Optimalisatie Drinkwaterwinning in het Noordhollands Duinreservaat; Toetsingsadvies over het milieueffectrapport

PWN Waterleidingbedrijf Noord-Holland wil bestaande wateractiviteiten (infiltratie en terugwinning en winning van natuurlijk duinwater) optimaliseren in het Noord-Hollands Duinreservaat. En is daarmee m.e.r.-plichti

Transient well flow in layered aquifer systems: the uniform well-face drawdown solution.

Previously a hybrid analytical-numerical solution for the general problem of computing transient well flow in vertically heterogeneous aquifers was proposed by the author. The radial component of flow was treated analytically, while the finite-difference technique was used for the vertical flow component only. In the present work the hybrid solution has been modified by replacing the previously assumed uniform well-face gradient (UWG) boundary condition in such a way that the drawdown remains uniform along the well screen. The resulting uniform well-face drawdown (UWD) solution also includes the effects of a finite diameter well, wellbore storage and a thin skin, while partial penetration and vertical heterogeneity are accommodated by the one-dimensional discretization. Solutions are proposed for well flow caused by constant, variable and slug discharges. The model was verified by comparing wellbore drawdowns and well-face flux distributions with published numerical solutions. Differences between UWG and UWD well flow will occur in all situations with vertical flow components near the well, which is demonstrated by considering: (1) partially penetrating wells in confined aquifers, (2) fully penetrating wells in unconfined aquifers with delayed response and (3) layered aquifers and leaky multiaquifer systems. The presented solution can be a powerful tool for solving many well-hydraulic problems, including well tests, flowmeter tests, slug tests and pumping tests. A computer program for the analysis of pumping tests, based on the hybrid analytical-numerical technique and UWG or UWD conditions, is available from the author

Transient well flow in vertically heterogeneous aquifers.

A solution for the general problem of computing well flow in vertically heterogeneous aquifers is found by an integration of both analytical and numerical techniques. The radial component of flow is treated analytically; the drawdown is a continuous function of the distance to the well. The finite-difference technique is used for the vertical flow component only. The aquifer is discretized in the vertical dimension and the heterogeneous aquifer is considered to be a layered (stratified) formation with a finite number of homogeneous sublayers, where each sublayer may have different properties. The transient part of the differential equation is solved with Stehfest's algorithm, a numerical inversion technique of the Laplace transform. The well is of constant discharge and penetrates one or more of the sublayers. The effect of wellbore storage on early drawdown data is taken into account. In this way drawdowns are found for a finite number of sublayers as a continuous function of radial distance to the well and of time since the pumping started. The model is verified by comparing results with published analytical and numerical solutions for well flow in homogeneous and heterogeneous, confined and unconfined aquifers. Instantaneous and delayed drainage of Water from above the water table are considered, combined with the effects of partially penetrating and finite-diameter wells. The model is applied to demonstrate that the transient effects of wellbore storage in unconfined aquifers are less pronounced than previous numerical experiments suggest. Other applications of the presented solution technique are given for partially penetrating wells in heterogeneous formations, including a demonstration of the effect of decreasing specific storage values with depth in an otherwise homogeneous aquifer. The presented solution can be a powerful tool for the analysis of drawdown from pumping tests, because hydraulic properties of layered heterogeneous aquifer systems with partially penetrating wells may be estimated without the need to construct transient numerical models. A computer program based on the hybrid analytical-numerical technique is available from the author

Analytic solutions for groundwater whirls in box-shaped, layered anisotropic aquifers.

Analytic solutions are derived for flow through an elongated box-shaped aquifer that is bounded on the left, right, top and bottom sides by impermeable boundaries; the head gradient normal to the ends of the box is specified to be constant. The aquifer consists of a number of horizontal layers, each with its own horizontal hydraulic conductivity tensor. When all horizontal conductivities are isotropic, streamlines are straight, but when the horizontal anisotropy is different between layers, streamlines have the shape of spirals. Bundles of spiraling streamlines rotating in the same direction are called groundwater whirls. These groundwater whirls may spread contaminants from the top of an aquifer to the bottom by advection alone. An exact solution for an arbitrary number of layers is derived using a multi-layer approach, which is based on the Dupuit approximation within each layer. The multi-layer solution compares well with an exact three-dimensional solution, which is derived by placing certain restrictions on the variation of the hydraulic conductivity tensor. It is shown that a hypothetical aquifer consisting of three layers may have one, two, or three groundwater whirls; adjacent whirls rotate in opposite directions. Another notable flow pattern is obtained with a four-layer model where one large whirl encloses two smaller ones, all rotating in the same direction. © 2004 Elsevier Ltd. All rights reserved