摘要:

Stream channel development in response to the eruption of Mount St. Helens on 18 May 1980, resulted in some of the largest sediment yields documented anywhere on earth. Development of new channels on the 2.7 km3debris-avalanche deposit in the North Fork Toutle River caused net erosion of as much as 1.3 x 105t km−2annually. Development of these channels followed a four-stage sequence of channel initiation, channel incision with relatively constant width-to-depth ratio, channel widening accompanied by aggradation, and channel widening accompanied by scour-and-fill with little change in average channel elevation. These channels remain unstable both in width and elevation. Lahars affected channel and valley morphology on all flanks of the volcano. Steep, upstream reaches generally incised and widened during the first year following the eruption and aggraded during the following three years. Gently sloping downstream reaches aggraded and widened during the first year and incised during the following three years. The most rapid adjustments occurred during the first two winters following the eruption. The principal effect of the blast on channels throughout the 550 km2devastated area was the subsequent rapid delivery of sand- and silt-size sediment eroded from hillslopes. Channels aggraded during early storms of the 1980–1981 winter but incised during later storms the same winter. Subsequent channel enlargement was constrained by logs deposited in channels by the blast and by post-1980 shallow debris slides. Since 1984, instability and sedimentation in laharand blast-affected channels have been within the range of pre-1980 levels.

ISSN:0262-6667    

DOI:10.1080/02626668909491318

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Some simulation results are presented with respect to the parameter-free flood magnitude estimator:where p is the estimated probability of a smaller annual maximum flood, and the riare the ranked annual flood maxima. The design magnitude estimates are obtained by solving for x with p specified. Root-mean-square values and probabilities of an underestimate are tabulated with respect to samples of size 20, 30 and 50 from a selection of “floodlike” distributions. As well as indicating the region of applicability of the estimator, the tabulated results provide a useful basis for measuring the improvement of future parameter-free estimators.

ISSN:0262-6667    

DOI:10.1080/02626668909491319

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The problem considered is that of the trade-off between complexity and accuracy of flood routing models and methods of determination of extreme flow statistics. A system is analyzed consisting of a channel reach, with a set of input flood waves which are routed through the reach by using a flood routing method. It is desired to evaluate the consequences for design of the error which is introduced if, instead of the complete St. Venant (SV) equations, the Kalinin-Milyukov (KM) model is used to calculate the outflow from the reach. This problem is investigated by means of an example. As a standard, the routing by the complete SV equations is used. It is found that the use of the linear KM method introduces an error as compared to the complete SV equations which is smaller than the uncertainty caused by the choice of extreme value distribution. As a consequence, the results from the KM method are found to be as acceptable for design as the results obtained from the SV equations.

ISSN:0262-6667    

DOI:10.1080/02626668909491320

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Digital mapping techniques are used increasingly in hydrology. One of the constraints on the application of those techniques is the digitizing process, which can be costly and time consuming. This paper describes the background and development of a low cost, easy-to-use system for digitizing maps, based on the use of a video camera as a scanner, and goes on to discuss the application of this system to the task of digitizing the hydrological soil maps of Europe.

ISSN:0262-6667    

DOI:10.1080/02626668909491321

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The spatial variation of the mean annual flood of both mean daily and instantaneous extremes and of the parameters of the Extreme Value Type 1 (EV1) distribution for catchments in the northwest and west regions of Greece are significantly explained in terms of physiographic and climatological characteristics of the catchments by using multiple regression techniques. The catchment characteristics used in the study are the following: drainage area, mean annual areal precipitation, stream frequency, main stream slope and length, intensity of the one-day rainfall of five-year return period, and a soil type index. The EV1 distribution has been found to describe adequately the annual frequency distributions of the daily and of the standardised by-their-mean-value daily extremes of the catchments. Based on the regional models for the parameters of the distribution, annual flood frequency curves, and thus flood quantiles of the assumed distribution, can be derived. The developed regional models are successfully used in predicting with satisfactory accuracy the mean annual floods and flood quantiles, needed in hydrological design, for ungauged catchments within the region studied.

ISSN:0262-6667    

DOI:10.1080/02626668909491322

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The objectives of a National Hydrometric Reference Network for New Zealand are specified, and the necessary standards for data collection are defined. Data are collected in New Zealand by several agencies, and a data quality assurance programme must be designed and administered to take account of this. The programme involves the full range of practices, from providing manuals and adequate staff training through to auditing of archived data, and disseminating audit results. It is not a formal programme like those implemented in industrial settings, but is an effective way of assuring users, at an acceptable cost, that hydrometric data meet the quality standards they require.

ISSN:0262-6667    

DOI:10.1080/02626668909491323

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626668909491324

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626668909491325

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626668909491326

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626668909491329

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor