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Artificial lakes (reservoirs) are regulated water bodies with large stage fluctuations and different interactions with groundwater compared with natural lakes. A novel modelling study characterizing the dynamics of these interactions is presented for artificial Lake Turawa, Poland. The integrated surface-water/groundwater MODFLOW-NWT transient model, applying SFR7, UZF1 and LAK7 packages to account for variably-saturated flow and temporally variable lake area extent and volume, was calibrated throughout 5 years (1-year warm-up, 4-year simulation), applying daily lake stages, heads and discharges as control variables. The water budget results showed that, in contrast to natural lakes, the reservoir interactions with groundwater were primarily dependent on the balance between lake inflow and regulated outflow, while influences of precipitation and evapotranspiration played secondary roles. Also, the spatio-temporal lakebed-seepage pattern was different compared with natural lakes. The large and fast-changing stages had large influence on lakebed-seepage and water table depth and also influenced groundwater evapotranspiration and groundwater exfiltration, as their maxima coincided not with rainfall peaks but with highest stages. The mean lakebed-seepage ranged from~0.6 mm day −1 during lowest stages (lake-water gain) to~1.0 mm day −1 during highest stages (lake-water loss) with largest losses up to 4.6 mm day −1 in the peripheral zone. The lakebed-seepage of this study was generally low because of low lakebed leakance (0.0007-0.0015 day −1 ) and prevailing upward regional groundwater flow moderating it. This study discloses the complexity of artificial lake interactions with groundwater, while the proposed front-line modelling methodology can be applied to any reservoir, and also to natural lake interactions with groundwater.

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resources sustainability under climate change, drought and increased usage was carried out by El-Kadi et al. (2014). While Appleyard and Cook (2009) paid attention to the problem of acidification and base cation depletion exacerbated by drought and groundwater withdrawal in Western Australia. This paper focuses on the problem of groundwater exploitation and mining drainage influencing decrease of water level during extreme conditions of drought periods taking into account that groundwater is the major source of potable water supply in the study area. Within the hydrological cycle, groundwater is normally the last to react to a drought situation, unless surface water is mainly fed by groundwater. Also, in deep aquifers the lag between a meteorological and a groundwater drought may amount to months or even years (Tallaksen and van Lanen, Eds., 2004; Calow et al. 1997; Rutulis 1987). That is due to a recharge process by indirect leakage of water to deep horizons from a shallow aquifer that is supplied from precipitation. When a meteorological drought appears as an immediate response in an unconfined aquifer the effects on deep aquifers are far postponed. That is why it is so difficult to establish clear and reliable ways of hydrogeological drought interpretation. It would be important to find out an optimal strategy for identifying relationships between the number of elements affecting the drought and the effective groundwater drought risk estimation, taking into account the deeper usable aquifers. However, it must be considered that in the mountain areas the first shallow aquifer is of high importance as well. Having the results of drought investigation, it is possible to establish some general indicative indicators dependent on frequency of the drought occurrence although this is simplified by the fact that it should be straightforward enough to setup in practice. Materials and methods Study area The study area is located in the south western Poland, in the region of Lower Silesia, occupying a territory administered by the Regional Water Management Board (RWMB) in Wroclaw. The southernmost part is in the Sudety Mountains which are divided into the Sudety Foreland, the Western Sudety, the Central Sudety, and the Eastern Sudety. The massif is approx. 300 km long and 50 km wide situated on the Polish-Czech border and the main range trends from NW to SE. It is characterized by a system of long ridges with gentle and flat plateaus and, domed peaks, broken through by valleys. More than Droughts may be caused by both natural and anthropogenic factors and delimitation of them is crucial for identification of exposed areas. This study concentrated on the application of the threshold level method combined with GIS modelling applied to hydrogeological drought characterization. The first step was to define groundwater drought periods and analysis of drought intensity and duration based on long-term monitoring data from points evenly spaced within the study area. Then the distribution of hydrogeological drought intensity was i...