CROSS-SPECTRUM ANALYSIS OF GROUNDWATER LEVELS IN AN ESKER

A study is made on 30-year records of precipitation, river water stage, and groundwater levels in the esker area south of Uppsala, Sweden, using cross-spectrum analysis. The results are summarized as coherence graphs for frequencies up to 18 cycles/year and tables of phase shifts for selected frequencies. The coherence between precipitation and the other variables is extremely weak or absent. The river water level and groundwater levels show appreciable coherence relatively independent of frequency, suggesting that variation in groundwater levels runs parallel to variations in river water stage. The coherence between groundwater levels, however, is such that interaction is suggested. The phase shift between river water level and groundwater level is approximately 10–30 days with the groundwater levels lagging. The magnitude of phase shift seems to depend on the distance between ground surface and groundwater level.