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Abstract Applicability of log-Gumbel (LG) and log-logistic (LL) probability distributions in hydrological studies is critically examined under real conditions, where the assumed distribution differs from the true one. The set of alternative distributions consists of five two-parameter distributions with zero lower bound, including LG and LL as well as lognormal (LN), linear diffusion analogy (LD) and gamma (Ga) distributions. The log-Gumbel distribution is considered as both a false and a true distribution. The model error of upper quantiles and of the first two moments is analytically derived for three estimation methods: the method of moments (MOM), the linear moments method (LMM) and the maximum likelihood method (MLM). These estimation methods are used as methods of approximation of one distribution by another distribution. As recommended in the first of this two-part series of papers, MLM turns out to be the worst method, if the assumed LG or LL distribution is not the true one. It produces a huge bias of upper quantiles, which is at least one order higher than that of the other two methods. However, the reverse case, i.e. acceptance of LN, LD or Ga as a hypothetical distribution, while the LG or LL distribution is the true one, gives the MLM bias of reasonable magnitude in upper quantiles. Therefore, one should avoid choosing the LG and LL distributions in flood frequency analysis, especially if MLM is to be applied. 相似文献
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Abstract The impulse response of a linear convective-diffusion analogy (LD) model used for flow routing in open channels is proposed as a probability distribution for flood frequency analysis. The flood frequency model has two parameters, which are derived using the methods of moments and maximum likelihood. Also derived are errors in quantiles for these parameter estimation methods. The distribution shows that the two methods are equivalent in terms of producing mean values—the important property in case of unknown true distribution function. The flood frequency model is tested using annual peak discharges for the gauging sections of 39 Polish rivers where the average value of the ratio of the coefficient of skewness to the coefficient of variation equals about 2.52, a value closer to the ratio of the LD model than to the gamma or the lognormal model. The likelihood ratio indicates the preference of the LD over the lognormal for 27 out of 39 cases. It is found that the proposed flood frequency model represents flood frequency characteristics well (measured by the moment ratio) when the LD flood routing model is likely to be the best of all linear flow routing models. 相似文献
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EUGENIUSZ DROZDOWSKI STANISLAW FEDOROWICZ 《Boreas: An International Journal of Quaternary Research》1987,16(2):139-153
Drozdowski, Eugeniusz & Fedorowicz, Stanislaw 1987 06 01: Stratigraphy of Vistulian glaciogenic deposits and corresponding thermoluminescence dates in the lower Vistula region, northern Poland. Boreas , Vol. 16, pp. 139–153. Oslo. ISSN 0300–9483.
Recent stratigraphical and sedimentological studies of Vistulian deposits in the lower Vistula region combined with the results of thermoluminescence dating substantiate the tripartite scheme of chronostratigraphic subdivision of the Vistulian glaciogenic sequence presented earlier by Drozdowski. All the thermoluminescence dates provided by till and intertill waterlain sediments refer to two major stadials which, in the light of sedimentological analyses, seem to represent two independent glacial cycles: an older, dated approximately to the period 59,000–51,000 years B.P., and a younger, dated to the period 17,000–15,000 years B.P. The dividing interval, named the Grudziadz Interstadial, was rather cool in nature. The evidence for this interstadial, apart from the significant break in glaciogenic sediment deposition, comprises some infills of subglacial stream trenches cut during the earlier deglaciation, loess-like silts, fossil sand wedges, and transgressive marine deposits, the latter occurring in restricted areas in the northern part of the region. 相似文献
Recent stratigraphical and sedimentological studies of Vistulian deposits in the lower Vistula region combined with the results of thermoluminescence dating substantiate the tripartite scheme of chronostratigraphic subdivision of the Vistulian glaciogenic sequence presented earlier by Drozdowski. All the thermoluminescence dates provided by till and intertill waterlain sediments refer to two major stadials which, in the light of sedimentological analyses, seem to represent two independent glacial cycles: an older, dated approximately to the period 59,000–51,000 years B.P., and a younger, dated to the period 17,000–15,000 years B.P. The dividing interval, named the Grudziadz Interstadial, was rather cool in nature. The evidence for this interstadial, apart from the significant break in glaciogenic sediment deposition, comprises some infills of subglacial stream trenches cut during the earlier deglaciation, loess-like silts, fossil sand wedges, and transgressive marine deposits, the latter occurring in restricted areas in the northern part of the region. 相似文献
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