15 ± 0·04 m, and is the same as the difference in mean depth of 0·15 ± 0·11 m between this area and the area deforested for 10 years. Erosion of regolith from hillslopes by processes other than landsliding appears to be minimal. The 0·15 m average surface lowering represents a regolith depletion rate of 1·8 ± 0±5 mm yr−1. For hillslopes steeper than 28°, where all post‐deforestation landslides occur, average surface lowering is 0·20 ± 0·05 m, and the regolith depletion rate is 2±4 · 0±6 mm yr−1. Average surface lowering is greatest at 0·23 ± 0·07 m on hillslopes steeper than 32° where most post‐deforestation landslides occur. Here, the regolith depletion rate is 2·7 ± 0·8 mm yr−1.

A large‐magnitude, low‐frequency storm in March 1990, produced an average surface lowering of 0·041 m. There were proportionately more landslides in the area deforested for 10 years, illustrating the importance of previous erosion history of hillslopes on the spatial distribution of landslides. There were also comparatively few landslides on steeper hillslopes because previous lower magnitude storms had already removed much of the deeper regolith.
Monitoring alluvial sand suspension by eddy correlation
Authors: Lapointe Michel
Published: February 2007

Eddy correlation techniques are standard tools in micrometeorology and oceanography to measure momentum and contaminant transport across turbulent boundary layers. They can, in theory, be used to estimate the net vertical suspended sediment flux directly over different areas of an alluvial channel boundary, and thus disclose ongoing erosion/deposition patterns. The basic principles and main problems in applying the technique to alluvial suspension are first introduced. Results from a trial application of the method in a large sand bed river are then presented; the focus of the analysis is on the substantial (and surprising) contributions of multi‐minute flow fluctuations to suspension work in the study environment.

The data were collected in a 10 m deep channel of the Fraser River near Mission, British Columbia, Canada. Turbulent fluctuations of flow components streamwise and normal to the bed, along with the output of an optical suspended sediment sensor, were monitored over 7 h, 1 m above the bed. Flow velocities averaged 0·9 ms−1 and mean suspended sediment concentrations 500 mgl−1, at sensor level above 1–5 dm high dunes.

Spectral analysis of the records reveals that approximately 30 per cent of the vertical suspended sand mixing across the sensor level (and roughly as much of the momentum exchange) was linked to gradual flow oscillations with periods between 1 and 13·6 min (underlying briefer, turbulent fluctuations). Extended periods of sediment‐rich, slightly upward directed but slower mean flow alternated with periods of sediment‐poor, slightly downward and faster mean flow; these slow fluctuations involved 10–20 cms−1 changes in 5 min average flow speed, 2–4· changes in vertical flow angle and 100 mgl−1 changes in mean sand concentration. To obtain accurate eddy‐correlation estimates of the vertical suspension flux in the study conditions, hour‐scale flow and turbidity records that include many of these multi‐minute cycles appear to be necessary.

The spectra of the Fraser River near‐bed signals do not conspicuously differ in overall shape (in terms of low‐frequency content and location of peak) from turbulent spectra encountered in some atmospheric boundary layers. Nonetheless, the long period fluctuations observed on the Fraser River may not be turbulent; rather they may reflect slowly evolving perturbations in the near‐bed streamlines, caused by bedform translation or gradual fluctuation within the large‐scale streamwise cells of the secondary flow.
Indicators of faulting events and periods of quiescence in desert alluvial fans
Authors: Gerson R. , Grossman S. , Amit R. , Greenbaum N.
Published: February 2007

The main objective of the present paper is to present an integrated approach to the study of faulting stages in coarse alluvial deposits. The study site is the alluvial fan of Nahal Shehoret, presently under an extremely arid regime. The exposure of fault scarps on the fan surfaces enables the identification of several geomorphic indicators employed in analysing and separating faulting events and periods of quiescence: (a) the nature of fault scarp topography; (b) soil catenary development on fault scarps; (c) buried paleosols in alluvial deposits; (d) colluvial bodies; (e) rotated clasts along fault planes. These indicators enable us to determine, at all sites studied, the total amount of displacement, to separate faulting events and the amount of their displacement per event, and to evaluate scarp stability and the duration of periods of tectonic quiescence.
Geomorphology and seismotectonic elements in the giarre area, sicily
Authors: Adorni G. , Carveni P.
Published: February 2007

A morphostructural analysis has been performed on the eastern flank of Mt Etna, located between the towns of St. Alfio and Linera and the Ionian Sea. The research has been carried out through analysis of aerial photographs, and has allowed recognition of morphoneotectonic elements such as: some scarps with rectilinear trend, laterally becoming morphological flexures, according to the lithology; anomalies in the hydrographic network, such as rectilinear tracts of drainage, valleys with simple or double bends, hanging valleys and truncated valleys, narrow deeply engraved valleys with meanders and fluvial captures. All these elements are caused by a fault system oriented NNW–SSE, with a mainly vertical component.

Seismic events with very shallow foci have been recorded in the study area; these earthquakes triggered several small landslides on the fault scarps and large series of coseismic and coaxial fractures.

It is possible to show that the morphostructures examined have been reactivated during many of the seismic events that have occurred in the area. The combination of these elements verifies that the morphostructures have a real neotectonic cause, which is associated with uplifts which have occurred in the area at different times.
Mechanisms responsible for streamflow generation on a small, salt‐affected and deeply weathered hillslope
Authors: George Richard J. , Conacher Arthur J.
Published: February 2007

This paper considers the contributions of overland flow, throughflow and deep seepage to the generation of streamflow in a salt‐affected, deeply weathered landscape.

Runoff mechanisms on a small hillslope in south‐western Australia were dependent on the extent and development of variable source areas. In winter, streamflow generation was controlled by returnflow, saturation overland flow and throughflow. In summer, post‐ponding, infiltration‐excess and saturation overland flow dominated. The extent of the variable source area and the magnitude of streamflow were due to antecedent soil moisture, rainfall and slope morphology. Concave hillslope sections accumulated soil moisture due to both saturated and unsaturated lateral flow processes.

Throughflow provided the mechanism and vehicle for solute movement from the groundwater discharge area to the stream. However, discharge from the deep aquifer was the primary mechanism responsible for soil salinity and maintaining the core of the variable source area. Estimates of throughflow which only take account of soil‐water movement and disregard returnflow, will underestimate the magnitude of throughflow.
Effects of incorporating two organic materials at varying levels on splash detachment of some soils from Borno state, Nigeria
Authors: Ekwue E. I. , Ohu J. O. , Wakawa I. H.
Published: February 2007

Splash detachment by raindrops was measured using a factorial experiment involving three soils (sandy loam, clay loam and clay) and two organic materials (cow dung and groundnut haulms) applied at five levels (0, 2, 4, 6 and 8 per cent by mass). A simulated rainfall intensity of 145 mm h−1 for 10 min duration was used for the tests. Detachment was described in terms of the direct effects and the first and second order interactions of the variables mentioned above. Results indicated that mean splash detachment was reduced significantly (P < 0·01) from 1·97 kg m−2 in the sandy loam to 0·67 kgm−2 in the clay soil. For each soil type, detachment was reduced significantly (P < 0.01) with increasing levels of added organic matter. Groundnut haulms produced lower values of detachment than cow dung. There were also significant interaction effects between the study variables. These interactions were used to describe the effect of added organic materials on splash detachment. For each soil type and organic material, negative exponential relationships were established to relate splash detachment to levels of added organic matter.
Role of in situ cosmogenic nuclides 10be and 26al in the study of diverse geomorphic processes
Authors: Nishiizumi K. , Kohl C. P. , Arnold J. R. , Dorn R. , Klein I. , Fink D. , Middleton R. , Lal D.
Published: February 2007

The central premises of applications of the in situ cosmogenic dating method for studying specific problems in geomorphology are outlined for simple and complex exposure settings. In the light of these general models, we discuss the information that can be derived about geomorphic processes, utilizing concentrations of in situ produced cosmogenic radionuclides 10Be (half‐life=1·5 ma) and 26A1 (half‐life=0·7 ma) in a variety of geomorphic contexts: glacial polish and tills; meteorite impact craters; alluvial fans; paleo‐beach ridges; marine terraces; sand dunes; and bedrock slopes. We also compare 10Be‐26Al data with results obtained by other dating methods. We conclude that the technique of measuring in situ cosmic ray produced nuclides holds promise for quantitative studies of processes and time‐scales in a wide range of geomorphological problems.
Establishing the role of pedogenesis in changing soil hydraulic properties
Authors: Brooks S. M. , Richards K. S.
Published: February 2007

Chronosequences provide suitable sources for the study of changes in soil hydraulic behaviour as a result of long‐term pedogenesis. For a podsol chronosequence in the Scottish Highlands, data are presented to indicate the changes that have occurred over 13000 years in the saturated hydraulic conductivity (Ksat) in each horizon. As the soil profile has evolved into a differentiated sequence of three horizons, the resulting hydrological changes can be both measured and quantified by relating Ksat to textural properties and bulk density. The results are significant for interpretation of changing runoff processes and slope stability.
Tracing sediment movement in interrill overland flow on a semi‐arid grassland hillslope using magnetic susceptibility
Authors: Parsons Anthony J. , Wainwright John , Abrahams Athol D.
Published: February 2007

Experiments were undertaken to determine the feasibility of tracing sediment movement in interrill overland flow. Crushed magnetite was introduced as a source‐line 10 cm wide by 8 m long on a runoff plot 18 m wide by 29 m long located in southern Arizona. Initial magnetic susceptibilities along this source line, and along three transects located 0·25, 2·95 and 5 m downslope of the source‐line, were measured. Movement of the magnetite in response to three rainfall simulation experiments was monitored. During the first two experiments, overland flow discharge was sampled at miniature flumes located along two cross sections on the plot downslope of the source‐line, and at a supercritical flume at the plot outlet. Magnetic susceptibilities along the source‐line and transects were measured after all three experiments. Results show that the magnetite moves very early in the experiments and that it reaches one of the flumes 2 m downslope of the source‐line in 3 min. Most of the tracer moves a very short distance: 29·7 per cent is deposited within 25 cm of the source‐line and only 2·2 per cent is deposited 2·95 m away. The deposition rate appears to decrease exponentially away from the source‐line. Very little magnetite is recorded in the flow through the miniature flumes: in general it makes up less than 1 per cent of the total sediment load. No temporal pattern in these percentages is observed. Magnetite appears to be an effective tracer of sediment movement in interrill overland flow, though its higher density than natural soil may affect its detachment and transport.
Velocity‐reversal hypothesis: A model approach
Authors: Keller E. A. , Florsheim J. L.
Published: February 2007

Hydraulic modelling of a riffle‐pool‐riffle sequence in a straight reach of Dry Creek near Winters, California, indicates that while at low flow the mean (section average) velocity at riffles exceeds that of an adjacent pool, during high flow the mean velocity of the pool exceeds that of adjacent riffles. This supports the velocity‐reversal hypothesis which is based on limited field measurements of near‐bed flow velocity. A velocity reversal does not occur at the same discharge in both riffle‐pool sequences modelled, and a more detailed explanation is necessary to account for complex aspects of channel form and process in riffle‐pool sequences. Nevertheless, the velocity‐reversal hypothesis helps to explain many of the observations and processes that operate in the riffle‐pool environment.
The application of confocal microscopy to the study of stone weathering
Authors: Rautureau Michel , Cooke Ronald U. , Boyde Alan
Published: February 2007

Confocal scanning light microscopy is a valuable new method for examining the nature and progress of stone weathering at a level of resolution between optical microscopy and scanning electron microscopy. Not only is it non‐destructive, but it can also create three‐dimensional images.
The soil erosion bridge: A device for micro‐profiling soil surfaces
Authors: Shakesby Richard A.
Published: February 2007

The soil erosion bridge is a simple, robust, cheap, lightweight device comprising a bar which, when mounted on two stakes, provides a stable datum for micro‐profiling the soil surface beneath. Its main advantage over similar devices is the unique combination of mounting clamps, which allow for variation in the distance and angle with respect to the vertical of the mounting stakes without loss of accuracy. The design, installation and measurement procedures are described. Applications and limitations are discussed.
Verification of a simple gravity technique for separation of particle size fractions suitable for mineral magnetic analysis
Authors: Walden John , Slattery Michael C.
Published: February 2007

Techniques for the separation of sediment samples into size fractions are reviewed and the use of repeated decantations to provide samples for mineral magnetic analysis is described. Results from a series of trials are presented and compared with other techniques.
Automated water sampling in ephemeral hydrological systems
Authors: Vivian B. J. , Quinton J. N.
Published: February 2007

A wide variety of sampling programmes may now be considered practical with the recent developments in data logger and water sampler technology. In ephemeral systems the water sampler remains idle for long periods between events. Two approaches are described which overcome the problems of sampling in ephemeral systems: short interval time dependent sampling (TDS) and automated flow proportional sampling (FPS). Both approaches utilize the data logger's ability to perform intermediate operations on incoming data to control the initiation of water sampling. The logger programs are described and allow many recorder/water sampler units to be controlled from one device. The relative merits of the two approaches are discussed in terms of experimental requirements and data precision.
Controls on bedrock channel incision along nahal paran, Israel
Authors: Wohl Ellen E. , Greenbaum Noam , Schick Asher P. , Baker Victor R.
Published: February 2007

Nahal Paran drains 3600 km2 of Egypt's Sinai peninsula and Israel's Negev Desert. Much of the channel is alluvial, but a canyon 10·5 km long has been incised into Late Cretaceous chert and dolomite in the lower portion of the basin. Slackwater deposits and paleostage indicators preserved within the canyon record approximately 10 floods of 200 to 2500 m3 s−1 over a period of at least 350 years. Step‐backwater simulations of flood‐flow hydraulics indicate extreme variations in stream power per unit area along the length of the canyon, and associated variability in energy expenditure and sediment transport. These variations reflect channel cross‐sectional morphology. The greatest values of stream power occur along the lower half of the study reach, in association with three pronounced knickpoints and an inner channel. The locations of these features reflect the exposure of thick, resistant chert layers along the channel. The presence of several similar, but buried and inactive, knickpoints along the upper study reach indicates that the locus of most active channel incision has shifted with time, probably in response to baselevel changes associated with tectonic activity along the Dead Sea Rift. Thus, the rate and manner of channel incision along the canyon of Nahal Paran are controlled by lithologic variability and tectonic uplift as they influence channel morphology and gradient, which in turn influence hydraulics and sediment transport.
Ten year remeasurement of chemical denudation on a magnesian limestone hillslope
Authors: Trudgill S. T. , Ferguson R. I. , Ball J. , Crabtree R. W. , Gent R.
Published: February 2007

Results from the measurement of microweight loss of Magnesian Limestone rock tablets placed at the soil–bedrock interface on a hillslope over 10 years (1982–1992) gave the same relative pattern of upslope increase in weight loss as did short‐term measurements (1979–1981), but the absolute values were an order of magnitude lower (0·01–0·03 per cent per year long term and 0·1–0·6 per cent per year short term). Microweighed rock tablets may therefore give unreliable absolute rates and can only be used to indicate relative spatial differences rather than to give reliable data on temporal changes.
Fingered flow: The creator of sand columns in dune and beach sands
Authors: Dekker Louis W. , Ritsema Coen J.
Published: February 2007

Sand columns, sand cones, sand mushrooms and other striking sand forms are frequently observed in the Dutch and German beach and dune sands. This paper aims to clarify the mechanism of sand column formation. Recently it has become evident that homogeneous beach and dune sands often become irregularly wetted by infiltrating rainwater. In otherwise dry sandy soils, wet preferential flow paths (‘fingers’) may develop. At two test sites the volumetric soil moisture content varied between 0·2 and 12·0 per cent. The wet fingers represent the premature state of sand columns. When the dry sand in between these fingers is blown away by the wind, the more resistant wet sand of the fingers will remain in its place and appear as sand columns at the surface. As a result of wind and erosive sand drifts, striking sand forms may be formed.
Critical discharge for entrainment of poorly sorted gravel
Authors: Ferguson R. I.
Published: February 2007

Entrainment criteria for gravel‐sized particles on river beds are usually defined in terms of shear stress, but some workers have proposed that critical‐discharge relationships are more reliable and more convenient. The critical shear stress in poorly sorted gravels is known from recent work to depend much more on relative than absolute grain size. It is shown that this effect can be included in a semi‐theoretical equation for the critical unit discharge to move individual grain sizes in a poorly sorted bed. Comparisons with published data on critical discharges in a variety of rivers show that both the sensitivity of critical discharge to grain size, and the absolute levels of critical discharge, are predicted quite well. However, any prediction of critical discharge is sensitive to the assumptions made, first about flow resistance and secondly about the critical stress to move average‐sized particles.
Temporal cycles of karst denudation in northwest Georgia, U.S.A.
Authors: Kiefer Rudi H.
Published: February 2007

Time patterns of karst denudation in northwest Georgia (U.S.A.) were investigated at three spring sites for 12 months and at five stream sites for 10 years. Rainfall was evenly distributed and showed no significant seasonality. At the springs, as well as the streams, water hardness was largely controlled by discharge. At the springs, soil pCO2 and water pH were strongly correlated (r + ‐0·69 to ‐0·83). Solute transport in spring waters was highly seasonal, with two conduit flow springs removing more limestone in the winter, and the diffuse flow spring removing more during the growing season. At the stream sites, most denudation occurred during the winter and spring seasons, and least during the summer.

Fourier analysis showed that variations in denudation occur on deterministic (long‐wave) as well as stochastic (shortwave) time scales. As contributing variables, discharge varied in short‐wave and long‐wave cycles, whereas soil pCO2 showed only a long‐wave cycle. The 12 month deterministic cycles were the most important, with changes in discharge taking precedence over soil pCO2. Time series regression explains up to 69 per cent of changes in denudation through rain and soil pCO2. Time cycles in available water are the key controlling factor of denudation, and amounts of available soil CO2 may not be as important in the temporal patterns of karst downwearing as has been believed previously.
Prediction of tension crack location and riverbank erosion hazards along destabilized channels
Authors: Darby Stephen E. , Thorne Colin R.
Published: February 2007

Riverbank erosion, associated sedimentation and land loss hazards are a land management problem of global significance and many attempts to predict the onset of riverbank instability have been made. Recently, Osman and Thorne (1988) have presented a Culmann‐type analysis of the stability of steep, cohesive riverbanks; this has the potential to be a considerable improvement over previous bank stability theories, which do not account for bank geometry changes due to toe scour and lateral erosion. However, in this paper it is shown that the existing Osman‐Thorne model does not properly incorporate the influence of tension cracking on bank stability since the location of the tension crack on the floodplain is indirectly determined via calculation or arbitrary specification of the tension crack depth. Furthermore, accurate determination of tension crack location is essential to the calculation of the geometry of riverbank failure blocks and hence prediction of land loss and bank sediment yield associated with riverbank instability and channel widening. In this paper, a rational, physically based method to predict the location of tension cracks on the floodplain behind the eroding bank face is presented and tested. A case study is used to illustrate the computational procedure required to apply the model. Improved estimates of failure block geometry using the new method may potentially be applied to improve predictions of bank retreat and floodplain land loss along river channels destabilized as a result of environmental change.
Rill erosion along the thalweg of a hillslope hollow: A case study from the cotswold hills, Central England
Authors: Slattery M. C. , Burt T. P. , Boardman J.
Published: February 2007

