TR-116 : Number of observation wells and their locations for an aquifer test in different geohydrological conditions

Abstract

A method has been proposed to estimate the transmissivity and the storage coefficient of an aquifer separately making use of the rise in stream stage and the consequent fluctuation in water level at observation wells located in the vicinity of the stream. A minimum number of three wells are required for the purpose. The first observation well with a small radius should be located near the stream bank. The second observation well with a radius more than 0. 5 m should be located within a distance of 50 to 100m from the first observation well. The third observation well with small radius should be located at about 100m from the second observation well. All the three wells should be in a line perpendicular to the stream boundary.

The Laplace transform method proposed is applicable to any type of change in stream stage. Continuous observation of stream stage and water levels at the observation wells would enable accurate determination of aquifer parameters. The applicability and limitation of the methods presented have been verified using published field data. It is found that the water level fluctuations simulated using parameter estimated by the methods presented here are close to the observed values.

The inverse problem has also been solved using Marquardt algorithm and synthetically generated data. The transmissivity and storage coefficient values could be re-established by the optimization technique.