ISSN:0262-6667    

DOI:10.1080/02626669909492198

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this paper, using Sicilian and Australian rainfall intensity data, a comparison between different estimators (modified Fournier index F, FFindex) of the rainfall erosivity factor in the USLE was made. The relationship between the modified Fournier index and the mean annual rainfall, P, was theoretically derived. The K constant, linking the FFindex and P, and its cumulative distribution function (CDF) were used to establish hydrological similitude among different geographical regions of southern Italy and southeastern Australia. To predict the erosion risk for an event of given average recurrence interval, the probability distribution of the annual value Fa.jof the Arnoldus index was studied. In order to establish the theoretical CDF to use as aregionalparent distribution, the descriptive ability of LN2 and EV1 distributions was studied by both an at-site analysis and a hierarchical regional procedure. The analysis showed that for each sub-region of southern Italy and southeastern Australia, characterized by a constant coefficient of variation, the erosion risk index is constant.

ISSN:0262-6667    

DOI:10.1080/02626669909492199

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A piezometric head method is proposed to estimate the impermeable layer depth used in drain spacing formulae. The method was tested and compared with soil texture changes and the US Bureau of Reclamation (USBR, 1978) criterion of impermeable layer being one with hydraulic conductivity one tenth to one fifth that of the weighted hydraulic conductivity of the upper layers. The proposed method, which works for below the water table conditions and does not require hydraulic conductivity measurements, gave approximately the same results as the USBR method. The soil texture changes method was erratic and not reliable.

ISSN:0262-6667    

DOI:10.1080/02626669909492200

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Soil erosion on agricultural land has become a global environmental problem and information on rates of soil loss is an important requirement both for quantifying the problem and for developing improved land management and soil conservation practices. The use of fallout137Cs measurements overcomes many of the difficulties facing traditional approaches to erosion monitoring and affords an effective means for obtaining estimates of soil redistribution rates on cultivated land. A number of empirical functions and theoretical models have been developed to establish the relationship between the change in the soil137Cs inventory relative to the local137Cs fallout input and the rate of soil redistribution. Of these approaches, physically-based mass balance models have received increasing emphasis, but their application may be hampered by their complexity and the need to specify values for a number of parameters. This paper presents a refined simplified point-based mass balance model for deriving estimates of soil redistribution rate from soil137Cs data for individual sampling points. This model incorporates a number of important factors which are included in more comprehensive mass balance models. A spatially-averaged mass balance approach is also presented. This can be used to estimate water-induced soil erosion rates at different spatial scales in situations where detailed information on within-field variation of soil redistribution rates is not needed but information on net erosion rates or sediment output from a field is required.

ISSN:0262-6667    

DOI:10.1080/02626669909492201

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Diurnal and seasonal variations in particle size characteristics of suspended sediments of Dokriani glacier meltwater were studied during the 1994 ablation period (May-October). Diurnal suspended sediment concentration curves exhibit two prominent peaks from May to mid-August and only one peak during the rest of the ablation period. The first peak resulting from dominance of fine and medium sand contributed to the rising limb of the diurnal hydrograph, whereas the second peak was dominated by fine and medium silt which coincides with the diurnal discharge peak. The trends observed on the appearance of silts and sand particles on diurnal scales at various stages of the ablation period suggest that the subglacial drainage system comprises a diurnally-reversing hydraulic gradient between the channels and distributed system along with translatory flow through the distributed system. This study suggests that the subglacial zone is the major source of sediments in the Dokriani glacier meltwaters. However, high intensity monsoonal rainfall has contributed supraglacial sediments and resulted in bimodal distributions. Fines (clay to medium silt) are the dominant classes in the suspended sediments except during the spring event; the supraglacial sediments had coarsely skewed distributions.

ISSN:0262-6667    

DOI:10.1080/02626669909492202

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Erosion processes and sediment yield over Serbian territory are reviewed, as well as the distribution of sediment load in the hydrological network in Serbia. The overview of erosion problems consists of an analysis of the main erosion factors over the Serbian territory, a review of field investigations of soil loss and a description of the erosion control measures implemented in the region. The review of sedimentation problems includes a presentation of the sediment budget of the hydrographic network of Serbia, an analysis of bed load transport in the main Serbian rivers and consideration of issues related to the reservoir siltation.

ISSN:0262-6667    

DOI:10.1080/02626669909492203

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Following a major expansion of the hydrometric network in the 1960s, flow gauging operations in Lebanon were curtailed from 1975 to 1990 due to the civil war and only a partial service has resumed since then. The implications of these limitations on flow data availability are examined from the standpoint of estimating the overall surface water resources of Lebanon and for developing regional estimation procedures for ungauged flows. Attempts are made to characterize both the spatial and temporal variations in key measures of flow availability such as the mean and the flow duration statistics, and comparisons are made between long-term flow records in Lebanon and regional rainfall records. The results show that flows in the 1960s, when measurements were at a peak, were well above average, and that, due to the high inter-annual variability in flows, records of many decades are required to adequately define some aspects of the flow regime. However, given the large variations in topography and climate, there is a surprising amount of spatial coherence in the records, although more data are required to adequately define this behaviour. These results highlight the need to resume hydrometric monitoring in Lebanon at the pre-war level in order to characterize and manage existing water resources adequately and to detect any future trends in flow behaviour which may arise from climate and land use changes and changing patterns of demand.

ISSN:0262-6667    

DOI:10.1080/02626669909492204

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The channel-geometry method is an indirect method of flood estimation which relies on the development of relations between flood discharges, measured at gauging stations, and channel dimensions, measured from natural river reaches in the vicinity of the gauge. Channel-geometry equations enable flood discharges to be estimated at ungauged locations on natural streams from measurements of channel size and by combining the index flood estimate (usually the mean annual flood) with regional flood growth factors. This paper reports on channel-geometry equations which have been developed and applied in four developing, tropical countries as part of hydrological investigations for road design and flood risk assessment (Java), irrigation and hydropower development (Burundi), design of all-weather roads (Ghana), and rehabilitation of railway bridges (Tanzania). The applications demonstrate the benefits of the channel-geometry method in situations where data on catchment characteristics are limited or may not offer the most appropriate basis for flood discharge estimation.

ISSN:0262-6667    

DOI:10.1080/02626669909492205

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Results of further evaluation tests of a monthly rainfall-runoff model used for extending streamflow data records in England and Wales are presented. In particular, since the objective of the record extension exercise was to make available long enough data records for reservoir yield assessment, model performance in reproducing the reservoir storage-yield-reliability relationship during calibration was examined. Finally, it can be argued that this type of test should be among the suite of performance checks on rainfall-runoff models in situations where low flow is the primary concern.

ISSN:0262-6667    

DOI:10.1080/02626669909492206

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669909492207

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor