Analysis of groundwater flow and stream depletion in the L-shaped fluvial aquifer

Understanding the head distribution in aquifers is crucial for the evaluation of groundwater resources. This article develops an analytical model for describing flow induced by pumping in an L‐shaped fluvial aquifer bounded by impermeable bedrocks and two nearly fully penetrating streams. A similar scenario for numerical studies was reported in Kihm et al. (2007). The water level of the streams is assumed to be linearly varying with distance. The aquifer is divided into two sub-regions and the continuity conditions of hydraulic head and flux are imposed at the interface of the sub-regions. The steady-state solution describing the head distribution for the model without pumping is first developed by the method of separation of variables. The transient solution for the head distribution induced by pumping is then derived based on the steady-state solution as initial condition and the methods of finite Fourier transform and Laplace transform. Moreover, the solution for stream depletion rate (SDR) from each of the two streams is also developed based on the head solution and Darcy's law. Both head and SDR solutions in real time domain are obtained by a numerical inversion scheme called the Stehfest algorithm. The software MODFLOW-2005 is chosen to check the accuracy of the head solution for the L-shaped aquifer. The steady-state and transient head distributions within the L-shaped aquifer predicted by the present solution are compared with the numerical simulations and measurement data presented in Kihm et al. (2007). The SDR solution is employed to demonstrate its use as a design tool in determining well location for required amounts of SDR from nearby streams under a specific aquifer pumping rate.

The hydrogeologic information in cross-borehole complex conductivity data from an unconsolidated conglomeratic sedimentary aquifer

Accurate estimation of the hydrological properties of near-surface aquifers is important because these properties strongly influence groundwater flow and solute transport. Laboratory-based investigations have indicated that induced polarization (IP) properties of porous media may be linked, through either semiempirical or fully mechanistic models, to hydrological properties including hydraulic conductivity. Therefore, there is a need for field assessments of the value of IP measurements in providing insights into the hydrological properties of aquifers. A cross-borehole IP survey was carried out at the Boise Hydrogeophysical Research Site (BHRS), an unconsolidated fluvial aquifer that has previously been well-studied with a variety of geophysical and hydrogeologic techniques. High-quality IP measurements were inverted, with careful consideration of the data error structure, to provide a 3D distribution of complex electrical conductivity values. The inverted distribution was further simplified using [Formula: see text]-means cluster analysis to divide the inverted volume into discrete zones with horizontal layering. Identified layers based on complex electrical conductivity inversions are in broad agreement with stratigraphic units identified in previous studies at the site. Although mostly subtle variations in the phase angle are recovered through inversion of field data, greater contrasts in the IP data are evident at some unit boundaries. However, in coarse-grained aquifers, such as the BHRS, the discrimination of mildly contrasting lithologic units and associated changes in hydraulic conductivity of one or two orders of magnitude are unlikely to be achieved through field IP surveys. Despite the difficulty of differentiating subtle differences between all units, overall estimates of hydraulic conductivity purely from our field IP data are typically within an order of magnitude of independently measured values.

A Reserva Ecológica Nacional (REN): sua importância para o ambiente e ordenamento do território

THE NATIONAL ECOLOGICAL RESERVE (REN): ENVIRONMENT AND MANAGEMENT IMPLICATIONS. The National Ecological Reserve (REN) defined in Decree-Law 93/90 of March 5th is the «basic and diversified biophysical structure that guarantees environmental protection, through the creation of restricted areas» at rish through erosion (littoral or slope), flooding and aquifer recharge. The REN valuation, whose main aspects are referred to here, was carried out by means of an analysis of Municipal Master Plans (PDM) and a survey sent to all local authorities. As it was impossible to analyse the PDM of every district, a dis- trict differentiation was completed based on the biophysical index (Fig. 1 and 2), subsequently crossed by the district human pressure to obtain the district spatial differentiation of the environmental strain (Fig. 3). This allowed a standard district to be selected where the REN was analysed in full detail (Fig. 4 to 9). The survey allowed for the evaluation of the main conflicts in other districts between the REN and the goals of the PDM to be assessed, including the issues concerning the delimitation and the way the REN is seen by the councils and the citizens. The REN includes physical and biophysical systems (slope, fluvial, aquifer and littoral) that tend never to coincide with the administrative divisions. It is urgent that a national network be created of REN areas, planned and managed through more integrated means and an inter-municipal collaboration that can only be effective if environmental education is promoted, on both formal and informal terms.