Identifying the impact of Energy Base Water Project on groundwater using high-frequency monitoring data in the Subei Lake basin, Ordos, Northwestern China

Groundwater is increasingly exploited for energy production in arid regions, which necessitates a deeper insight into the impact of the enhanced human pressure on the groundwater. This study applied an integrated method (statistical analysis, water table fluctuation method, hydrograph analysis and remote sensing) to identify the impact of Energy Base Water Project on the groundwater in the Subei Lake basin. Groundwater levels in eight observation wells at 30 min intervals during the 2013–2014 period were monitored using automatic groundwater monitoring data loggers. Results showed that precipitation infiltration, irrigation return flow, groundwater pumping and evapotranspiration controlled the hydrodynamics of unconfined groundwater. The average evapotranspiration rates in the Quaternary phreatic aquifer and the Cretaceous phreatic aquifer were 6.15 and 12.48 mm/d. The unusual hourly hydrographs fall into three patterns (mutational, irregular and gradual hydrographs). Different recovering times after being influenced by pumping may be related to the presence of the mudstone lenses. The extent of the groundwater depression cone was qualitatively identified by gradual hydrographs, which may spread from the center area to the western boundary. Only some individual wells from Haolebaoji waterworks had conducted the intermittent pumping activities at random times and caused the atrophy of lakes.