Rill erosion is an important erosional form on agricultural soils in England, causing large losses of soil, particularly on cultivated slopes. This paper describes a rill system that developed in a small agricultural catchment in north Oxfordshire during the winter of 1992–93. The rill system comprised two components: a system of ‘feeder rills’ along the valley‐side slopes, which were the result of flow concentration and erosion along wheelings, and a thalweg rill, which formed along a dry valley bottom as a result of surface runoff concentration from the feeder rills. Total volumetric soil loss from the rill system was 32·28 m3, equivalent to 3·01 m3, ha−1 for the rill catchment area, or 3·91 t ha−1. Mean discharge for the thalweg rill and feeder rills, calculated during a storm event, was 31·101s−1 and 1·171s−1, respectively. All flows were fully turbulent and supercritical. We emphasize the need for a spatially distributed approach to the study of runoff and erosion at the catchment scale.
Dimensionless critical shear stress evaluation from flume experiments using different gravel beds
Authors: Petit F.
Published: February 2007

Flume experiments were conducted using four different gravel beds (D50 + 12–39 mm) and a range of marked particles (10–65 mm). The shear stresses were evaluated from friction velocities, when initial movement of marked particles occurred. Two kinds of equations were produced: first for the threshold of initial movement, and second for generalized movement. Equations of the type 0c + a(Di/D50)b, as proposed by Andrews (1983) are applicable even if the material is relatively well sorted. However, the values of a and b are lower (respectively 0·050 and ‐0·70) for initial movement. Generalized movement requires a higher shear stress (a + 0·068 and b + ‐0·80).

D90 of the bed material and y0 (the bed roughness parameter) were also used as reference values in place of D50. They produced lower values than in natural streams, mainly owing to the fact that the material used in the flume is better sorted: clusters are less well developed and the bed roughness is lower.
Seepage erosion and its implication to the formation of amphitheatre valley heads: A case study at Obara, Japan
Authors: Onda Yuichi
Published: February 2007

Seepage erosion was investigated in an amphitheatre with a semicircular valley head, steep slopes, and a flat bottom developed in granodiorite hills at Obara, Aichi prefecture, Japan. A high sediment yield occurred where the measuring sites were located at the base of the landslide debris in the base of the convex slopes, whereas sediment outflows were small where the measuring sites were located at the base of the strong convex slopes. This implies that the seepage erosion was an effective agent for removal of debris deposited at the base of the slope. Small landslides can be found at the lower slopes within the area of the observed amphitheatre. The slope stability analysis and subsurface water observation of the lower slope suggest that the small landslides in this amphitheatre are due to over‐steepened slopes, and relatively insensitive to subsurface water status. Colluvium in the flat valley bottom thinly covers the bedrock surface. Therefore the topography of the amphitheatre was found to be formed by parallel retreat of slopes by the repetition of basal seepage erosion and subsequent small landslides.
Excel modelling of hydrological systems
Authors: Trudgill Stephen , Ball Jason , Ferguson R. I.
Published: February 2007

This short paper describes the use of Excel spreadsheet Solver facility for deriving estimates in a solute mixing model equation with more than one unknown.
Visualization of the turbulent flow structure in a gravel‐bed river
Authors: Kirkbride Alistair D. , McLelland Stuart J.
Published: February 2007

A novel technique for visualizing turbulent flow data from a gravel‐bed river is presented. The time development of flow velocity and shear stress at three heights is displayed using a computer program. This can be used to observe how the fluctuations of velocity and shear stress interact both spatially and temporally. We highlight examples of flow events which are important for the understanding of flow dynamics. The visualization suggests that the turbulent flow‐field is characterized not only by coherence over time at a point, but also by spatial interdependence between points. We suggest that this new visualization approach will assist further interpretation of statistical analyses of turbulent signals, as well as focusing future measurement strategies by providing a clearer spatio‐temporal picture of the flow structure.
Digital data acquisition and analysis: An introduction
Authors: Rand Chris
Published: February 2007

There is no doubt that although the price of PCs has fallen, the performance for money continues to rise. As this happens, so the suitability of using general‐purpose computing platforms, especially PCs, for specific technical applications increases. This article discusses recent developments and reviews some of the systems which are currently available for data acquisition and analysis in the environmental sciences.
Potentialities, uncertainties and complexities in the response of coral reefs to future sea‐level rise
Authors: Spencer T.
Published: February 2007

Coral islands formed of largely unconsolidated sands only a few metres above sea level are thought to be particularly vulnerable to sea‐level rise consequent upon global warming. However, scenarios which predict catastrophic flooding and loss of island area need reassessment, particularly in the light of the continued downwards revision of projected rates of future sea‐level rise. Revised questions concern the interactions between reef growth and sea‐level change, biophysical constraints on coral growth, and the importance to reef systems of potential changes in the magnitude, frequency and location of tropical cyclones and hurricanes. It is clear that most reefs have the growth potential to meet even the highest of future sea‐level rise scenarios, but too little is known about physiological and physical constraints to reef growth to adequately evaluate the importance of these two factors in constraining this potential at the present time. Future sea‐level rise in the tropical oceans, and coral reef responses, will take place against a backdrop of inter‐regional differences in Holocene sea levels, resulting from the varying interaction of eustatic and hydro‐isostatic processes. These differences have generated varying constraints on the development of modern reefs and varying inherited topographies upon which future sea‐level changes will be superimposed. These controls are particularly important in assessing differences in vulnerability to future sea‐level rise for reef islands in the Pacific Ocean and the Caribbean Sea.
Rock‐weathering by the lichenLecidea auriculatain an arctic alpine environment
Authors: McCarroll Danny , Viles Heather
Published: February 2007

Scanning electron microscopy reveals thatLecidea auriculatapenetrates rock surfaces, detaching, incorporating and expelling flakes of rock. Measurements on an age sequence of moraine ridges illustrate changes in the extent and intensity of weathering over time. A minimum rate of surface lowering (0·0012 mm a−1) is 25 to 50 times faster than weathering due to other processes in the same area. The spatial pattern of weathering is influenced by the narrow ecological range of the species. Surface rocks on dry, exposed sites are probably weathering much more rapidly than those in adjacent damp hollows and beneath snowpatches.
Surface stone cover on desert hillslopes; parameterizing characteristics relevant to infiltration and surface runoff
Authors: Dunkerley D. L.
Published: February 2007

Surface stones are a common feature of desert hillslopes. They influence slope processes ranging from the interception and partitioning of rainwater to the dislodgement and transport of regolith particles. The aspects of a stone mantle which relate to these various influences are diverse, and include surface cover fraction, dimensions of the infiltration annulus, and geometric and packing effects.

Analyses of the characteristics of stone cover at two study sites were made using photographic methods and are used to evaluate different means of reporting mean stone sizes. It is found that mean diameter based on weight, as conventionally employed in sieve analysis, is insensitive to important stone cover characteristics and may be influenced greatly by uncommon, large stones. Similarly, mean diameters based on count become inappropriate if large numbers of small stones dominate the calculated mean, concealing other site‐to‐site differences in stone cover. As a more appropriate parameterization of stone geometry, the use of mean diameters weighted by stone surface area and perimeter length are proposed. These weighting factors have the advantage that they relate closely to stone characteristics relevant to slope hydrology and erosion processes.