The Istanbul Strait, which separates the European and the Asian parts of Istanbul, is one of the narrowest straits in the world that is used for international shipping. The Strait has very special ecological conditions in terms of marine environment (atmospheric/oceanographic conditions, plant and animal diversity) and terrestrial environment. It also has roles as biological corridor and biological barrier between the Mediterranean Sea and the Black Sea and form an acclimatization zone for migrating species. Due to being the only maritime access for the neighboring Black Sea states and the Central Asian Turki Republics, the Istanbul Strait has been exposed to dense marine traffic for centuries and substantial increase has occurred in size and tonnage of the ships passing through the Strait with hazardous cargo varieties and amounts they carry. Increase in the number of vessels that navigates on the Strait and being on the transportation way of hazardous and dangerous materials pose serious environmental and safety hazards for the Istanbul Strait, Marmara Sea and the surrounding residential areas. Geographic and oceanographic features of the Istanbul Strait makes the navigation on the Strait rather difficult and consequently the Strait has faced many casualties that caused severe environmental problems due to thousands tons of oil spill occurring in recent decades.
Aquifer tests yield estimations of hydrogeological parameters through suitable analytical models from field data recorded as drawdown variations by time or distance. In practice, most often a single model iK adopted with a set of assumptions, and unfortunately, field data deviations from the model type curves are not considered in interpretations . This is a rather mechanistic approach which implies assumptions that the aquifer is geologically homogeneous and isotropic. Stich an approach cannot be true because within the aquifer test area there may appear heterogeneities and anisotropics which hinder the application of a single model. It is, therefore, necessaryto try several available models for the saris aq uifer test data, in orderto extract possible variabilities in hydrogeological parameters . Such an extensive Study can only he done when there is a set of aquifer test data with main and obsen-ation wells at different distances and directions .This paper presents an analysis of an aquifer test in a thick alluvial valley in Pakistan . The aquifer consists of extremely heterogeneous sediments. Ditferent approaches including [tie Theis, Jacob, Hantush, and Singh analytical models . are used to analyse the drawdown data from several observation wells. Several conventional and computer-based methods are available for analysing (Kruseman and De Ridder, 1991). Due to a different set of assumptions on each method, the hydrogeological parameter estimates are quite different from each other. Efforts have been made to developsimple calculation methods for aquiferparameters since Cooper and Jacob (1946) proposed their simple and widely used method . The main limitation of this method is that the dimensionless time factor, u, should be less than 0.01 . However, according to Singh (2000) it cannot be applied to estimate aquifer parameters when most of the data have u > 0.01 . On the other hand, the curve-matching method proposed by Theis (Lohman, 1972) involves much subjectivity in judging the best match between the observed and theoretical curves, especially when only early drawdowns are considered (Singh,2000). Furthermore, Sen (1987) proposed a unique storage coefficient determination approach for large diameter wells which experience steady or quasi-steady groundwater flow conditions . The application of the method does (2000) proposed a simple method forexplicit determination of confined aquifer parameters from early drawdown data . This method makes use of a few early drawdown data at an observation well andyields accurate values of confined aquiferparameters with no curve matching requirement. The method converges to the Cooper-Jacob method for late drawdown data . Application of the method on published data sets shows that the estimates of the aquifer parameters using only a few initial drawdowns are as good as those obtained by Theis curve matching when all data, including the late drawdowns (u < 0.01), are used. Singh (2001a) has also proposed another robust optimisation method for the calculation of aquife...
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