Wyznaczanie terenu ochrony pośredniej ujęcia wód podziemnych. Porównanie wyników uzyskanych metodami analitycznymi z modelowaniem numerycznym

Abstract

Delineation of wellhead protection area. Comparative study of results obtained by analytical methods and numerical modeling.A b s t r a c t. In case of groundwater intakes with a low well discharge, localized in simple hydrogeological conditions, the wellhead protection area (WHPA) can be delineated by one of available analytical methods. The differences between the WHPA ranges delineated by analytical methods, give rise to the question which method would be optimal to be used to handle simple hydrogeological conditions. Analytical methods considered in the study include the Wyssling method, the Krijgsman and Lobo-Ferreira (K&L-F) method, and the Analytical Element Method (AEM). WHPA delineated using analytical methods are compared with data obtained from hydrogeological numerical model, which becomes the reference method. The study was performed for two single wells, and a simplified case was considered too, whereby two wells were represented by an equivalent one. The criterion used in the assessment is the distance upstream from the well to the zone boundary (Lu ), for various time-of-travel to the intake (1, 2, 3, 4, 5, 10, 15, 20, 25 years), and the shape and lateral extent of the WHPA. Discrepancies between the analytical methods vary depending on the time-of-travel, reaching 11% at most. Discrepancies between the analytical methods and numerical modelling results for single wells vary depending on the time-of-travel and the employed analytical approach, reaching 25% at most. For time-of-travel longer than 5 years, the maximal distancesLu calculated by the analytical methods are found to be smaller than those obtained by the reference method. The study indicate that results obtained by compared analytical methods are rather similar each other, but not similar to numerical modelling data. For scenario with the equivalent well there is major discrepancy between the reference values and analytical data.