ISSN:0262-6667    

DOI:10.1080/02626660009492301

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Estimation of direct runoff, peak discharge or hydrographs is often necessary in small to medium-sized ungauged basins. Different models are used in practice for these purposes, depending on the type of problem, the available data and the prevailing runoff mechanisms in the study basin. This paper discusses the applicability of the curve number procedure developed by the US Soil Conservation Service (SCS) to estimate direct runoff in basins characterized by small to gentle undulating slopes mainly covered with natural grasslands. Rainfall and runoff data measured in the Cañada de Los Chanchos basin in Uruguay is used to fit the curve numbers and to analyse the antecedent soil moisture condition proposed by the SCS.

ISSN:0262-6667    

DOI:10.1080/02626660009492302

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The capability of the Surface inFiltration Baseflow (SFB) conceptual rainfall-runoff model to simulate streamflow for three catchments selected from northern Iraq is investigated. These catchments differ in their climatic regimes and physical characteristics. Three versions of the model were tested: the original three-parameter model (SFB), the modified five-parameter model (SFB-5), and the modified six-parameter model (SFB-6). The available daily precipitation, potential evapotranspiration and runoff data were used in conjunction with a simulated annealing (SA) optimization technique to calibrate the various versions of the SFB model. A simple sensitivity analysis was then carried out to determine the relative importance of the model parameters. The study indicated that use of the original three parameter model was not adequate to simulate monthly streamflow in the selected catchments. The modified version (SFB-5) provided better runoff simulation than the original SFB model; overall a 19% increase was observed in the coefficient of determination (R2) between simulated and observed monthly runoff. The SFB-5 model performed with varying degrees of success among the catchments. The model performance in the validation stage was reasonable and comparable to that of the calibration stage. The sensitivity analysis of the SFB model for arid catchments revealed that the baseflow parameter (B) was the most sensitive one, while the S and F parameters were less sensitive than the B parameter.

ISSN:0262-6667    

DOI:10.1080/02626660009492303

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Three approaches to modelling the duration of streamflow droughts at eight southern African sites are considered; a non-parametric method (that of Kaplan-Meier) is compared with the fitting of two simple parametric models: the exponential and Weibull. All techniques allow the instantaneous probability of a drought coming to an end to differ between wet and dry seasons, using the concept of censored data. Model-fitting is discussed, and the Kaplan-Meier estimates permit an assessment of the fit of the parametric models, with the aim of finding a parsimonious model for the data, which can be used for predictive purposes. In most cases considered herein, either the exponential or Weibull approach is found to be adequate.

ISSN:0262-6667    

DOI:10.1080/02626660009492304

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

L'Opération Sources du WWF (Worldwide Fund for Wildlife) est une action éducative de sensibilisation à la qualité des eaux souterraines. Elle implique principalement les élèves de cinquième et sixième primaires de Belgique. Depuis 1994, des centaines de dosages des ions nitrates ont été effectués dans un grand nombre de sources et de puits à l'aide de bandelettes colorimétriques. A l'issue de chaque campagne, les points d'eau surveillés ont été reportés sur une carte de Belgique où leur couleur indique leur qualité eu égard à la concentration en nitrates. L'objectif pédagogique étant atteint, la validation de ces cartes en tant qu'image de la réalité pose le problème de la vérification du lien entre la concentration réelle (mg 1−1) du point d'eau visité et sa couleur sur la carte. A cette fin, des vérifications ont été réalisées sur 308 points d'eau choisis au hasard dans l'ensemble des sources et puits visités. L'analyse statistique révèle que la relation entre le test colorimétrique et le contrôle réalisé en laboratoire est hautement significative. Ce résultat justifie des investigations ultérieures, notamment la mobilisation de l'information régionale pour la qualification d'un point d'eau peu surveillé et la comparaison des cartes dans le temps.

ISSN:0262-6667    

DOI:10.1080/02626660009492305

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A field experiment was conducted on a sloping grassland soil in southwest England to investigate the downslope transport of nitrogen in soil water following the application of cattle manure, slurry and inorganic fertilizer. Transport of nitrogen (N) species was monitored on hydrologically isolated plots. Manure (50 t ha−1), slurry (50 m3ha−1) and fertilizer (250 kg N ha−1) were applied in February/March 1992. Subsurface water movement, by both matrix and preferential flow, was the dominant flow route during the experiment. Subsurface and surface nutrient flow pathways were monitored by analysing soil water and surface runoff for NO3-N, NH4-N and total N. Subsurface flow chemistry was dominated by NO3-N, with concentrations usually between 2 and 5 mg NO3−N dm−3. Differences between fertilizer and manure treatments and the untreated control were not significant. Significantly elevated NO3-N concentrations were observed in soil water in the buffer zone, indicating the importance of a buffer zone at least 10 m wide between manure spreading zones and an adjacent water course.

ISSN:0262-6667    

DOI:10.1080/02626660009492306

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A water balance model of Lake Victoria that can be used to assess rainfall from lake level, is derived. The model utilizes satellite estimates of rainfall directly over the lake. The model, initially derived and calibrated for the period 1956–1978, is reformulated here in such a way that all water balance terms except evaporation can be calculated from a combination of catchment rainfall and level of the lake. The reformulated model is validated and used to predict lake level fluctuations during the period 1931–1994. An error analysis is also performed. The model is then “inverted” to solve for mean rainfall conditions during various intervals of changing lake levels. For modern periods with known rainfall conditions, the error in model estimates is of the order of 1%.

ISSN:0262-6667    

DOI:10.1080/02626660009492307

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A new technique is developed for identifying groups for regional flood frequency analysis. The technique uses a clustering algorithm as a starting point for partitioning the collection of catchments. The groups formed using the clustering algorithm are subsequently revised to improve the regional characteristics based on three requirements that are defined for effective groups. The result is overlapping groups that can be used to estimate extreme flow quantiles for gauged or ungauged catchments. The technique is applied to a collection of catchments from India and the results indicate that regions with the desired characteristics can be identified using the technique. The use of the groups for estimating extreme flow quantiles is demonstrated for three example sites.

ISSN:0262-6667    

DOI:10.1080/02626660009492308

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The behaviour of the shear velocity along a gravel-bed channel is investigated experimentally in the presence of a negative pressure gradient (accelerating flow). Different methods of estimation of the shear velocity, derived from vertical profiles of the mean longitudinal point velocity, are examined and a new method is proposed. Results show that the proposed method of estimation is comparable to the St Venant and Clauser's methods. At a specific cross section, for constant bottom slope and relative roughness, shear velocity increases with discharge.

ISSN:0262-6667    

DOI:10.1080/02626660009492309

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A theoretical model is described for estimating the impacts of changes in Lake Victoria levels on river flows, lake levels and swamp areas in the upper White Nile basin. The basis of the model is to represent the main river channel by a series of interconnected lakes and swamps, whose water balances are described by differential equations relating outflows to levels, areas and the net basin supply at each point. Closed form solutions are obtained for two situations: (a) a long-term change in the mean level of Lake Victoria, and (b) a return to equilibrium levels following an initial disturbance in Lake Victoria levels. A simple model for the net basin supply to Lake Victoria is also used to relate these changes in levels to changes in climate and runoff in the basin. The results illustrate the extreme sensitivity of White Nile flows to changes in Lake Victoria levels and outflows, and in particular to variations in the direct rainfall on the lake surface. Estimates are also presented for the various time scales and time delays which affect the White Nile system.

ISSN:0262-6667    

DOI:10.1080/02626660009492310

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor