摘要:

Variations of temperature, precipitation and snow depths during the last 50–100 years, up to 1984, are investigated for mean cold season values (November to April) for 110 locations in the Former Soviet Union (FSU). Following quality checking, statistical analyses are performed on the data. There is cold season warming after 1953 or after 1966 over almost all the FSU apart from eastern Siberia, but temperature variations significantly affect the mean snow depths only in some sensitive areas of the Caucasus, central Asia, and the western European territory. Mean snow depth time series reveal contrasting local trends. Higher precipitation and snow depths are measured in eastern European Russia from 50° to 65 °N and in some areas of western Siberia at the beginning of the twentieth century. Otherwise, precipitation variations have little influence on the mean cold season snow depths over much of the FSU after 1930. Some predominant periodicities are detected for mean cold season temperature, but not for precipitation and snow depths.

ISSN:0262-6667    

DOI:10.1080/02626669709492031

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Transient water table systems under the influence of decaying groundwater mounds are studied in terms of the Dupuit-Forcheimer approximation, its linearization and linear potential theory. Parabolic mounds spreading and shrinking due to gravity and evapotranspiration are derived from the general class defined by Polubarinova- Kochina (1945). The penetration curves are calculated as characteristics of the water table response at prescribed observation wells. The Polubarinova-Kochina solutions for rectangular mounds are used to derive isochrones, a “resting lens” into which a mound transforms, and a distortion picture of reference volumes. These characteristics are obtained from numerical solution of a system of ordinary differential equation. The plume illustrating the advective spread of a contaminant from a reference area is computed as a composition of all path lines passing through this area.

ISSN:0262-6667    

DOI:10.1080/02626669709492032

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In August 1975, an extraordinary storm hit the Hongru River basin in Henan Province, China. Two dams were overtopped, breached and totally destroyed and the river basin experienced a severe flood. Various methods for assessing the return period of the peak discharges and changes in hydrological response due to the dambreak have been investigated: Annual Maximum Series (AMS), Partial Duration Series (PDS) and regional analysis. The three approaches gave different estimates of the T-year discharge event and of the observed 1975 event, which leads to the question whether probability-based methods are applicable for very extreme events. Although not capable of giving consistent estimates, extreme value analysis shows that the catchment response has changed because of the dambreak in 1975, which change in turn can be used for future designs. The uncertainty in the estimated design peak flows suggests that probability-based estimation methods for extrapolation should be complemented with research into historical events and simulations based on rainfall-runoff models.

ISSN:0262-6667    

DOI:10.1080/02626669709492033

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The Genetic Algorithm (GA) is often associated with local search optimisation techniques in the calibration process of Conceptual Rainfall-Runoff Models (CRRMs) (Wang, 1991; Franchini, 1996), i.e. the GA is used for approaching the region encompassing the global solution and then its results are used as a starting point for the local optimizer in the subsequent “fine-tuning” process. However, the GA can be formulated in very many ways. This study analyses various GA structures and their robustness and efficiency. In addition, a sensitivity analysis of the various schemes to their own parameters is performed. The analysis is conducted using an 11-parameter CRRM, called A Distributed Model (ADM), applied to both a theoretical case without model and data errors and two cases of the real world in which there are both model and data errors. Finally, assuming the same role as the GA for the “Pattern Search” (PS) method in a two-step optimisation technique (Hendricksonet al., 1988), the results of the two algorithms are compared, showing that, in the calibration of the ADM, the PS may give a slightly superior performance.

ISSN:0262-6667    

DOI:10.1080/02626669709492034

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The linear mathematical model for springflow suggested by Bear (1979) can simulate springflow for an initial instantaneous recharge. A springflow model has been developed, using the Bear model and uhamel's approach, which can simulate springflow for time variant recharge. The suggested model can also be used to compute the time variant recharge to the springflow domain from a given springflow time series. The inverse problem, which contains linear recharge terms and nonlinear depletion terms, has been solved using the Newton-Raphson method for solving a set of nonlinear equations. The model has been tested to compute recharge for Kirkgoz spring, a first magnitude karst spring in the Mediterranean region of Turkey. The estimated annual recharge computed by the model on a monthly basis compared well with the annual recharge which had been estimated (Korkmaz, 1990) using the Bear model.

ISSN:0262-6667    

DOI:10.1080/02626669709492035

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Israel is a small country which experiences wide variations in magnitudes of extreme discharges. A consistent model has been constructed for prediction of such discharges throughout the country. Extreme flow characteristics, geographical proximity, lithology, soils, and rainfall properties are the major factors in the delineation of relatively homogeneous regions within the country. For each region, discharge-area relationships are formulated in association with low exceedance probabilities. These relationships follow at-site predictions which have been prepared by fitting the log Pearson type III distribution to annual maxima series of peak discharges. For catchments larger than 100 km2in area, the differences between the regional and the at-site predictions are small. Relatively high extreme discharges are found for the arid area where rainfall depth is low, for an area of steep slopes, for areas of low permeable lithology and soils, and for areas where the fraction of intense rainfall in the total depth of precipitation is high. For large arid catchments, the discharge- area relationships exhibit a negative trend. The model is simply applicable and appears suitable for other semiarid and arid areas.

ISSN:0262-6667    

DOI:10.1080/02626669709492036

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Caesium-137 (137Cs) measurements have been used to investigate the delivery of sediment from the hillslopes to a lake which marks the downstream limit of the small agricultural Start basin in Devon, UK. Total137Cs inventories and137Cs depth distributions in sediment cores were used to estimate that the eroded sediment stored within the fields and on the flood plain of the main river was equivalent to sediment yields ofca.21 and 30 t km−2year1, respectively. Based on published information on sediment accumulation in the lake, the minerogenic sediment yield from the basin was estimated to beca.29 t km−2year−1. The erosion rate on the hillslopes in the basin, calculated as the sum of the sediment yield to the lake and the two storage components, isca.80 t km−2year−1. Of the soil eroded from the slopes more than 60% is stored at intermediate locations and the sediment delivery to the lake is less than 40%. The calculated soil erosion rate for the Start basin is consistent with an estimate of the erosion rate for the basin of the nearby Old Mill Reservoir ofca.63 t km−2year−1.

ISSN:0262-6667    

DOI:10.1080/02626669709492037

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Univariate and bivariate spectral analyses were applied to the study of two karstic systems in the Central Apennines (Italy). The analyses allowed the characterization of the transformations between the input rainfall and the output discharge. Although the development of the karstification is very different, the two aquifers show very similar behaviour. Both systems present very high memory effects which modulate the input signal. The baseflow component predominates in both systems which seem to behave like porous aquifers.

ISSN:0262-6667    

DOI:10.1080/02626669709492038

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669709492039

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669709492040

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor