摘要:

Agricultural flood embankment failure frequency within the Tay drainage basin in Scotland is explored by examination of breach data (228 breaches in total) collected during an eight-year period in which a large number of high discharge flood events (with return periods of up to 120 years) occurred. The data illustrates that overtopping is the main mechanism of failure, that certain reaches and specific locations are particularly vulnerable to failure, and that a near-linear increase in number and total length of flood embankment failures occurs with percentage increase in flood peak discharge. Non-hydrological factors contributing to flood embankment instability include construction over former river channels, location on the outside of meander bends and “honeycombing” of embankments as a result of rabbit burrowing. Hydrological data suggests an increase in the frequency of high magnitude flood events since 1988 in the drainage basin and an identifiable spatial variability; catchments draining more westerly regions exhibit the greatest shift in pattern. The significance of these shifts and future possible changes in flood magnitude and frequency for flood embankment failure risk are quantified; 5% increases in flood magnitude result in increases in the number of flood embankment failures of between 13 and 26%. Similarly a 5% decrease in flood peak discharges leads to decreases of between 11 and 25%. More generally it is shown that land next to rivers with flood embankments is sensitive to modest changes in flood generating conditions.

ISSN:0262-6667    

DOI:10.1080/02626669909492231

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Statistical analysis of daily water level data from four gauging stations along the Hungarian Danube reach has been carried out with the purpose of analysing the impact of the Austrian hydropower plants on the floods of the river. Conditional probability distribution functions of annual flood load maxima and annual number of floods were generated for the periods 1957–1976 and 1977–1996. By comparing these distribution functions, it could be shown that the flood load maxima have decreased, while the number of small and medium floods have increased during the past forty years. These changes indicate a decreased rate of flood superposition resulting from the barrages constructed in this period. The significantly decreased flood load maxima indicate that the Austrian barrage system has a positive impact on the flood control safety of the Hungarian Danube reach.

ISSN:0262-6667    

DOI:10.1080/02626669909492232

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Karst hydrological investigation of the sinking stream problem of the River Zrmanja is presented. The aim of this analysis is to assess the feasibility of constructing three hydroelectric power plants (HEPP) along the River Zrmanja course. This paper presents a suitable and simple hydrological methodology that can be applied to scarce available data obtained on complex karst terranes. The paper presents a complex but common case of water circulation in a karst system. The primary objectives of the investigations were: (a) to analyse the underground karst connections, (b) to analyse discharge conditions along the River Zrmanja, and (c) to define variations in the catchment area along the River Zrmanja. The fact that the hydrological regime of the River Zrmanja is highly variable, due to the water losses along the open streamflow, strongly influenced the selection of the locations and heights of the HEPP dams. In spite of many hydrological, meteorological and hydrogeological measurements, the River Zrmanja catchment is insufficiently gauged. This dictates the use of a simple, empirically-based hydrological methodology. The Turc (1954) and Coutagne (1954) formulas were used in determination of annual total runoff. Using these simple hydrological methods, some important engineering answers were obtained. This is a first step towards application of sophisticated hydrological models, needing large amounts of reliable data.

ISSN:0262-6667    

DOI:10.1080/02626669909492233

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Water level data have been collected since 1968 for small wetlands within a 385 ha area in the northern prairie region of Canada. The uplands around the wetlands were under dryland cultivation prior to 1968 and there was no significant change of land use until 1980. Between 1980 and 1983 about one-third of the area was converted to a permanent undisturbed cover of smooth brome grass (Bromus inermis) and some alfalfa (Medicago saliva) with the purpose of providing improved bird nesting habitat. The remainder of the area continued in cultivation. Wetlands within the grassed area dried out within a few years after conversion of their catchments to permanent brome grass, whereas wetlands in the neighbouring cultivated area retained water as before. Within the area of permanent grass cover springtime snowmelt runoff essentially ceased. These observations demonstrate that the water balance of prairie wetlands is very sensitive to the land use on the surrounding uplands.

ISSN:0262-6667    

DOI:10.1080/02626669909492234

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Fitting flood prediction curves by eye to the data of return period plots is an intuitive approach to estimating n-year flood discharge magnitudes from single-site data. However, the subjective nature of this “procedure” means that it is unlikely to be adopted as a recognized flood estimation technique. An experiment with a group of volunteers demonstrates that some individuals are capable of subjectively fitting generalized extreme value curves to yield flood quantile estimates from simulated data with an accuracy comparable to probability weighted moments. This encourages the development of alternative formal flood estimation procedures based on some form of pattern recognition. Such procedures might mimic the more talented individuals' approach to curve fitting, without the disadvantage of subjectivity.

ISSN:0262-6667    

DOI:10.1080/02626669909492235

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Satellite gravity measurements expected in the next few years will provide unprecedented views of the Earth's gravity field and, given sufficient duration, its changes with time. Gravity changes directly reflect changes in the masses of the ocean (thus allowing the separation of steric (heat induced) and non-steric contributions to sea-level rise), the Greenland and Antarctic ice sheets, and the water stored in the continents. Not only can measurements of those changes provide a truly global integrated view of the Earth, they have, at the same time, sufficient spatial resolution to aid in the study of individual regions of the Earth. These data should yield information on water cycling previously unobtainable and be useful to both fundamental studies of the hydrologic cycle and practical assessments of water availability and distribution. Together with complementary geophysical data, satellite gravity data represent a new frontier in studies of the Earth and its fluid envelope.

ISSN:0262-6667    

DOI:10.1080/02626669909492236

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In the last decade, there have been many destructive floods in various parts of the world. Despite the extensive investment in flood control works, neither flood occurrences nor damages are decreasing. A possible consequence of climate change is an increased frequency of extreme meteorological events that may cause floods. Discussion is offered of some recent large floods in the world and of the experiences in combating floods in Japan. Floods change over time as societies change. There is no single universal remedy against floods and site-specific local efforts are necessary. It is essential to undertake damage mitigation measures together with physical control measures for flood management in an integrated approach, using a mixture of structural and non-structural means. A more disaster conscious society needs to be built with better preparedness and safe-fail (safe in failure) rather than, unrealistic, fail-safe (safe from failure) design of flood defences.

ISSN:0262-6667    

DOI:10.1080/02626669909492237

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A stochastic model for generating hourly hyetographs has been developed using data from observed precipitation records to simulate rainfall patterns. This model makes it possible to study maximum precipitation distributions for normal or exceptional frequencies over long periods of time. The modelling provides observations (up to 10-year frequency) of quantiles similar to those observed by directly fitting a law of statistical distribution onto an observed distribution. Differences occur for rare frequency quantiles. Modelled rainfall frequency distributions behave in an over-exponential way (i.e. greater than strictly exponential) at infinity, yielding higher results than those obtained using standard fittings. One factor that is considered in modelling can explain this behaviour: the persistence of storms within a rainfall episode which causes high rainfall accumulation. Thus modelling the observed phenomenon provides an innovative approach in studying extreme occurrences.

ISSN:0262-6667    

DOI:10.1080/02626669909492238

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Wetting front instability (fingered flow) accelerates solute transport through the unsaturated zone to the groundwater table. Whether fingers widen or dissipate close to the groundwater is unclear. Water flow in a two-dimensional artificial capillary fringe below a dry layer exhibiting fingered flow was investigated. The flow diverged strongly in the wet soil, suggesting that fingers dissipate. Expressions for the finger radius in dry and wet soil were combined and adapted to a soil hydraulic property parameterization popular in numerical modelling. The modified equation provided finger radii for soils in humid and arid climates. The fingers in the arid soil were excessively wide. The finger radii were used to model solute transport, assuming fingers dissipated in the subsoil. Modelling was cumbersome for the arid climate. One shower may often be insufficient to trigger fingering in arid regions with short, heavy showers. In soils with shallow groundwater, the diverging subsoil flow determines solute leaching.

ISSN:0262-6667    

DOI:10.1080/02626669909492239

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The growing use of surface water resources calls for more intense research on low flow causes and characteristics. This paper presents an investigation linking regional streamflow drought to the occurrence of atmospheric circulation patterns (CPs). Streamflow drought events of 74 basins in southern Germany were determined using the threshold level approach. The regional classification of the basins through a cluster analysis of the drought series provided the basis for the definition of a regional drought index and the following investigation of the influence of CP occurrence on drought. Frequency cross-tabulation showed several high-pressure and anticyclonic CP types to be strongly associated with streamflow drought in southern Germany. The influence of these CPs on streamflow drought was quantified using a logistic regression model. The model results revealed important regional differences concerning the time lag of the drought response and the relevant CPs.

ISSN:0262-6667    

DOI:10.1080/02626669909492240

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor