SHALLOW-WATER FLOW IN A DEEPLY WEATHERED GRANITE AQUIFER AND IMPLICATIONS FOR HYDROCHEMICAL MODELS

Starting in 1987, comprehensive investigations in the 4.2 km(2) Lehste nbach catchment in the Fichtelgebirge (South Germany) were performed t o determine water and matter fluxes. The catchment is nearly totally c overed by Norway Spruce stands. The measurements indicate that the ver tical profile of groundwater flow is strongly heterogeneous: lateral f low in the upper aquifer layers seems to prevail. As the upper layers show marked acidification, only a small portion of precipitation water infiltrating during storm events can be buffered here, resulting in a cidic catchment runoff. On the other hand, this implies a remarkable r etardation of acidification of the deeper layers. The purpose of this paper is to investigate the hydrological specifics of the catchment, e specially to identify and characterize the flowpaths. To that end, we use two different modelling approaches. Results of these model runs ca n be used to assess the impacts on hydrochemical models.