摘要:

AbstractThe effect of peat on crust strength was investigated using ten soils with organic matter levels ranging from 1‐50 to 18‐23 per cent. As peat content increased, the crust strength reduced. This occurred in spite of the inability of peat to increase the stability of soil aggregates. Peat reduced crust strength by acting as a mulch on the soil surface, thereby reducing breakdown of soil aggregates. Peat also formed a source of weakness on the soil, reducing crust formation.Using a factorial experiment involving a further seven soils with different levels of peat treatment, exposed to four rainfall durations and with two aggregate sizes, crust strength was described in terms of the direct effects and the interactions of these factors. Most of the crust strength values reduced with increasing peat content. For each soil, crust strength increased significantly with increasing rainfall duration. Crust strength was greater for the smaller aggregate size.The most significant interactions affecting crust strength were between soil and aggregate size, rainfall duration and aggregate size, and soil and rainfall duration in that order. These interactions were used to describe the effect of organic matter in form of peat on crust strength. For each soil and aggregate size, polynomial relationships were established to relate crust strength to total kinetic energy of rainf

ISSN:0197-9337    

DOI:10.1002/esp.3290160602

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA 1:50 scale hydraulic model was designed, based on Froude number similarity and using hydrological and sediment data from a small braided gravel‐bed river (the North Branch of the Ashburton River, Canterbury, New Zealand). Eighteen experiments were conducted; seven using steady flows, and eleven using unsteady flows. The experiments were carried out in a 20 m × 3 m tilting flume equipped with a continuous sediment feed and an automated data acquisition and control system. In all experiments water at 30°C was used to reduce viscosity‐related scale effects.Analyses of the experimental data revealed that bedload transport rates in braided channels are highly variable, with relative variability being inversely related to mean bedload transport rate. Variability was also found to be cyclic with short‐term variations being caused by the migration of bedforms.Bedload transport was found to be more efficient under steady flow than under unsteady flow, and it was postulated that this is caused by a tendency for channel form to evolve towards a condition which maximizes bedload transport for the occurring flow. Average bedload transport rate was found to vary with channel form, although insufficient measurements were made to define a relat

ISSN:0197-9337    

DOI:10.1002/esp.3290160603

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractExperiments were carried out in order to measure the sediment transport capacity of interrill flow with and without rainfall and to relate the transport capacity to selected hydraulic parameters, such as effective stream power and shear velocity. Different sediments were used in order to study the effect of grain size. The proposed relationships show considerable variations with grain size and there is only a minor effect of rainfall on the transport capacity which also seems to be grain size dependent.The proposed relationships can be used to predict sediment transport capacity of interrill flow and can therefore contribute to the development of physically based erosion models.

ISSN:0197-9337    

DOI:10.1002/esp.3290160604

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIron geochemistry of the sediments and interstitial waters of the Roaring River alluvial fan in the Rocky Mountain National Park, Colorado was studied using a chemical equilibria approach. Large concentrations of colloidal Fe in the filterable Fe of the interstitial waters results in considerable overestimation of Fe2+ activity. The overestimation of Fe(II) seriously hampered the usefulness of chemical equilibria approach in the study of Fe geochemistry. Buried soil organic matter and a high water table within the alluvial fan has produced a highly reduced environment which results in elevated colloidal and filterable iron concentrations in the interstitial waters. The source of the iron is probably iron oxides within the buried soil and primary iron‐bearing minerals in the sediments. When the iron‐rich solutions reach the surface, the water rapidly oxidizes and amorphous ferric hydroxides precipitate. Between 190 to 370 mmol of iron per kg of surficial material were precipitated at the surface within two months. Noticeable decreases in the total amount of C and extractable iron (20 per cent and 30 per cent respectively) in the buried soil were observed during the study period (1985‐1987) which implies a significant reduction in iron dissolution and subsequent deposition across the alluvia

ISSN:0197-9337    

DOI:10.1002/esp.3290160605

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractSilcretes from Queensland (Australia) were dated by means of the electron spin resonance dating technique. The results range from 1.5 to 10.8 million years; therefore, these silcretes were formed between the upper Miocene and the early Pleistocene. For a conclusive interpretation of the data geochemical and thin section analyses were also carried out. ESR dating of silcretes for the first time offers a direct approach to a chronostratigraphic framework of the genesis of these duricrusts, and of the palaeoclimatic events attributed to them.

ISSN:0197-9337    

DOI:10.1002/esp.3290160606

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe idea that the isostatic response to progressive denudational unloading can be episodic over cyclic timescales is widely cited in the geomorphological literature. We demonstrate, however, that this notion, which has been regarded as a possible mechanism of widespread landscape rejuvenation, is based on a fundamental misunderstanding of the principles of flexural isostasy. Rather than a discontinuous response, in cases where the half‐width of the applied load is greater than a few tens of kilometres the lithosphere experiences a continuous compensation which is dependent upon the wavelength of the applied load rather than upon a lateral, or vertical, threshold of unloading which has to be exceeded before isostatic recovery is initiated. Although a flexural isostatic response cannot account for episodic uplift during a denudational cycle, it can explain the growth and persistence of significant marginal upwarps along passive margins across which there is a marked contrast in denudation rates. Such marginal upwarps, in turn, probably play a critical role in the long‐term evolution of drainage systems and landscapes in adjacent continental hinterla

ISSN:0197-9337    

DOI:10.1002/esp.3290160607

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractRock resistance to erosion is an often described factor in geomorphic studies, and is generally considered to strongly influence the shape of erosional landforms. However, the property of the rock mass that enables it to resist erosion is rarely considered, and its measurement is rarely justified and assessed adequately. Allison (1988, 1990) examined the intact strength properties of several types of carbonate rocks and considered that dynamic Young's modulus is a good indicator of rock material strength for geomorphic purposes, and cast doubts on the reliability of Schmidt hammer tests for this purpose. Alternative approaches to rock characterization from the view point of evaluating rock intact strength are considered.

ISSN:0197-9337    

DOI:10.1002/esp.3290160608

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290160609

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290160610

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0197-9337    

DOI:10.1002/esp.3290160611

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY