A multi-method approach revealing the groundwater-stream water interaction in the Inbuk stream, Korea.

We examined groundwater and stream water interaction in the Inbuk stream, Korea, using various approaches including hydrologic, thermal, hydrochemical, and isotopic methods. For this purpose, we installed four piezometers (IYHW1-4) in the streambed at 10 m interval across the stream and at depths of 0.90 to 1.54 m. We monitored water levels and water temperatures every hour using automatic transducers at the piezometers and in the stream (IYSW1) from September 2013 to April 2014. We also analyzed chemical and isotopic compositions for the hyporheic waters, stream water, and nearby groundwater in early September and late November in 2013. The water levels and hydraulic gradients revealed that three (IYHW1, 2, and 4) of the piezometers were in upwelling conditions for most of the monitoring period, except for the earliest short period (considered to be the wet season), whereas one piezometer (IYHW3) showed a reverse behavior, indicating that the gaining was dominant in the dry period. The mean calculated influx to the stream was 3.04 × 10 cm/sec. Observed temperatures of stream water, hyporheic waters, and groundwater also revealed that stream water was downwelling in the early monitoring period (wet season), whereas the groundwater was generally upwelling in most of the resting period, which is consistent with the water level interpretation. Chemical composition analysis indicated that most of the waters were Ca-HCO type for both seasons. However, no distinctive difference between chemical compositions of water without substantial seasonal variation negated any inference on the flow conditions. The mixing ratios computed from oxygen and hydrogen isotopic compositions indicated that losing conditions were dominant in the wet season, whereas gaining conditions prevailed in the dry season. The interpretations of stream water and groundwater interactions based on these different methods are relatively consistent for this study area, indicating that such combined methods will be very useful in enhancing understanding of groundwater and stream water interaction. [ABSTRACT FROM AUTHOR]