ISSN:0197-9337    

DOI:10.1002/esp.3290100103

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractThis study attempts to investigate the distribution of ventifacts in Qatar. It is believed that ventifacts are confined to the areas within about 5 km of the Miocene or Mio‐Pliocene Hofuf formations and the spreads of continental gravels derived from them. Three hypotheses were formulated: (1) Ventifacts in Qatar are confined to areas within about 5 km of the Hofuf formations and the spreads of continental gravels derived from them. The distribution of ventifacts within these areas varies according to the nature of the ground surface; (2) The most active ventifaction areas are where the continental gravels merge with the Eocene limestone because of the increase in saltation particle speed in these areas where bedrock or bare limestone is exposed; (3) The unit area ratio of ventifact to non‐ventifact pebbles varies inversely with the total amount of pebbles. To test these hypotheses, nine land class categories were identified in the three major Hofuf formations. Line transects were carried out from randomly selected stations near the middle of the Hofuf formations. Along each transect systematic sampling was carried out at 200 m intervals. The data were processed using a WANG MVP 2200 computer with software developed for the project. It was found that ventifacts tend to concentrate on the outer edges of the continental gravels in areas of limestone outcrop and limestone pavement. Higher areas have big gravel counts and a low ratio of ventifacts while the low‐lying plains have small gravel counts and a higher ratio of ventifacts. In certain areas ‘ventifact fields’ were found where the density of ventifacts was as high as 30 per m2. Many of the ventifacts in these fields were buried beneath the surface suggesting that the ventifaction predates the present site conditions. Other high ventifact density areas were discovered where the ventifacts have collected in shallow depressions or hollows on the limestone plateaux. Water action has washed these ventifacts, a high proportion of which are dreikanters, into the hollows, where they have been partially buried in fine alluvial silts. These ‘ventifact graveyards’ are generally only a few metres wide but contain large numbers of f

ISSN:0197-9337    

DOI:10.1002/esp.3290100104

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractPeat deposits in a gully at the inland margin of the Firth of Tay carselands contain a transgressive wedge of estuarine sediments laid down at the culmination of the Main Postglacial Transgression. In previous work, the sequence of deposits in the gully and their age have been examined at one location. The present study both extends and evaluates that previous work, employing further field work and laboratory analyses. The detailed stratigraphy of the deposits is identified, whilst from a borehole close to the limit of the transgressive deposit, diatom analysis and geochemical analyses, involving the determination of Al, Mg, C, and δ13CPDBare outlined. Eight14C assays from peat at the transgressive and regressive contacts in four boreholes along the wedge of estuarine sediments are described. Whilst the results of diatom analysis are inconclusive, the geochemical analyses indicate that the sediment accumulated broadly continuously without major changes in the depositional environment. It is concluded that the Main Postglacial Transgression in the gully was at first rapid, then slowed and culminated between 6240 ± 80 and 6030 ± 80 (or 6170 ± 90) radiocarbon years, B.P. It is subsequently maintained that the geochemical analyses described here may be of value in determining the continuity of transgressive deposits, whilst the practice of obtaining multiple radiocarbon assays at such locations should enable assessment of age to be refined. This may in turn assist in testing the hypothesis of shoreline diachroneity in glacioisostatically affected ar

ISSN:0197-9337    

DOI:10.1002/esp.3290100105

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractPollen and spores form a significant part of the suspended organic load of a New Forest stream. Flood concentrations reach 230 grains ml−1while baseflow carries under one grain ml−1. Hydrographs from different seasons show differing hysteretic loops for pollen and spore concentrations against discharge and suspended sediment. These variations reflect not only factors of production, but the type and distance of the contributing sources. This investigation suggests that variations in flood pollen and spore concentrations may be used to trace such suspended sediment sources as: eroding bedrock, channel banks, or hillslopes under specific vegetation cov

ISSN:0197-9337    

DOI:10.1002/esp.3290100106

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractAcontinuousrecord reveals that the incidence of bedload in a coarse‐grained river channel changes from flood to flood. Long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood‐wave. But when floods follow each other closely, the bed material is comparatively loose and offers less resistance to entrainment. In this case, substantial amounts of bedload are generated on the rising limb. This is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season. This produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse‐grained channels. Besides this, the threshold ofinitialmotion is shown to occur at levels of bed shear stress three times those at the thresholds offinalmotion. This adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory. Bedload is shown to be characterized by a series of pulses with a mean periodicity of 1.7 hours. In the absence of migrating bedforms, it is speculated that this well‐documented pattern reflects the passage of kinematic waves of particles in a slow‐moving traction carpet. The general pattern of bedload, including pulsations, is shown to occur more or less synchronously at different points across the strea

ISSN:0197-9337    

DOI:10.1002/esp.3290100107

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractSediment yields estimated from contemporary stream monitoring of suspended sediment in the Merevale forested catchment, North Warwickshire, were compared with the sediment yield record obtained from analysis of lake sediment in the downstream reservoir. Total sediment volume and mass for nine periods since 1861 were calculated by extrapolation of synchronous levels in 54 cores, identified from magnetic susceptibility and other magnetic measurements, and by using210Pb and137Cs analysis to provide an absolute sediment chronology. Sediment yield estimated from the two methods show comparable but low (50‐200 kg ha−1yr−1) levels of sediment loss. While suggesting that lake sediments can be a useful means for extending the period over which contemporary monitoring exists, the study stresses the need for detailed historical records of land use and climate against which long term sediment yield records can be eval

ISSN:0197-9337    

DOI:10.1002/esp.3290100108

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractThe relevance of drop shape for erosivity was tested for different combinations of drop sizes and fall heights. For all test combinations together the introduction of the observed drop shape in erosivity parameters only produces minor improvements in the relation between erosivity and detachment and transport by splash. This result is attributed to the dominance of oblate shapes in high velocity conditions. Using small fall heights and low fall velocities as in many rainfall simulators and drop tests it is shown that prolate drops produce a splash detachment which is 2 to 3 times higher than that produced by drops with an oblate shape at impact. As drop production in rainulators or for aggregate stability drop tests may result in more or less uncontrolled variations of drop shape, it is concluded that in addition to other test conditions drop shape should be specified. Moreover it is noted that the erosive capability of prolate drops can explain partly the high splash erosion amounts below vegetation.

ISSN:0197-9337    

DOI:10.1002/esp.3290100109

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractAbsorbance at 360 nm was measured on 44 filtered streamwater samples of different dissolved organic matter (DOM) contents. A regression equation of DOM on absorbance predicted DOM with a standard error of estimate of 1.26 mgl−1, Use of a published equation relating dissolved organic carbon (DOC) to absorbance gave DOC values for the samples which were consistent with measured DOM. The method offers considerable potential for rapid quantification of dissolved organic matter concentrations in streamwate

ISSN:0197-9337    

DOI:10.1002/esp.3290100110

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

摘要:

AbstractEight forest areas, totalling 128.7 hectares, located near the northern border area of the Belgian Ardennes, have been surveyed for soil material brought to the surface by burrowing animals. It appeared that at least 7003.6 kg/ha were present, brought up by badgers and rabbits. The amount turned out to vary a factor 103between the eight regions. During the half year survey period badgers added some 570 kg to their mounds. On this basis the rate of mass transport effected directly by badgers may be estimated at an insignificant 0.02 gcm−1y−1. Also, production of available sediment by these animals is relatively unimportant in this temperate humid forest environm

ISSN:0197-9337    

DOI:10.1002/esp.3290100111

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290100112

出版商:John Wiley&Sons, Ltd    

年代:1985

数据来源: WILEY