Showing papers in "Earth Surface Processes and Landforms in 1987"
TL;DR: In this article, a system which determines slope, aspect, and curvature in both the downslope and across-slope directions is developed for an altitude matrix, and the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix.
Abstract: Land surface topography significantly affects the processes of runoff and erosion. A system which determines slope, aspect, and curvature in both the down-slope and across-slope directions is developed for an altitude matrix. Also, the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix. A FORTRAN 66 program performs the analysis.
1,316 citations
TL;DR: In this article, the authors used a rating curve to predict unmeasured river loads from continuous discharge data but relatively infrequent sampling of sediment, solute, or pollutant concentrations.
Abstract: River loads often have to be estimated from continuous discharge data but relatively infrequent sampling of sediment, solute, or pollutant concentrations. Two standard ways of doing this are to multiply mean concentration by mean discharge, and to use a rating curve to predict unmeasured concentrations. Both methods are known from previous empirical studies to underestimate true load. Statistical considerations explain these biases and yield correction factors which can be used to obtain unbiased estimates of load. Simulation experiments with normally-distributed scatter about log-linear trends, and sampling experiments using a natural data set, show that the corrected rating curve method has lower sampling variability than other unbiased methods based on average instantaneous load and is thus the recommended procedure when the rating plot is of the assumed form. The precision of all methods increases with sample size and decreases with increasing rating-curve slope and scatter.
293 citations
TL;DR: In this article, the physical processes of raindrop impact and water flow on the leaves and branches of selected tropical tree species were examined under laboratory conditions using simulated rainfall, and inclined branches were found to be particularly efficient in detaining impacting water droplets.
Abstract: The physical processes of raindrop impact and water flow on the leaves and branches of selected tropical tree species were examined under laboratory conditions using simulated rainfall. Inclined branches were found to be particularly efficient in detaining impacting water droplets. This efficiency in raindrop detention increases linearly as a function of branch inclination on branches that are initially dry. On branches that have been thoroughly wetted, this increase in raindrop detention with branch inclination is best expressed as a logarithmic function. At branch inclinations of 60" above the horizontal, the quantity of branchflow was found to be > 80 per cent of the total quantity of impacting rainfall, indicating that < 20 per cent was lost to rainsplash. The strong positive relationship between branchflow and branch inclination explains why trees with large projected areas of steeply inclined upthrust branches have significant quantities of intercepted water draining from their branches and trunks under heavy rainfall conditions. This drainage from the woody frame of trees influences surficial processes by generating both stemflow and large throughfall droplets.
185 citations
TL;DR: In this article, the authors investigated the nature of channel adjustments downstream from a total of 46 channelization works located in low and high energy environments in England and Wales, and found that the maximum increase of channel size was 153 per cent.
Abstract: Relatively little attention has been given to river channel adjustments that occur downstream from channelization works. This study is concerned with the nature of channel adjustments downstream from a total of 46 channelization works located in low and high energy environments in England and Wales. Channel changes are identified principally by the method of field survey and by reconstructing the original positions of eroded beds and banks. Use is also made of maps, aerial photographs, and engineering drawings of different dates and the technique of space-for-time substitution is applied.
Enlargement of channel cross-sections through erosion had occurred downstream from a variety of types, sizes, and dates of channelization works. The maximum increase of channel size was 153 per cent. Out of a total of 14 sites with enlarged channel cross-sections, seven had undergone a change of width only, at a further three width increased rather than depth, and at the remaining four sites depth increases were dominant. These sites all have relatively high stream powers.
Factors causing spatial variation of erosion included tree roots locally binding bank sediments and the occurrence of bends. Planform change had taken place at only one site. A further three high stream power sites had downstream reaches incised into bedrock and therefore did not exhibit adjustment.
Channel enlargement is explained in terms of increased flood flows downstream from channelization works causing higher stream velocities, which in turn cause erosion, thereby increasing channel width and/or depth. Examination of flow records for 35 stations revealed flood events which would formerly have spread overbank but are now confined by the channelization works and are therefore likely to alter downstream flows. At sites with downstream change it is proposed that the energy of increased flows was sufficient to exceed a threshold required for erosion of perimeter sediments. By contrast the absence of change at a majority of sites in low energy lowland areas could be a reflection of both the incompetence of increased flows to erode and resistance provided by perimeter sediments. Sites with erosion features appear not to have yet attained new equilibrium conditions.
