摘要:

AbstractBagnold's theory of bedload stresses and bedforms requires that the tangential stress exerted at the base of a moving bedload dispersion in high stage plane beds is carried entirely by the grain stressT. Derivation ofTfrom experimental data in flow channnels shows, however, that the fluid contribution τ′ is still dominant (≈ 1 to 2 ×T). Particle concentrations in the experimental bedload dispersions approached 10 per cent and it is inferred that no appreciable concentration gradient exists. Grain collisions are thought to be most probable whenever more than 1 former stationary grain layer is in forward motion. High stage plane beds may be unstable when grain collisions cease. Current ripples evolve from the amplification and migration of chance defects due to unsteady fluid impulses generated by injection, or burst, phenomena in the viscous sublayer and not through any inherent static shear resistance deficit exerted by stationary bed g

ISSN:0360-1269    

DOI:10.1002/esp.3290020102

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractSimulation models may be used to explore the implications of making specific assumptions about the nature of a real world system, and then to make predictions of the behaviour of that system under a set of naturally occurring conditions. It is important that understanding generated by the former should be gained before predictive use of the system model. This paper describes and uses a finite‐element model of transient, partially saturated water flow within a hillslope soil mantle overlying an impermeable bedrock, to make an investigation into the effects of parameter variations and initial conditions on the hillslope hydrograph. The results clearly demonstrate that the response of the hillslope system to rainfall is highly non‐linear and that the initial conditions, particularly in the unsaturated zone, are of paramount importance in governing the timing and magnitude of the hydrograph peak. Hillslope convergence appears as the dominant topographic parameter but the non‐linearity of the response and the complex interdependence between the soil and topographic parameters restrict the possibility of further definite conclusions about the relative sensitivity of the simulated hillslope hydrograph to changes in these param

ISSN:0360-1269    

DOI:10.1002/esp.3290020103

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractThis paper examines present and future resource utilization in the tidal section of the Georges River in the southern part of Sydney. Over the last 30 years, the physical characteristics of the river have changed as a result of urbanization, changed hydrologic regime and sand dredging. Urbanization has resulted in an increase in population from 190,000 in 1947 to 550,000. This has resulted in an increase in runoff, sediment input to the river and waste disposal. The change in hydrologic regime has resulted in a substantial increase in the magnitude and frequency of flooding which has increased erosion. Sand dredging has increased the channel capacity, enlarged the tidal prism and increased water turbidity. It has also resulted in extensive bank erosion in the upper part of the river and extensive deposition lower down as tailings are deposited. Although most of these changes have resulted in the deterioration of environmental quality, use of the river for recreation and as an urban amenity has increased.

ISSN:0360-1269    

DOI:10.1002/esp.3290020104

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractArroyo cutting that began in the American Southwest in the 1880s is associated with sudden runoff, a circumstance characteristic of this semiarid region in which occasional intense rainfall exceeds the capacity of the ground to absorb water. This report describes two arroyos in an area of moderately dissected bolson deposits southwest of Santa Fe, Cañada de la Cueva and Pueblo Cañon, where arroyo cutting since 1970 has been closely related to runoff from summer rain. The area is vegetated chiefly by grama grass and scattered juniper. Cutting is monitored by repeated surveys of channel floors, cross‐sections, and headcuts, and by repeated photographs taken as stereopairs. Rainfall and discharge are measured simultaneously in 5‐minute intervals by dual digital recorders at a gauging station on Cañada de la Cueva (drainage area 4.64 km2). Discharge has been as much as 18.2 m3/s from rainfall of 25.2 mm. The maximum 15‐minute intensity for this storm was 64.0 mm/hr, and runoff was 7.9 mm. The flood peak arrived in 20 minutes, by which time 80 per cent of the rain had fallen, and the flow subsided to a tenth of its maximum in less than an hour. This storm at Pueblo Cañon (drainage area 13.3 km2above the place of measurement) resulted in an estimated discharge of 140 m3/s, and features produced by hail on the channel floor suggest that the duration of flow could have been as brief as 30 minutes. Observed increments of headward cutting at Cañada de la Cueva range from 0.28 m for 1.8 mm of runoff to 4.9 m for 12 mm of runoff. Aggregate cutting in 5 years has been as much as 13.7 m, resulting in erosion of 570 m3of alluvium. Headward cutting near the mouth of Pueblo Cañon has been observed in increments of 10.3, 14.6, and 20.7 m, for an aggregate of 45.6 m, as measured from 1971 to 1974. This cutting removed 1,770 m3

ISSN:0360-1269    

DOI:10.1002/esp.3290020105

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractSedimentological analysis of particle size data from a hillslope profile in mid‐Wales allows the identification of two distinct upper slope units. These are described and analyzed in greater detail for clay and organic matter distribution. The original slope subdivision is substantiated by the results and the major differences in soils between the upper units are attributed to drainage contrast

ISSN:0360-1269    

DOI:10.1002/esp.3290020106

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractDeformation structures, within some Quaternary calcretes of Botswana and South Africa, have been classified into five types. Type 1 folds are small‐scale (20 m), but low amplitude (<1 m), anticlines in hardpan calcrete; structural evidence suggests dominantly horizontal compression within the hardpan due either to an overall increase in volume of the calcrete, or to the disruptive formation of calcrete in joints in the synclinal areas. The mineralogy of the calcretes is dominated by low‐Mg calcite which may have inverted from a high‐Mg form; the deformation in type 1 and 2 folds was probably caused by the disruptive and displacive growth of calcite during calcretization. Type 3 folds are saucer‐shaped depressions in hardpan calcrete and may be due to the removal of soluble salts below the folded layer during or after calcretization. Finally, type 4 folds are small, diapiric anticlines resulting from the upward injection of swelling clays into calcrete or calcreti

ISSN:0360-1269    

DOI:10.1002/esp.3290020107

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractIn Pakistan various brick building structures are currently disintegrating in the Indus Valley. These include the Harappan site of Mohenjo‐Daro. The environment of this site is described, the nature and speed of the disintegration problem is outlined, and the cause of disintegration is discussed Weathering occurs in association with the development of salt efflorescences and some bricks disintegrate only a few years after being laid down. Chemical and X‐ray diffraction analyses show that the predominant salt is the sodium sulphate mineral thenardite. The reasons for its effectiveness are discussed. They include its high solubility, the rapid change of solubility with temperature, and its hydration characterist

ISSN:0360-1269    

DOI:10.1002/esp.3290020108

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractThe nature and strength of the correlation between stream gradient and valley side slope angle are seen to vary according to the order of the stream segment. In addition, it is suggested that the relationship will depend on the efficiency of slope processes, and that this may contribute to tye different from of relationship obtained in different regions.

ISSN:0360-1269    

DOI:10.1002/esp.3290020109

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3290020110

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3290020112

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY