摘要:

AbstractThe occurrence of two ‘rare’ floods (August 1973, August 1977) in the Plynlimon experimental catchments has confirmed the susceptibility of small upland catchments to summer flooding and provided clues to complications in the geomorphological interpretation of floods in terms of their magnitude and frequency. Magnitude may be treated both in terms of work and effectiveness; the emphasis here is on effectiveness, as revealed by simple surveys. The first Plynlimon flood was more effective on slopes and the second in channels, despite peak discharges of similar return periods and almost identical rates of work revealed by bedload trapping. Effectiveness/frequency studies are likely to require a much more detailed approach, subdividing both the characteristics of the flood and the spatial elements of the affected catchments; a simple slope/channel subdivision is found to be suitable for accounts of effectiveness found in the literature on British floods this century. Effectiveness studies also require regular surveys throughout the recovery period following major flooding; in upland catchments these surveys should concentrate on identifying threshold phenomena and illustrating the relationship between effectiveness and work assessments of magnit

ISSN:0360-1269    

DOI:10.1002/esp.3760050102

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractIn two steady uniform flows at different physical scales in a small open channel, with variables characterizing flow, sediment, and fluid adjusted for dynamic similitude by means of four dimensionless modelling parameters (a Reynolds number, a Froude number, a density ratio, and a length ratio), measured frequency distributions of height, spacing, and migration rate of current ripples were almost identical when scaled, thus verifying that exact Reynolds‐Froude modelling of loose‐sediment transport is valid and workable. Modelling should be valid as well for a wide range of other transport conditions in the same kind of flow, because no additional kinds of forces or effects would be present in transport of loose grains in modes other than as ripples. In scaled‐down modelling, a scale ratio of 2.5 is attainable without recourse to exotic fluids by use of water at 85°C to model natural flows a

ISSN:0360-1269    

DOI:10.1002/esp.3760050103

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractRillenkarren are patterns of tightly packed, small solution rills found upon bare, sloping surfaces of soluble rocks in all climates. They head at the crest of a slope and are replaced downslope by a planar solution surface, theausgleichfläche.Development has been simulated successfully using a rainfall simulator and plaster of paris blocks. Ten principal experiments were completed with blocks at inclinations ranging 22½–60°, temperature and rainfall intensity being constant. Results suggest that rillenkarren develop within a hydrodynamic zone ofrim effectwhere the depth of threads or sheets of runoff is insufficient to prevent direct raindrop impact upon the underlying soluble solid. Where depth of runoff becomes sufficient rills are replaced by the ausgleichfläche. Between upper and lower limits, rill length is proportional to slope in a log linear manner. Rill cross‐sections approximate the parabola, the most effective shape for focussing raindrop erosion in the axis of the trough: this explains the tight packing characteristic. Ausgleichfläche and rill troughs evolve by parallel retreat at the original slope angle, the erosion rate being greatest at a

ISSN:0360-1269    

DOI:10.1002/esp.3760050104

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractPrior to the occurrence of a shallow surface slip on a clay embankment a tensiometer system was installed to continuously monitor pore water conditions. It is shown that high pore water pressures can develop in clay embankments after periods of continuous low intensity precipitation. Using stability analyses it is demonstrated that for this first time slide, the clay fill material had a shear strength above residual values and a small but finite cohesion.

ISSN:0360-1269    

DOI:10.1002/esp.3760050105

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractStream networks used in studies of basin morphometry, network topology, flood hydrology, and sediment production should be defined as precisely as possible. Previous work has drawn attention to the way in which stream network definition varies on maps of different scales, on maps employing different conventions devised in relation to the dynamic network, and according to whether maps, remote sensing or field survey sources are used. Networks also vary in extent according to the date of survey and after considering the instructions to surveyors it is shown that such changes, over periods of 100 years reflect changes in network extent. For three areas of Britain, network change can be identified by comparison of maps of different dates, by comparison of these changes with the results of field survey, and by reference to dateable features such as inclosure boundaries. Changes of drainage networks since the nineteenth century are shown to be significant in extent and they have often occurred as a result of the replacement of flushes by clearly defined stream channels. This transformation has often occurred as a result of new or modified systems of stormwater drainage from roads, tracks or farms, and the planning of the future disposal of road drainage should be considered carefully in relation to such stream network changes. The changes of drainage networks identified from maps of different dates and editions can provide a useful data base for studies of network topology and may also be significant in relation to palaeohydrological investigations.

ISSN:0360-1269    

DOI:10.1002/esp.3760050106

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA computer‐based study of the impact of the proposed Wabo hydroelectric scheme on the Purari River, Papua New Guinea was carried out. The HEC‐6 model,Scour and Deposition in Rivers and Reservoirsdeveloped by the Hydrologic Engineering Centre was used to simulate the effect of the dam on sediment transport and erosion in the lower Purari. Two runs with the model were carried out. The first one was used to establish baseline conditions and the second modelled dam impact.Before the study was carried out, data had to be collected on channel geometry, sediment input, river bed material size composition and hydraulic conditions in the river. Supplementary models also had to be developed to fill in gaps in runoff records and to describe flow in the river during power generation.Results of the investigation indicate that limited erosion will occur because of bed‐armouring and the river will adjust towards a new equilibrium condition quite rapidly. The sediment output of the river into the Purari delta will change, load in the clay, silt and sand/gravel fractions decreasing by 22, 53 and 78 per cent respect

ISSN:0360-1269    

DOI:10.1002/esp.3760050107

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3760050108

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractMagilligan Point is a recurved cuspate foreland at the mouth of Lough Foyle. Two wave regimes intersect in the estuary mouth and the manner of their interplay controls shoreline changes. Ocean swell waves from the N and NE are refracted around the recurve, losing both height and energy longshore. Width of the surf zone decreases and waves tend to steepen, although both these changes and wave refraction owe something to nearshore geometry. Angle of wave approach becomes more acute and a westerly flowing longshore current moves sand S and SW along the beach. Estuary waves from the S and SW are wind‐driven with high‐frequencies and steepnesses. They generate a northeasterly current which returns material N, but dies out as the waves become obliterated by nearshore attenuation and breaking of swell. It is possible to identify a time‐averaged null‐point where shoreline wave power is balanced, although this tends to shift over short periods causing rapid morphological changes. The existence of two independent, but counteractive cells ensures the long‐term maintenance of the foreland, without requiring major or continuous supplies of fresh

ISSN:0360-1269    

DOI:10.1002/esp.3760050109

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractCalcium and magnesium levels have been monitored in slope foot drainage waters on a dolomite bedrock. Both calcium and magnesium rich pulses occur. Short term dissolution experiments demonstrate high calcium levels in solution while other authors have suggested that long residence time groundwater has relatively high levels of magnesium due to calcite precipitation. Patterns of field fluctuations in Ca: Mg ratios can thus be tentatively interpreted in terms of short residence time water of high calcium content mixing with long residence time water of high magnesium content. Fluorometric dye tracing has been used to indicate the orders of magnitude of soil water residence times, suggesting that quickflow components are resident in the system for a few hours to a few days. Further work is in progress.

ISSN:0360-1269    

DOI:10.1002/esp.3760050110

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

ISSN:0360-1269    

DOI:10.1002/esp.3760050112

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY