摘要:

ABSTRACTReforestation of headwater slopes of the Ganaraska River basin in southern Ontario following World War II has resulted in decreased peak flows and has likely reduced sediment yields. Changes in channel morphology produced by these modifications to the hydrologic regime were examined for a 6.7 km section of river in the context of Schumm's (1977) qualitative model of channel response to reforestation. Flood channel width (measured from air photographs) has decreased since 1928, while cross-sectional measurements during stream gauging in the study section revealed a decrease in the channel's width/depth ratio between 1960 and 1975. Both of these trends agree with Schumm's model. Changes in channel planform were dominated by downstream translation of meander bends and by meander cutoffs. The model predicted an increase in channel sinuosity in response to decreased peak flows and bed-material yield from the basin. However, sinuosity for the entire river section decreased significantly between 1928 and 1988, and only one reach experienced an increase in sinuosity following reforestation. A possible explanation for the model's failure to describe temporal changes in the Ganaraska's sinuosity involves a negative feedback whereby the increased sinuosity produced by decreased flow and sediment yield enhances potential for ice jams and meander cutoffs, which in turn reduce sinuosity. This limited test of Schumm's model suggests that caution be used when applying the model and its variants to reconstructions of basin palaeohydrology, and predictions of channel response to anthropogenic and natural changes to the hydrologic regime.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880432

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTSoil surface partitioning of rainfall into overland flow and infiltration will greatly determine the amount of soil water and groundwater resources in an area. The partitioning depends on factors linked to natural processes as well as to the action of man. In the present study, conducted in semi-arid Botswana and Tanzania, soil surface and subsoil characteristics were studied along transects. Factors such as surface seals, soil texture, vegetation cover, slope gradient and land use were observed. The infiltration capacity was measured by means of the double-ring method and the dropper method. It was found that the soil texture and the vegetation cover were important factors for infiltration. The percolation rate depending on subsoil conditions was shown to vary up to five times. However, the infiltration rate depending on soil surface conditions has been shown in other studies to vary up to 20 times. This indicates that the surface is sensitive to land use practices and will highly influence the overall amount of water moving through the soil profile. In the present study it was shown that the occurrence of surface seals was related to soil conditions, vegetation cover and microtopography. Therefore, aerial photographs can give easy access to factors which influence rainfall partitioning.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880433

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTThe aim of this paper is to review the history of vegetation and land use from the end of the nineteenth century to today. The study area is Kassala Province, Eastern Sudan. Historical maps and statistics were digitised and analysed with a PC Arc/Info system. A summary of information in travel reports is presented. The conclusions are that the rainfall trends have decreased between 1949 and 1990. Areas of trees, bush and cultivation have increased. Kassala Province has been more mechanised during the last hundred years. In the past there seems to have been a greater variety of species and game than today.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880434

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTA photogrammetric survey of the movement of supraglacial boulders together with field survey of surface markers has revealed the spatial and temporal change in velocity on the debris-mantled tongue of Tasman Glacier, New Zealand. Between 1957 and 1986 a general reduction of glacier velocity is recorded, and towards the terminus the local effects of thermokarst erosion on flow vectors became more influential as the downvalley component of velocity decreased. Onlyca.2% of the debris-covered glacier area had no measurable movement, and mature thermokarst sinkholes formed on ice moving at>24 ma-1. Increases in ice velocity and surface elevation 10 km above the terminus were not recorded 2.5 km above the terminus in 1986. Changes in ice volume have been manifested by changes to ice levels and velocity, not by fluctuations of the terminus. The study shows that extensive supraglacial debris mantles and thermokarst forms can exist on actively-moving ice in alpine regions of high debris supply and ablation, and that shear-zone formation is not necessary to explain debris-mantling of such glaciers.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880435

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTThree forms of unusual patterned ground are described from the Falkland Islands, South Atlantic.1.Stone polygons have developed on residual peat following clast transport from adjacent exposures of angular rock debris, desiccation of the peat surface and reworking of clasts into the network of open cracks.2.In areas of abundant sand supply, sand polygons are present on lake-bed and lake-margin peat surfaces that have experienced desiccation. Sections through these polygons reveal sand-filled cracks reaching 25 cm in depth.3.The movement of sheep and cattle across erosion scars has created numerous hoof-print depressions which have become filled with small stones and now form roughly circular to irregular stone-filled hoof prints.These features do not result from frost-related processes and appear not to have been recorded in other regions. The exact mechanisms by which clasts and sand have been transported are not known with certainty although aeolian action, sheetflow, and wind-generated wave action in shallow water may have acted separately or in various combinations.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880436

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

ABSTRACTThis paper maps the likely changes in growing season strength in Northern England which would be associated with a variety of temperature change scenarios. Estimates of future temperature change, obtained through application of regression analysis and analytical theory, are converted into attendant changes in“thermal potential”(measured by annual accumulated temperatures above 6°C). The scenarios include warm and cold analogues, uni-directional airflow scenarios, arbitrary warming scenarios and two GCM simulations: UKHI (United Kingdom Meteorological Office High Resolution GCM Equilibrium Experiment) and GISS (Goddard Institute for Space Studies). Considerable changes in the thermal potential of Northern England result, especially at high altitudes, and there is great inter-scenario variation. The amount of cultivable land, defined as areas with an annual temperature accumulation of 1000 d°C and above, varies from 74.6% in the control model to over 99% in the two GCM scenarios (2×CO2). This is to be expected in maritime upland areas such as the Pennines, where growing season strength is extremely sensitive to small changes in mean temperature. Problems in the interpretation of the results are discussed and outlines for future work are given.

ISSN:0435-3676    

DOI:10.1080/04353676.1995.11880437

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor