Grundvattenpåverkan kring schakter. - En jämförelse mellan olika analytiska beräkningsmetoder

Abstract

To be able to predict the effects on groundwater related to drawdown is of great importance to make sure that protected objects, such as drinking water wells and vulnerable ecosystems, are not affected. To predict the size of the area that will be affected by a drawdown, an analytical solution is often used to calculate the radius of influence. However, there are several different possible solutions and as of now there is no national Swedish standard on which solution is preferable. To deal with this issue, the Swedish geological survey (SGU) has created a guidance document (SGU, 2019a) in which some recommendations for choice of analytical solutions are included. In this study, three different analytical solutions from SGU:s document have been put to practice at three sites with varying geological conditions. The three solutions were originally published by Krešić (1997), Marinelli and Niccoli (2000) and Todd and Mays (2005), respectively. All three are described as eligible to calculate the radius of influence related to drawdown in unconfined aquifers. The results from the calculations have been compared with actual measured groundwater levels as well as estimated areas of influence from previously published studies. The results from this study shows that the solution from Todd and Mays repeatedly overestimates the area of influence. The solutions from Krešić and Marinelli and Niccoli, on the other hand, generates results with better consistency to recorded drawdown. Furthermore, the solutions from Krešić and Marinelli and Niccoli produce identical results when used on the three test sites. However, when put to test on fictive scenarios with very large well radii the results differ between the two methods. All three solutions are most sensitive to the hydrological conductivity parameter. Therefore, it is of great importance to determine this parameter with as high certainty as possible. The well radius is also essential to take into consideration as there are multiple ways of defining it. An analytical solution, together with a thorough hydrogeological investigation, can give a good estimate on the future extent of drawdown affected areas.