122 citations
TL;DR: Using meteorological records (1957-1984) in Australia, formal definitions are proposed of four types of dust event: dust storms, blowing dust, dust whirls, and dust haze.
Abstract: Using meteorological records (1957–1984) in Australia, formal definitions are proposed of four types of dust event: dust storms, blowing dust, dust whirls, and dust haze. Australia-wide maps of the extent of these four dust event types are presented.
110 citations
TL;DR: The authors examined the amount and processes of landscape modification by Quaternary ice sheets and found an inverse correlation between the distribution of landforms of glacial erosion and pre-glacial landscape remnants in northeast Scotland.
Abstract: The paper uses a case study in Scotland to examine the amount and processes of landscape modification by Quaternary ice sheets. There is an inverse correlation between the distribution of landforms of glacial erosion and pre-glacial landscape remnants in northeast Scotland. The implication is that in places ice sheets can preserve a pre-glacial landscape unscathed, while elsewhere they remove the pre-glacial weathered rock. The location of glacial protection or erosion is strongly influenced by the topography and its influence on former ice sheet flow and basal thermal regime. The classic glacially eroded landscape of areal scouring can be produced by the removal of only 10–50 m of weathered rock. Furthermore rock basins, often regarded as the hallmark of glacial erosion, may be directly inherited from the pre-glacial pattern of deep weathering.
103 citations
TL;DR: In this paper, a topography-based model of catchment hydrology (TOPMODEL) is described and applied to the problem of predicting flood frequency characteristics, which can simulate infiltration excess, saturation excess, and subsurface runoff contributions to peak flows.
Abstract: A further development of a topography-based model of catchment hydrology (TOPMODEL) is described and applied to the problem of predicting flood frequency characteristics. The model can simulate infiltration excess, saturation excess, and subsurface runoff contributions to peak flows. Catchment geomorphology plays a central role in predicting the nature of the hydrological response. Using stochastic rainfall and initial condition inputs based on measured data, the model satisfactorily reproduces the mean hourly flow flood frequency growth curve for the Wye catchment, but not the mean number of peaks greater than 3mm h−1 each year. Suggestions for further improvements are made.
96 citations
TL;DR: In this article, a series of slopes along the Kall valley in the northern Eifel is reproduced by a developmental sequence of model slopes, and the spatial and temporal variations of the components of slope development systems are discussed by means of mass movement and wash denudation models.
Abstract: The model SLOP3D is used to identify characteristic aspects of slope development under different conditions. A series of slopes along the Kall valley in the northern Eifel is reproduced by a developmental sequence of model slopes. The spatial and temporal variations of the components of slope development systems (relief, slope form, weathering rates, denudation rates) are discussed by means of mass movement and wash denudation models. The negative feedbacks between system components create a tendency towards the establishment of a dynamic equilibrium which is reached, however, only if the endogenic and exogenic conditions remain constant for the required relaxation time. The latter is shown to be a function of slope length, of the rate of uplift, of the denudational process type, and of the intensity of exogenic inputs (e.g. precipitation). Varying rock resistance leads to the development of shield inselbergs only if the rate of denudation becomes higher than the maximum possible weathering rate of the resistant bedrock.
88 citations
TL;DR: Natural piping doubling the dynamic contributing area on the upper Maesnant stream in mid-Wales, mainly through linking points well beyond the riparian zones of seepage to the stream as discussed by the authors.
Abstract: Natural piping doubles the dynamic contributing area on the upper Maesnant stream in mid-Wales, mainly through linking points well beyond the riparian zones of seepage to the stream. Both discharge and sediment transport rates in the major pipes are closely related to the size of shallow surface microtopographic hollows in which they lie, and which themselves are largely created by piping erosion. However, pipe dischrges are frequently generated by contributing areas larger than these surface depressions and some pipes run counter to the surface topography. The redistribution and acceleration of hillslope drainage processes by piping has implications for theories of hillslope development, especially through plan-form modifications, and also for channel discharge and erosion.
80 citations
TL;DR: In the Bowland Fells, Lancashire, northwest England, in the headwater valleys of the Hodder river system, is a suite of Holocene fluvial landforms.
Abstract: In the Bowland Fells, Lancashire, northwest England, in the headwater valleys of the Hodder river system, is a suite of Holocene fluvial landforms. Debris cones and alluvial fans at tributary junctions, and river terraces along the main valleys post-date late Pleistocene forms and pre-date the modern valley floor alluvial forms. Eight 14C dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of Holocene erosion to be identified with debris cone/fan deposition taking place after c. 5400 BP but before c. 1900 BP and again at c. 900 BP. Some of the fans and cones are complex with deposits attributable to both phases; others are simple and attributable only to the later phase. In the headwaters an upper terrace at c. 5400 BP pre-dates the cones and a lower terrace is contemporaneous with the first debris cone phase. Lower downvalley the youngest of three terraces date from c. 5000 BP or earlier indicating that the sequence is less complex downstream.
71 citations
TL;DR: In this article, a model that effectively describes dispersion of copper in ephemeral stream sediments in a simple mixing model is presented, where Cr is the resultant concentration beneath the confluence of the main channel with a tributary, Ct is the concentration of metal in sediments of the tributarial, Cm is the metal concentration in main channel sediments, and Xm and Xt are the basin areas or sediment yields.
Abstract: Sediment transport related parameters in ephemeral streams may be used to model and delineate: (1) average dispersion patterns of copper-laden sediments; (2) differences in dispersion of copper in bedload and suspended sediments; and (3) variability in the copper-sediment dispersion patterns. A model that effectively describes dispersion of copper in ephemeral stream sediments in a simple mixing model:
where Cr is the resultant concentration beneath the confluence of the main channel with a tributary, Ct is the concentration of metal in sediments of the tributary, Cm is the metal concentration in main channel sediments, and Xm and Xt are the basin areas or sediment yields of the main channel and tributary channel at their confluence. Variability in metal concentrations about values predicted by this model may be due to the different responses of bedload and suspended load to changes in stream hydraulics, the dynamics of bedload transport, the spatial and temporal variability rainfall within the drainage basin, and chemical mobility of the copper.
TL;DR: In this article, the authors compare two views of the soil-covered landscape surface from two viewpoints: the intuitive view is of a smooth, absolutely continuous surface with continuous contour lines and measurable in integral dimensions and the alternative view emphasizes the roughness, a surface of little regularity and at the limit of no contours, the appropriate measure being that of fractional Hausdorff dimension.
Abstract: The soil-covered landscape surface can be idealized from two viewpoints. The intuitive view is of a smooth, absolutely continuous surface with continuous contour lines and measurable in integral dimensions. The alternative view emphasizes the roughness, a surface of little regularity and at the limit of no contours, the appropriate measure being that of fractional Hausdorff dimension. Regularity is a local property and both idealizations need to stop far short of the limit to avoid awkward consequences.
The dichotomy of viewpoint can be matched in the theory of Gaussian random fields. These, if they are smooth, are very smooth but if they are irregular they are highly irregular (erratic); there is no middle ground. This Belayev dichotomy is defined and both modes applied to the soil-covered landscape. On the one hand, if the landscape is subject to a general diffusive type degradation or more generally a Davisian downwasting regime then the curvature of the landscape surface is progressively straightened and the distribution of gradient (increments) along a typical traverse will eventually adopt a Gaussian form. Then from the irregular viewpoint the surface is ultimately well represented by a fractional Brownian surface of low Hausdorff dimension (2·0 < dim < 2·3). The Hausdorff dimension is directly related to the entropy of the landscape and as degradation proceeds both quantities decrease in value.
On the other hand, if the surface is regarded as smooth and well represented by an absolutely continuous Gaussian field then the mean value of the number of upcrossings of a level or the extent of an excursion set will also be Gaussian. This analysis is restricted to one dimension; the number of times a profile curve crosses or the amount of time it spends above any given level.
Predictions from both viewpoints are substantially corroborated in a map analysis of 15 sites on varied terrains in Southern England and the map analysis checked against one based upon digital tape data for one of the sites.
TL;DR: In this paper, geomorphic evidence along bedrock-confined reaches of the Salt River in east-central Arizona provides a record of the river's largest flood events, where fine-grained flood slackwater deposits accumulated at channel margin irregularities several metres above the low-flow channel.
Abstract: Geomorphic evidence along bedrock-confined reaches of the Salt River in east-central Arizona provides a record of the river's largest flood events. Fine-grained flood slackwater deposits accumulated at channel margin irregularities several metres above the low-flow channel. Discharges associated with flow events responsible for the deposits were estimated by computer flow modelling. These estimates document flood magnitudes in excess of gauged historic streamflows. Relative and radiocarbon dating suggest that a flood record in excess of 600 y is preserved in the slackwater sequences. A prominent flood scar cut into grussy hillslope soils allows the extension of the prehistoric flood record to several thousand years.
A maximum discharge estimate of 4600 m3s−1 affixed to the flood scar represents the largest flood event in the record, and is given a minimum recurrence interval of 1000–2000 y. The 1952 flood is the largest historic flow event experienced along the study reach and is estimated at 2900 m3s−1. Two palaeoflood events preserved in the slackwater stratigraphy exceed the 1952 event, and are given recurrence intervals of 300 and 600 y. The latter flood event had an estimated discharge of 3200 m3s−1. It is apparent that discharge estimates affixed to these infrequent, large-magnitude flood events approach a maximum with decreased probabilities (large recurrence intervals). This suggests that a physical limit on discharge may exist within the Salt River drainage basin and is perhaps directly related to drainage basin size.
TL;DR: In this paper, the authors determined if variation in small-scale wind gustiness (on the order of several seconds duration) has a significant effect on sand movement, detailed field measurements were made of wind speed and transport rate.
Abstract: Estimates of aeolian sand transport generally use an average wind speed to assess the wind energy. To determine if variation in small-scale wind gustiness (on the order of several seconds duration) has a significant effect on sand movement, detailed field measurements were made of wind speed and transport rate. Average wind speed and several gust parameters were derived from the wind data. The results indicate that small-scale gust information does not improve prediction of transport rates.
TL;DR: In this paper, the first appearance of OPb dating models reproduced the 'known' chronology, and correlation analysis showed no significant relationship between original "Pb (unsupp.) concentration and grain-size, sedimentation rate or loss on ignition.
Abstract: Cores taken at Burrinjuck Reservoir in southeastern New South Wales have been dated using the first appearance of OPb dating models reproduced the 'known' chronology. Correlation analysis shows no significant relationship between original "Pb (unsupp.) concentration and grain-size, sedimentation rate or loss on ignition. Differences in sediment source may explain the variations in OPb. A simple provenance model has been used to interpret the ratio of original 'OPb (unsupp.)/226Ra as a tracer of topsoils and subsoils. High ratios in the reservoir sediments probably indicate eroded topsoils and low ratios eroded subsoils. 37Cs, charcoal/bushfire correlations, and annual grass pollen peaks. None of the main
TL;DR: The Gran Desierto Sand-Sea contains dunes of crescentic and star form in simple, compound, and complex varieties as mentioned in this paper, and the dunes have developed in bimodal to complex wind regimes of intermediate energy.
Abstract: The Gran Desierto Sand-Sea contains dunes of crescentic and star form in simple, compound, and complex varieties. The dunes have developed in bimodal to complex wind regimes of intermediate energy. Transitions from simple through compound to complex crescentic dunes are associated with regional changes in wind regimes. Growth of large star dunes takes place by merging of smaller crescentic and reversing dunes from southerly directions and reworking of sand by northerly and westerly winds. Although wind regimes appear to be the major control of dune morphology in this sand-sea, there is a close correlation between the spacing of simple crescentic dunes and the grain size of the coarse 20th percentile.
TL;DR: In this paper, a theoretically-based erosion criterion is developed for gravel-bed rivers which incorporates the effect of both grain geometry and turbulent velocity fluctuations, derived from a balance of instantaneous drag, lift, and gravity forces operating on individual grains and is calculated for spherical grains arranged in three distinct geometries.
Abstract: A theoretically-based erosion criterion is developed for gravel-bed rivers which incorporates the effect of both grain geometry and turbulent velocity fluctuations. It is derived from a balance of instantaneous drag, lift, and gravity forces operating on individual grains and is calculated for spherical grains arranged in three distinct geometries. To accommodate the temporal variation in bed shear stress, the model includes a stochastic element based on the characteristics of turbulence derived from the flume evidence of McQuivey (1973a, b). In terms of the Shields parameter, results show reasonable agreement with the range of observations quoted from the field and with the experimental data of Fenton and Abbott (1977). Finally, the argument is generalized to cover applications in the wider context of field conditions including a range of grain sizes and flow conditions.
TL;DR: In this paper, aeolian materials carried on the trade winds from Africa, volcanic ash from the island of St Vincent, and quartz from Tertiary bedrock on the island itself are the parent materials for the soils.
Abstract: Well-developed, clay-rich soils dominated by interstratified kaolinite-smectite are found on the uplifted coral reef terraces on the island of Barbados The reef limestone is unlikely to have been the soil parent material however, because it is 98 per cent CaCO3 and geomorphic evidence argues against the 20 m of reef solution required to produce the soils by this process The mineralogy of the sand, silt, and clay fractions of the soils, and trace element geochemistry, suggest that aeolian materials carried on the trade winds from Africa, volcanic ash from the island of St Vincent, and quartz from Tertiary bedrock on the island itself are the parent materials for the soils
TL;DR: In this paper, the form and structure of a tributary confluence bar in a regulated channel were analyzed and related to channel adjustment to the imposed flow regime, characterized by a tripartite structure with two facies, and by marked lateral coarsening.
Abstract: The form and structure of a tributary confluence bar in a regulated channel are analysed and related to channel adjustment to the imposed flow regime. The bar is characterized by a tripartite structure with two facies, and by marked lateral coarsening, characteristics which relate to the changing hydraulic conditions within the narrowing channel form.
TL;DR: In this article, the authors found that DOC is strongly associated with Fe, NO−3-N and NO−2-N, but essentially independent of other chemical properties of the peat water, such as pH, Ca, Mg, K, P, and NH+4-N.
Abstract: Samples of water from poor to very rich fens in the Schefferville region of subarctic Quebec revealed strong spatial and temporal variations in dissolved organic carbon (DOC), ranging from 2 to 40 mg 1−1. Concentrations of DOC tend to increase during the summer and decrease in the autumn, at most sites, which probably reflects increased plant tissue decomposition and higher rates of evapotranspiration. Principal components analysis revealed that DOC is strongly associated with Fe, NO−3-N and NO−2-N, but essentially independent of other chemical properties of the peat water, such as pH, Ca, Mg, K, P, and NH+4-N. Based on observed concentrations of DOC and estimates of summer runoff (June to September), export of DOC from four peatlands ranges from 1·1 to 4·9 gCm−2, with the lowest values for peatlands underlain by dolomite. Molecular weight fractionation of four samples revealed significant differences in the dissolved organic matter (DOM), with the largest fractions (GF/C to 10 000 nmw) being dominant in the more acid samples. The ratio of absorbance at 400 and 600 nm wavelengths (E4:E6) has been used as a simple indicator of differences in DOM type, ranging from 3 to 15. There is a strong seasonal pattern of increasing E4:E6 ratio during the summer at many sites, though this ratio is essentially independent of other chemical properties of peat waters.
TL;DR: In this article, four genetic types of tower karst are identified, the most typical consisting of residual hills protruding from a planed carbonate surface veneered by alluvium.
Abstract: Four genetic types of tower karst are identified, the most typical consisting of residual hills protruding from a planed carbonate surface veneered by alluvium Two extreme possibilities for tower karst evolution are recognized: a direct development that is independent of any previous morphology and a sequential development that depends explicitly on the morphological characteristics of a previous cockpit karst phase Examples of both are described, although the latter appears the more common South China tower karst is examined in this light Palaeomagnetic analysis of cave deposits in a tower near Guilin indicate the feature to be a time-transgressive landform Four principal controls of tower development are discussed and a model of tower evolution is presented
TL;DR: In this article, Canadian examples suggest that karst landforms may be divided into eight types in terms of their temporal relationships to the record of repeated Quaternary glaciations.
