Master thesis

Fritz Kalwa (2016)
Physical and numerical modeling of a laboratory scale aquifer-well system for predicting the injection behavior of a small-diameter well. Master thesis, Technische Universität Dresden, January 2016

Abstract

Managed Aquifer Recharge (MAR) is constantly gaining popularity and one very promising technique in this context is the use of infiltration wells. However, the near-well surrounding of these wells is still object of many open questions. For a better understanding of the processes taking place here, a physical laboratory-scale aquifer-well model was designed and compared to a numerical model, set up in Hydrus3D.

The physical model was assembled in a tank with a height of 1.1 m and a diameter of 1 m. Water was introduced via a small-diameter well screen in the center and conducted out of the model via side outlets. Furthermore, a drainage system was attached to the tank's wall to assure circular flow from the well to the wall. The setup of the this model was attended by unexpected challenges, requiring a complete redesign of the drainage system and the need for analysis of hard-to-define pressure losses in other parts of the outflow system. Finally, the pressure-losses were predicted with a half-empirical formula and the obtained impoundment heights were included into the numerical model for correction, allowing good prediction of infiltration behavior in the physical model for infiltration rates between 0.025 l/s and 0.15 l/s. Furthermore, the numerical model was compared to a modified version of the Dupuit-Thiem-formula for stationary pumping tests, which was adapted for saturated injection through a well and showed comparably good prediction quality. However, using this formula is only possible, when the piezometric head in the infiltration well is known, since it uses this as a reference level. Unfortunately, the physical model showed significant deviations from the numerical model inside the well, possibly due to flow resistance of the well screen. Therefor, Dupuit-Thiem did not give appropriate results, allowing a comparison with the measured values from the physical aquifer-well model.

The study showed that it is possible to model the injection cones and infiltration behavior of the physical model with a numerical model, allowing the future use of these models in the planning phase for future infiltration designs, especially with regard to clogging and underground heterogeneities.