Unconfined Aquifer Flow Theory - from Dupuit to present

Analytic and semi-analytic solution are often used by researchers and practicioners to estimate aquifer parameters from unconfined aquifer pumping tests. The non-linearities associated with unconfined (i.e., water table) aquifer tests makes their analysis more complex than confined tests. Although analytical solutions for unconfined flow began in the mid-1800s with Dupuit, Thiem was possibly the first to use them to estimate aquifer parameters from pumping tests in the early 1900s. In the 1950s, Boulton developed the first transient well test solution specialized to unconfined flow. By the 1970s Neuman had developed solutions considering both primary transient storage mechanisms (confined storage and delayed yield) without non-physical fitting parameters. In the last decade, research into developing unconfined aquifer test solutions has mostly focused on explicitly coupling the aquifer with the linearized vadose zone. Despite the many advanced solution methods available, there still exists a need for realism to accurately simulate real-world aquifer tests

Evaluation of Analytical Methods to Study Aquifer Properties with Pumping Tests in Coastal Aquifers with Numerical Modelling (Motril-Salobreña Aquifer)

Two pumping tests were performed in the unconfined Motril-Salobreña detrital aquifer in a 250 m-deep well 300 m from the coastline containing both freshwater and saltwater. It is an artesian well as it is in the discharge zone of this coastal aquifer. The two observation wells where the drawdowns are measured record the influence of tidal fluctuations, and the well lithological columns reveal high vertical heterogeneity in the aquifer. The Theis and Cooper-Jacob approaches give average transmissivity (T) and storage coefficient (S) values of 1460 m2 /d and 0.027, respectively. Other analytical solutions, modified to be more accurate in the boundary conditions found in coastal aquifers, provide similar T values to those found with the Theis and Cooper-Jacob methods, but give very different S values or could not estimate them. Numerical modelling in a synthetic model was applied to analyse the sensitivity of the Theis and Cooper-Jacob approaches to the usual boundary conditions in coastal aquifers. The T and S values calculated from the numerical modelling drawdowns indicate that the regional flow, variable pumping flows, and tidal effect produce an error of under 10 % compared to results obtained with classic methods. Fluids of different density (freshwater and saltwater) cause an error of 20 % in estimating T and of over 100 % in calculating S. The factor most affecting T and S results in the pumping test interpretation is vertical heterogeneity in sediments, which can produce errors of over 100 % in both parameters.This research has been financed by Project CGL2012-32892 (Ministerio de Economía y Competitividad of Spain) and by the Research Group Sedimentary Geology and Groundwater (RNM-369) of the Junta de Andalucía

The bailer test: a simple effective pumping test for assessing borehole success

A new pumping test method has been designed around the practical requirements of those working in rural water-supply projects in developing countries. The bailer test needs only simple equipment and can be completed in under 1 h. The test involves removing 20–50 bails from a borehole over a 10-min period and then measuring the recovery. The test is analysed using large-diameter-well analysis (which accounts for well storage) and is appropriate for testing low productivity aquifers (transmissivity 0.1–10 m2 d–1), where water levels are shallow (<20 m depth). The bailer test was developed and trialled in a rural water supply project in Nigeria where it was found to predict similar transmissivity to 5-h constant rate tests (r 2=0.9). Analysis of the test was further simplified to provide guidelines for field staff such as community health workers. The likelihood of a borehole sustaining a handpump for 250 people can be indicated by measuring the maximum drawdown and time for 50 and 75% recovery from a bailer test and comparing to a simple table. This simplified test is now being used in this and other rural water-supply projects, and has been modified to indicate whether a borehole can sustain higher yields for small-scale irrigation.RésuméUne nouvelle méthode de pompage d’essai a été élaborée à partir des exigences pratiques de ceux qui travaillent sur des projets d’adduction d’eau dans les pays en voie de développement. Le pompage d’essai par écopage n’a besoin que d’un équipement simple et peut être réalisé en moins d’une heure. L’essai implique le prélèvement de 20 à 25 écopes dans un forage pendant une période de 10 min et ensuite la mesure de la remontée. L’essai est exploité en utilisant l’analyse destinée aux puits à grand diamètre (ce qui rend compte de l’emmagasinement du puits) et est indiqué pour tester les aquifères à faible productivité (transmissivité de 0.1 à 10 m2 d–1), où les niveaux d’eau sont peu profonds (<20 m de profondeur). Le pompage d’essai par écopage a été développé et testé dans un projet d’adduction d’eau rural en Nigeria où on a trouvé qu’il prévoyait des transmissivités similaires à celles des essais à débit constant de 5 heures (r 2=0.9). L’analyse de l’essai a été davantage simplifiée afin de fournir des lignes directrices à du personnel de terrain tel que des chargés de la santé publique. La probabilité qu’un forage accepte une pompe à main pour 250 personnes peut être démontrée par la mesure du rabattement maximum et de temps de remontée de 50 et de 75% à partir d’un pompage d’essai par puisage et par comparaison avec une simple abaque. Ce test simplifié est utilisé maintenant pour ce dernier et pour d’autres projets d’adduction d’eau ruraux, et a été modifié pour montrer si un forage peut supporter des débits supérieurs pour une irrigation à petite échelle.ResumenUn nuevo método de bombeo se ha desarrollado con la practicidad que requieren aquellos que trabajan en abastecimiento de agua en ámbitos rurales de países en vías de desarrollo. El ensayo de extracción de agua (bailer test) requiere equipamiento muy simple y puede completarse en menos de una hora. El ensayo consiste en extraer de la perforación 20–50 volúmenes del contenedor en un período de 10 min y luego medir la recuperación. El ensayo se analiza utilizando pozos de gran diámetro (que tiene en cuenta el almacenamiento en el pozo), y resulta apropiado para verificar el comportamiento de acuíferos de baja productividad (transmisividad 0.1–10 m2 d–1), con niveles de agua someros (profundidad <20 m). El ensayo de extracción de agua se desarrolló y se implementó en un proyecto de suministro de agua en un sector rural de Nigeria, y se halló que era capaz de predecir transmisividades similares a aquellas provenientes de ensayos de bombeo de 5 horas a caudal constante (r 2=0.9). El análisis del ensayo fue simplificado a fin de facilitar la tarea del personal de campo, tales como trabajadores comunitarios. La probabilidad de que una perforación provista con una bomba de mano pueda abastecer a 250 personas puede deducirse midiendo el descenso máximo de nivel, el tiempo que requiere una recuperación del 50 y del 75% según el ensayo de extracción de agua, y comparándolos con los datos de una tabla simple. Este ensayo simplificado está siendo usado en el proyecto mencionado y en otros de abastecimiento a áreas rurales, y ha sido modificado para indicar si una perforación puede servir para extraer mayores caudales para proyectos de riego de pequeña escala

Evaluating groundwater resource of an urban alluvial area through the development of a numerical model

As established in the European Water Framework Directive, the development of groundwater numerical models is fundamental for adopting water management plans aimed at preserving the water resource and reducing environmental risks. In this paper, authors present a methodology for the estimation of groundwater resource of an alluvial valley, in an urban area characterized by a complex hydrostratigraphic setting and scarcity of hydrogeological data; the study area is the urban and sub-urban area of Rome (Italy). A previous, elaborated hydrostratigraphic model set the base for the development of 3D, steady state, sub-basin scale numerical model, implemented by the finite-difference code MODFLOW 2000; the water system components were derived by elaboration of available data. The alluvial aquifer of the Tiber River Valley, which runs in the middle of the City in a NNW–SE direction, has been analyzed in detail, since it is covered by a densely populated area hosting most of Rome’s historical heritage, and it is characterized by low quality geotechnical parameters. Results suggest that in areas with high hydrostratigraphic complexity and scarcity of hydrogeological data, a sub-basin scale, and steady-state numerical model can be very helpful to verify the conceptual model and reduce the uncertainty on the water budget components. The proposed steady-state model constitutes the base for future applications of transient state and local scale models, required for sustainable water management