Abstract: Canadian examples suggest that karst landforms may be divided into eight types in terms of their temporal relationships to the record of repeated Quaternary glaciations. Two types are postglacial, two are subglacial, one type occurs where glacial features are adapted to karstic drainage, and three types display sequences of karstic and glacial action. Glacier effects upon karst landforms and their underlying aquifers display the gamut of possibilities. They may destroy, inhibit, preserve, or stimulate karst development. Where continuous permafrost is maintained when covered by glacier ice, postglacial karst is limited to the active layer epikarst. Where permafrost is thawed beneath ice or during deglaciation there are a variety of postglacial karst developments, depending in part upon climate and in part upon local lithologic and relief conditions.
TL;DR: In this article, a sediment budget was constructed in order to determine the relative contributions of various channel and valley slope processes to sediment output in the Schrondweilerbaach catchment.
Abstract: In the forested catchments of the Luxembourg Keuper area, deeply-incised valleys have developed in which streambank erosion is a widespread phenomenon. For one of the catchments in this area, the Schrondweilerbaach catchment, a sediment budget was constructed in order to determine the relative contributions of the various channel and valley slope processes to sediment output.
Streambanks contributed 53 percent of the output with bank scour and subsoil fall being the main processes while to a lesser extent bank material was supplied by bank failures, splash erosion, and soil creep. The remaining 47 per cent of the sediment was derived from the valley slopes mainly through the combined action of rainsplash detachment and overland flow transport. During the two years of investigations sediment output from the drainage basin almost equalled sediment input from streambanks and valley slopes. The results of the measurements of the various streambank processes are integrated in a descriptive model for the present-day widening of valley incisions in the study area and used to hypothesize the palaeohydrological development of the basin. Special attention is paid to the (in)direct effects of the forest vegetation on streambank erosion and sediment transport through the stream channel.
TL;DR: Agarwal et al. as discussed by the authors observed that blue-green algae have been observed to affect limestone weathering on Aldabra Atoll, Indian Ocean, and three different habitats can be identified on the rock surface, i.e. epilithic, chasmolithic, and endolithic.
Abstract: Blue-green algae have been observed to affect limestone weathering on Aldabra Atoll, Indian Ocean. Three different habitats can be identified on the rock surface, i.e. epilithic, chasmolithic, and endolithic. Algae in each habitat may affect weathering in various ways. Samples of blue-green algae and rock were taken from various terrestrial and coastal environments on Aldabra Atoll. Samples of limestone tablets and calcite crystals after one year in situ were also studied. Light and S.E.M. microscopy revealed that endolithic boreholes were present on many samples, especially those from frequently wetted sites, to a maximum depth of 800 μm. An ‘altered zone’ of micrite and algal filaments was also discovered in many samples. From morphological and petrographical evidence blue-green algal influences on weathering on Aldabra Atoll seem to be very complex and cannot easily be related to small scale landforms.
TL;DR: In both sand quarry faces and boreholes, the Old Alluvium of Singapore is a matrix supported pebbly sand with minor beds of better sorted sands and clays.
Abstract: In both sand quarry faces and boreholes the Old Alluvium of Singapore is a matrix supported pebbly sand with minor beds of better sorted sands and clays. The beds can be grouped into four textural classes (pebbles, coarse sand with fine pebbles, medium to coarse sand, clay, and silt), each with characteristic sedimentary structures. The deposit appears to be the proximal facies of an ancient braided river alluvium of possible Pleistocene age.
This widespread but scattered alluvium is found both on land and offshore on the Sunda Shelf in Southeast Asia. It is believed to have been deposited during low sea levels. In Singapore, the mineralogy of the grains forming the Old Alluvium suggests a mixed provenance of granitic and low-grade metamorphic origin. The volume and freshness of the deposited material indicate an environment of considerable relief, seasonal rainfall, and extremely active erosional processes, conditions considerably different from the current ones. The Old Alluvium was probably deposited by seasonal rivers which experienced periodic large floods. Such regional conditions could have prevailed over much of Southeast Asia at the time of deposition of the Old Alluvium.
TL;DR: In this paper, the most important variables for slope processes and their interrelations were studied by simple means along slope profiles on a representative hill, showing the enormous importance of a protective ground cover.
Abstract: The landforms of the study area at the margin of the Central Kalimantan Mountains are relatively young and covered by undisturbed primary rain forest receiving an annual rainfall of 4147 mm. The most important variables for slope processes and their interrelations were studied by simple means along slope profiles on a representative hill. Weathering and erosion appear to be in a dynamic equilibrium leading to parallel slope retreat. Measurable denudation occurred within a fortnight with rates of 10 to 22 mm, varying with litter cover and slope exposition. As the forest is planned for ‘limited production’, the soil-erosion risk for changing conditions was estimated using the model by Morgan et al. (1982). Results from field work and from calculations alike show the enormous importance of a protective ground cover.
TL;DR: In this article, three common types of manganese-rich rock coatings are described in Iceland and they are interpreted as being due to the different microenvironments in which they form.
Abstract: Manganese-rich rock coatings are widespread in Iceland, especially in fractures in basalt lavas. Three common types of coating are described. A thick subsurface coating is found on whaleback forms on high plateaux. The most common type is thinner and occurs in hydrothermal clay-filled fracture systems which are especially well developed in tholeiite lavas. A third type occurs in younger rocks and is associated with tephra-rich, loessic sediment which fills open fractures and vesicles. There are differences in the chemistry, morphology, and mineralogy of these coatings which are interpreted as being due to the different microenvironments in which they form. The fracture microenvironment is regarded as being of much more importance to coating thickness and chemistry than simple age and in this respect the hydrothermal clays seem to favour rapid manganese concentration. On the other hand, there are variations in coating type, both laterally and vertically through the lava succession, which are related to regional distribution of hydrothermal alteration and rock type. The regional patterns are the result of Iceland's lateral drift and as a result there is an incidental connection between coating type and rock age. There is some evidence to suggest that the manganese coatings may be both forming and being degraded rapidly in the present environment.
TL;DR: In this article, the development of a simple slope under a single process can adopt a variety of forms depending on initial and boundary conditions, and a given form can be derived from several different processes.
Abstract: Slope profile sequences are as much influenced by their boundary conditions as they are by the processes operating. The development of a simple slope under a single process can adopt a variety of forms depending on initial and boundary conditions, and a given form can be derived from several different processes. For example, convexo-concave forms develop under soil creep with basal accumulation, under wash with an initial step form, and under mixed wash and creep processes.
TL;DR: In this paper, a detailed investigation of the A5 debris flow in a narrow concave track 585 m long, x slope 27·8°, descending 282 m is presented.
Abstract: Intense rainfall after the abnormally dry and warm summer of 1983 triggered debris flows in mountainous terrain in North Wales. This preliminary investigation concentrates on a flow which blocked the A5, requiring £56,000 of remedial work. An estimated 118·4 mm of rain fell over steep, rocky catchments in 5 hrs (peak intensity 39·9 mm hr−1) and water emerging from a rock chute mobilized colluvium on lower slopes, in which pore water pressure was probably already rising fast and bulk properties and other geotechnical conditions, including low shearing resistance, were favourable. Debris flowed in a narrow concave track 585 m long, x slope 27·8°, descending 282 m. The scoured channel, levees and debris lobes typical of documented flows elsewhere suggest that flow was rapid, turbulent, and pulsing.
TL;DR: In this article, a simple queueing model which generates bed topography consistent with the mechanics of gravel motion is presented, and the equations on which it is based are derived from the application of simple theoretical ideas and an analysis of published flume data.
Abstract: A simple queueing model which generates bed topography consistent with the mechanics of gravel motion is presented. The equations on which it is based are derived from the application of simple theoretical ideas and an analysis of published flume data (Meland and Norrman, 1966; Francis, 1973; Abbott and Francis, 1977). The simulation produces an extremely variable bed topography in which at least two scales of bedform may be identified. Features of 5–10 grain wavelengths, similar to pebble clusters, are superimposed on other forms whose wavelength is up to 30–40 grains and which resemble step-pools systems and antidunes. Sediment transport shows many of the characteristics found in the field and the model is, therefore, thought to provide a useful starting point from which to examine the interaction between flow, sediment transport, and bedforms in gravel-bed and cobble streams.