ISSN:0197-9337    

DOI:10.1002/esp.3290140402

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290140403

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractRed Creek, in the Red Desert area of the Great Divide Basin, Wyoming, is an arid‐region anastomosing stream. The narrow, deep, and sinuous main channel is flanked by anastomosing flood channels, or anabranches. Most anabranches are initiated at meander bends. The primary mechanism of anabranch initiation is avulsion during overbank floods. Anabranch enlargement occurs by headward erosion. Anabranches act as distributary channels during floods, when water and sediment from overbank flows are transported to and deposited on the floodplain via the anabranches. During periods of low discharges, the anabranches act as tributaries to the main channel, transporting runoff from the floodplain and surrounding hillslopes to the main channel of Red Creek.Aggradation is occurring in the main channel and on the floodplain throughout the study reach. Infilling of the main channel occurs primarily by lateral accretion, while the floodplain accretes vertically through deposition of overbank sediment from the main channel and anabranches. Infilling of the main channel may cause avulsion of the main channel into an anabranch. The abandoned main channel segment may then fill completely or act as an anabranch. Because lateral migration of channels is inhibited by the high cohesion of the silt and clay channel sediment, periodic avulsion is the primary form of lateral mobility in the syste

ISSN:0197-9337    

DOI:10.1002/esp.3290140404

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractComparative erosion rates provide a rational basis for evaluating reclamation success because the work performed by erosion processes is a function of both forces and resistances operating on a surface. Sheetwash erosion data collected by the LEMI technique over several years at the Dave Johnston Mine in east‐central Wyoming show that, based upon average values, there is generally little difference between the erosion rates of natural and reclaimed hillslopes at this locale. Therefore, it is permissible to infer that the reclamation programme has been successful from a geomorphic perspective. However, there is considerable variation in erosion rates about the average for individual hillslopes in both the natural and reclaimed groups.Examination of these data by hillslope element and segment show that, based upon average values, the concave elements of natural and reclaimed hillslopes experience the highest rate of sheetwash erosion. Again, however, there is considerable variation about the average and considerable erosion can occur in any element or segment of particular hillslopes.Lastly, there are seasonal oscillations of hillslope surface elevation with frost‐heaving prevalent during the late autumn to early spring months and erosion prevalent during the late spring to early autumn mon

ISSN:0197-9337    

DOI:10.1002/esp.3290140405

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe concept of a ‘niveo‐aeolian influence’ on the genesis of northwest European Pleistocene aeolian sand and loess deposits has been advocated in the past both to explain the presence and the absence of lamination. Field experiments were carried out on artificially deposited alternating layers of sand and snow, and of loess and snow, to investigate the role of a niveo‐aeolian mode of deposition on resulting sedimentary structures.Field observations of sand plots revealed minor changes in surface morphology typical of denivation surfaces. The thin sections showed a characteristic porous structure. Deformations of the depositional structure and indications for erosion and redeposition were limited. However, the originally smooth aeolian sedimentary surface of the loess changed considerably. The thin sections showed also a porous, spongy structure. Indications were found for disturbances by frost action, liquefaction during melting of the snow and ice, and redeposition of loess by meltwater.The experimental results strongly suggest that sand and loess deposited as niveo‐aeolian material are characterized both by a porous structure, and that the original sedimentary structure of the sand is not affected by snowmelt, whereas loess becomes non‐laminated. Thus, the intercalation of snow during sedimentation of sand and loess does not in itself induce a laminate

ISSN:0197-9337    

DOI:10.1002/esp.3290140406

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIn tackling the apparently intractable problem of linear dune initiation and maintenance there has been a move away from large‐scale deductive models to smaller‐scale field studies of individual dunes. This paper reports a study of surface change on a large, complex linear dune in the Namib Desert, southern Africa.The dune surface responds to a markedly seasonal wind regime. In summer westerly winds erode sand from the west flank of the dune and deposit it on the easterly lee side of the dune crest. In winter this pattern is reversed. Easterly winds erode sand from the east slope and deposit it on the west slope. The crest therefore moves back and forth some 15 m each year returning at the end of a year's cycle to its position at the beginning. The position of the base of the dune appears to remain fixed, even though sand is moving throughout the dune system. The dune does extend northward along some resultant of the westerly and easterly winds.Despite relatively high levels of activity, especially at the dune crest, there is no evidence of the breakdown of the linear dune form. The conclusion must therefore be that linear dunes can be maintained in bimodal wind regimes and are not necessarily related to unidirectional parallel regimes as others have sugges

ISSN:0197-9337    

DOI:10.1002/esp.3290140407

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe mining of alluvial tin in the Ringarooma basin began in 1875, reached a peak in 1900–20, and had virtually ceased by 1982. During that time 40 million m3of mining waste were supplied to the main river, quickly replacing the natural bed material and requiring major adjustments to the channel.Based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load, the river's transport history is reconstructed using a mass‐conservation model. Because of the lengthy time period (110 years) and river distance (75 km) involved, the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream. Peak storage is predicted in that part of the river where braiding and anastomosis are best developed.Aggradation was most rapid in the upper reaches close to major supply points, becoming slower and later with distance downstream. Channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common. Bridges had frequently to be replaced. While bed levels were still rising in lower reaches, degradation began in upper ones, notably after 1950, and by 1984 had progressed downriver over 30 km. Rates of incision reached 0·5 m yr−1, especially in the early 1970s when record high flows occurred. As a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions. Also a narrower unbraided channel has developed. The river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining

ISSN:0197-9337    

DOI:10.1002/esp.3290140408

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290140411

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290140412

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290140413

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY