Abstract: After the completion of Baihetan reservoir construction in Qiaojia County, Yunnan Province, a large number of cavities were exposed by boreholes in the resettlement land of residents, which is located in the water-rich alluvial fan on the right bank of Jinsha River. A Two-day tracer test was carried out to explore the groundwater seepage law and cavity connection characteristics. Fluorescein sodium was selected as tracer, and the V1600 visible spectrophotometer was used to detect the absorbance of sodium fluorescein in the sample with a wavelength of 495 nm. The absorbance of sodium luciferin concentration was converted according to the standard curve of sodium luciferin concentration versus absorbance with R²=0.945 1. The time series curve of sodium fluorescein concentration with single peak was also obtained. The tracer test unveil that groundwater flows from the east to the west in general and discharges to the Jinsha River at the lowest datum level of regional discharge. Two main channels of groundwater runoff were revealed in the field area: borehole BK4163-BK4114-BK486 direction and borehole BK4163-BK4224 direction. In addition, the structural parameters and hydraulic parameters of runoff channels were acquired via quantitative analysis of concentration curve of the tracers by using Qtracer2 calculation model.

Key words: tracer test, groundwater, fluorescein sodium, seepage channel, underground cavity