摘要:

In the case of straight flow but with hydraulic conductivity varying in a transverse direction, the distribution of hydraulic conductivity has been determined for which the breakthrough curve due to convection only will have the same analytical form as the onedimensional convection/dispersion equation solution at the outlet end of a porous medium. That distribution is found exactly and it is very similar to the lognormal distribution. This result is significant since field evidence indicates that the logarithm of hydraulic conductivity is normally distributed. For the case considered, a simple relation between dispersivity and the coefficient of variation of hydraulic conductivity is found. One can thus determine very simply dispersivity in terms of the parameters of the distribution of hydraulic conductivity. This is particularly useful to estimate dispersivity in various cells of finite difference or finite element models when the distribution of hydraulic conductivity is not stationary, i.e. varies in space.

ISSN:0262-6667    

DOI:10.1080/02626669209492570

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Le régime des eaux souterraines en milieu cristallin altéré (zone intertropicale humide d'altitude de Madagascar) est analysé à grande échelle au cours de trois cycles climatiques successifs: (a) par l'étude hydraulique du milieu (tests par pompages et piézométrie en écoulement naturel); et (b) par des données isotopiques (18O et2H). Le caractère bicouche de l'aquifère est précisé, en particulier par la mise en évidence de drainances verticales dont le sens dépend de l'époque de la recharge. L'infiltration des eaux de pluie sur les interfluves altéritiques est rapide, sans évaporation, la réalimentation de la nappe étant très tamponnée par la zone non saturée. Durant les trois cycles climatiques, le suivi piézométrique dans des forages montre que les réponses du milieu souterrain au signal pluie sont perceptibles pour des précipitations cumulées inférieures à 100 mm.

ISSN:0262-6667    

DOI:10.1080/02626669209492571

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In the southern part of the Great Hungarian Plain, chemical analyses of groundwater were performed during the period 1975–1989 in two water flow systems. Three types of temporal variations can be distinguished: a long term trend; a variation depending on sudden pressure decrease (both these types of variation can be seen in water hardness and iron concentration); and a regular fluctuation in COD and NH4+. The first and second types occurred in both flow systems and are correlated with pressure depletion which in turn is reflected by water level decrease in wells. It was supposed that water with higher hardness and higher iron content moves from clayey layers to sand formations because of pressure depletion caused by withdrawal. Regular fluctuations of COD and NH4+occurring only in the River Danube deposits were similar to the phenomenon of chemical oscillation but with different time and space scales between chemical and geochemical processes, the former having periods which are very long: 1.5 to 3.0 years.

ISSN:0262-6667    

DOI:10.1080/02626669209492572

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Indian Remote Sensing Satellite-1A Linear Imaging Self Scanning System (IRS-1A-LISS-I) multispectral digital data acquired over the Tawa reservoir region have been analysed to evaluate the turbidity in the surface water. Tawa reservoir water samples were collected on 20 October 1988 concurrent with an IRS-1A overpass. The turbidity was measured at each sampling point in the field with a nephelometer. Reservoir water samples were analysed for total suspended matter, grain size and mineralogy. IRS-1A-LISS-I computer-compatible tapes were obtained from the National Remote Sensing Agency (NRSA), India. The relationship between the LISS-I digital data of 20 October 1988 and the measured values of turbidity was established. The results indicate that, in the turbidity range between 15–45 NTU (nephelometric turbidity units), a positive relationship exists between the turbidity and the visible wavelength band 1, 2 and 3 (0.45 to 0.68 μm) mean pixel values. Shorter wavelengths, especially in band 3 (0.62–0.68 μm), are more useful than longer wavelengths (near infrared) in quantifying turbidity. The concentration, mineralogy and grain size of the suspended matters are the main factors which influence the reflected radiance at low concentration levels (15–45 NTU) of turbidity. There is a positive correlation between reflectance, turbidity and suspended sediment concentration. It can be concluded that, as turbidity increases in the 15–45 NTU range, the spectral response increases. It appears that IRS-1A-LISS-I data could be developed as a practical tool in water quality monitoring.

ISSN:0262-6667    

DOI:10.1080/02626669209492573

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The hydrological regime of a mountainous catchment, in this instance the Mesochora catchment in Central Greece, was simulated for altered climates resulting when using the Goddard Institute for Space Studies (GISS) model for carbon dioxide doubling. The catchment snow water equivalent was predicted on the basis of the snow accumulation and ablation model of the US National Weather Service River Forecast System (NWSRFS), while the catchment runoff, as well as actual evapotranspiration and soil moisture storages, were simulated through application of the soil moisture accounting model of NWSRFS. Two scenarios of monthly climate change were drawn from the GISS model, one associated with temperature and precipitation changes, while the other referred to temperature changes alone. A third hypothetical scenario with temperature and precipitation changes similar to those corresponding to the mean monthly GISS scenarios was used to test the sensitivity of the monthly climate change of the hypothetical case on catchment hydrology. All three scenarios projected decreases in average snow accumulations and in spring and summer runoff and soil moisture, as well as increases in winter runoff and soil moisture storage and spring evapotranspiration.

ISSN:0262-6667    

DOI:10.1080/02626669209492574

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669209492575

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669209492576

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669209492578

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669209492579

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669209492569

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor