摘要:

The Geostationary Operational Environmental Satellite (GOES) system can be a very effective retransmitter of environmental data. One of the most efficient transmission protocols has Data Collection Platforms (DCP) reporting randomly and adaptively to environmental inputs. Although efficient, such protocol may lead to interference and loss of information when many platforms are simultaneously excited. This work presents a methodology and guidelines to design a national network for hydrological data collection which considers the climate of the contiguous United States. Specifically, the probability of the joint occurrence of rainfall at points over the USA is used to obtain the transmission reliability of the network.

ISSN:0262-6667    

DOI:10.1080/02626668509490967

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626668509490968

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Rival candidate distributions for modelling flood series may give markedly different magnitude-return period (Q-T) relationships, particularly at high T, A priori theoretical arguments, empirical criteria for distribution choice and previously used methods of discrimination between candidate distributions are discussed. The effects which method of parameter estimation, treatment of outliers, inclusion of large historical flood values, data transformations and causal composition of the flood population may have on choice of distribution are also considered.

ISSN:0262-6667    

DOI:10.1080/02626668509490969

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Flood data were assembled for 168 Scottish basins containing 3071 station-years of record. Multiple regression techniques were used to produce equations for predicting mean annual flood from physiographic and climatological basin characteristics. Mean annual rainfall (SAAR) gave better results than measures of extreme rainfall (M52D and RSMD). Percentage area of lake storage (LOCH) was found to be a better predictor than fraction of the basin draining through a lake (LAKE). Apart from SAAR and LOCH, the recommended equation requires the basin area (AREA), stream frequency (STMFRQ) and an index of the soil type (SOIL). Measures of average basin slope (AVES) and main stream slope (S1085) were not statistically significant. The standard error of the estimate of the predicted mean annual flood is 0.147. The equation has a coefficient of determination, R2, of 0.914 and appears robust over a wide range of basin types without requiring regionally derived multipliers or coefficients. No significant improvement in fit was acheived by ridge regression, Stein estimation or use of the influence function.

ISSN:0262-6667    

DOI:10.1080/02626668509490970

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The two-component extreme value (TCEV) distribution, suggested for modelling Italian annual flood series (AFS), is shown to account both for the presence of flow outliers and for the high variability of the skewness of historical AFSs. Using such a model, it is found that the T-year flood varies with log(T) much more rapidly for large values of T than is the case for small values of T. The presence of four parameters in the TCEV distribution introduces great uncertainty in estimating the T-year flood when the parameters are estimated from a single series. Regional analysis, which exploits basin similarities, is then needed, not only at ungauged sites but also at gauged ones. Regionalization techniques, by which all flood data over a region are combined to produce a single regional flood distribution, are described and their application to Italian data is shown.

ISSN:0262-6667    

DOI:10.1080/02626668509490971

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Hydrological regionalization is an important tool for the analysis of the spatial pattern of variations in hydrological phenomena. Regionalization means areal classification, i.e. the ability to attach to some location a label or number which is hydrologically meaningful. With the use of statistical methods, hydrological regions are analogous to areal classes. In this present study, pairwise grouping as well as principal components are applied to Swedish river runoff data in order to analyse the patterns of variation and to delimit regions where hydrological behaviour may be regarded as uniform. Pairwise grouping is the appropriate method to use on a national scale with heterogeneous hydrological regimes. Principal components (empirical orthogonal functions) demand homogeneity but within such regions describe very well the trends and variations.

ISSN:0262-6667    

DOI:10.1080/02626668509490972

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The algorithm for estimating the regional flood frequency hazard contained in the 1975 Natural Environment Research Council Flood Studies Report (FSR) can occasionally lead to upper quantile estimates that appear unrealistic when compared with engineering judgement. Tests with the FSR algorithm were made for several sets of observed flood sequences and a great variety of synthetic data in a Monte Carlo simulation study. Similar tests were conducted with many other regional and at-site flood frequency estimation procedures including a regional generalized extreme value distribution (GEV) procedure and a regional Wakeby distribution (WAK) procedure, both of which used biased probability weighted moments (PWM) in their formulation. For the Monte Carlo simulations, for which the true quantiles to be estimated were known, it was found that the FSR algorithm yielded quantile estimates that were always more variable, often by a factor of as much as 4 or 5, than those obtained by either the GEV/PWM or WAK/PWM algorithms. Further, the FSR algorithm was found to yield quantile estimates that were nearly always more biased than those obtainable by either the GEV/PWM or the WAK/PWM procedures. The above results were quite general, and were particularly noticeable when the simulations used data bases that were of similar size to those customarily encountered in hydrological practice. The available data base for the UK should now be much larger than it was at the time of the preparation of the Flood Studies Report, and it is suggested that an immediate effort is needed to produce an augmented, complete, consistent UK flood data base for the current period of record. Further, it is believed that analysis of this new data base using the GEV/PWM algorithm may well lead to more accurate and more consistent estimation of the extremal flood hazard for the UK.

ISSN:0262-6667    

DOI:10.1080/02626668509490973

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The influence of “seasonality” on the distribution of maxima of a hydrological variable has been studied theoretically and through examples relating to flood discharges of three Italian rivers. Results obtained lead to the conclusions that: (a) The shape of the distribution function of annual extremes is not related to that of the seasonal components which determine it. In particular it is not stable (extreme values asymptotic distribution) even if the components are stable. This property weakens all the more the reasons for the preference usually given to these distributions. (b) In addition, the analysis of seasonal maxima does not seem to be useful for increasing the reliability of estimates of rare events. In fact, the observations available in addition to the analysis of only the annual maxima, are, by their nature, found mostly in the range of small discharges. Therefore these additional observations produce more noise than information and often cause notable errors even in the range of the largest discharges observed.

ISSN:0262-6667    

DOI:10.1080/02626668509490974

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A linear approach is presented for analysing flood discharge series affected by measurement errors which are random in nature. A general model based upon the conditional probability concept is introduced to represent random errors and to analyse their effect on flood estimates. Flood predictions provided by quantiles are shown to be positively biased when performed from a sample of measured discharge. Though for design purposes such an effect is conservative, this bias cannot be neglected if the peak discharges are determined from stage measurements by means of the extrapolated tail of the rating curve for the gauging station concerned. Monte Carlo experiments, which have been carried out to analyse small sample effects, have finally shown that the use of the method of maximum likelihood is able to reduce the bias due to measurement errors in discharge data.

ISSN:0262-6667    

DOI:10.1080/02626668509490975

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A new method of grouping basins prior to regional flood frequency analysis is presented which is based on measured basin characteristics rather than on geographical regions. Statistical procedures for identifying efficient groupings are described and the explanatory ability of groups formed on the basis of catchment area, rainfall and soil type suggests that the method offers an attractive alternative to geographical regionalization.

ISSN:0262-6667    

DOI:10.1080/02626668509490976

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor