Assessment of the value of microgravity to estimate the principal directions of the anisotropic transmissivity of aquifers from pumping tests: A study using a Hough transform based automatic algorithm

Estimation of the hydraulic parameters of an aquifer is usually performed via interpretation of pumping tests. This invasive method requires drilling both pumping and observation wells. As the process is expensive, only a single pumping well and one or two observation wells or piezometers are generally drilled, at most. The interpretation is done assuming aquifer isotropy and homogeneity. However, in many aquifers, horizontal anisotropy in hydraulic conductivity greatly affects the flow regime. Its disregard may lead to important misinterpretations, especially for environmental impact assessments. This paper studies the capabilities of gravity for the identification and determination of the principal directions of anisotropy. This has been automatized using a methodology based on the Hough Transform. The results show how a microgravity survey could be an adequate and relatively cheap monitoring tool for the identification of anisotropy. This is valuable information that can be used in the decision making process for performing or discarding additional studies. Even more, the presented methodology can be extended to other studies in which contour maps are used to identify directionality in any process or property.