Detection and evaluation of changes induced by the diversion of River Danube in the territorial appearance of latent effects governing shallow-groundwater fluctuations

•Relationship of shallow groundwater, precipitation and surface water is analyzed.•Dynamic factor analysis used.•Background factors in groundwater time series determined.•Spatial distribution of factor scores plotted.

SummaryThe paper assesses the impact on the fluctuation of the shallow-groundwater table of the diversion of the Danube upstream from the Gabčikovo/Bős hydroelectric power plant in a hydraulically connected, geologically identical, and structurally not decomposable geological area in North-West Hungary. On the basis of shallow-groundwater level monitoring data the impact was traced back to the effect of the Danube's changed flow course, and quantized for the whole study area.To this end the influence of the river had to be separated from the effect of precipitation. The means chosen was the application of dynamic factor analysis to the registered hydrograph time series. We conclude that the originally homogeneous and dominant effect of the Danube has split and now consists of a diverted and a returning component (downstream from the power plant), and that this is a likely cause of ram-effect and river bed clogging. Furthermore the effect of precipitation ceased to be suppressed, and came to the fore.