摘要:

AbstractField investigations in the Front Range of Colorado, U.S.A., confirm that the spatial distribution of vegetation in watersheds exerts strong control on the entrenchment of streams in the montane zone. When tractive force in channels exceeds threshold values of resistance on the valley floors, cutting of arroyos begins, producing forms that change allometrically. An algorithm based on the Cooke Method for discharge, the Manning Equation for depth of flow, and the DuBoys Equation for tractive force can be used to evaluate force for observed and experimental conditions. In small (<5 km2) basins in the Front Range of Colorado, forces for the 10‐year discharge commonly range from 1 to 5 dynes, but the resistance offered by valley floors is usually unable to withstand forces from channel flows greater than 2 dynes. Biomass of vegetation on the valley floor exerts significant control on the trenching process, with threshold values of biomass commonly between 1.5 and 9 kg/m2, the range of semi‐arid vegetation cover. Thresholds exist in the montane erosion system for gradient, mean biomass in the basin, biomass on the valley floor, channel roughness, and channel width. Each threshold value, however, depends on the interrelationships among other variables in the system. Manipulation of the vegetation cover is the primary human impact on the montane channels, and management of the distribution of vegetation offers the most efficient method of maintaining the stability of chann

ISSN:0360-1269    

DOI:10.1002/esp.3290040102

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe paper reports the first research on karst solution processes and rates in New Zealand. The study area is an IHD representative basin in the northwest corner of the South Island in a mountain range consisting principally of Ordovician marble. The climate is sunny and warm (17°C) in summer and wet and cool (7°C) in winter. Average precipitation is 2,158 mm of which 525 mm evapotranspires, yielding a discharge of 51–75 l/s/km2in the river basin studied. Almost half of the catchment of 45.1 km2consists of karst which occurs mainly as a doline covered plateau at 600–900 m within which most drainage is subterranean. Water tracing is with fluorescein defined drainage patterns. Marble solution was established by estimating inputs, throughputs and outputs of water and dissolved calcium and magnesium in both autogenic and allogenic karst drainage systems. Particular attention was paid to estimating errors. Water samples for chemical analysis were taken irregularly for approximately one year, and a rating curve relating chemical load to discharge was established. The best estimate of solution loss from the basin yields a mean rate of 100 ±M24 m3/km2/a. Of this 80 per cent is derived from solution of marble by autogenic waters, mostly in the top 10–30 m of the marble outcrop. The remaining 20 per cent is accomplished by allogenic stream solution. Approximately 9.9 per cent of the dissolved calcium and magnesium load leaving the basin originates from non‐karst rocks and 4.6 per cent is initially introduced by rainfall.River flows that are exceeded only 5 per cent of the time transport approximately 44 per cent of the annual dissolved load, while mean to low flows that occur for 75 per cent of the time transport 35 per cent of the annual solute load. This confirms the importance of low frequency‐high magnitude events, but indicates also that in corrosion systems high frequency events of moderate to low magnitude can also accomplish sign

ISSN:0360-1269    

DOI:10.1002/esp.3290040103

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractRegression equations with the form y =f(q), whereyis a channel characteristic andqis a discharge of a particular frequency are widely used in fluvial geomorphology. They imply that channel geometry is related to a dominant discharge. For this to be so, the river must be ‘in regime’ i.e. its characteristics must fluctuate about a mean condition which is effectively stationary at the time scale considered. The static regression‐dominant discharge approach does not fully describe the relationship between channel characteristics and discharge and an alternative model is proposed with the formy(t)= ∞ 00h(u)‐q(t‐u)du. This model states that channel form is a product of the whole series of discharges experienced by the channel. The dominant discharge‐static regression approach provides a working approximation of the relationship between channel characteristics and discharge only when temporal variations inqare small or whenyis insensitive to

ISSN:0360-1269    

DOI:10.1002/esp.3290040104

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractAlthough a number of studies of the variation of soil transport with increase in slope angle have appeared, few include an information on the interaction of sheetwash and rainsplash on high slope angles, which is necessary to test Horton's proposed polynomial relationship. Virtually no studies are available which compare the influence of changes in soil type or antecedent moisture on established relationships. This paper reports the testing of eight soils from Alberta, Canada, under simulated rainfall on ten slopes from 3° to 30°. Material eroded was separated into that transported by rainsplash and that by sheetwash. In general, it was found that the influence of changes in slope angle on soil transport is best described by polynomial relationships, but these are shown to vary considerably between rainspash and sheetwash, between different soil types and for different antecedent moisture conditions. Despite careful control of all factors other than slope angle very high variability of results was experienced. Causes of variability are examined and the need for evaluation of the effect of test plot size on variability of results is suggeste

ISSN:0360-1269    

DOI:10.1002/esp.3290040105

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractFeedback mechanisms, which operate upstream through drawdown and backwater effects and downstream through sediment discharge are responsible for channel evolution. By combining these mechanisms with channel processes it euables a dynamic process‐response model to be developed to simulate the initial evolution of straight gravel‐bed channels.When erosion commences on a land surface, sediment entrained in the headwater reach by hydraulic action is selectively transported, deposited and reworked. This produces a damped oscillation between degradation and aggradation as the channel and valley respond to spatial and temporal variations in sediment calibre and hydraulic conditions. The initial cut and fill phases are responsible for valley incision and floodplain development while secondary and subsequent activity can produce river terraces.Eventually sediment entrainment in the headwaters declines as slopes are reduced. Subsequent channel evolution is relatively insignificant because it is dependent on local weathering activity producing material that can be transported on declining slopes. Therefore landforms produced during the initial phase of development, when local weathering was non‐limiting, dominate the land

ISSN:0360-1269    

DOI:10.1002/esp.3290040106

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractA modified design of seston trap is described which has been used in Brotherswater, U.K. (Ordnance Survey NY 40 12). The trap was designed to collect larger quantities of seston than were found to collect in conventional types of seston trap. A simple concealed trap‐location device is also describe

ISSN:0360-1269    

DOI:10.1002/esp.3290040107

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe use of radiography is illustrated in four areas of interest to the hydrologist and geomorphologist. Soil samples analysed show that zones of varying hydraulic conductivity can be identified by X‐ray analysis, as can the extent of the root zone. In addition examples are presented which illustrate that radiography may have potential in the examination of overland flow erosion and deposition characteristics, and in the analysis of the behaviour of clay soils during and after an extreme dry perio

ISSN:0360-1269    

DOI:10.1002/esp.3290040108

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3290040109

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3290040110

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3290040112

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY