Search

A simple method is presented for estimating the specific storage of a confined aquifer from an overdamped slug test in a fully penetrating well. This method is based on the quasi-steady flow model developed previously by the authors, simplified to decoupled algebraic equations upon using Hvorslev's estimate of the hydraulic conductivity. The model equations are solved efficiently on a spreadsheet sequentially. The ability of the algebraic method to estimate the specific storage of a confined aquifer is assessed against slug test data from three field cases and against sets of synthetic data generated with the rigorous Cooper-Bredehoeft-Papadopulos method, which is used as reference. The algebraic method estimates the order of magnitude of the specific storage correctly in all three field cases, with two of them arithmetically very close to the Cooper-Bredehoeft-Papadopulos solution, while the hydraulic parameters computed with the numerical quasi-steady solution nearly match the reference values. In the cases of synthetic data, the algebraic method estimates the specific storage reliably when the storage parameter α equals 10−4 and within an order of magnitude when α equals 10−5. [ABSTRACT FROM AUTHOR]

Slug tests offer an efficient method for estimating the hydraulic parameters of an aquifer without water pumping. Two inverse methods are typically used to assess the slug test data and derive parameter estimates of a confined aquifer. The first method provides estimates of both hydraulic conductivity and specific storage, is visual (hence difficult to automate), and is based on the transient-flow analytical solution of Cooperet al.The second method, proposed by Hvorslev, is very straightforward, but provides only hydraulic conductivity estimates. In this study, we are testing the recently proposed quasi-steady method of Koussis and Akylas, which enables the estimation of both hydraulic parameters and, furthermore, can be easily implemented in computer code or an electronic spreadsheet. This quasi-steady method was coupled with the shuffled complex evolution optimization method to fully automate parameter estimation. This coupling is tested using data from field observations, synthetic data produced from the transient-flow analytical solution, and synthetic data with noise. The results show the usefulness and the limitations of the proposed method.Editor Z.W. Kundzewicz [ABSTRACT FROM AUTHOR]

We generalize Batchelor's parameterization of the autocorrelation functions of isotropic turbulence in a form involving a product expansion with multiple small scales. The richer small scale structure acquired this way, compared to the usual Batchelor function, is necessary so that the associated energy spectrum approximate well actual spectra in the universal equilibrium range. We propose that the generalized function provides an approximation of arbitrary accuracy for actual spectra of isotropic turbulence over the universal equilibrium range. The degree of accuracy depends on the number of higher moments which are determinable and it is reflected in the number of small scales involved. The energy spectrum of the generalized function is derived, and for the case of two small scales is compared with data from high-resolution direct numerical simulations. We show that the compensated spectra (which illustrate the bottleneck effect) and dissipation spectra are encapsulated excellently, in accordance with our proposal. [ABSTRACT FROM AUTHOR]

The authors discuss the complete form of the extended Boussinesq equation. They mention the mathematical foundations of subsurface flow on a sloping base based on the Dupuit-Forchheimer theory of unconfined flow. They also mention the analytical steady-state solution of the nonlinear extended Boussinesq equation of Henderson and Wooding in 1964 and its linearisation solutions.

In the great majority of slug tests performed in wells fully penetrating confined geologic formations, and for over-damped conditions, the response data are evaluated with the transient-flow model of Cooper et al. (1967) when the radial hydraulic conductivity Kr and the coefficient of specific storage Ss are to be estimated. That particular analytical solution, however, is computationally involved and awkward to use. Thus, groundwater professionals often use a few pre-prepared type-curves to fit the data by a rough matching procedure, visually or computationally. On the other hand, the method of Hvorslev (1951), which assumes the flow to be quasi-steady, is much simpler but yields only Kr estimates. In this work, we develop a complete quasi-steady flow model that includes a storage balance inside the aquifer and allows estimating Kr and Ss simultaneously, through matching of the well response data to a type-curve. The new model approximates the model of Cooper et al. closely and has the practical advantage that its solution type-curves are generated easily using an electronic spreadsheet, so that the optimal fit of data by a type-curve can be readily automated. [ABSTRACT FROM AUTHOR]

Summary: We study the interaction of a stream with a sloping unconfined aquifer that the stream is assumed to fully penetrate. The analysis applies to flow in a vertical section, considers the existence of a low-conductivity streambed layer and the flow in the aquifer to be induced by variations of the stream stage. Invoking the Dupuit assumption yields the 1-D Boussinesq equation, extended for a sloping base. The Boussinesq equation is linearised, the derived flow model is critiqued and an objective procedure for determining the linearisation level is developed. We solve the linear governing equation by the method of Laplace transform, with analytical inversion; the horizontal-aquifer case is treated in the zero-slope limit. The system response function is derived for the general case (sloping aquifer, sediment bed layer) and for several specific cases, and solutions are verified against known analytical results. Responses are contrasted for aquifers on positive, negative and zero slopes to step changes in the stage of streams with and without a sediment bed layer. The solutions give the aquifer stage and flow rate, the flow exchange rate at the stream–aquifer interface and the exchanged water volumes (bank storage/release). [Copyright &y& Elsevier]

Summary: We convolve the system response functions of the linearised 1D equation of Boussinesq (extended for slope, Dupuit approximation) derived in the companion paper of Akylas and Koussis [Akylas, E., Koussis, A.D., (submitted for publication). Response of sloping unconfined aquifer to stage changes in adjacent stream: I. Theoretical analysis and derivation of system response functions, J. Hydrol] and develop solutions for the interaction of a fully penetrating stream with a sloping unconfined aquifer, taking also into account a low-conductivity streambed layer. These solutions give the aquifer stage and flow rate, the flow exchange rate at the stream–aquifer interface and the exchanged water volumes (bank storage/release). The solutions are analytical, when the flow-inducing stream stage variations are common functions; otherwise, the convolution integral is evaluated numerically. Responses are compared for aquifers on positive, negative and zero base slopes to a wave-like change in the stage of the stream. Analytical and numerical convolution-derived solutions are used to model the interaction of Cedar River and its adjacent unconfined aquifer near Cedar Rapids, Iowa. In the model, the aquifer base is taken to be horizontal or inclined and the streambed clogged by a low-conductivity sediment layer; the model is verified against data not used in the calibration and is found to perform very well. [Copyright &y& Elsevier]

In this work, the two-point probability density function (PDF) for the velocity field of isotropic turbulence is modeled using the kappa distribution and the concept of superstatistics. The PDF consists of a symmetric and an anti-symmetric part, whose symmetry properties follow from the reflection symmetry of isotropic turbulence, and the associated non-trivial conditions are established. The symmetric part is modeled by the kappa distribution. The anti-symmetric part, constructed in the context of superstatistics, is a novel function whose simplest form (called "the minimal model") is solely dictated by the symmetry conditions. We obtain that the ensemble of eddies of size up to a given length r has a temperature parameter given by the second order structure function and a kappa-index related to the second and the third order structure functions. The latter relationship depends on the inverse temperature parameter (gamma) distribution of the superstatistics and it is not specific to the minimal model. Comparison with data from direct numerical simulations (DNS) of turbulence shows that our model is applicable within the dissipation subrange of scales. Also, the derived PDF of the velocity gradient shows excellent agreement with the DNS in six orders of magnitude. Future developments, in the context of superstatistics, are also discussed. [ABSTRACT FROM AUTHOR]

Seaborne movement underpins frontier research in prehistoric archaeology, including water-crossings in the context of human dispersals, and island colonisation. Yet, it also controls the degree of interaction between locations, which in turn is essential for investigating the properties of maritime networks. The onset of the Holocene (circa 12,000 years ago) is a critical period for understanding the origins of early visitors/inhabitants to the island of Cyprus in the Eastern Mediterranean in connection with the spread of Neolithic cultures in the region. The research undertaken in this work exemplifies the synergies between archaeology, physical sciences and geomatics, towards providing novel insights on the feasibility of drift-induced seaborne movement and the corresponding trip duration between Cyprus and coastal regions on the surrounding mainland. The overarching objective is to support archaeological inquiry regarding the possible origins of these visitors/inhabitants—Anatolia and/or the Levant being two suggested origins. [ABSTRACT FROM AUTHOR]

Offshore wind offers an excellent opportunity for domestic renewable energy production with a vast potential for future energy systems. Offshore wind resource assessment, however, can be challenging. Remote sensing data e.g., Synthetic Aperture Radar (SAR), provide high spatial resolution detailed information on the spatial variability of offshore wind and have been used for wind resource assessment, as well as for the long-term validation of wind speed estimates from other sources (e.g. Numerical Weather Prediction models). This paper focuses on the evaluation of a 26-month time-series of Sentinel-1 SAR Level 2 OCN products for wind resource assessment in the offshore areas around Cyprus. Sentinel data were evaluated against a 10-year regional reanalysis dataset (UERRA) time-series and wind measurements from 5 coastal meteorological stations in Cyprus. Comparison revealed an overall agreement between the fitted stations and Sentinel Weibull distributions while discrepancies exist between the two data sources and UERRA. Bias observed between Sentinel and UERRA Weibull-derived statistics appears to be spatially dependent. Preliminary wind power assessment results indicate a significant wind power potential for the southwestern offshore areas of Cyprus, surpassing 400 W / m 2 on average, offering thus economically viable solutions in terms of a future offshore wind power project development. [ABSTRACT FROM AUTHOR]

The article focuses on the Data Interpolating Empirical Orthogonal Functions (DINEOF), sea surface temperature (SST) collected by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) for Black Sea and Eastern Mediterranean Sea. Topics discussed include the availability of the data online, the schedule of updating the data, and the accessibility of the study at Ocean and Sea Ice Satellite Application Facility OSI-SAF's homepage.

ROMS-AGRIF (Regional Ocean Model System, Adaptative Mesh Refinement In Fortran) is a free surface numerical ocean model that solves the primitive equation with the Boussinesq approximation with respect to hydrostatic vertical momentum balance. The model uses terrain-following vertical coordinates that allow differential stretching, within orthogonal, curvilinear, spherical horizontal coordinates. Equations are solved with short time steps for barotropic dynamic (ssh and 2D momentum) and a much larger time steps for baroclinic dynamic (T,S, 3D momentum) in a split explicit scheme. It uses rotated tensors to reduce diapycnal mixing and improved calculation of horizontal pressure gradient, following surface and bottom KPP turbulent closure model, thus obtaining high advection scheme. It uses adaptive mixed radiations/nudging open boundary conditions and it uses parallelization by two-dimensional subdomain partitioning, providing shared (OpenMP, as in our case) and distributed (MPI) parallelization. Also, it provides dynamic nesting capability with the AGRIF (Adaptive Grid Refinement in Fortran) library. It is an open source Fortran code coupled to several models including biogeochemistry, waves, sediments, bio-optical and sea ice. It offers great flexibility for configuration and is widely used by the scientific community for a diverse range of applications.ROMS-AGRIF version 3.1.1,(2014), has been applied on Eastern Mediterranean and, specifically, for first time over the Levantine and Cyprus Seas, covering the area that is defined by the geographical coordinates, 30.05º E to 36.25º E longitude and 30.99º N to 36.96º N latitude. The model's horizontal resolution is approximately 5.5km x 4.6km (122 XI x 142 ETA cell points) with an internal nested grid of 1.8km over the area defined by longitude 33.03 E to 34.06 E and latitude 33.68 N to 34.44 N (62 XI x 56 ETA cell points), at 30 vertical, terrain following, s-levels The model is using initial and boundary conditions from Marine Copernicus Portal data and surface fluxes from NOAA Global Forecast System. The grid has been created based on EMODNET Bathymetry portal data (tile 241). All data used are free open source.The model is running in operational prognostic mode, producing results every six hours, for a period of ten days, with daily averages included. Comparisons of the results with the CYCOFOS system (Cyprus Coastal Ocean Forecasting and Observing System) and with ARGOS float profiles shown compliance and very high accuracy. [ABSTRACT FROM AUTHOR]