摘要:

New solutions in the Laplace and time domains are developed that describe the transient response of a leaky aquifer to constant and transient discharge into a fully or partially penetrating sink with storage, A parameter estimation procedure based on the Newton-Raphson algorithm is found to be robust in a synthetic example involving a pumping test of a large-diameter well situated in a leaky strip aquifer. The analytical solutions presented may find applications in describing water movement in strip aquifers, in aquifers discharging into channels or streams, or in thin laboratory tanks.

ISSN:0262-6667    

DOI:10.1080/02626669709492002

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The threshold level approach is used to define drought characteristics, i.e. drought duration and deficit volume from time series of daily streamflow. Three different procedures for pooling dependent droughts are compared: a method based on an inter-event time and volume criterion (IC), a moving average procedure (MA), and a method based on the sequent peak algorithm (SPA). The extreme values of drought duration and deficit volume are analysed using both an annual maximum series (AMS) and a partial duration series (PDS) approach. Two Danish catchments with very different flow regimes were used in the study. The IC and MA methods provided virtually the same sample statistics of the AMS of drought duration and deficit volume for all thresholds considered. The results of the SPA method differed significantly from the other two methods for high thresholds due to the presence of multi-year droughts. For analysis of seasonal droughts the SPA method is restricted to low thresholds. The occurrence of a large number of zerodrought years for low thresholds may significantly reduce the information content of the AMS, and in this case the PDS model is superior. The problem of minor droughts in the PDS was implicitly reduced by using the MA and SPA methods, and in this respect these methods have an important advantage as compared to the IC method.

ISSN:0262-6667    

DOI:10.1080/02626669709492003

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Following the results of a study carried out for the neighbouring Sicilian region, this paper reports a study of the applicability of the annual value, Faj, of the Arnouldus index to represent the erosion risk in Calabrian region. Firstly, By using 214 values of the mean annual value of the erosivity index, FF, and a Kriging interpolation method, an isoerosivity map is plotted. Then, in order to predict the erosion risk for an event of any return period, the probability distribution of the Fajindex is studied. Anin situstatistical analysis, carried out by using candidate distributions with two parameters (Gauss, LN2, EV1 and Weibull distribution), showed that the EV1 and LN2 laws were characterized by the best fit to the empirical Cumulative Distribution Function (CDF). In order to establish the theoretical CDF to use as aregionalparent distribution, the descriptive ability of the LN2 and EV1 distributions was also studied by a hierarchical regional procedure. Finally, the analysis showed that for each Calabrian sub-region, characterized by a constant value of the coefficient of variation, the erosion risk index was constant.

ISSN:0262-6667    

DOI:10.1080/02626669709492004

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A numerical model developed to simulate stable and unstable flows in unsaturated porous media is described. Results of numerical studies carried out to simulate laboratory experiments with the assumption of stable flow demonstrate the occurrence of unstable flow for the initial conditions of both air dry and field capacity for unsaturated infiltration in sands. This indicates that the Richards flow equation based on moisture content and potential variables averaged over total crosssectional area may not be applicable for flow under instability-prone boundary conditions. The unstable flow due to wetting front instability is modelled using the steady-state theory proposed by Hillel & Baker (1988). Simulation results for fingered flux calculated with the theory represent the experimental data reasonably well. The pore water velocity remains constant irrespective of the incident flux as long as the flux is smaller than the hydraulic conductivity value at the water entry suction of the porous media. The effect of antecedent wetness on the unstable flow behaviour is to reduce the pore water velocity drastically from air dry to field capacity conditions.

ISSN:0262-6667    

DOI:10.1080/02626669709492005

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Alluvial aquifers can often supply large quantities of water but if they are overlain by a low permeability zone, the recharge may be restricted with the result that the long term safe yield of the aquifer is greatly reduced. This paper describes a study of an alluvial aquifer in Bangladesh where there is a low permeability layer overlying the main aquifer. Pumping tests carried out in this aquifer were analysed using a numerical model which represents both the main aquifer and the overlying low permeability zone. Using the aquifer parameters deduced from the pumping test analysis, the numerical model was then used to represent five years of pumping. This long term simulation indicated that there would be a serious decline in the pumped levels and that a water table would develop in the main aquifer and would fall at a rate of almost five metres per year.

ISSN:0262-6667    

DOI:10.1080/02626669709492006

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper presents an investigation of trend in historic hydrological time series of areal annual precipitation on and mean annual runoff from the basin of the Evinos River in western Greece. Using different tests for randomness, a statistically significant long lasting decreasing trend was found in the precipitation record, whereas an also significant fluctuating “local” trend was detected in the runoff record. Further, it is shown that the effects of precipitation change on mean annual runoff can be quantified through a magnification factor.

ISSN:0262-6667    

DOI:10.1080/02626669709492007

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Brackish karst springs are common along every karstic sea shore consisting of limestone and dolomite. On the Croatian sea coast there are more than 300 permanent or temporary brackish karst springs. From the standpoint of water supply, the problem of karst spring water salinization is quite significant because large quantities of high quality fresh water are not available to be used either as drinking water or for industrial and agricultural purposes. The salinity of brackish karst springs situated along the Adriatic coast varies from 10 to more than 18 000 mg C1 1−1with an unfavourable distribution during the year. In the wet winter period, when water quantities in the region are abundant, the salinity is exceedingly low. In the warm and dry summer period the chloride concentration is high. At that season, when a shortage of fresh water in the region occurs, especially due to tourism, karst spring water is so salty that it cannot be used at all. The mechanism of sea water intrusion is relatively well known but the problem of karst springs desalinization has not been solved in practice. The Ghyben-Herzberg relationship is formulated exclusively on the basis of hydrostatic equilibrium, and its use under dynamic conditions is limited. The dynamics of fresh water circulation towards karst spring exits are very specific for each individual spring. Using numerous hydrological, hydrometric, hydrogeological and speleological investigations of the brackish Blaž (Croatia) karst spring, this paper gives the plausible position and dimensions of the main karst conduits through which sea water penetrates into the spring exit.

ISSN:0262-6667    

DOI:10.1080/02626669709492008

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

La nappe alluviale de l'Oued Laou, avec 18 km2de surface, reçoit en moyenne une recharge de 17.1 hm3an−1; son épaisseur saturée varie entre 40 et 60 m et les valeurs de la transmissivité vont de 500 à 4000 m2jour−1. Les eaux présentent un faciès bicarbonaté calcique à magnésien, avec des teneurs en sels allant de 200 à 600 mg 1−1. La construction d'un nouveau barrage sur l'oued et la surélévation de celui qui existe déjà risque de modifier le fonctionnement hydrogéologique du système oued-nappe.

ISSN:0262-6667    

DOI:10.1080/02626669709492009

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669709492010

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669709492011

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor